[IMAGE: FRONTISPIECE. 50-K. W. Tandem-Compound Set for Kearsarge and Kentucky.]
(From lectures delivered before the U. S. Naval War College.)
Introductory.
The entire scheme and system of our electrical installations have been, from the nature of the case, progressive, and we may confidently say have shown a steady march toward improvement in details and efficiency. Ever since the introduction of electricity on board ship there has been a constantly increasing demand for this form of energy, and it is to be anticipated that much larger demands are shortly to be made upon the adoption of electrical power for turning guns as well as turrets, for operating auxiliaries, for all purposes, in short, which will minimize the present objectionable heat of long lines of steam piping, the annoying leaks of hydraulic apparatus and the excessive weights of pneumatic appliances; to this may be added that a break in a steam or hydraulic pipe could easily drive every one from the compartment.
As a simple matter of weight, the installation of any particular device is very evenly balanced between the electrical, hydraulic or steam, but when the proposed three-wire system is installed. at a saving of motor weight and 67 per cent. of copper in the leads, electricity will be far in the lead in that respect also.
Perhaps the greatest weight of argument in favor of electricity is the ready change from electrical to hand control in emergency, and the facility of maintaining and repairing the leads.
Conservatives declare that we should be slow in making such a radical change, that too many eggs are going into the same basket, that electrical science is still experimental and in its infancy, and that a stalled gun or turret in action would mean destruction.
To these we can confidently answer that the question of applicability to gun and turret use has been settled by the trolley long ago. Minute control of the power to be applied to turret or gun has been discovered in separately exciting the fields of both dynamo and motor; irregularities of turret load is a mechanical question of balance applying with equal force to any system of power.
The proof of the ready perfect control of electrical power as applied to turrets was instanced in the recent trials made on the Brooklyn at Cramp's shipyard, when the turret was successfully started and stopped thirty-seven times in a peripheral distance of one inch in the same direction; this result easily challenges competition; reports from trials at sea are that the turrets were handled with ease.
Our naval electrical history began in 1871 with a small Farmer's series dynamo whose armature was revolved by a hand crank and whose output did not exceed 100 to 150 watts, which then sufficed for all needs, but whose total energy would in this day be consumed by a single 32-C. P. lamp.
In 1897 the Iowa and Alabama require an output of 96,000 watts, supplied by four steam-driven compound generators of a capacity of twenty-four kilowatts each in the one case, and three of thirty-two kilowatts capacity each in the other. The Brooklyn is furnished with a total capacity of 150,000 watts; the Kearsarge and Kentucky will have 350,000 watts distributed between two double sets (100 K. W.) in the lower dynamo room and three single sets (50 K. W.) in the upper room in each ship. (See frontispiece.)
Two-thirds of this energy is for use as power, and in line with the increased and increasing demands has come the necessity for increased voltage in order to reduce wire size,[*] motor dimension, weight and cost. The same demands have necessitated a change in the type of our dynamos from the "smooth body" to the "slotted core" design, by reason of superior induction and less weight and cost, and this in turn has indicated automatic circuit breakers to operate at either of the failure of the line voltage or overload. The "smooth body" armature has served us faithfully and well, but has been forced to yield to superior considerations.
The voltage selected for the three-wire system is 160 volts, thus preserving a pressure of 80 volts at the lamps. It is often asked why we do not use commercial voltage at 125 or 250 volts and thus avoid the extra expense of special machines, lamps and supplies, for which we are paying from ten to twenty per cent. in addition. The answer advanced is that, while our insulation can easily stand the higher voltage, we are insuring good insulation at the lesser voltage and avoiding the exorbitant losses in search-light rheostats; the commercial practice of placing two search-lights in series has some mechanical difficulties in ship installation.
The application of electricity to naval purposes is now so generally understood that it requires no mention here; the results of those uses as obtained from ship discussion, quarterly returns, official complaint and the large bills for repairs and supplies are the factors with which we are concerned, and which have occupied the attention and close study of those directly in charge of the branch, in order that the faults and remedies could be certainly ascertained and specifications made more stringent to avoid recurrence.
Notwithstanding all the discussion, complaint and repair, it has only been within the past two years that any range of information could be obtained upon which to base new specifications which would ensure what we want and are entitled to have.
This has been chiefly clue to the fact that the information at hand has been repetitions of facts already canvassed, particularly as regarded increased or increasing coal consumption in the A and B types of the General Electric engines, long since known and admitted as poor types, inefficient and wasteful, if indeed they can, after reasonable service, be pushed to their rated outputs; again, a large mass of suggestion for improvement has been predicated upon experience and device as associated with the single plant at hand without recourse 0 changes that have been made or are making elsewhere.
The visits of officers, for acquirement of new information, to the electrical store-rooms and workshops of a well-equipped Navy Yard, where inspection, test, assembling and manufacture of electrical material, appliances and supplies are continually in progress, are rarer than the eclipses of the sun or moon. A navigator or his assistant occasionally appears to look up delayed articles of an approved requisition; a dynamo man strolls in now and then for permission to " look about and pick up a few points," but his thirst for knowledge is quite apt to terminate abruptly at a stray tool whose isolation and position he has probably located previously and which may " come in handy some time." The ship which is building at the dock, with all the newest wrinkles and points, is passed by and forgotten.
So it has resulted that, until a year ago, when opportunity was afforded to repair and overhaul the installations of twelve ships representing almost all the types and classes in the service, information on the general subject has been too meagre to form a good basis for specifications for future work and material, especially regarding the ever vexed and much abused subject of interior communications.
New specifications have been issued this year, which to this date, September 1, 1897, have stood the test of criticism and revision on all cases presented, and are made an appendix to this article.
The general aim has been:
To restrict contract ships to the limits of good workmanship in original installation;
To reduce experimental work and devices to a minimum, i.e., by establishing a system of standards both as a guide to requisition and to ensure uniformity of details and strict interchangeability in our ships.
It is understood that any system of standards is to meet severe opposition from many quarters, but much time and study have been devoted to these electrical standards on the lines of continuity of service, sound electrical principles and simplicity, and needed changes can be made as progress demands. We at least secure for the present that our new battleships shall be installed in the best manner to date. Even then we are trammeled in obtaining the best, as far as some supplies are concerned, by the two stumbling-blocks, "barring competition " and "proprietary article," which by law prevent us from obtaining in open market what we know to be the desideratum. A familiar example of barring competition is that of lubricating oil, which can be mixed and juggled to pass any devised or devisable set of specification; ever issued.
Good special oils can be obtained by purchase from especial makers and the grade be satisfactorily maintained. Bids must be issued under the law; monopolies crush out the smaller dealers.
Any oil costing less than thirty-five to forty cents per gallon is, for dynamo use, an object of distrust.
“Proprietary article” is a favorite recourse with contractors when "barring competition" will not fit or fails of success.
Our engine indicators have had an especial experience under this head. Whatever may be the niceties and novelties of device in these instruments, faith in their operation must be pinned entirely to the integrity of the spring. The Ashcroft-Tabar indicator, so long in successful use in the service and elsewhere, is fitted with a "duplex" spring-two spirals coiled in opposite directions with containing caps-which is patented, but whose longevity, and therefore integrity of action, is far superior to any device in the market; all other like instruments depend on a single spring, whose operation becomes in a short time dubious and unreliable. Spare springs are provided if one only could tell just when the old should be replaced; with the Tabor instrument there can be little doubt on the subject.
Two instances of the results of the above examples:
Ten thousand gallons of mineral oil (nearly 200 barrels) were delivered into store at the New York Navy Yard in the fall of 1896; were inspected later on, having time to settle meanwhile, and passed into store; the bid was seventeen cents per gallon.
The first issued was used on the journals of the 8-inch shaft of the 250 H. P. engine driving the electric plant of the Navy Yard. and at a critical time when the plant was supplying light for getting up steam on a ship about to be undocked. So excessive was the amount of grit and dirt in the oil that the plant could be kept going only by use of a liberal stream of water from a hydrant until better oil could be obtained; filtering produced but little effect; the oil was also very deficient in "body," a matter that no amount of filtering can reach.
Until recently the Tabor indicator has been our regular supply, but some makers of single spring instruments have supplied a lot by underbidding and successfully over-riding rejection by reason of the patent held on the duplex spring.
These cases are growing fewer in number since the standards have been adopted; contractors are not prone to face the expense of delivery, removal and redelivery where it is expressly stated on the face of the schedule that samples are to be seen on application.
The unsettled questions of to-day, fortunately few in number, are rather those of mechanical details than electrical principles. Good design, efficient insulation, sound connections and thorough water-tightness mark the not uncertain road to security and success in original installation. of which design alone will be progressive and variable. Continuity of service and confidence on board ship rest upon intelligent operation and mechanical aptitude.
Continuity of service and endurance of our plants is now suffering from lack of interest, and apathy on the part of officers. The pioneers of our naval electric installations, and who are perhaps, popularly supposed to be still at the head of affairs, have been called away by the exactions of rank or duty, and but little new blood is being infused.
It is difficult even to obtain inspectors for the various works of contractors, or, at least, difficult to obtain at those points the services of an officer who feels himself in a position to cope with the subject.
The navigator on board ship is charged by regulation with the responsibility of the whole installation; his duties in the other branches of his department, coupled with correspondence when off the bridge, leave him but scant time for the electric plant in its numerous details; his duty ashore has often been in connection with other branches of the service, which gave him but little time for anything more than a very general interest in electricity or its details in ship construction. Placed on board ship, in charge of a large and expensive plant, he must rely on the assistance of the Navy Yard force or be relegated to a dependence on his head dynamo man, which is usually leaning upon a broken reed.
Our installations have been brought to a high state of efficiency through the research and stiff-necked insistence of those who worked out its early details; what we need most now are care and skill in manipulation.
We have the right to point with pride to the achievements of our early pioneers, who came into the field to face the difficulties of a proposition entirely in the air, environed by a fast changing and improving science, without so much as a satisfactory generating set for ship use, with ill-matured appliances and poorer wire; to the fact that it was a naval officer who first suggested direct connection of dynamos to their engines, now so popular commercially, and imperative on board ship; that another officer designed and inspired the first successful fire-proof installation in this country, that of the Broadway Theatre in Kew York; and it is to be regretted that their sort is seemingly to disappear from the field unless some measure is taken to supply their place.
Short-Stroke Engines and Water Consumption.
The final summation of all energy developed by the generating sets, both useful and wasted, is the consumption of water, of which the practical evidence is the coal account and expenditure. The wasted energy can be properly divided into two heads:
1. That which is common and necessary to all engines, somewhat increased by wear and tear, but still approximating a fixed maximum.
2. That which is due to losses from the faults of which we treat.
Losses comprised under the second head are those which are remediable and should be eliminated; those comprised under the first head are remediable only in design, and form the basis of competition amongst engine-builders. particularly amongst those builders who are interested in the modern short-stroke types.
