Louis Duncan

“ Usually the characteristic of the booster is so calculated that the amount by which it raises the voltage for a given current just equals the fall of potential in the feeding-line for the same current. The result is that the potential at the end of the liner will be the same as that at the station. The question of economy, as between putting in additional copper and wasting energy in the booster, is easily calculated; the advantage is more and more on the side of the latter as the distance increases and the car service becomes more infrequent. ”

“ Another method of braking is by arranging the connexions of the two motors so that one acts as a dynamo driven by the motion of the car and supplies current to the other, which works as a motor, tending to turn the wheels in the direction opposite to that in which the car is moving. The production of current by the one motor and the reverse effort of the other give a powerful braking effect. ”

“ When a number of machines are to be run in parallel—as is usually the case—they are provided with “ equalizing ” switches, which serve to throw the series fields in parallel. As a result, if one of the machines tends to increase its armature current beyond the proper amount, the current in the series fields does not increase with it, but retains its normal proportion. The armature reaction and resistance fall of potential, in this machine, would both tend to increase, thereby decreasing its armature potential, and therefore its current would return to its proper value. ”

“ The installation of an overhead electric line costs less than a cable system, though the expense of a conduit electric line is about the same. By the extension of the urban tramway systems into the suburbs and the construction of inter-urban lines, electricity has come into competition with steam. Here the conditions are different. For ordinary suburban service, the electric cars, running through the city streets and on the highways, cannot, in speed, compete with steam trains operated on private rights of way. ”

“ For smaller vehicles, a single four-wheel truck is used, the wheel base being limited by the curvature of the track, but not as a rule exceeding 71⁄2 ft. For the longer and heavier cars, two four wheeled bogie trucks are employed. If two motors are used on a double-truck car, and if the grades on the road are very heavy, the trucks are made on the “ maximum traction ” pattern, in which one pair of wheels in each truck is of smaller diameter than the other and the greater part of the weight of the car is on the larger motor driven wheels. ”

“ One of the most important parts of the equipment of an electric car or locomotive is the controlling device. In the early days of electric traction a number of different methods of regulating the speeds of the cars were used, but they have been reduced to practically one standard method. In the old Sprague system there were at first no resistances outside of the motors themselves, but the field coils of the motors were divided into sections, and by changing the relative connexions of these sections the total resistance of the circuit could be changed ”

“ A number of patents have been granted in various countries for electric traction systems in which one or both of the fixed conductors are installed in a conduit underground, communication being had with them by means of an open slot, into which projects a current-taking device of some nature carried by the car as it moves along. ”

“ The third-rail system has been adopted in many instances where large and powerful trains are to be operated on private rights of way, but it is nowhere in use for electric traction upon highways or in streets where there is any passing of foot passengers or vehicles. ”

“ When the size and speed of the car increases, however, these hand-brakes do not give sufficient control, and power brakes have to be adopted. Of these there are several forms that have proved successful in practice. The one most extensively used in electric railways is the air-brake, which is similar in its mechanical operation to the air-brake used on steam railways. The compressed air required for the operation of the brake is obtained by means of an air-pump driven by an electric motor, the circuit of which is controlled by a switch actuated by the pressure of the air in the receiving tank. ”

“ A motor and controlling system designed to save and utilize the, power produced by a car running down an incline has been developed and is termed the "regenerative system." A car running over a line having heavy grades must have sufficient energy given to it to overcome its frictional resistance to motion and also to lift the weight of car and load from the bottom to top of each up-grade. ”

“ In some cases the working-conductor, or trolley wire, is suspended at one side of the track, connexion with it being made by a side-bearing trolley, but its usual place is directly over the track, as this arrangement leads to simpler and, more efficient construction of the trolleys and their accessory parts. For certain special cases, where very large currents are employed, the overhead conductor is made of bar metal or structural shapes. ”

