Part 11

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=: I. 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. II. On first point: 1. Grounded resistance near R 1. 2. Grounded controller cylinder. 3. Bridging between the insulated sections of cylinder. III. Near last point series: 1. Grounded resistance near R 3, R 4 and R 5. 2. No. 1 motor grounded. IV. 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.

[Illustration: Fig. 101.]

[Illustration: 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.

[Illustration: 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.

CAR REPAIR SHOPS.

Every electric railway system has a repair shop in which the cars are overhauled. Hardly two shops are built alike. In those shops where only a few cars are cared for, the work is sometimes all done in one room. The shop plan shown in Fig. 103 was presented to the American Railway Mechanical and Electrical Association by W. D. Wright. It contains the idea upon which the larger shops are now being constructed, having a transfer table between the separate departments on either side. In the general design of shops the blacksmith shop, machine shop and truck shop or equipping shop should be close together as a great deal of heavy material is carried between these departments. The paint shop should be separated as much as possible from the other departments in order that flying dust and dirt be avoided. The wood shop may occupy a position at a considerable distance from the other departments as no heavy material is carried from this shop to them.

The tracks of the motor and truck repair shop are usually provided with pits so that trucks and electrical equipment may be repaired and inspected from below. The tracks in shops are usually about 15 or 16 feet between centers. This gives a clearance of about 6 or 8 feet between cars when adjacent tracks are occupied.

A large portion of the work done in the average shop consists of the repairing of trucks and the motors mounted on them. With the smaller car, especially those with single trucks, much of this work is done from the pit below while the trucks are in position under the cars. In this case the armatures are either removed by letting them down with the lower half of the motor shell by means of a pit jack, or the lower half of the armature shell is swung down by the use of a chain and block placed in the car and the armature rolled out on a board.

The trucks of double truck cars are usually taken out from under the car body when repairs are to be made. In this case the motor leads, the sand box connections and the brake rigging are disconnected and the car body either raised or the trucks lowered from it. Several methods of raising the car body are in use. Where no special apparatus is at hand, this is done by means of jacks, hydraulic or mechanical, placed under the side sills of the car near the end to be raised. Sometimes an overhead crane is employed to lift the car body. A special apparatus to raise the body is employed by the St. Louis Transit Company. This consists of four screw jacks located below the floor of the shop. An I-beam extends over the tops of the two located on the same side of the car. The jacks are motor driven by means of one sprocket chain so that they rise at the same speed. When a car is to be raised it is run on the track between the jacks, bars are placed under the car resting across the I-beams and the jacks raise the car off the trucks. The trucks are then rolled out from under the car and the repairs made.

Sometimes, as has been stated, the trucks are dropped from the car body. In this case the car is so placed that the truck rests on an elevator or section of track that drops to the floor below. After the car is blocked up the trucks are dropped and the repairs made. This method is also used in changing wheels in small shops. The old pair of wheels is dropped by a hand-operated drop section of track. A new pair is then elevated into position. This saves jacking up one end of the car.

[Illustration: ONE OF THE SINGLE-PHASE LOCOMOTIVES ON THE NEW YORK, NEW HAVEN & HARTFORD RAILROAD CO.

Note the two pantograph bow trolleys for collecting the current.]

THE SINGLE-PHASE ELECTRIC RAILWAY.

In no other line of electrical activity have developments during the last few years been so rapid as in that of electric railway work, and from all indications the limit has not yet been reached.

Until recent years all electric traction has been dependent upon direct current as a motive power. This is due principally to the fact that the series direct-current motor is admirably adapted for such work, and no alternating-current motor had been developed which could be substituted for it. One of the great advantages possessed by the direct-current series motor is its large starting torque, which may be several times greater than that required to propel a car at full speed. This type of motor is also essentially a variable speed machine, and lends itself very well to wide variations in speed control; consequently, for many years, in this country at least, all advance was made along direct-current lines.

The trolley voltage used at first was from 450 to 500 volts, this being supplied directly to the cars by means of a trolley wire, the rails being used for the return circuit. It is evident from the outset that the comparatively low voltage, necessitating as it did a correspondingly large current for a given amount of power, would place a definite limitation on the use of such a system for anything other than purely local distribution. To overcome this difficulty as far as possible, the trolley voltage was gradually raised to 600 or 650. This of course decreased the required current, thus increasing the scope of the system accordingly. The limit of increase of direct-current voltage on the trolley was reached at about this point, and the fact was recognized that some means must be devised for using a still higher voltage, since there are difficulties to increasing the trolley voltage beyond 600 or 700, due to flashing of the motors, which seems to increase directly with the voltage.