Defined as those used for driving machinery which runs at a high speed of rotation, such as dynamos, centrifugal pumps and the like, short-stroke engines have of late been the subject of much rivalry amongst designers, both as to the merits of single-acting as opposed to double-acting engines and simple versus compound.
The questions involved are not those of high-speed engines alone; the difference exists in the fact that "high-speed engines" is the title of a class as opposed to "low-speed engines," and includes engines used for torpedo boats and locomotives in addition to the short-stroke types; the last-named types, having a stroke of from but five to six inches, are alone those with which we are concerned.
The most concisely stated review of the short-stroke types is contained in a paper read in January, 1897, by Mr. J. S. Raworth, a well known English builder and designer. This paper presents the very remarkable statement that, from observations of experiments with over 100,000 I. H . P., it is established that modern short-stroke engines are at least quite equal to long-stroke engines in mechanical efficiency; as it cannot be accounted for on a simple theory of constant thrust, ready explanation is to be found in the better lubrication of the working parts, and in the better distribution of stress by reason of the increased inertia due to the high rate of reciprocation of the pistons.
The necessary waste steam consumption in an engine is usually distributed amongst four well established sources of loss:
1. Clearance.
2. Port friction.
3. Condensation.
4. Leakage.
Clearance must be provided for easing the racking strain of fast piston reversals, and must necessarily increase in percentage as the number of reversals is increased.
The volume of clearance in any given pattern of engine varies with the area of the piston and is nearly independent of the length of stroke; but when expressed as a percentage of the volume of the cylinder it will obviously increase as the stroke diminishes the usual 3 per cent. on a five-foot stroke would become 36 per cent. if the stroke were reduced to 5 inches.
This clearance loss is severe in all short-stroke engines and is practically constant for the type.
Port friction may be defined as a sort of added clearance, the volume necessary for the ports, combined with a choking of the steam in its passage to the cylinder. This loss is nearly a minimum in our dynamo engines, as the ports are fairly large and straight.
Condensation is found in all reciprocating engines, and is principally due to the fact that the wall of the cylinder is alternately exposed to high and low temperatures. It is stated that the temperature difference approximates 180° F., about that between boiling water and ice.
In a compound engine the temperature difference is approximately halved in each cylinder, with necessarily great reduction in condensation.
It is obvious that the rate of cooling will vary with the time of exposure, that is, it will be less with increased speed, and in general it is established that there will be a saving of nearly one-half by doubling the speed. This is only an approximation, however, as part of the condensation is due to the radiation of the atmosphere, and another part to the direct conduction of heat from the cylinders to the bedplate and working parts of the engine. The Case engine used with some smaller types of machines is a familiar example of this conduction. In almost every test the water and oil will boil out from the well in the base, at first slowly, and then violently, as the temperature rises from the heated crank. An air tube has lately been suggested as a remedy for the difficulty. but thus far has had no practical trial.
This Case engine will generally slow down of itself as the temperature rises, then, as the temperature falls, is will work back slowly to the original speed, causing a very objectionable fluctuating voltage in the circuits.
Steam jacketing is naturally suggested as a remedy for condensation, but in short-stroke engines, even when compound, the gain in the cylinder is so evenly balanced by the large loss in the jacket as to render the expedient expensive and unnecessary.
The fourth source of loss, leakage, is one with which we are especially concerned, as it is an inherent vice of piston valves our usual type-and is not only much increased by wear, causing back pressure and increased loss from that source, but it appears in the cylinders as well, as the pistons wear, destroying pressure, which means more coal.
Valve leakage will be readily understood when it is stated that from this loss alone it has been found that engines. Apparently in good order, even when standing still, took as high as 30 to 40 per cent. more than their normal requirement of steam; and, though the automatic governor handled them well as new engines and when running without load, they ran practically independent of the governor under the new conditions until loaded to about 20 per cent.
From 15 to 20 per cent. of the steam delivered at the throttle is the plain statement of the summation of these four losses in a new dynamo engine that has been subjected only to those preliminary trials necessary to put it in proper order for turning over to a commanding officer, and the statement is believed to be conservative. It does not include water in the cylinder, which is practically indeterminate.
What occurs in service is best illustrated by the case of the Marblehead; in that ship the coal expenditure for auxiliaries increased over one hundred per cent. above the amount necessary at first commission. This is unquestionably a serious matter, especially when, on protracted voyages, economy in the visible coal supply must be rigorously observed and enforced.
The dynamo engines do not use all the coal charged up to auxiliaries, but from the nature of their use they are responsible for a large proportion of the expenditure, certainly for a lion's share of the increase.
Several commanding officers have recently inaugurated experiments for the purpose of ascertaining this increase. Usually such results are in error for the simple reason that there is rarely an opportunity on board ship when the dynamos can be run to the exclusion of all other auxiliaries. The following means of obtaining a fair approximation are suggested:
The best time for the test is probably between six and eight o'clock in the evening, as steam for the galley, flushing pumps and blowers can be best spared at this time.
Shut down everything using steam except the dynamo under test.
Break the joint of a pipe leading to the feed tank, or better, the auxiliary condenser if practicable.
Provide a steep-tub for catching and measuring the water, and carefully measure into it enough water to fill it to within two inches of the top; this will be about 30 gallons, 250 pounds, for the ordinary tub that is used about the galley. Mark the level on the inner side of the tub. It is merely necessary to count the number of times the tub is filled, emptying each time directly into the bilge and catching the water for the moment with a bucket.
The dynamo should be run with at least 75 per cent. of full load, as dynamos are never efficient or economical at loads below that percentage.
The voltage and load should be kept as steady as possible, and the voltmeter and ammeter should be read every fifteen minutes in order to obtain a good mean.
An hour and a half is sufficient time for the test, but it is better to run for two hours if it can be done.
A set of cards should be taken each hour.
The ratio of the output, as determined by the product of the mean current and voltage, to the horse-power obtained from the cards is the over-all efficiency for that load; the water consumption per K. W.-hour or per I. H. P .-hour is readily obtained from the quantity of water used.
This may appear, at first blush, a rather rough method, but in reality the results will be found to be quite satisfactory.
Data of this kind are very much wanted, especially in engines where the coal consumption has increased.
On acceptance tests the water is measured directly at the surface condenser by draining into a barrel which rests on a platform scale and can be emptied by a stop-cock The water is weighed every fifteen minutes, the instruments being recorded every half-hour throughout the four-hour-heat run.
What the water consumption of our engines should be has never been determined, that is, no specification is made which covers the important point; at the same time if a specification were made the engine-builder would be quite sure to step in and say that it was too stiff and unreasonable.
For 24-K. W. types and upward it would seem that a new engine should not require more than 35 pounds of water per K. W.-hour if compound, or 42 pounds if simple.[*]
A 50-K. W. set has recently been built on the designs for the single sets of the Kearsarge and Kentucky which consumed, on acceptance test, but 30 pounds per K. W.-hour, confirming the liberality of the above figures.
There seem to be no data as to the water consumption of the numerous engines of the General Electric Company's manufacture which we have, but in the A, B, and those of the C types which have no packing rings, the consumption must originally have been between 50 and 60 pounds per I. H. P.-hour. The two A type machines in the Maine are now using over a hundred pounds per I. H. P.-hour, which, of course, is very excessive.
The remedy for large water consumption is more closely fitting valves and, in engines not so fitted, packing rings en the piston; a number of engines have been repaired in this way aboard our ships and the coal expenditure materially decreased.
Throttling clown, reducing pressure when running under light loads, particularly at night, is a common practice of dynamo men which cannot be too strongly condemned. They do it usually under the impression that they are saving steam and also because the governor is inclined to be a little noisy at small loads if the throttle is wide open. The valve fit is what is known as an expansion fit, the best results being secured at the steam temperature of the standard pressure of the design, viz., 100 pounds for compound engines and 80 for simple engines; throttling down, reducing pressure and therefore temperature, must therefore promote leakage past the valve.
At any load the governor will regulate the expenditure of steam more efficiently than can any dynamo man at the throttle, and it should be the invariable practice to run at the prescribed number of revolutions as shown on the name-plate[*] with the throttle wide open and let the governor take care of the steam, as it was designed to do.
The theoretical governor for best economy is one that cuts off from full to half load and throttles from half load to no load; thus far all governors constructed on the principle have been mechanical failures.
Reduced steam pressure is another fruitful source of waste steam on board ship. Engines are run at pressures as low as 35 pounds, for the reason that no higher pressure is to be had; neither the engine nor governor was ever designed to work economically at any such pressure, nor will they. If no higher pressure than 50 pounds for a simple engine, or 65 pounds for a compound can be had, and coal economy is desirable, it is better to shut down the plant and burn oil; it may not prove an economy in so far as the ledger account is concerned, but it is the certain way to save coal. The remarks made on throttling down apply here with equal force.
A corollary to reduced pressure and throttling down is throttle governing. When the governor has quit, so to speak, as our very troublesome one on the General Electric types A and B generally does within a short time, dismantling the governor or blocking it, thus reducing the system to a mere fly-wheel arrangement, is the only resource, and throttle governing is made compulsory. It is necessarily, though unavoidably, wasteful of steam, and is attended with some danger to the engine if care is not taken to raise the carrying capacity of the dynamo main fuse at the switchboard. Take, for example, the case of a 32-K. W. machine running along with a load of 350 amperes, the throttle practically wide open, governor dismantled or blocked, and governing by the throttle. Presume now a sudden overload to push back to the switchboard a heavy momentary current which we will assume to be 600 amperes ; the main fuse would immediately blow, as its carrying capacity is only 400 amperes, and the armature would be safe. Not so the engine; all load has been suddenly removed from it when under full head of steam and no automatic means of shutting off steam is at hand; it is apparent that unless the dynamo man gets quickly to the throttle the engine can do itself any damage up to racking to pieces.
If that dynamo main fuse had had a capacity of, say 800 amperes instead of 400, and the same large current had rushed through, the overload would have slowed the engine and the dynamo armature would have had to stand the brunt. This state of affairs is rather undesirable, but as our dynamos can be relied on to carry, for a brief time, an excess of at least 50 per cent. above their rated capacity. overloading the dynamo is far the lesser evil as compared with wrecking the engine.
The matter is not fanciful or exaggerated; it has occurred in the service, resulting in that instance in a broken connecting rod, attributed, however, to water in the cylinder. Water in the cylinder is a ready explanation of most of these accidents to small engines, for the reason that the cylinder heads are very strong in comparison with those of larger types, and will not usually blow out; in the case of the Katahdin the four stanchions which support the cylinders carried away, tumbling the engine on the deck, but the cylinder heads held.
In the case of the connecting road the presence of water was not well established, while the evidence showed that the engine suddenly raced away and broke the rod before the attendant could get to the throttle; the main fuse of the dynamo was found to have blown.
In one ship in the service, running with blocked governor and throttle-governed, the head dynamo man has reduced the carrying capacity of his main fuse; this means that he has weakened the safeguard to his engine and brought the verge of disaster a little closer home.