“ Most manufacturers, in giving a certain horse-power capacity, mean that at the given rating the motor will run an hour with a rise in temperature of a certain number of degrees, not that it can be run continuously at the power given. Another system of rating depends on the draw-bar pull which the motor can develop under normal conditions of voltage and speed. Uniformity is greatly needed. ”

“ If the speed be too high, the excessive current generated will tend to retard the car and reduce its velocity, while if too low the small current produced will set up but little opposition to motion and the car will accelerate.
Obviously, series motors cannot be used for this service. The motors have shunt fields, and their speed is varied by varying the field strength. Motors of this type are larger, more costly and slightly less efficient than series machines, so that a regenerative system has no place on roads that have a fairly level contour. ”

“ The working current is fed to the field magnets, and the rapid reversals of magnetization induce currents in the armature coils, which currents, working with the field magnetization, cause rotation. Several types of repulsion motors have been developed, and in general their characteristics are similar to'those of the plain series type, They have not, however, come into extended commercial use. Single-phase motors for a given power are much larger, heavier and more expensive than the ordinary direct current motors, owing to the low magnetic densities at which the iron is worked. ”

“ For freight service, especially on railways having heavy grades, electricity also possesses many advantages, due principally to the peculiarity of the electric locomotive, which admits of its maintaining its tractive effort or so-called “ draw-bar pull ” when running at relatively high speeds. This steam locomotives cannot do. Thus a steam locomotive Weighing 100 tons may exert a draw-bar pull of say 45,000 lb at a speed of 6 m. per hour, while at 1 5 m. per hour the continuous draw-bar pull will not exceed about 25,000 lb. ”

“ Animal Traction.—The oldest form of motive power is that of animals, those most commonly employed for draught purposes on ordinary roads being horses, mules, donkeys and oxen. On the continent of Europe dogs are often harnessed to light carts or barrows, but in England their use in this way was prohibited by the Cruelty to Animals Act of 1854. Camels and elephants are only rarely used as draught animals in special circumstances. ”

“ In general, it is customary to divide the working-conductor into sections of from 1000 to 5000 ft. in length, insulated from one another and fed separately through manual or automatic cut-out switches, so that an accident causing a short-circuit or break in continuity on one section will not impair the operation of others.
In ordinary street railway construction two' methods of suspending the trolley wire are in vogue. The most usual construction is to hang it from insulators attached to transverse wires running between pairs of poles set on opposite sides of the track. ”

“ The increased speed of the electric cars and the comfort rendered possible by larger vehicles always increase the receipts when horse traction is replaced by electric, while the latter, as compared with the cable, allows better and easier control of the car and a much greater possible speed variation. ”

“ This fact has led to the use of high-potential alternating currents for the distribution of energy, the voltage being reduced at the points of consumption, and in most cases changed to a continuous current by rotary converters. If alternating currents are used for the car motors, the economical distribution of energy is greatly simplified, the rotary converters being eliminated an their first cost and losses and expense of operation saved. ”

“ Most of the troubles that have occurred have been due to lack of experience, but on the whole they have not been more serious than those experienced with overhead systems. The great expense of the open conduit has led numerous inventors to bring out systems of operating electric railways by means of Closed closed conduits or sectional third rails, in which the c Mt working-conductor is laid on the surface of the ground between the rails, and is connected with the source of current only as the car passes over each section. ”

“ As a rule, the cars used for electric traction have varied but slightly from the type of tramway car prevalent in different localities. The tendency, however, has been to increase their size.Cars. For electric railway work, as distinguished from tramway work, the cars generally follow the pattern that is standard on American steam lines. The trucks used for electric cars are made of steel, with heavy axles and suspension bars for carrying the electric motors. ”

“ When men and animals carry burdens, or draw or propel loads in certain vehicles, it is difficult, and sometimes impossible, to determine the duty performed in foot-pounds of work, because of the uncertainty of the amount in pounds of the resistance overcome. In this case, for the purpose of comparing performances of the same kind with each other, a unit is employed called a foot-pound of horizontal transport, meaning the conveying of a load of 1 ℔ 1 ft. ”