LOCATING DEFECTS IN MOTOR AND CONTROLLER WIRING.

Defects in the wirings are those due to (1) open circuits, (2) short circuits. Open circuits make themselves evident by no flow of current, short circuits usually by a blowing of the fuse or opening of the breaker. The point of the short circuit or “ground” can be located roughly by noting on what point the fuse is blown. Accurate location can be made by cutting out the motors, disconnecting, etc., according to directions in the following pages. The tests outlined apply particularly to the K type of controller with two-motor equipment.

OPEN-CIRCUIT TESTS.

No current:
On 1st point,
Open circuit but not located.
On 1st point multiple,
Motors most probably O. K.
On series-resistance points after trying 1st point multiple,
Open circuit outside controller and equipment wiring.

With an open anywhere between trolley and ground no current will flow on the first point. Opens are most likely to occur in the motors and these may be tested first. However, as will be explained later, one open in an armature will not stop the current. To test the motors open the breaker and put the controller on the first point multiple. Then flash the breaker quickly. Current flowing indicates that one or the other of the motors has an open circuit. In the series position this open prevented the flow but in multiple the current flows through the other motor. Which one is at fault can be quickly determined by returning the controller to the off position and cutting out one or the other of the motors by means of the cut-out switch and then trying for current. The car can in any event be run on the remaining motor. On returning to the shop the open can be determined definitely by the use of the lamp bank.

But should no current flow when the breaker is flashed on the 6th point it is reasonable to presume that the motors are O. K. and that the open is elsewhere. The ground for such a supposition is that as there is a path through each motor normally, there would necessarily be an open in each one to stop the current. It is hardly probable that such a coincidence would occur.

After failure to find fault with the motors, doubt as to the resistance may be removed. The controller should be placed on progressive series-resistance points and the breaker flashed on each one. If current is obtained on any point, the open is in the resistance or the resistance lead just behind the one being used. Special care should be used to flash the breaker quickly for otherwise the fuse may be blown.

The tests indicated are sufficient for the motors, controllers and resistance wiring. If no current is obtained on either of them, the trouble is evidently caused by a bad rail contact, ground wire off if both motors are grounded through the same wire, an open in the blow-out coil, at the lightning arrester, circuit breaker or on top of the car.

None of the tests applied locate the open definitely, but this can easily be done in the shop or wherever a lamp bank is at hand. Connect one terminal of the lamp bank to the trolley just behind the circuit breaker and the controller on the 1st point series, then with the other terminal begin at ground and trace backwards up the circuit until the lamps fail to light. The path in a K type of controller is readily traced with the help of [Fig. 22].

SHORT-CIRCUIT TESTS.

The location of short-circuits is much more tedious. The blowing of the fuse or opening of the breaker will locate them as shown below. The separate tests can then be followed until location is definite.

These tests it must be kept in mind are more especially adapted to cases on the road or where no facilities for testing are at hand.

Rather than blow fuses as frequently as indicated it would in most cases be better to place a lamp bank across the open circuit breaker and note the flow of the current by the lights.

Fuse Blows:

  1. When overhead is thrown on may be due to:
    1. Grounded controller blow-out coil.
    2. Grounded trolley wire or cable.
    3. Grounded lightning arrester.
  2. On first point:
    1. Grounded resistance near R 1.
    2. Grounded controller cylinder.
    3. Bridging between the insulated sections of cylinder.
  3. Near last point series:
    1. Grounded resistance near R 3, R 4 and R 5.
    2. No. 1 motor grounded.
  4. Near last point multiple:
    1. No. 2 motor grounded.
    2. Bridging between lower sections of cylinder.
    3. Armature defective.

CASE I.

Fuse Blows when overhead is thrown on:

  1. Grounded controller blow-out coil.
  2. Grounded trolley wire or cable.
  3. Grounded lightning arrester.

The blowing of the fuse immediately on closing the overhead switch or circuit breaker, when the controller is on the off position, indicates that the fault exists somewhere between the overhead and the upper or trolley finger of the controller.

Should the defect occur during a thunderstorm, it may be presumed at once that lightning has grounded the blow-out coil of the controller.

CASE II.

Fuse Blows on first point:

  1. Grounded resistance near R 1.
  2. Grounded controller cylinder.
  3. Bridging between sections of cylinder.

When the controller is on the first point all of the wiring of the system with the exception of the ground wire for No. 1 motor is connected with trolley. But a defect in the wiring beyond the resistance will not show itself on the first point by an abnormal rush of current because the resistance of the rheostats is sufficient to prevent any excessive flow of current.

Fig. 101.

Fig. 102.

The resistance and leads and the controller cylinder are the only parts to be tested when the fuse blows on the 1st point.

CASE III.

Fuse Blows on 3rd or 4th point:

  1. Grounded resistance near R 4 or R 5.
  2. No. 1 motor grounded.

With either of the above defects the car will most probably refuse to move as the current is led to ground before passing through the motors.

Fig. 103. Plan of Car Shop.

No. 1 motor may be tested by cutting it out of service by means of its cut-out switch. If this removes the ground, the motor is at fault.

CASE IV.

Fuse Blows near last point multiple:

  1. No. 2 motor grounded.
  2. Either armature short-circuited.

The fact that the fuse did not blow on the series positions excludes the resistances and No. 1 motor from investigations for grounds.

Cut out both motors. If the ground still exists the controller is defective. If not, the fault may be located in either one of the motors by cutting out first one and then the other.

ARMATURE TESTS FOR GROUNDS.

With a lamp bank at hand tests for grounded armature can be made as follows:

Throw the reverse on center. Attach one terminal of the lamp bank to the trolley. Put the other terminal on the commutator of the armature to be tested. No current shows the armature O. K. If current flows remove brushes and try again, to be certain that the ground is not in the leads.

FIELD TESTS FOR GROUNDS.

Disconnect field leads and put test point of the lamp bank on one side of the terminals. No current indicates that the fields are O. K.

REVERSED FIELDS.

In placing new fields in the shell it often happens that one or more are wrongly connected. Reversed fields make themselves known by excessive sparking at the brushes in each case.

In [Fig. 101] all of the fields are connected correctly. The flow of magnetism is in one pole and out of the adjacent one. Some of the magnetism leaks out of the shell and affects a compass held near the outside. The direction taken by the compass needle in the different positions is shown. The needle should point in opposite directions over adjacent coils and should lie parallel to the shell in positions half way between two coils.

[Figure 102] shows the flow of magnetism when one field is reversed. In such a case the compass will take the position shown. The field marked “X” is the one reversed.

With one reversed field a machine will usually operate, as the magnetism in three of the poles is in the normal direction. But an excessive flow of current that has no effect in turning the armature will take place on that side of the armature next to the reversed field.