The Use of Oil in Cylinders.
The majority of the difficulties with our generating sets, of the troubles at least which occasion most frequent remark, complaint and repair, reside in the engines; the dynamos usually give little annoyance.
These difficulties are met with mostly in the A and B types of the General Electric engines, which types constitute over 50 per cent. of all that have been installed, and are admittedly inefficient and uneconomical after short service use; that they are so is the silent protest against the prohibition of the use of oil in cylinders.
Immediately after this prohibition was promulgated, other makers of short-stroke engines, Armington and Sims, Ball and Wood, and Westinghouse, for example, simply refused to build engines under such a restriction, withdrew from our market and declined to make any bids on the specifications.
The General Electric Company then stepped in and undertook to supply the engines as specified, and after a long series of efforts and designs, of which their A, B, and C types are familiar service examples, they finally put packing rings on an engine supplied to the Massachusetts in January, 1897, and used a little oil The company has now practically retreated from the field, as the experimental set representing the design intended for the Kearsarge and Kentucky has a lubricator on the steam pipe.
The consensus of opinion amongst builders of the short-stroke types seems to be that cylinder oil is a necessity to endurance and economy, and it is the fact that in but one ship in our service, and this after supplying packing rings to the piston, has the water surface proved satisfactory; in that ship the plant was under the supervision of an officer high up in the electrical councils of the Navy, which is "another story.'" The saving in coal from the use of rings in this case was over 30 per cent.
It cannot be gainsaid that oil in the exhaust steam exercises a very pernicious effect upon condensers and main boilers, and that the ground against its use is well taken. On the other hand, it is quite certain that the effort to run engines without any lubricant in the steam has been very costly for us in coal, due to bad governing and to the large increase in water consumption from abnormal wear of cylinders, pistons, and valves; this wear, as before stated, has for its remedy packing rings on the piston and closer fit, both demanding, practically, oil in the steam, though the statement is disputed.
Those who protest against the use of oil, comprising about all who are responsible for boilers, usually point out that main engines, such as those of the New York and Cushing, are continually run without any cylinder lubricant: but it is also the fact that the cylinders of main engines, when at rest, are coated with a heavy oil or vaseline for the purpose of preventing the pistons from " freezing" (rusting) to the cylinder walls, and it may be an open question whether an oil-coating, once formed, will permit the formation of a water surface thereafter. In the case of the Cushing it is very difficult to get into the cylinders at all, and for that reason her pistons must usually work on the lubrication of the water surface. In neither case have we an example of a short-stroke engine, which fact is entitled to its due weight.
The solution of the matter for both sides seems to rest in the use of an appliance on the exhaust which will extract the oil from the steam on its way to the condenser. Several designs of this nature, variously styled steam-washer, grease extractor and oil eliminator are to be had in the market, showing efficiencies as high as 75 to 80 per cent.: assuming the proper amount of oil to be used at ten ounces per diem, this appliance would undoubtedly protect the boilers and condensers sufficiently to remove all objection.
Unfortunately all types of the many designs in successful use commercially are for atmospheric exhaust only, and thus far not a single one has been found that can be recommended for a condensing engine.
Experiments in that direction are making.
Engines.
The discussion of engine faults resolves itself mainly into treating of those of the General Electric types, as well for the reason that they constitute so large a majority of all we have in use, as that it is in those types that the faults have been chiefly observed, whether due to the particular designs themselves or to inherent characteristics of engines in general; and it is but just to remark parenthetically, that on original test no engines could operate more satisfactorily or accord more closely with the rigid letter of the specifications, except, perhaps, in the matter of the noise and want of balance of those having 90° cranks.
We can dismiss from the consideration the types of other makers with a brief remark for each.
A few generating sets with especial types of generators have been introduced from time to time for experiment; they have generally been small sets of 2 and 4 K. W. capacity, in which neither efficiency nor economy was sought or expected. Of these the Sturdevant engine (Crocker-Wheeler generator) showed the remarkable regulation of one per cent. from full to no load, five revolutions at a rated speed of five hundred. The set is shown in Fig. 1; it is installed in Torpedo boat No. 8 (Rowan). The General Electric Company have supplied a very pretty little engine for the boat sets, having a rotary valve. The set is shown in Fig. 2. Its operation is absolutely noiseless. The engines of both these sets are quite heavy for the capacity, and develop an over-all efficiency of between so and 6o per cent., as against 83 to 86 per cent. in larger machines.
The Ericsson set, with Case engines, is shown in Fig. 3.
The remaining large engines are mainly those of Bellis, Armington & Sims, and the Union Iron Works; all use a lubricant in the cylinder.
The Bellis-Siemens sets (Fig. 4) were bought in England. The engine is of good, strong construction and works well. It has the disadvantage that the governor action is that of throttling, which occasions poorer regulation and economy than we have a right to expect now-a-days. It is possible to adjust the governor for any steady load, but the adjustment will not answer for any other load. If left to govern according to the design, the speed becomes variable at fluctuating loads, resulting in irregular voltage.
The series field of Siemens generators is wound outside of one shunt coil only, causing a difference of intensity at the periphery of the armature, making it a little one-sided, so to speak. In addition the dynamo has the large stray field common to all bipolar constructions. The sets, however, give little trouble and are for that reason quite popular on the ships in which they have been installed.
The Armington & Sims and Union Iron works types have proven very satisfactory alter extended use; the latter are generally cross-compound, even in sets of four kilowatts.
The general appearance of the A and B types of the General Electric Company's manufacture is shown in Fig. 5 In reality the two types are practically one, as the only important difference lies in the construction of the engine bearing nearest the dynamo. In the A type this bearing consists of two bearings, one of which is boxed off from the engine frame; in the B type the box bearing is omitted, the other being made a little longer; this arrangement adds materially to convenience in handling the shaft.
The engines are simple and designed to work at 80 pounds of steam.
The valve chests are located between the cylinders, and directly under them on the shaft is the governor carrying the eccentrics for the valve stems. The crank shaft and armature shaft are in one without coupling, the dynamo end being provided with ring oilers of the type shown in Fig. 6. The cranks are at an angle of 90°, causing the want of balance and noise predicted for them in a previous article of the Institute.
Cylinders.
The chief fault has been abnormal erosion and wear, of which the Marblehead, and to a lesser degree the Columbia, have furnished the best examples.
When the bonnets were removed it was expected that the wear would be practically equal all around, but there was found, in addition to a deep scoring, an oval wear, in the plane perpendicular to that of the shaft; the edges of the piston were worn and the rim rounded off. The leakage of steam from the steam side to the exhaust side of the piston must have been very great.
This oval wear is unquestionably caused by the cocking of the piston. The cross-head is supposed to prevent this, and it is evident that there must have been a lateral play of the crosshead in the guides, which had not been taken up. In a C type machine, lately supplied, the pistons are centered by a tail rod; but it is doubtful whether in small engines the device is worthy of the trouble or expense.
The steam leakage around the piston is best remedied by packing rings. Fig. 7 shows a 16 K. W. piston so fitted, and also the original design without rings. A worn cylinder requires reboring.
The section of the packing ring shown in the figure is square.
Rings of this section are prone to break or to cause a clicking noise from want of sufficient bearing surface in the grooves. The later and better practice is to make the ring width from two to four times the thickness, deepen the groove accordingly, and divide the ring into two or three pieces for convenience in entering.
These wider rings are designed to take against elliptical springs held to the bottom of the grooves by set-screws.
Fig. 8 shows the usual type of piston valve in use. It has ordinarily been made of bronze, presumably for the purpose of lessening friction and wear. A number of instances of wear in these valves rather demonstrates that the idea is not well borne out. Cast iron is now used as it not only insures a good expansion fit, from similarity of expansion with the material of the seat, but answers all the practical demands of wear.
Wear of valves and lack in tightness of fit are indicated by the balloting of the valves against the side of the chest and always means increased leakage. In some large engines packing rings have been fitted; this entails a danger of catching at the ports. best obviated by bridging; in small engines, however, the bridges would probably need to be diagonal, an annoyance and expense in casting.
Valves often show anomalies even for the same type and size of machine; in some engines the valves are not interchangeable, this is in direct violation of the specifications; in others the lap or lead will be quite different, a troublesome matter in valve setting, which is at best an undertaking of no mean proportions with some of our engines.
The available method is to lengthen or shorten the travel by means of the nuts on the valve stem. In setting valves on the Amphitrite it was found that only a quarter of a turn of the nut on a thread pitched eleven to the inch, would entirely change the character of the card. What the valve really needed was a little more lead, not attainable for the reason that the eccentric is bolted solidly to the governor casting and cannot be given angular advance. The best that could be clone, pending the construction of a new eccentric, was to adjust the work between the cylinders as evenly as possible; When completed the cards showed that one of the cylinders was doing four-fifths of the work, instead of one-half as it should.
The large amount of breakage of valve stems is a question of valve guides and governors, which will be touched upon later on. Fig. 9 shows a section of the valve used with the 32-K. W., smooth body types.
Piston Rods.
These give little trouble; they are very strong comparatively, and escape the effects of water in the cylinder. But a single case has been observed arising at this point, and it was really a matter of the stuffing box; the gland had not been properly entered on the thread, canted instead of catching fair, resulting in binding the rod and stopping the engine.
Crossheads.
It is always at the crosshead that the first trouble with a new engine develops. Fig. 10 shows two views of the pattern used on the large engines of our sets. The connecting rod is fitted to it with the ordinary strap, gib and key. The first fault appears as a rattle, then a decided knock at the pin, with considerable lost motion. It would seem almost unnecessary to point out that the set should be stopped at the earliest possible moment after any rattling or knocking develops and the key set up, yet ships come to the Yard hammering at the crosshead until it would almost seem that the system was to fall to pieces, and in almost every case from sheer carelessness and neglect.
Now, lost motion in any of the working parts, whether it be crosshead , link, governor weight, or bearing, always exists at the expense of speed, slowing the engine as the load is increased, which means low voltage, or racing as the load is decreased, which sends the voltage up.
In the latter case we can usually reduce the voltage by the shunt rheostat; but a slowed engine will usually prevent all efforts to get the voltage up to normal. the lights burn dimly with an annoying flicker and no remedy can be applied until the set can be shut down and the governor spring screwed down.
There is seldom any good excuse for lost motion; liner material in all convenient thicknesses is in store to be required for, and even if these are not available, there is always sheet brass, or tin, or coffee boxes about, which can be hammered to the thickness and small area required.
Crosshead guides wear in time, permitting the lateral play, which is chiefly responsible for the oval erosion of the piston disk before mentioned. This requires some machining, but is quite within the capacity of the ship's force. In most cases the wear of the guides can be traced to insufficient lubrication; bad oil is especially pernicious at this locality, inasmuch as considerable wear may take place before it can be detected by noise.
Cranks.