It may be mentioned in passing that one prominent electric traction expert has stated that a direct-current trolley voltage of 1500 can be used, but it remains to be proven whether or not he is correct. A very satisfactory solution of the problem for large city street railway systems and long interurban roads, consists in the use of a combination alternating-current direct-current system in which three-phase high tension alternating current is generated and distributed on high tension lines to substations along the road. It is here stepped down by means of transformers, and then changed to direct current by rotary converters, and supplied to the trolley wire as direct current at the usual voltage of say 600. This system has many advantages, as there is but small loss in the high-tension lines, and these lines can be made comparatively small, thus effecting a considerable saving in investment for copper.

The above mentioned system of distribution is very generally used, and has been found quite satisfactory. The substations can be located at frequent intervals, and the distance that the 600-volt current must be conducted to supply the cars is not great. By this means current can be distributed over wide areas with a small loss, where it would be impossible to use the straight direct-current system of distribution.

While, as stated, this furnishes a fairly satisfactory solution of the problem, it is far from perfect, as it necessitates the intervention of the rotary converter substation, in which the investment must be large; and moreover the cost of operation is high, as such a station requires skilled attendance on account of the somewhat intricate nature of the rotary converter. The ideal system, therefore, is one which does away altogether with the use of direct current, the power being generated, distributed, and utilized by the motors, as alternating current.

Three-phase induction motors have been used quite extensively and with considerable success in Europe for many years past. The three-phase motor, however, is not entirely adapted for railway work, since it possesses the characteristics of the shunt rather than of the series motor, being a constant speed, not a variable speed machine. Moreover, two trolley wires are necessary instead of one, and still another disadvantage consists in the low power-factor of the three-phase induction motor at starting.

The recent application of the single-phase alternating current to railway work has opened up a new field, which bids fair to supplant all other forms of distribution to a great extent at least, and it is impossible to predict at the present time just what its limitations may or may not prove to be. This has been made possible by the development of a _practical commercial_ single-phase motor, which permits of the use of alternating current on the trolley wire with all its advantages, and yet sacrifices few, if any, of the advantages of the direct-current series motor on the car.

[Illustration: INTERIOR OF SUB-STATION SHOWING ROTARY CONVERTER AND TRANSFORMERS.

The three-phase current is delivered to the transformers where it is stepped down to the voltage required for the rotary converter. In this machine it is transformed to direct current and delivered to the trolley wire.]

This motor, which is the latest and most important development in the electric railway field, is of the series commutator type, and does not differ in principle from its direct-current contemporary. It is called the _commutator type single-phase motor_, and is the one type of alternating-current motor which has the same desirable characteristics for railway work as the direct-current series motor.

[Illustration: Compensating Alternating-Current Railway Motor.]

At first thought it may seem strange that a motor built fundamentally on the same lines as a direct-current machine would operate on an alternating current, as it might appear that the motor would tend to turn first in one direction and then in the opposite direction with no resultant motion. This, however, is not the case, because the direction of rotation of a motor depends upon the relative direction of its field and armature currents. If now the field were maintained in a constant direction and the armature supplied with alternating current, then the tendency would be to rotate first in one direction and then in the other, it is true, but as a matter of fact the alternating current is supplied to the field in series with the armature, so that when the direction of current in the armature changes it also reverses in the field. The result is that the relative direction of current in the field and armature is constant and the motor has, therefore, a tendency to turn continuously in one direction as long as the alternating-current power is supplied.

This being true, the question may arise as to why the single-phase motor was not brought to the front for railway work long ago. The answer is that there were certain inherent difficulties to be overcome, and the development of the single-phase motor has been simply the removal of these difficulties, rather than the design of an entirely new type of machine.

The most serious obstacle to overcome is the sparking at the commutator, due to the fact that when the terminals of a coil are bridged by a brush, the coil acts like the short circuited secondary of a transformer of which the field winding constitutes the primary. Also there is an iron loss due to the alternating magnetic flux through the magnetic circuit; while another objectionable feature is the counter E.M.F. induced in the field coils.

[Illustration: Alternating-Current Railway Motor Field.]

