Electric railways

by American School of Correspondence; James Raley Cravath

ELECTRIC CAR ACCESSORIES.

Canopy Switch. An overhead switch, sometimes called a “canopy switch,” is commonly placed over each street-car platform where a controller is located, usually in the deck or canopy above the motorman’s head. This is simply a single-point switch that may be used by the motorman to cut the trolley current off from the controller wiring so that the controllers will be absolutely dead. When two such switches are used, one on each end of the car, they are connected in series.

Fig. 32. Grid Type of Resistance.

Car Circuit Breaker. Frequently on large equipments an automatic circuit breaker is provided instead of this overhead switch. This circuit breaker can be tripped by hand to open the circuit whenever desired; and is also equipped with a solenoid magnet, which can be adjusted so that it will trip or open the circuit breaker at approximately whatever current it is set for. This circuit breaker protects the motor and car wiring from excessive current, such as would occur in case of a short circuit in motors or car wiring, or in case the motorman turned on current so rapidly as to endanger the windings of the motors. Circuit breakers, however, are most commonly used on cars having controllers located at only one end in a motorman’s cab.

Wiring of Circuit Breakers and Canopy Switches. Figs. 33, 34, and 35 show the methods of wiring circuit breakers and canopy switches for double-end cars.

Fig. 33.

In the parallel connection as shown in [Fig. 33], the trolley leads after passing through the choke coils go directly to the blow-out coil of the controllers. Aside from the fact that two lightning arresters and choke coils are required, this method is preferable for automatic circuit breakers.

Fig. 34.

Fig. 34 shows the hand-operated circuit breakers connected in series. This method is used where non-automatic breakers are employed, but for automatic breakers it has the objection that an overload would throw the breaker set at the lowest point. This might be the breaker on the opposite end to that occupied by the motorman and in such an event would necessitate a trip to the other end to set the breaker. Fig. 35 shows a method of parallel connection requiring but one lightning arrester. This method has the objection that the motorman on the front end would have no assurance that by throwing the breaker over him the power would be cut off. The rear breaker might have been carelessly left set.

Fig. 35.

Fig. 36.

Fuses. A fuse is placed in series with the motor circuit before it enters the controller wiring, but where circuit breakers are used instead of canopy switches, the fuse box may sometimes be dispensed with. The fuse box on street cars is usually located underneath one side of the car body where it is accessible for replacing fuses, but where a motorman’s cab is used, the fuse may be placed in the cab. The fuse may be of any of the types in common use, either open or enclosed. In the Westinghouse fuse box it is necessary only to open the box and drop in a piece of straight copper wire of the right length and size. The closing of the box clamps this wire to the terminals and establishes a circuit through the copper wire as a fuse. Of course this copper wire is of small enough size to be fused by a dangerously heavy current.

Lightning Arresters. A lightning arrester is used on all cars taking current from overhead lines. The lightning arrester is connected to the main circuit as it comes from the trolley base, before it reaches any of the other electrical devices on the car, so that it may afford them protection. A common type of lightning arrester is shown in [Fig. 36]. One terminal of the lightning arrester is connected to the motor frame so as to ground it, and the other is connected with the trolley. In most forms of lightning arrester, a small air gap is provided, not such as to permit the 500-volt current to jump across, but across which the lightning will jump on account of its high potential. To prevent an arc being established across the air gap by the power house current after the lightning discharge has taken place and started the arc, some means of extinguishing the arc is provided. In the General Electric Company’s lightning arrester, the arc is extinguished by a magnetic blow-out, which is energized by the current that flows through the lightning arrester. The instant the discharge takes place the current flows across the air gap. The magnetic blow-out extinguishes the arc, and this opens the circuit, leaving the arrester ready for another discharge. In the Garton-Daniels lightning arrester a plunger contact operated by a solenoid opens the circuit as soon as current begins to flow through the arrester. This plunger operates in a magnetic field, which extinguishes the arc. A choke coil, consisting of a few turns of wire around a wooden drum, is placed in the circuit leading to the motors at a point just after it has passed the lightning arrester tap. This choke coil is for the purpose of placing self-induction in the circuit, so that the lightning will tend to branch off through the lightning arrester and to ground, rather than to seek a path through the motor insulation to ground.

Fig 37. Diagram of Light Circuit.

Often, however, the choke coil is omitted, the coils in the circuit breaker and the blow-out coil in the controller being depended upon to prevent the lightning charge from passing.

Lamp Circuits. The lamp circuit of a car is protected by its separate fuse box, and usually each lamp circuit has a switch. As explained before, five 100-volt or 110-volt lamps are placed in series between the trolley wire side of the circuit and ground. If one lamp in the series burns out, of course, all five are extinguished until the defective lamp is replaced with a new one. Enclosed arc lamps are sometimes used for car lighting.

Cars to be operated from either end are often wired so that by turning a switch the platform light on the front end, a light for the sign and another for the headlight on the rear end will be extinguished and corresponding lights on the rear and front ends lighted. This is accomplished by the method of wiring shown in [Fig. 37]. The interior of the car is lighted by six lights. Headlights of 32 candle power are used. This method requires the use of two switches. In all light wiring schemes a switch should be placed on the trolley side of the lights. This permits the current to be cut off in the event of a ground occurring in the system.