The crank end of connecting rods is almost invariably a stub-end connection; the brasses are made of the hardest obtainable bronze, and fitted brass-and-brass, that is, no parting piece or liner is placed between the flanges to be removed or reduced as the brasses wear, and it is practically intended that all probable wear will be resisted by the metal alone, except for some little lining up between the top brass and connecting rod, at the same time planning or filing away the flange surface.
If the metal is hard, but little heating, poor lubrication and tight fit apart, will be noticed; if soft, the wear is apt to be rapid, necessitating the taking of a good cut from the flange surface, true-boring in a lathe and new oil-ways. Scraping generally meets with little success, for the reason that the bearing surface is frequently reduced, which, in itself, is a direct invitation to further heating.
The calculations of the bearing surface of brasses are based on the thrust and weight to be applied at the journal, an empirical allowance of energy per square inch determining the total area required. Any reduction of this area must then cause heating. The proof has been directly demonstrated on board the Puritan, where all measures suggested proved tentative until the brasses were rebored.
A frequent cause of reduction in the bearing surface of crank brasses is want of alignment of the shaft, particularly if the wear on the oil-ways is at all serious.
Fitting these brasses, either new or repaired, requires good mechanical skill; it can be materially assisted by simply roughing the bearing surface of the brass with a half-round file, after the oil-ways are cut. The advantages are:
1. The roughed surface provides a slight clearance, which is not usually allowed, enabling the pin to establish a good working surface.
2. There is a polishing action on the journal which reduces friction.
3· The lubricant spreads more freely to all parts of the journal, particularly to the "dry line "-the line on which the pin is for the moment pressing. The expedient has met with good success in a number of cases, and is well worth trying.
Babbitt plugs and linings as used on ship's main engines prove inexpedient for cranks in the dynamo room. Babbitt boxes will replace brasses in most future engines, and are now fitted to the 32-K. W. sizes; they cannot be fitted to the present engines of smaller sizes from lack of sufficient clearance on the crank discs.
The rule that cranks should be placed at an angle of 180 degrees is imperative; to this any one will assent who, when in quarters aft, has listened to the pulsations of an A type engine located in a forward compartment. Ninety-degree cranks are quite certain to entail bad balance, racking strains on working parts, frequent lining up, vibration, lost motion and irremediable noise.
There is no manner of use in temporizing with a hot crank; dynamo men will make an effort, but the use of oil and water will only lead to the same result, which is shutting down and running another set while the crank cools and is examined for the cause of heating.
Shafts.
Springing and bending are the cases we meet with; flaw in material and breakage are rare.
A sprung crank-shaft is direct evidence of want of alignment as well as of an improperly drained cylinder on starting up. The ordinary case, however, is the springing of the line shafting carrying the armature, which has no support between the engine bearing and the ring oiler bearing at the end of the shaft. Referring to Fig. 5 and noting that the upper part of the dynamo
frame cannot be lifted, it will be clear that a 1200 to 1800 pound armature, with small clearance and handled with tackles, is liable at any time to permanently spring the 2½-inch shaft as it is moved out. It is from a knowledge of this fact that aligning a shaft is so often put off until the last possible moment, when Navy Yard facilities and workmen are not at hand. All of this handling of armatures can be avoided by cutting down the end bearing boxes, making the shaft end accessible, and should be done at the first convenient opportunity, and, in addition, a short trolley rail and car should be installed for handling the armature to prevent some of the injuries to the insulation of armature coils due to the pressure of blocking.
Later engine shafts have a flanged coupling between the engine bearing and the armature, trolleys are provided, the dynamo field coils are laid in planes of 45 degrees with the vertical (Fig. 17), and the upper half of the frame with its two coils can be lifted off out of the way.
It requires but a small spring in these shafts to send them under the hammer and to the lathe; a new shaft is the more probable result, a matter of fully six weeks after the order has been placed.
Governors.
There is seldom a case of repair in which one or more parts of the governor is not involved. It has been admittedly a troublesome and annoying device. Much of the blame lies at the door of the device; a part of the remainder is attributable to the fact that repairs which would have helped matters somewhat were not made; the rest, to a hazy idea in some quarters regarding the mechanism and its action.
Fig. II is an assembly drawing of the 32-K. W. governor, A and B type engines. Fig. 12 is a sketch, not drawn to scale or corresponding with the actual assembly, drawn to show the connection and action of the principal parts.
A fly-wheel with fifteen-inch flange is divided medially by a light diaphragm (solid web in later engines, having lightening holes as shown), and secured to the engine shaft by a sleeve, feather and set-screws. The wheel is divided into two halves to admit of assembly. On each side of the diaphragm are the following parts:
A governor weight, E, working on roller bearings; a short link, D; a long link, J; a weight-shaft lever, K; a sheave block, B; a shaft, M, which pierces the diaphragm and is secured to the weight on the opposite side; and a stiff, coiled spring. The eccentric, C, is rigidly bolted to the sheave block.
The action is this:
The weight, E, thrown out by centrifugal force, pushes on the short link, D, which transmits the power to the sheave block, B. This block is mortised at H to allow a motion across the shaft, the amount of motion being controlled by the spring; the eccentricity of the eccentric on the shaft center A, and consequently the travel of the valve, is thus changed by every motion of the sheave block. The sheave blocks on opposite sides of the diaphragm work at right angles, since the cranks are at 90°. The roller bearing is shown at F, and with the rollers in Fig. II. The position of the block as shown is for greatest valve travel.
By merely tightening or slacking the governor spring, by means of a socket wrench entered through a mortise in the rim of the wheel, we can increase or decrease the number of revolutions for any given opening of the valve ports, or, having set the spring by trial for a desired number of revolutions (usually 400), any increase in the number of revolutions will automatically shorten the travel of the valve and admit less steam, any decrease will lengthen the travel and admit more steam; the governor thus automatically keeps the engine to the prescribed speed.
The long link, J, weight-shaft lever, K, and weight shaft. M, are merely connections between the two weights for the purpose of ensuring uniformity of action.
The first trouble with these governors appears as an elongation of the holes through which the link pins are inserted, and on which pins the links journal. Lost motion then causes a rapid increase in the elongation from the hammering action of the heavy governor weights; elongation of the holes in the long links appears, resulting in stress of the weight-shaft lever, and in some cases in breakage. The weight-shaft levers are made of cast iron, but should be of tough forged steel.
Lost motion in a device designed for the direct control of the engine speed is necessarily that to which that engine would be most sensitive, it is more than established in the case of links.
That a device so simple in construction as the link represented by the sketch of Fig. 13, and which can be readily made from boiler-plate or plate steel, is not at once substituted for the worn link has no other explanation than inattention and neglect. The noise of a loose link is unmistakable, even at some distance, and it will not do to attribute all noise in the governor to the hammering of the weights "against the rim of the wheel," as it is often said. The weights cannot hammer against the rim of the wheel; they can, when running at light loads, hammer against the stops on which the weights take when at rest-particularly noticeable in starting up or shutting down-but at half load or more the feat is practically impossible, and any noise at such loads should immediately cast suspicion on the operation of the links.
Another expedient is to bush the link holes with bronze or steel.
The adjustable link shown in Fig. 14 is furnished with the C type engines; it is simple enough to admit of manufacture with our ordinary shipboard facilities.
The serious fault of the governor is in the roller bearings; it is purely a fault of design. In order to carry out the principle of "across-shaft governing." some means must be provided to relieve the friction clue to the pressure of the weight upon its journal; roller bearings were adpoted for the purpose; the pin, rollers and sleeve are shown in Fig. 15. Referring to Fig. 12, the weight, E, actuated by centrifugal force and having its fulcrum at the link, D, exerts a pressure on the rollers which are on the shaft side of the pin. If the weight revolved about the pin the wear would be equal all around, but with the steady loads in use and the small amount of motion of which the weights are capable, the pressure is exerted at practically the same region at all times. The hard rollers bite into the case-hardened surface of the pin and sleeve, gradually producing deep grooves which, when once the case-hardening is penetrated, rapidly increase; the rollers then act as a sort of key to prevent rotation of the weight or jump from groove to groove, causing very jerky regulation, fluctuating voltage and flickering lights; for motor supply such a condition is very objectionable.
Fig. 16 shows one of the corrugated pins, originally like that of Fig. 15, which was taken from the governor of a new engine after only six months' use; it is not the worst example.
When the worn pin and sleeve cannot be repaired or replaced the only recourse is to reduce the governor to a fly-wheel by blocking and govern with the throttle, involving steam waste and danger to the engine unless the carrying capacity of the main fuse of the dynamo is immediately raised as before explained.
Severing the gordian knot of this difficulty probably resides in abandoning the principle of "across-shaft" governing and adopting another which has proved successful under long use. Of these may be mentioned "line-shaft governing" as used with the Armington and Sims machines. also the tangential method of Ball and Wood, and the slip eccentric used by Sturdevant; both of the latter devices require that the governor is to be placed on the end of the shaft, where it always should have been, and where it is now placed in our C type engines and those for the Kearsarge.
The remedies at our disposal are to replace the worn pin, sleeve and rollers by new, which necessitates that spare ones should be on board; these should be of hard tool steel; or, to make a new pin, remove the sleeve and rollers and substitute a bronze bushing of equal thickness, a method that has met with great success at New York. The engine will not regulate as closely under the latter method, but by using a thinner oil-the usual lubricant thinned with kerosene-and making changes of load gradually it will be found to work successfully.
Governors are easily influenced by gummed oil or dirt and should be cleaned frequently; this point is much neglected. A pertinent instance occurred on the ship from which the corrugated pin of Fig. 16 was taken.
Repair had been made by bushing with hard phosphor bronze, the first repair of the kind. At the end of about a week word was received that the governor would not work. Upon taking it apart it was found to be completely choked with gummed oil and dirt-had not been cleaned at all, in fact. When cleaned and oiled it governed as well as before. The head dynamo man naively remarked that his hands were "too large to clean those small holes."
Valve Stems.
The too frequent breakage of valve stems has its ultimate cause in a jerky governor or shaft out of line. The original causes are that the length of the unsupported part of the stem is too great and that the guide casting is too light or has not sufficient strength for the purpose. Vibration and stress soon work the fastenings of the casting loose until, with loose guide and irregular stress from the working parts of the engine, the stem snaps. Two have been known to break in a single night.
Substituting a heavier guide casting and taking up lost motion will bring about a decided improvement.
The C-Type Engine.
The C-type engine, of which we now have about fourteen in use, is shown in Fig. 17. Many of the faults cited have been eliminated in its design.
The engine frame is made more compact and is much stronger than the light, stilt-like construction of the former types; a flanged, through-bolted coupling is inserted between the engine and armature on the shaft, thus minimizing the chances of springing when handling the armature; the cranks are set at an angle of 180°, ensuring good balance and lack of noise; the governor is put on the end of the shaft and connected by a rod and rockshaft to the valve links which operate shorter stems in secure guides. In the last engine of the type furnished packing rings are put on the piston. It is a good engine, but has the old fault of roller bearings.