In order that it may overcome these difficulties, to some extent, at least, the single-phase motor presents certain modifications from the direct-current type, in that it has more field poles, and the entire magnetic circuit of field frame, cores, and pole pieces, is carefully laminated. The number of commutator segments is also increased, thus reducing the number of armature turns per coil, and there are special features introduced to prevent sparking, such as compensating windings which neutralize the effect of armature distortion; the use of narrow brushes; a type of armature winding which gives a low reactance per coil; the use of high resistance leads between the armature coils and commutator segments, etc.

The single-phase motor is then a refined and highly perfected type of direct-current motor, and this explains the fact that it will operate on either alternating- or direct-current circuits. In fact some claim that it will operate even more efficiently on direct current than the regulation direct-current motor itself.

[Illustration: Single-Phase Armature, Unmounted.]

The field for which the single-phase motor seems particularly adapted is that of heavy service and interurban work, where it has many distinct advantages, among which may be mentioned the following:

The alternating current on the trolley allows the use of a high voltage and correspondingly smaller current, which reduces the line loss and permits of the use of smaller wire, which of course means a saving in the investment for copper. Moreover, the difficulty of collecting a large current from the trolley wire is overcome. Rotary converter substations are eliminated, being replaced by simple and cheap transformer substations, which require no attendance. The capacity can be easily increased by merely increasing the number of these transformer substations.

The efficiency of speed control is a point particularly worthy of mention. In direct-current speed control, the series-parallel method is used almost exclusively. This consists of putting the motors in series for low speed and in parallel for high speed. This permits of two, and only two, economical running points; the one at full speed, and the other at approximately half speed. All intermediate points must be obtained by the insertion of dead resistance in which the voltage is simply wasted as heat, thus causing a large loss particularly at starting.

With the single-phase motor the current is supplied to the car with a voltage of say 3300. It is then stepped down by means of transformers on the car to the voltage of the motors, which may be 200 or 250 volts. The speed is, of course, dependent upon the voltage applied to the motors, and this voltage is cut down from the maximum, to obtain various gradations, by means of an induction controller, or by taps from an auto-transformer. Thus the motor takes from the trolley only slightly more power than is actually required to operate it at any given speed, instead of taking full voltage from the line and absorbing part of it in dead resistance.

[Illustration: Auto Transformer.]

The effect of electrolysis upon neighboring water pipes paralleling an electric road, which is the cause of so much trouble with direct current, is entirely eliminated, as electrolysis evidently will not take place with alternating current.

In connection with this system a sliding contact device or bow trolley has in many cases been substituted with considerable success for the ordinary current collecting device, or trolley wheel, one advantage of this being that the car can be run in either direction without reversing the contact device. Another very satisfactory form of trolley is of the pantograph type with sliding shoe, shown on the New York, New Haven and Hartford locomotive.

A new form of trolley suspension known as the catenary has been developed to meet the demand for more substantial construction necessitated by the high trolley voltage. This consists of a stranded galvanized steel messenger or supporting cable, from which the trolley wire is suspended at intervals of about 10 feet, thus keeping it at a uniform distance above the track.

[Illustration: Master Controller Used in Connection with the Multiple-Unit System as Applied to Single-Phase Work.]

The multiple-unit system of control can be used in connection with single-phase motors, this being the scheme which has been in use for a long time on elevated and other roads using direct current, whereby several cars can be operated in a train from a single point, each car being equipped with its individual motor and controlling apparatus. The entire system is then controlled as one unit by a single motorman stationed usually in the front of the first car. This method of control has become of such tremendous importance that any system to which it cannot be applied would be seriously handicapped. Cars equipped with single-phase motors can be operated on either direct-current or alternating-current lines, with high or low tension, with trolley or third rail.

It must not be supposed, however, that with all the above mentioned advantages, the single-phase system has no disadvantages, as such is not the case. The car equipment, due to the transformers and the nature of the motors, is considerably heavier. The motors themselves are more expensive on account of their special construction. The equipment is not always adapted for operation on existing lines. There is a slight increased “apparent” resistance of the trolley line and a considerable increased “apparent” resistance of the rails, due to reactance caused by the alternating nature of the current. There is also an active electro-motive force between the field coils, which is objectionable, and there is a possibility of interference with neighboring telephone lines. Furthermore, there is slight loss in power in the transformers on the car, while the power-factor of the motors is less than unity.

Summing the matter up as a whole, however, the advantages seem to overbalance the disadvantages, at least for many kinds of work, and it is safe to predict that this new system of operation will have a very wide and increasing application in the near future.