CONTROLLERS.
In an ordinary electric car, current is taken from the wire through the trolley wheel and pole, and is first led from the trolley base through overhead switches or a circuit breaker, and then to the controller, from which it passes through the motors and thence through the motor frames, car truck, and wheels to the rails and ground. If the car is designed to be operated from either end, an overhead switch or circuit breaker is placed over each platform of the car so that current can instantly be cut off entirely from the controllers by throwing the switch or circuit breaker at either end of the car.
Fig. 17. Armature Axle and Wheels.
The lighting circuit is run from the trolley base independently of the motor circuit, and has its own switch and fuse box. Current for the lights is taken from the trolley circuit before it reaches the main switches or circuit breakers. Current for electric heaters, if such are used, is likewise taken from a separate circuit. On a 500-volt system five 100-volt lamps are usually connected in series for car lighting. As many multiples of five can be employed as are necessary to light the car.
Rheostat Control. The simplest form of controller is that employed where only one motor is used on a car. A rheostat is placed in series with the motor when started, just as on a stationary motor; and the function of the controller is to short-circuit this resistance gradually until it is entirely cut out and the motor operates with the full voltage. The controller also has a reversing switch by means of which the relative connections of the armature and fields are reversed, which, of course, changes the direction of rotation of the motor armature. Such a simple equipment as this, however, is rarely to be found in practice.
Series-Parallel Control. Single-truck cars usually have two motors, one on each axle; and on such cars a series-parallel controller is the kind usually employed. Diagrams of connections on the various points of a series-parallel controller (Type K6) of the General Electric Company, are given in [Fig. 18].
Fig. 18. Diagram of K6 Controller Combinations.
From these diagrams it is seen that the motors are first operated in series until all the resistance is short-circuited by the controller. When this has occurred, the cars are running at about half speed. The next point on the controller puts the two motors in multiple, with some resistance in the circuit, which resistance is cut out upon the following points, until at full speed the two motors are in multiple, without any resistance in the circuit.
Fig. 19. Motor in Series.
Four Motors. Where four motors are used on a car, as is frequently the case with double-truck cars, the motors on each truck are usually controlled just as in case of the two-motor equipment that has been described; but each pair of motors is operated in multiple. That is, on the first points of the controller, the two motors of a pair are in series, as in [Fig. 19], and the two pairs are in parallel; and on the last points of the controller, all the motors are in parallel, as in [Fig. 20].
Fig. 20. Motor in Parallel.
Controller Construction. The controller (Type K) shown open in [Fig. 21], which in its various forms is the type most commonly used on street cars in the United States, has a contact cylinder or drum mounted upon the main shaft of the controller. This contact drum carries contact rings insulated from the drum, and is suitably interconnected, as indicated in [Fig. 22], which shows the contact rings of the controller as they would appear if rolled out flat. Contact fingers are placed along the left side of the controller, as seen in [Fig. 21], one for each ring on the drum; and as the controller handle is turned to revolve this drum, the contact fingers make contact with the rings on the drum and give the various connections. Alongside the main controller drum is a reverse drum which simply reverses the armature connections of the two motors. Controller Wiring. The connection between motors, controllers, and resistances, with two motors and a K6 controller is shown in [Fig. 22]. A careful study of this will show the combinations to be the same as indicated in the diagram, [Fig. 18]. The wiring is rather complicated; and in practice, to avoid confusion, the ends of each wire are labeled with tags showing the terminals to which they belong.
Fig. 21. Controller.
Car Wiring for K-6 Controllers with two Motors
Fig. 22
Fig. 23. Motors in Series.
Fig. 24. Motors in Parallel.