The governor, a radical departure in design from the old, but on the same principle of governing, is shown in Fig. 18.
Both weights are on the same side of the web, which does away with the long links, weight-shaft levers, weight shafts and nearly half the width of wheel rim, the necessary weight at the periphery being obtained by thickening the rim. The construction is as follows:
The mass A, shaped somewhat like a guitar body, is cast in one with the web. A pin journal B, about which oscillates the cam C (shown separately in Fig. 19), taps into this mass. The cam carries the adjustable links D, and the journal of the governor rod E, which rod operates the rockshaft F. The spring acts directly on the weights through the pin H.
The outward motion of the weights actuated by centrifugal force-and resisted by the spring-Jrags the links D and with them the cam C, which in turn shifts the center of the governor rod journal toward the center of the shaft K. The amount of throw at the rockshaft evidently depends on the eccentricity of the center of the governor rod journal, the full throw being represented by the position of the figure.
The weights take against the buffers N when at rest, and as these are cushioned, much of the pounding when starting or stopping is avoided.
The roller bearing trouble has come to the front in almost every one of these engines so far examined. In the Indiana the pins of all three sets were renewed last spring and fitted with bronze bushings.
Similar repair on the Massachusetts is awaiting a convenient opportunity, except that in this case it has been practically decided to put in new roller bearings of tool steel. The new set for the Massachusetts, from which Fig. 18 was taken, broke the pin of the roller bearing M, due to a flaw in the metal not discernible at the surface. When the pin was taken out a very decided corrugating action was found on its surface; the set had been in use but three weeks.
The governor of the Kearsarge and Kentucky sets has but one weight on roller bearings. The pin is made of hard tool steel and increased in diameter from 1 5/8 to 3 inches. There has been no experience as yet with the action on tool steel except in the case of the experimental set, representing the battleship (single set) design; this has been run at Schenectady for hours over a range of several months, submitted to all sorts of crucial tests, but now shows no sign of wear of the hard steel surface at the larger diameter.
Perhaps this may be the solution of our vexatious governor troubles in design. We who have the care and handling and annoyance on board ship sincerely trust that it may.
Dynamos
Our dynamos are all of the constant-potential, "direct-current" order. Since the introduction of the smooth body armature-the modified Gramme rings shown in Fig. 5-but two types have been designed, the A type or form having the pole pieces in the vertical and horizontal plane as represented in the set shown in that figure, and the B type in which the pole pieces are in the diagonal planes; the frame is divided in the horizontal plane, flanged and bolted to admit of ready removal. These constitute the only important differences between the types. Experience with the type of Fig. 5 shows a great exposure of the lowest coil to all drippings of oil and water. This was particularly observed in the port set of the Cincinnati on her return this summer; the coil was so saturated with oil that it dripped from the wire when running it through the wiper.
Apart from the ordinary advantages of multipolar over bipolar constructions, our machines have put out of the consideration the effect of stray field upon the compass. Sir William Thompson has asserted that all dynamos will influence the compass on board ship, and points out that the danger is greatest at night, when heavy loads are carried and when the opportunities for observation are often impracticable. Tests made with both machines at full load on board the Puritan failed to show any disturbance, it is therefore supposed that the foregoing statement, made some years ago, refers to bipolar constructions, as the multipolar was not in general use at that time.
Extensive trial has also proved that the electric lighting or binnacles produced no appreciable effect. The new type V binnacles are fitted with electric lamps, except for those binnacles which are to be located at the hand wheels.
Sparking.
Almost any violation of electrical or magnetic principles in design will produce sparking; it is also true of some errors of mechanical construction. These faults of design are matters for original and acceptance tests; the ship problem presents but few cases.
We have, however, in use two types of machine which, after a short time, spark beyond redemption at any stage of load or position of the brushes on the commutator; these are the Thompson-Houston and Siemens-Halske patterns; there are six all told in the service, and all 4-K. W. machines. Both types have a modification of the "ironclad" construction of armature, which, though very successful in small motors, will not answer for a dynamo. This construction differs materially from the slotted core design, whose teeth and slots are deep and narrow, and whose windings are practically cooper bars. The brushes also should make contact on three bars.
The Siemens-Halske machines in use in one of our ships spark so badly that the commutator is sand-papered two or three times a week to keep it in even fair condition.
Overload is the frequent cause of sparking, and will be shown by the ammeter, except in cases of grounds in the machine itself. It is not usual for the case to occur from extra loads on the lines in circuit, for the reason that the loads of the circuits are known; the general case is a ground somewhere, which should be tested out and removed; this the ground detector should show.
There is an occasional case of sparking from a broken coil, which can be readily detected by holding a file or screw-driver between any two pole pieces; the tool will be dragged in the direction of rotation Whenever the broken coil passes. The repair consists in winding in another coil. A similar case is abrasion of armature coils; if the damage is slight it can be repaired with tape and shellac; if serious, a new coil must be put in.
Improper adjustment of the brushes is a common cause of sparking on board ship. It is intended that the connection be tween brush and commutator shall be a rolling and not a friction contact; this is a little difficult to explain, but can be demonstrated by trial.
A rolling contact can be assured by keeping the brush carefully trimmed to the angle at the bar and setting it with a light, complete touch. A brush jig is always furnished, and it is only necessary to file the brush to the exact bevel of the jig. Gauze brushes will seldom spark under these conditions. They are the only brushes worth trying; this of course does not apply to slotted core machines, in which carbon brushes are practically a necessity. A material assistance to good working between brush and commutator is the use of a little oil, that which can be taken from an end bearing on the finger, preserving that smooth, dark-brown color on the bars which is the best evidence of good working.
It is not rare aboard ship to see brushes bent by pressure, producing friction and wear on the commutator, the small area at the heel of the bevel making the contact which may not spread across the space between the bars, and causing sparking which is to be relieved by more pressure; this pressure, assisted by sparking, has one sure result, the scoring of the commutator or flats, both of which tend to farther and more severe sparking, and can be remedied only by dressing down the bars.
The proper trimming of brushes is much neglected; brushes require careful inspection to see that the contact is not ragged, scored or dragging shreds of waste.
Low Voltage
The voltage of a dynamo for a unit of time is equal to the product of three factors expressed m the formula:
E=CNR,
in which
E =Total E.M.F. of the generator.
C =Number of coils in the armature.
N =Total number of lines of force passing through the armature, i. c., the intensity of the magnetic field.
R =Number of revolutions of the armature, also of the engine in direct connected sets.
This formula affords us an excellent means of tracing faults in voltage.
The quantity C, the number of coils, is fixed by the design, leaving R and N, the speed and strength of the magnetic field, as the variables. The revolutions are tested by applying a tachometer to the end of the shaft and can be regulated by the governor to the rated speed (usually 400 revolutions); R then becomes a constant and the fault must lie in the field.
The intensity of the field depends upon the number of ampereturns which is equal to the number of single coils around a core multiplied by the current passing through the coils. Since the number of coils is fixed by the design, there must be a fixed number of amperes for any given strength of field. The problem thus becomes one of current alone, and shows that low voltage depends upon the simple principle that some by-pass is robbing the field coils of their due proportion of current.
There are several causes of weak field which are beyond the control of the shunt rheostat, or regulator as it was formerly called.
1. Loose connections or bad contacts. Every bolt and nut and screw which has anything to do with the shunt or series coils, and at the rheostat, should be slacked up, dirt and oil cleaned away and the contacts brightened up with sandpaper. All should then be securely set up.
2. By-passes and grounds. These occur from a collection of dirt, oil or water, or any combination of them, which can form a train to a neighboring wire or the metal parts either about the machine or rheostat.
A case of low voltage occurred on the Columbia which was finally traced to a train of copper dust and filings leading to the shunt field connections. Cleanliness of engine and dynamo should be rigorously exacted; it applies with especial force to motors.
There is an especial case of ground of the shunt rheostat which is a common cause of low voltage. Fig. 20 shows the shunt rheostat complete and also with the brass case removed.
A coil of "resistance" wire is wound continuously on each of two metal frames, as shown at A, the coils being connected in parallel to one of the shunt wires; the other shunt wire connects with the brush B at C.
The brush is insulated from a lever (not shown) which is operated through a rockshaft by the handle D. This brush makes contact with the resistance wire on top of the frame, the wire being laid bare on the upper surface. Though neatly and tightly wound around the frame, the wire is likely to bulge after a time, be touched by the lever on the inside of the frames as it passes to and fro, and be chafed until the insulation is cut through and the wire grounded on the lever.
A sheet of mica or thick paraffined paper will remedy the difficulty until new wire can be obtained for rewinding the coils.
3. The series shunt. The office of this device, commonly but erroneously spoken of as "the compounding," seems to be little understood.
A short explanation of the effects of the shunt and series coils and of the series shunt on voltage will make the subject clear.
Fig. 21 represents a theoretical characteristic (the ''indicator diagram" of the dynamo) of a compound dynamo in which the ordinates are volts and the abscissae amperes. In starting up since no current is passing in the external circuit and hence none in the series field-the voltage is raised by the shunt field alone, hence all curves originate at A. Were the shunt field to continue to act alone (we will presume there is no shunt rheostat) the curve produced would be AB, which curve indicates that the voltage of an unaided shunt field falls as the load is increased, and at full load would be insufficient for anything but redness in the lights. The desired curve is the line AC, but as a matter of experience engines tend to slow at high loads, producing the curve AD, and for that reason a slight up-curve, as shown by AE, is preferred to AC. To supply the increments of voltage pn, p, n, necessary to bring the voltage of the curve AB to that of AE, is the function of the series field. The action of the combined fields makes the dynamo compound and self-regulating.
It is mechanically inconvenient, if not impracticable, to obtain those nice lengths and resistances of series and shunt windings which are the necessities of the case, and coils are cut to lengths convenient for construction; the series coils are designed for less than the required resistance, and a series shunt is connected across the terminals of the series fields to afford a shunt or bypass for the current to be abstracted; the shunt rheostat regulates irregularities of resistance due to original construction, temperature. etc.
Fig. 22 shows diagrammatically the system for both fields. LL is the external circuit or line; S1 and S2 the terminals of the shunt field S; T1 and T2 are the terminals of the series field T; H1 and H2 the terminals of the series shunt H. It will be apparent that any current in H does not pass through T, but goes out to the line through H only.
The actual series shunt is sketched in Fig. 23. It is usually located on the back of the head-board, with a removable cover whose top is made of wire gauze. It consists of copper strip zigzagged around insulators A. on which clamp-sliders, Fig. 24. are placed. By moving the sliders to the left the resistance of the shunt is decreased and more current is taken from the series circuit; by moving to the right the opposite effect is produced.[*]
The series shunt is adjusted on acceptance test and it is not expected that any alteration should afterwards be made or necessitated.