On interurban cars arc headlights are almost invariably used. The circuit for the headlight after passing through a switch in the motorman’s cab goes through a resistance frame usually underneath the car and terminates in a socket near the car bumper. The brackets on which the lamp is hung are grounded so that whenever the plug from the lamp is inserted in the socket and the switch in the cab is turned on, the circuit is made.

Usually there is a pressure of about 60 to 70 volts at the terminals of the lamp. The remainder of the voltage drop, from 500 or 600 volts (or whatever the line may be), is in the resistance under the car. The current through the lamp is usually about four amperes. With 60 volts at the arc and 500 volts on the line, this gives a consumption in the lamp of 240 watts and a loss in the resistance under the car of 2,000 watts, or about 90 per cent. The use of the headlight resistance to cut the voltage down is therefore a very inefficient method. Some schemes of wiring use the incandescent lamps used in lighting the car as resistance for the headlight. Another way is to light the interior of the car with arc lamps placed in series with the arc headlight.

Fig. 38. Trolley Base.

Trolley Base. The trolley base upon which the trolley pole swivels, and which furnishes the tension that holds the trolley wheel against the wire, is designed to maintain, by means of springs, an approximately even tension against the trolley wire, whether the trolley wire is high above the track or near the car roof. This is done by changing the relative leverage which the springs of the trolley base have on the trolley pole according to the height of the trolley pole.

Fig. 39. Trolley Wheel.

Fig. 38 shows one form of trolley base. The trolley base is bolted to a platform constructed for it on the roof of the car; and the supply wire to the motors and other electrical devices on the car, except in cases where a wooden trolley pole is used for certain special reasons, is connected directly to the trolley base. An insulated trolley wire is run down the wooden trolley pole, and connected through a flexible lead to the car wiring.

Trolley Poles. The trolley poles in general use are of tubular steel, which gives the greatest strength for a given weight, and which can usually be straightened if the pole has been bent by striking overhead work when the trolley wheel leaves the wire.

Trolley Wheels. Trolley wheels are from four to six inches in diameter over all, the small wheels being used in the city service, and the large wheels in high speed interurban service. A typical trolley wheel is shown in [Fig. 39]. Various companies use various forms of groove in the trolley wheels, some adopting a groove approximately V-shaped. The U-shaped groove, however, is the most common. The trolley wheel is made of a brass composition selected for its toughness and wearing qualities.

Fig. 40. Trolley Harp.

Trolley Harp. The trolley harp, which is placed on the end of the trolley pole and in which the trolley wheel revolves, usually has some means for making electrical contact with the wheel in addition to the journal bearing. In the harp illustrated in [Fig. 40], which is a typical form, this additional contact is secured by a spring bearing against the side of the hub of the wheel.

Fig. 41. Third Rail Shoe.

Since trolley wheels revolve at a very high speed, some unusual means of lubrication must be provided, since there is no opportunity for ordinary oil or grease lubrication. Graphite, in the shape of what is called a “graphite bushing,” is most commonly used. This is a brass bushing, which is pressed into the hub of the trolley wheel. In this bushing is a spiral groove filled with graphite which is supposed to furnish sufficient lubrication as the bushing wears. Roller-bearing trolley wheels have been used to a limited extent, with considerable success in some cases. Some companies have done away with the graphite bushing, and have provided a very long journal for the trolley wheel instead of the usual short bushing.

Contact Shoes. The contact shoe most commonly used on roads employing the third rail is shown in [Fig. 41]. This is simply a shoe of cast iron hung loosely by links. The weight of the shoe is sufficient to give contact. The motion of the links permits the shoe to accommodate itself to unusual obstructions and variations in the height of the third rail. The shoe is fastened to the truck frame by means of a wooden plank which furnishes the necessary insulation.

Fig. 42. Sleet Wheel.

The Potter third-rail shoe which has been used to a limited extent, employs a spring for giving the necessary tension to make electrical contact between the shoe and the third rail. In some ways this is superior, because a spring tension is quicker in its action than gravity, and the shoe accommodates itself better to variations in the height of the third rail at very high speed. The wear on the shoe, however, is likely to be greater.

Sleet on Trolleys and Third Rails. The deposit of sleet on trolleys and third rails hinders greatly the operation of cars. Often sleet wheels of the type shown in [Fig. 42] are used as a trolley wheel. These cut the sleet off instead of rolling over it.

On the third rail, scrapers and brushes in advance of the contact shoe are usually effective where trains are frequent. Several roads are now melting the sleet on the rails by the use of a solution of calcium chloride. The solution is stored in a tank on the car and is led through small pipes to the rail immediately in front of the collecting shoe. About one gallon of solution is used per mile, making the cost about 7½ cents per mile. The effects of one treatment last for two or three hours during the continuance of a storm.

Solutions of common salt have been used in the same manner, but it is claimed that the corroding action on the iron of the calcium chloride is not as great as that of a salt solution.