With the aid of Figs. 22, 23 and 24, the wiring of a type K6 controller with two motors may be followed. Figs. [23] and [24] are for a different controller but can be used to assist in an understanding of the complicated diagram 22. The current leaves the choke or kicking coil of the lightning arrester and passes through the blow out coil of the controller. It then goes to the top finger T of the controller. On the first point the circuit is as shown in [Fig. 23]. The top segment A makes contact with the top or trolley finger. All but the lower five segments of the cylinder are electrically connected together by means of the iron cylinder upon which they are mounted. On the first point then the current passes from the cylinder over R1, and with straight series connections of the resistances, it goes through all of the rheostats under the car, and returns to the controller over the last resistance lead, R7. Behind the motor cut-out switches at the base of the controller this lead is tapped into a wire one end of which leads to finger 19 of the controller, and the other end through the cut-out switch and reverse cylinder to No. 1 armature. The current takes the latter path, passes through the armature of the motor and returns by way of the reverse cylinder, thence through the fields of No. 1 motor and then through the cut-out switch of No. 1 motor and to finger E1, of the controller. Segments O, M, N and L, shown in [Fig. 23], and corresponding segments of Figs. [22] and [24], are insulated from the remainder of the controller cylinder. From finger E1 and segment O ([Fig. 23]) the current passes over finger 15 through No. 2 cut-out switch and the reverse cylinder to the armature of No. 2 motor. Returning it passes through the reverse cylinder, then back through the fields of No. 2 motor and to the ground, which is usually through a connection on the motor casing.
On points 2, 3, 4 and 5, the successive series points of the controller R1, R2, etc., make contact with segments B, C, etc., Figs. [23] and [24], until finally finger 19 rests on segments J, the resistance is all cut out and the motors are connected in series directly across the line. A further movement of the controller handle changes the motors from series to multiple connection and inserts in the circuit a portion of the external resistance. There are four separate stages in making this change. First, the resistance fingers slide off their segments and the resistance is inserted in the line. Second, fingers E1 and G make contact with segments P and Q. Motor No. 1 is then across the line in series with the resistance; the circuit being from E1 to ground over G. When the lower finger E1 makes contact with P, the upper one has not yet left segment O. This short-circuits No. 2 motor, the path being from the ground, up wire G, thence by way of segments P and Q and through connecting clip V, between the two E1 fingers back through finger 15 to the motor.
A further movement of the controller handle causes the fingers to leave segments M and O and No. 2 motor is open-circuited until finger 15 makes contact with segment N. When this takes place the motors are in multiple. On the successive points after this the external resistance is cut out in the same manner as previously described.
By reference to [Fig. 22], it will be noticed that the leads to the motors and the resistances are tapped on wires of the cables connecting the two controllers on the ends of the car. The two ends of these wires, with the exception of the armature wires, lead to similar binding posts on the two controllers. The armature wires are interchanged connecting at one controller into binding post A A, while the other end connects into binding post A. This change of connection is necessary in order that the reverse handles be forward for forward direction of movement of the car.
Fig. 25. Forward Position of Reverse.
To reverse a series motor it is simply necessary to reverse the direction of flow of the current in either the armature or field. For several reasons, it is advantageous in the case of the street railway motor to reverse the current in the armature rather than in the field. Figs. [25] and [26] show how this is accomplished. The squares shown in the figures represent the lugs on the reverse cylinder as shown in [Fig. 21]. With the reverse handle in one position ([Fig. 25]), the large lugs are under the reverse fingers, and current passes from finger 19 to finger A1, and from finger 15 to finger A2. [Fig. 26] shows the relative position of reverse fingers and lugs for the reverse position of the controller handle. In this case the current passes from finger 19 to A A1, and from finger 15 to finger A A2. The effect is to change the direction of flow in the armatures while that in the fields remains the same as may be observed by the arrows.
Fig. 26. Reverse Position of Reverse.
Wiring of Type L Controllers. The type L controller, shown in [Fig. 27], while accomplishing the same results as the type K, is wired in a radically different manner. The circuit is opened in changing from series to multiple connections. The controller handle makes two complete revolutions in moving from the series to the multiple position. It is geared to the rheostatic cylinder in such a manner that the first half of both the first and second revolutions gives this cylinder one complete turn. During the second half of the revolution the cylinder is returned to its original position. The controller handle is so connected to the commutating arm that this stands in a central position for the off position of the handle. At the beginning of the first revolution it is swung to the left, throwing the motors in series. At the beginning of the second revolution it is moved to the right, putting the motors in multiple.