On acceptance tests, immediately after taking the cold resistances, the sliders are clamped to the series shunt, preferably midway from the terminals; the rheostat handle is set midway between high and low, or on the middle point or block of circular type rheostats, these midway positions affording the greatest range of control of regulation. When the machine is started the voltage is adjusted to So volts by the series shunt sliders for the heat run of four hours, and then adjusted for a full clue while the machine is hot. The sliders should be on the same line and a permanent mark made on the case to indicate the proper position. Usually a machine which develops the proper voltage both at full load and no load will produce that same voltage at any other load, that is, within the limits of a volt on either side; anomalies occur.
In a 2-K. W. machine tested last winter, having no series shunt, the voltage at full and no load was exactly 80 volts, but at six amperes the voltage increased to 90. In testing engine regulation with this machine the voltage reached 110 when breaking from full to no load in one step; this would be sufficient to burst every lamp in circuit. In a 24-K. W. set tested a close regulation to 80 volts occurred at full and no load, but increased to 89 volts at half load; adjustment of the series shunt brought the characteristic nearly to the ideal over the whole range.
No harm can come of readjusting a series shunt (unless it be overlooked in paralleling machines) if only it is done intelligently; at the same time it is a bad school for dynamo tenders. Nor should an occasion arise until, in old age, the machine develops erratic action which the ordinary expedients will not reach.
The foregoing explanation demonstrates that the voltage of a machine is easily deranged by tampering with the series shunt. This has been developed in the case of a ship that came to the Navy Yard with an apparently inexplicable case of low voltage. Connections were overhauled, grounds tested out, shunt rheostat examined, and all to no purpose; finally recourse was had to the series shunt, and the sliders found to have been shifted by a man who, in cleaning out some oil and dirt, had moved them and put them back as nearly as he could remember. No one on board had been able to locate the difficulty.
Our dynamo troubles are so few that a little care and intelligence should control them handily, and these qualities will be improved by frequent inspections, above all things for cleanliness.
A certain crack ship in the service had a dynamo room whose bright shellac and general condition would please the eye of any captain; when it came to repairs there was dragged forth from the spiders, armature body and field coils a collection of oily muck and dirt that could have produced a series of troubles; it had deteriorated the insulations as it was. This sort of cleanliness does not, as far as electricity is concerned, partake of any approach to the godliness mentioned in the adage.
Lack of cleanliness, and salt water are the inveterate enemies of electricity on board ship.
One of the difficulties in design of armatures and field coils is obtaining good radiation of the heat generated in the coils. Heat not only increases the coil resistance, occasioning the waste energy of internal losses, and hence decreased efficiency, but deteriorates the insulation of the coils. The non-conducting property of insulation dictates that it be reduced to the lowest advisable thickness; at the same time there is a limit of reduction which it is not safe to pass; our restriction that the heat rise in the coils shall not exceed 50° F. above that of the surrounding atmosphere after a four hour run has necessitated a large armature comparatively; the necessity of this limitation is apparent when we consider the high temperatures of the average dynamo room and the influence of the ultimate temperature to which the coils will be subjected. Oil, in addition to its evil effect on rubber and dirt; increase the difficulties of non-conduction in their cycle of effects.
In some ships paint has been put on the end conductors for appearance' sake, a material more baneful to armature coils than oil and dirt, not only on account of the deteriorating effect of its oil on rubber, but through the non-conducting layer established; once applied it cannot be removed, and when dirty is to be cleaned by another coat of paint, producing more resistance to radiation.
When an armature burns out the accident usually occurs, from a variety of causes, at these very end conductors.
The end conductors of a ship in the service were painted blue; the men of a rival ship, consumed with envy, painted theirs green.
A plea is entered here for more frequent exercise in paralleling.
A veil of mystery and danger is thrown around the subject which it little deserves. Compound machines are paralleled everywhere in this country now-a-days; they will not do it in Europe. But it was not until an electric light station became practically wrecked in New York that our best experts found the solution; they now run the negative leg straight, fuse the equalizer and put an automatic circuit breaker on the positive leg; a machine can be in no danger with this arrangement.
Paralleling compels a man to know his machine or trouble ensues.
The dreaded danger lies in the fact that if one machine A gets a certain increase of voltage over the other machine B, A will cause B to reverse and the whole load will fall on A; B becomes a motor and is likely to rip out its brushes, if of the ordinary copper type, when turning backwards; if the current thrown on A is over so per cent. above A's rated capacity, A's armature will probably burn out. This is a rather startling array, but is quite within control when the conditions are known, so much so that commercial machines run along in parallel for hours and days together without a thought of danger, but they know their machines.
Reversing an armature, and therefore paralleling, depends on the internal resistance, and hence upon the efficiency; the lower the internal resistance, the higher the efficiency, the less will be the voltage to turn that armature backwards. Taking a characteristic by noting the voltage for each load thrown on, no change being made in the shunt rheostat, will show whether the two machines differ sufficiently, at any load or loads, in their voltages to endanger the lower machine's reversal. With our machines there is little chance of it; they are compounded very closely to the straight line, and have characteristics so nearly similar that the matter can be taken on trust, but this does not mean that it is always to continue so; a characteristic should be taken from time to time to see that it is so.
As long as the difference of voltage does not exceed three (3) volts everything is safe, but the voltages should be kept as nearly as possible to the standard by the rheostat to ensure safety.
First see that both machines are poled right; being in alternate use the voltmeters ought to be connected right and would tend to move in the wrong direction, would not indicate, if the poles were reversed; get both machines up to 80 volts and divide the load as equally as possible between the machines, then close the equalizer switch, called in the instructions the multiple switch. (See Appendix A.)[*]
Each machine will take up half the load and both will run along practically synchronously and need only the attention of a motion of the rheostat handle now and then. It is better to parallel two machines than overload one, and it is good practice whenever heavy loads are to be carried. It is better not to put motors carrying variable loads on the same bus bar with lights, as a flickering is sure to occur; and for the reason that the mushrooms of a search-light occasion sudden jumps of current within wide ranges, that light is preferably to be run by another machine.
Vibration.
The vibration of a generating set in good working order is purely a question of foundation s; with well braced decks, heelplates resting on two inches of oak to cushion the tendency, and thorough bolting, the difficulty is rare. Two service examples will illustrate the fault
In the Columbia the dynamos rest on a light deck over a very high coal bunker. Sufficient support is given by stanchions in the bunker but no lateral strength is afforded other than that of the deck framing.
So great was the vibration produced that the captain could not write at his desk until the engine was slowed to 350 turns; the greatest obtainable voltage at this speed was 70, the lights showed a bright red.
Four heavy stanchions for each machine were securely bolted to the deck and to the protective deck overhead, with flanged toes bolted to the bedplate. This expedient checked all vibration.
In the Amphitrite vibration was partially remedied by shoring up the deck underneath. The vibration still exists to a marked extent, as any one can testify who will stand on the port side of the quarterdeck or take hold of the bridge rail.
As a matter of physical interest it may be mentioned that in both of these cases distinct nodes and loops were developed. In the Columbia the captain’s desk was near the center of a loop, and hence received the full amplitude of the wave.
Noise.
Many noises which occur have been mentioned; generally speaking, none should be allowed to exist.
Piston valves develop a little pounding due to wear, by balloting against their seats; oil will delay its occurrence. There is a very good valve in the market whose wear is as regular as that of the D-slide valve, and whose wear rather enhances its fit; it is known as the telescopic valve. It will operate even with the valve chest bonnet removed, and has the distinct advantage of acting as a voluminous relief valve in a critical case of water in the cylinder.
There is a noise peculiar to cylinders explained as a combined whistle and grunt. It is due to the friction of the piston, and is quickly relieved by a little oil in the· steam. Pounding in the cylinder is generally clue to water; if free of water it is good evidence that the load is not evenly distributed between the cylinders and that the valves need resetting.
Reducing Valve.
The frequent complaint against these valves is that they are not adjustable. A gauge with its branch to the steam pipe would be a great convenience and assistance as showing the actual pressure of steam delivered to the dynamo room. An adjustable reducer is in a sense a throttle, and will produce the evils of throttling down if so used.
Separator.
The Stratton pear-shaped design, shown in Fig. 25, is that ordinarily installed ; there is also a cylindrical type. They work well if properly handled, and can be highly recommended. Those furnished have been too small; the rule should be that the capacity should be from four to five times the volume of the cylinder, in order to cushion the engine pulsations and avoid the objectionable vibrations of the pointer of the steam gauge dial. A large capacity separator will also take care of much of the water which comes over to the cylinder on that critical occasion when a machinist shifts from one boiler to another without sending word to the dynamo room beforehand.
The breakage or blowing out of water glasses is a common case. In some cases it is due to accident, but is more often due to poorly annealed glass. Any effort to work a separator without a water glass is merely courting accident; it was the occasion of the breaking of a connecting rod and the four stanchions of an engine in one of our ships.
The glasses furnished to the chief engineer are trustworthy, will fit, and will be found to last for long periods.
There is a point about separators which has come under observation and which has a bearing on occult cases of water in the cylinder.
The separator is a condenser; owing to the fact that the trap sometimes-though rarely-gets out of order, or needs cleaning, the water is drained through a pipe leading directly into the dynamo room. The dynamo watch can make use of this connection for the purpose of obtaining an odd bucket of water or two; it is a case that can be remedied best by some vigorous administration.
The Switchboard and Circuits.
Before entering upon faults in this direction, and which have been covered in specifications, it may be well to consider the unsettled problem of the behavior of our installations in action. Circuits are now installed to the greatest possible extent below the protective deck or behind armor, exposed branches are run in the most direct manner feasible, and all lines that could be reasonably exposed to the action of shot and shell or develop grounds that would affect or derange the working of any electric light or device needed in action arc provided with cut-outs where they do not connect to the switchboard.
Lieutenant W. S. Sims, U. S. N., in a report made on the battle of the Yalu in 1894. says:
"Captain James" (now retired, but formerly connected with the Japanese naval establishment) "says that long before the end of the engagement every electrical communication in the· Japanese vessels had entirely failed; that candles and lamps bad to be used in all lower compartments, engine rooms, fire-rooms, bunkers and magazines; that the search lights were useless; and that, fearing the torpedo boats, they were unwilling to risk continuing the action after dark. It is not clear how the electrical communications were damaged, but it is said to have been due to the large and complex vibrations set up in the ship by the discharge of the heavy and secondary battery guns and by the impact of the enemy's shot. It is said that the lights were at first fitful and finally failed entirely."
No more succinct information has been obtained as far as is known.
The responsibility for the results reported has been laid by a high naval authority upon the dynamos, their method of installation, and the circuit appliances in use.
Applying the experience to our own case, we have little to fear from our machines or their installation, excepting as regards location. It has often been pointed out and urged, and becomes more pertinent day by day, that ships, especially battle-ships, should have their plants divided between two dynamo rooms widely separated in the length of the ship.
It needs no argument, but is for some reason completely ignored.