The rheostats instead of being wired in series are connected in multiple. Current passes from the blow-out coil to the bottom fingers of the controller S, and thence to the rheostats. On the first point the current returns over R1 to the controller cylinder. It passes off through a collar at the base of the cylinder through No. 1 cut-out, and the reverse, which is shown in the central position, to No. 1 motor. On returning to the controller over E1 it passes to the upper section of the commutating arm. In the diagram this is shown in the central position. In series it is thrown to the left. The current then passes from the commutating arm to No. 2 cut-out, and to No. 2 motor. Movement of the controller handle further multiplies the paths through the rheostats and finally, when fingers S rest on the cylinder, the rheostats are short-circuited. If the controller handle is moved still farther, the rheostat cylinder is returned to the off position and the commutating arm is thrown to the left. With the arm in this position the current divides, one portion passing to No. 1 motor as before and to ground by way of the upper section of the commutating arm; while the other branch goes by way of the lower section of the commutating arm to the cut-out switch for No. 2 motor and thence to the motor.
Fig. 27.
Diagram of Connections
for
L2 Controller
Reversing is accomplished by one-quarter revolutions to the right and left of the segments shown. It is evident that this will connect either A1 or A A1, to the trolley. And likewise connect the other armature leads.
Reversal. The reversing handle and the main controller handle are made interlocking so that the motors cannot be reversed without first throwing the controller to off position. This is to prevent damage to the motors through careless or inadvertent throwing of the reverse handle when the controller is on some of its higher points. Such a reversal would cause an enormous current to flow through the motors, and would be likely to damage them and to open all the circuit breakers and fuses in that circuit. The reason for the enormous flow of current is, of course, that the counter-electromotive force of the motors, when reversed with the car going at some speed, would materially add to the electromotive force of the trolley line, instead of opposing it as when the cars are in operation. The current flowing through the motor circuit would then be equal to (electromotive force of line + electromotive force of motors) ÷ (resistance of motors), which would result in a very large current.
Magnetic Blow-Out. On the Type K controller as well as on most other successful controllers, the flashing or arcing between contact rings and fingers, which occurs when the circuit is broken, is materially reduced by a magnet that produces what is called the magnetic blow-out to extinguish the arc. This magnet derives its current from the main circuit, and is so arranged as to create a strong magnetic field in the neighborhood of the place where the arc is formed. [Fig. 21] shows a Type K controller open with the magnetic blow-out magnet thrown back on a hinge. The coil which produces this magnet is seen in the right side of the controller. The main contact drum is in the middle, and the reversing drum at the right hand. There are in use a number of other controllers built upon these same general principles but differing in mechanical arrangement.
Controller Notches. All controllers are provided with some device which prevents the motorman from stopping the controller handle between the various points or notches, as the stopping between points might result in drawing an arc or an imperfect contact. The most common arrangement to prevent this is a notched wheel on the controller shaft, against which bears a small wheel of just the right size to enter the notches. The small wheel is held against the notched wheel by a strong spring. As the tendency of the small wheel is to seek the bottom of the notches, it is difficult to stop the controller handle anywhere between notches, and the motorman is thus given a guide which tells him without any effort on his part just where the notches are.
To prevent advancing the controller handle too rapidly and avoid the jerking of passengers, excessive currents and slipping of wheels during acceleration, several devices have been planned. On the multiple unit control systems, a limit switch is usually provided which prevents the controller advancing when the current exceeds a predetermined amount. A device to accomplish the same results on the K type of controllers is termed the Automotoneer. A cam connected with a dash pot prevents movement of the controller handle to the successive notches faster than a previously prescribed rate.
A switch is usually provided in a controller, for cutting out of service one motor or a pair of motors if defective, and allowing the car to proceed with the good motor or motors.
Fig. 28a. Car Wiring for G. E. Train Control System.
WESTINGHOUSE 300 K.W. DIRECT CURRENT ENGINE TYPE THREE-WIRE GENERATORS.
Pittsburgh, Cincinnati, Chicago and St. Louis Railroad, Columbus, Ohio.