It may be an open question whether our switchboards and the porcelain insulating blocks of wiring appliances-feeder boxes, junction boxes, switches and the like-will stand up under the shocks and vibration of the Yalu report, especially under a heavy shock within the ship.
The panels of the switchboard are of slate, a fairly fragile material, and have many perforations for the circuit leads which increase their weakness; still slate has a distinct advantage over marble, from the diagonal nature of its cleavage. To the very fragile nature of porcelain for insulating blocks is added the fact that the holes for the screws which hold the electrical connections to the blocks are near the edges and corners of the block; the blocks are most likely therefore to break at these screw-hole and release the connections; mere hammering on a bulkhead where wiring appliances are installed is often sufficient to break the blocks.
It is submitted that these loose and vibrating connections, the possible contact-particularly a vibrating contact-of connections of opposite polarity to make short circuit, and the jarring together of circuit connections at the switchboard to cause grounds and by-passes, will occasion that very flickering and failing of lights spoken of in the report.
It is now required that each panel of the switchboard shall be held by a separate framing of oak-like a picture in its frame which will afford more security.
The certain safeguard is to make the switchboard panels and insulating blocks of a strong, tough insulating material which will minimize all liability to breakage. Fibre and vulca-bestin (a vulcanized mixture of asbestos and rubber composition) have been suggested, but both are disposed to absorb oil and become poor insulators. The material par excellence is micanite; mica would be preferable, but cannot be obtained commercially of sufficient size. Micanite is manufactured by pressing together thin, formed pieces of mica laid in cement; any desired form and thickness can be obtained. Micanite has the objections that it splits, scales or becomes ragged, but these can be prevented by casing or facing with some insulating substance, vulcanized rubber composition for example.
As for search-lights, the exposed condition of their leads almost ensures that they would be destroyed within a short time. In a day action the projectors would be sent below; the leads should have a connection installed behind armor to which loose wires could be connected when needed for night use, and when the projectors can be mounted for use; the subject has not been taken up thus far.
The general excellence and convenience of the present switchboard design, except in so far as the material of the panels is concerned, eliminates it from the question of faults; some changes or rather additions will have to be made, however, to accommodate it to the use of the number and variety of power circuits for which no design has as yet been presented. Small motors can be grouped on lines from the ordinary switchboard; others will probably have panels and circuit connections of their own, carrying knife switches and automatic circuit breakers similar to those used in electric light stations.
The automatic circuit breaker consists of a double pole switch which closes against a strong spring and is held to its closed position by a spring catch. A solenoid adjustable for the permitted overload actuates an enclosed plunger which trips the catch and the switch flies open. Differences in design arise chiefly from the manner of extinguishing the heavy spark at break. In the "I. T. E." design a block of carbon is fitted to both the switch tongues and jaws, the blocks extending far enough to preserve a contact after the tongue and jaws have separated. The resistance of the carbon somewhat reduces the spark, which at the end acts on the carbon alone and not on the copper connection. The carbons can be readily and cheaply renewed. In the General Electric Co.'s design an electromagnet is placed near the sparking contact and breaks the spark by drawing it aside, as in the well known experiment of a magnet on the electric arc; this design is commonly called " the magnetic blow-out."
Automatic circuit breakers are much more reliable and positive in their action than fuses, and, what is better, can be easily tested for operation, which, of course, the fuse installed cannot.
The voltmeters and ammeters are constantly in state of improvement, and even now, notwithstanding the excellence of Mr. Weston's designs, which can be safely recommended as unequaled, experiments are making at his works in perfecting the alloys. The circular type of instrument is standard, the ammeters being shunted from one leg of the circuit instead of taking the entire load.
Fig. 26 shows the switchboard of the Puritan. The upper board is for the search light instruments; the boxes for the ammeter shunts appear at the right and left near the top; the transformer, Crocker-Wheeler type, is shown resting on the battery transfer case ; the rheostats for the search lights and shunt fields are at the bottom. This switchboard has a position which is very much exposed to particles of oil, when the oil-guard of the neighboring engine is not in place, but no other place is available, one side of the dynamo room having to be left clear for access to the armor bolts.
The lamp ground detector should, and no doubt will, be replaced by the Weston circuit tester and ground detector shown in Fig. 27, which is simply a voltmeter reading both ways from a central zero. The great fault of lamp detectors is that unless there is a dead ground the lamp will not flash up; imperfect insulation resistance as low as 100 ohms will produce no indication. In the Weston device lowered insulation is at once indicated by the deflection of the pointer and its direction; it is not necessary that it should be direct reading, which would occasion expensive design: the deflection is sufficient, the calculation being made mentally or by reference to a table used when testing insulation resistance by the simple, excellent method known as the voltmeter test, to be explained later on.
Many of our switchboards have been insufficiently supported, thereby bringing a stress upon and loosening the circuit connections of the panels. The weight should be taken by a shelf, or at least a plank supported by posts. Accessibility of the connections at the back of the board is imperative.
Safety in paralleling dictates that each set should have its own voltmeter; the practice has been to allow two voltmeters in case of three machines.
Wire. The use of so many kinds and conditions of wire has rendered it absolutely necessary to co-operate with manufacturers and tie down the construction to minute details. Lead covered wire has fallen into disuse from the difficulty of its repair, the manipulation of its weight, and the almost certain breakage at bends and angles. It has fallen far short of the anticipated advantages claimed for its use in heated locations, and is peculiarly susceptible to any electrolytic action; in the underground work of cities where trolleys are run the companies will no longer guarantee it, and lengths have been taken up in Brooklyn on which no evidence of the lead remains beyond a blackish-white salt, due to the action of the trolley currents.
The general principles of construction of standard wire are;
1. A protection against grounds, should the vulcanized rubber strip or flake, by means of a thin laYer of pure Para rubber adherent to the copper conductor.
2. Insulation by vulcanized rubber for the voltage to be used. The combined insulation of the two foregoing coats is nearly double that required by the underwriters' specification for 125 volts.
3. Circularity of section over the vulcanized rubber by a layer of cotton tape soaked in an insulating compound, to ensure a neat water-tight fit of the gaskets-the conical, perforated plugs use in the wiring appliances-mere braid forming too rough a surface for the purpose.
4. Preservation of these layers from stripping or flaking off, or from mechanical injury, by means of braid.
A test of the insulating quality of our wire was made by subjecting to the stress of 5000 volts, static charge, which it resisted for nearly an hour. It stood the voltage of an X-ray machine for nearly a minute; this voltage could not be measured but must have been very high.
One great improvement in wire has been the introduction of cables for the interior communication leads by which a few hundred feet will replace the miles of single wire heretofore made necessary. The cable is not only applicable to the bell circuits, but will answer for a number of instruments. These cables are shown in section in Fig. 28, and have from 2 to 20 conductors. They are installed in the same way as other wire and run into connection boxes taking 20 or 40 wires. Within the connection boxes are the tags for the leads and from them branches can be run to the desired locality by smaller cables, the whole admitting of a thoroughly water-tight connection. A wire in each layer is braided in white for convenience in counting.
An example of some inferior wire which has been used occurs in the bunker and water alarms of the Montgomery and Detroit. This wire is ordinary blasting wire, consisting of a copper conductor and a light layer of vulcanized rubber. Installed over and within a couple of feet of the main boilers the insulation has stripped and flaked, short-circuiting both systems.
Circuits. It may -be better perhaps to predicate this subject upon specifications which, apart from the ordinary rules of wiring, have been drawn from experience in service.
"Conduit will be used for all spaces in the water-tight system. It is to be preferred" (to molding) "in all other localities; but in spaces where it may not be desirable to run it over woodwork, as in chart houses, emergency cabins and officers' quarters, standard wooden molding may be used."
Naval constructors define the upper limit of the water-tight system as the stability deck; this would take in all the ship below the main deck and include the superstructure of constructions like the Maine; hence conduit is to be used everywhere, practically, which is not excepted in the specification.
The conduit is iron or steel pipe, brass about the magazines, etc., lined with rubber or bituminized paper; paper is the better for heated locations, such as engine and boiler spaces, drum rooms, etc., rubber where bends and angles occur and where paper would be apt to burr and interfere with drawing the wires.
Molding is open to many objections. It is made of wood, lately expunged from ships as far as practicable; fireproofing is said to detract from the insulating properties of the molding. It requires excessive drilling and tapping of the bulkheads, a screw every six inches of the length, to secure the backing strip of each line run, a serious and expensive delay in addition to weakening the plate.
As the electrical installation must wait upon the other details of construction about the ship, the wiring plans undergo frequent changes from the original design and molding lines are turned and twisted for every sort of device or lead of piping; it is too expensive or involves delay to rip out a whole line and re-install, and a makeshift must be designed involving numerous joints and turns, or, in case;; where the piping is to set well off the bulkhead, recourse must be had by way of the interior of a bunker, where coal will soon use up the molding; in the New York many of the lines in bunkers are now bare, the molding having disappeared.
The capping warps and exposes the wires; if the screws are placed at the side, much the better plan, there is still exposure at the edges, particularly those of mitred joints. It requires an expensive line of tubes through bulkheads and beams.
Conduit requires only a strap and screws at each frame or about every three or four feet. It can be bent around piping without other support. It can be screwed into flanges at bulkheads and beams without other device. It can be used as a bracket or pendant for fixtures, especially in machinery and boiler spaces, where the use of molding would only admit of the installation of a hand portable. It is available for approaches to the turret leads, where hydraulic power is used, when molding would be inadmissible; within the turrets most of the leads must have a flexible covering, rubber-lined hose or flexible conduit for example.
Some former trials of unlined conduit did not prove satisfactory on account of the effects of condensation. Paper and rubber are non-conductors of heat, and if the original installation is exposed, inside and out, to a moderately cool temperature, the dew-point should be sufficiently low to obviate such a result, and no access of air for a long period of time should afterwards occur provided care is taken to keep the boxes of wiring appliances closed and tight in conformity with their water-tight design. It is from this cause that condensation is most likely to appear; it would ordinarily be trivial in amount and drain into the distribution boxes and be eliminated from there. In repairing a ship so caps to the boxes were missing and the boxes found to be filled, choked and short-circuited by a mass of ashes and dirt caked by oil and verdigris, the latter the result of the use of hose in washing down bulkheads. These caps are now fitted with a chain secured to the corner screw of the cover, and not only should the caps be set up hard with a wrench, to prevent tampering with by unauthorized persons, but the screws of the cover should be set up occasionally to ensure close fit on the rubber washers; the difficulties occur mostly in fire-rooms. Engine and fire rooms are the most difficult to install satisfactorily and require a good share of attention afterwards.
Fig. 29 shows a distribution box and the method of leading conduit as installed in the fire room of the Puritan. The box is of cast-iron, in which are placed as many of the ordinary interior fittings of junction boxes as may be required for the branches. Bosses are cast at convenient intervals, and those bosses alone are tapped which are to be used for the leads; the branch for a single light would be run in one pipe with double conductor, plain (formerly hemp portable-the term portable is now used for its proper signification of something to be carried).
''Lighting circuits will comprise the following divisions, according to the service required.''
These divisions may at first seem complex, but there are really but three sets of feeders, continual service battle service, and general service, each with its especial variety of lights on mains led off from the feeders or on submains run from the mains themselves. The chief idea is to obtain control of a large number of lights at one point and do away with the endless number of individual switches. Of all our appliances the switch is the most unsatisfactory; the insulating blocks on the stems are readily broken by thoughtlessly turning against the sun instead of with it; the contacts oxidize, heat or are indifferent in action from tension of the springs, thus introducing uncontrollable resistance.
Switches on a battle circuit are undesirable; such circuits should be handled directly from the switchboard to prevent unauthorized lights; the switch and receptacles of the light boxes and a key socket in the armory are all that can be needed. As usually installed heretofore individual switches have been a necessity, but in future installations of battle circuits none should be allowed. The mains for fire and engine room circuits are thrown on through the interconnections.[*]
It is intended that when a loop main is run off there shall be but one loop, the submains to be run off with branches to the lights; the loop-on-loop method involves too many connections when searching for a fault or ground.
The advantage of the loop is shown in Fig. 30. If a set of lights are fed on a main as shown, the farthest lights B will not burn as brightly as those marked A on account of the drop (fall of potential) clue to the resistance of the main. If, however, two pieces of wire, as shown by the dotted lines, are connected in the drop will be equalized all around the "loop" and all the lights will burn with practically the same brilliancy.
The method requires a little more wire than a straight lead with lateral branches, but in a large crew-space, especially where submains are necessary, the benefits overreach the small additional expense.
"The maximum load for all lighting feeders, excepting those for search lights, shall not exceed 75 amperes. In case the current required for any service exceeds 75 amperes, a sufficient number of separate feeders shall be provided … Motors below 4 K. W. will be supplied by the same feeders, the maximum load on any one feeder not to exceed 75 amperes … No feeder or main will have a less area of cross-section than 1000 circular mils per ampere at the normal load, to be reckoned at the rate of nine-tenths ampere per lamp of r6 candle power … Feeders which interconnect shall have an area of not less than 1500 circular mils per ampere at the normal load … Not more than two feeders shall ever be interconnected, and no feeders shall be interconnected through their mains …
The area of cross-section of the feeders and mains on the lighting circuits shall be such that the fall of potential from the dynamo terminals to the most distant outlet shall not be more than 3 per cent." (2-4 volts) "at the normal load of the feeder … The area of cross-section of the feeders on circuits for motors of and above 4 K. W. shall be such that the fall in potential from the dynamo to the motor terminals shall not be more than 5 per cent." (4 volts for 80-volt circuits, 8 for 160-volt) "at the normal load of the feeder; for other motor feeders to be as prescribed for lighting feeders."
These rules have been revised, and are derived from experience in the great irregularity and want of system in wire sizes and are intended:
1. While limiting the increasing number of feeders by the large load permitted, to regulate the sizes in different ships and still provide a convenient number of circuits for the total load.
2 . While allowing full carrying capacity by a stipulation of the number of circular mils per ampere, to prevent wires of undue size, weight and cost from being used by a per cent. allowance for drop. This drop, or fall of potential, is due to the resistance of the lead and is, numerically,
Drop = CRs,
in which C is the current carried by the lead and Rs is the resistance of the lead or section of the line.
3. To prescribe a minimum carrying capacity for interconnections, which has heretofore been more or less disregarded and, in many cases, made through mains whose capacity was much too small, considering the fact that the load of both feeders must be provided for.
The general method of determining wire size has been published before, but will be briefly explained here.
The lights, outlets, etc., are first located and preliminary drawings made for tracing the feeders and mains. In large spaces lighting is based on an allowance of one 16 C. P. lamp for a floor space of one hundred (100) square feet; other spaces are lighted as deemed necessary for their use or for convenience.
The feeder sizes can then be directly calculated on the allowance of nine-tenths ampere per lamp--900 circular mils; a 75-ampere feeder can thus carry about 83 outlets, that is, provided the most distant outlet is not farther from the dynamo terminals than 111 feet.
The general formula for the area of a wire, for any distance, is
Circular Mils (C.M.) = 2DxCx10.83/d
in which 2D is the total length of the wire (both positive and negative legs), C is the current to be carried and reckoned at nine-tenths ampere per lamp, a margin of 1¼ per cent. on the actual necessary current, and d is the drop in volts. The formula is derived as follows :
The resistance of a conductor varies directly as the length and inversely as the cross-sectional area (in circular mils by our notation), and is equal to,
R = Lxs/C.M.
L = Length of wire or twice the distance to be run.
s = specific resistance of the conductor, i. c., resistance of a square inch or square centimetre at unit length at 32° F.
s, for pure copper, is 9.612, and 10.83 at 70° F., allowing 4 per cent. for twist of the strand in the length (properly a correction of L).
Now d=CR, from Ohm's law.
Substituting we get the general formula given. If in this formula C is unity and C.M. is 1000, 2D becomes 111, that is, the longest feeder line possible at the allowance of 1000 circular mils per ampere is 111 feet; for greater distances the area must be calculated by the formula.
Wiring charts are made up for different values of the variables, from which the necessary size can at once be picked out and that size taken from the standard table which best corresponds.
In order to obtain circularity of section a strand must contain a certain number of wires of the so-called "geometrical series," that is, it must be laid with 1, 7, 19, 37, 61, 91, 127, etc. (1 + 6 + 2x6 + 3x6 + 4x6 + 5x6 …) of the unit wires of convenient size; this is exemplified in the table of standard wires of the specifications.
These wires increase in cost and weight in more rapid proportion than the size, and for that reason a percentage of drop is allowed to keep the size at a safe minimum.
An example of improper wire size is taken from one of our ships in the case of an 8-H.P. motor; the permissible drop at the time was 3 per cent. The wire size used for this motor was about 350,000 circular mils.
Assuming that 8 H. P. (6 K. W.) was developed by the motor, and the efficiency on terminal energy was 20 per cent., also that the distance was I so feet, we obtain a wire size of 136,000 circular mils for which the 125,000 standard wire (124,928 actual) would suffice. The size used is then nearly three times as large as it need be, with proportionate great weight and cost. The discrepancy is accounted for apparently by the fact that no drop was allowed for.
Our allowance of 1000 C. M. per ampere provides a large margin; the requirements of underwriters' specifications average about 725. "No tapering to be permitted."
The Tree system of wiring was quite popular at the time some of our former installations were put in. The general idea was to decrease the size of the leads as loads were tapped off to the mains or branches, and thus save wire. But it is an inflexible law of connections that wherever a wire size is reduced a fuse must be inserted, i.e., a junction box, and most of the troubles that have occurred with the system have been from violations of this law. Besides, an overload on the lighter wires has but one result, overheating, ending in fusing or fire. The installation of extra junction boxes, at $5.60 apiece, brings the cost above that of the safer straight lead at the same size throughout; the fewer the breaks in a line the better.
''There shall be no soldered or other joints in feeders or mains except those made in the standard appliances.''
This is to prevent piecing out leads with fag ends and remnants of wire, a too frequent practice in contract ships.
''Fuses for branch junction boxes to be for the normal rated load of 4 amperes, and to blow at 8 amperes."
This specifies tile protection to be afforded to branch circuits, and is the basis of construction of the familiar glass tube fuses.
The proper fusing of circuits is more sinned against on board ship than any other repair which is attempted; as long as the original supply of glass tube fuses holds out there is no need for further expedient than merely replacing. When this supply fails those tubes in which the glass has not been cracked by the heat can be made as good as new by putting in a piece of fuse wire from spare stock, being careful to securely solder the wire to the brass caps; as practiced, the wire is bent over the ends of the caps and no solder is used; the fuse is put in the clips, trusting to the pressure of the clips, vibration shakes it loose and the lights on the branch go out because there is either no connection or that the fuse has blown, owing to the vibratory contact. When the unfused tubes run short recourse must be had to fuse wire alone, readily accomplished by running one length of fuse wire across and expending the end around the clips. A common, erroneous practice has been to run several turns in the figure-of-eight fashion across, thus adding to the carrying capacity of the total fuse with every run; presuming two complete turns to have been made, a reasonable assumption, there would be four runs of wire and the fuse would not blow under 30 amperes instead of at 8, as good protection to the circuit demands.
The use of iron nails for fuses, or rather as a connection, is common in fire-rooms; it usually results in fusing of the clips.
The latest fuse device taken from a ship consists of an ordinary match about which eight turns of fuse wire were wound kitestring fashion; this fuse could scarcely have blown under 60 amperes.
(To be concluded in No. 87.)
[*] The energy of a circuit is equal to the product of the voltage (electromotive force) and current, that is,
Energy (Work) = CE.
Evidently if E is doubled we halve C, and the wire size is proportionally decreased.
[*] A kilowatt is a thousand watts; a horse-power is 746 watts, practically 750 watts. A kilowatt is therefore equal to 1 1/3 horse-power, and a horse-power to three-fourths a kilowatt.
[*] Name plates usually show the name of the manufacturer and the type or form together with the rated speed and capacity of the machine, thus:
M. P.--4--50--40.
which signifies--Multipolar, four poles, 50 K. W., four hundred revolutions per minute. A plate is attached to the bedplate of both dynamo and engine and should show the fram number of the dynamo and the number of the engine for convenience iin ordering spare parts. The armature number is generally stamped on the end of the sleeve or shaft.
[*] Left and right here refer to the fiture only, the terminals being on the left. In actual machines the location of the terminals is determined by convenience. In narrow dynamo rooms like those of Boston and Atlanta the generating sets must be installed end-to-end in order to obtain room, and in this case one armature would turn righ-handedly (with the sun), the other left-handedly, and the terminals would be different.
[*] As long as the characteristics of the machines are practically the same it does not matter whether the equalizer is closed first and hte circuits turned on, or the circuits divided equally between the machines before the equalizer switch is closed; the above is the method prescribed by thte Instructions in the Electrical Journal of the ships and, of course, is official. It is beyond doubt the safer plan for the reason that, having divided the load beforehand and adjusted the voltage for that load, no change in the voltage of the machines can occur, as it might if they were allowed to adjust the loads for themselves, that is, provided the loads remain constant; if they do not and there is any difference of potential created by the extra load sufficiently great to be critical, reversal will occur.
Safety lies in keeping the characteristics the same for all machines at all stages of load and keeping to the instructions implicitly.
[*] Inquiry has been frequently made for an answer to the examination question, "What is a balance circuit?"
The technical term of the authorities refers to a balance of resistance as in the Wheatstone bridge, or else to a mer question of polarity, neither of which fits the case. The expression has apparently been coined in the service to mean a circuit which is connected at one or more points to another circuit in order that in case of a break (from short or otherwise) it will be fed by that other.
Balance as expressed in the quesiton is probably synonymous with interconnection, the present term.