Chapter 1 of 12 · 3978 words · ~20 min read

Part 1

[Illustration: INTERIOR OF 160-TON B. AND O. ELECTRIC LOCOMOTIVE.

General Electric Company.]

Electric Railways

_A Treatise on the_ MODERN DEVELOPMENT OF ELECTRIC TRACTION, INCLUDING PRACTICAL INSTRUCTION IN THE LATEST APPROVED METHODS OF ELECTRIC RAILROAD EQUIPMENT AND OPERATION

ELECTRIC RAILWAYS _By_ +James R. Cravath+ Western Editor “The Street Railway Journal”

THE SINGLE-PHASE ELECTRIC RAILWAY _By_ +Harris C. Trow+, S.B. American Institute of Electrical Engineers. Editor Textbook Department, American School of Correspondence

ILLUSTRATED

CHICAGO AMERICAN SCHOOL OF CORRESPONDENCE 1908

Foreword

In recent years, such marvelous advances have been made in the engineering and scientific fields, and so rapid has been the evolution of mechanical and constructive processes and methods, that a distinct need has been created for a series of _practical working guides_, of convenient size and low cost, embodying the accumulated results of experience and the most approved modern practice along a great variety of lines. To fill this acknowledged need, is the special purpose of the series of handbooks to which this volume belongs.

¶ In the preparation of this series, it has been the aim of the publishers to lay special stress on the _practical_ side of each subject, as distinguished from mere theoretical or academic discussion. Each volume is written by a well-known expert of acknowledged authority in his special line, and is based on a most careful study of practical needs and up-to-date methods as developed under the conditions of actual practice in the field, the shop, the mill, the power house, the drafting room, the engine room, etc.

¶ These volumes are especially adapted for purposes of self-instruction and home study. The utmost care has been used to bring the treatment of each subject within the range of the common understanding, so that the work will appeal not only to the technically trained expert, but also to the beginner and the self-taught practical man who wishes to keep abreast of modern progress. The language is simple and clear; heavy technical terms and the formulæ of the higher mathematics have been avoided, yet without sacrificing any of the requirements of practical instruction; the arrangement of matter is such as to carry the reader along by easy steps to complete mastery of each subject; frequent examples for practice are given, to enable the reader to test his knowledge and make it a permanent possession; and the illustrations are selected with the greatest care to supplement and make clear the references in the text.

¶ The method adopted in the preparation of these volumes is that which the American School of Correspondence has developed and employed so successfully for many years. It is not an experiment, but has stood the severest of all tests—that of practical use—which has demonstrated it to be the best method yet devised for the education of the busy working man.

¶ For purposes of ready reference and timely information when needed, it is believed that this series of handbooks will be found to meet every requirement.

[Illustration]

Table of Contents

+Car Equipment+ Page 3

Classification of Electric Railways — Motors — Armature Winding — Armature and Field Coils — Armature and Motor Leads — Brushes and Brush-Holders — Gearing — Lubrication — Bearings — Motor Suspension — Electric Locomotive Motors — Controllers — Rheostat and Series-Parallel Control — Controller Construction — Multiple-Unit Control (Sprague, General Electric, Westinghouse Electro-Pneumatic) — Car-Heaters — Car Wiring — Electric-Car Accessories (Canopy Switches; Circuit-Breakers; Fuses; Lightning Arresters; Lamp Circuits; Trolley-Base; Trolley-Poles, Wheels, and Harp; Contact Shoes; Sleet Wheels) — Single Trucks — Swivel Trucks — Maximum-Traction Trucks — Car Wheels — Brake Rigging — Air-Brakes (Compressor, Automatic Governor, Storage Tanks) — Momentum Brakes — G. E. Electric Brake — Westinghouse Electromagnetic Brake — Track Brakes — Motors as Emergency Brakes — Brake Shoes — Track Sanders — Drawbars and Couplers.

+Car Construction+ Page 67

Car Bodies — Steel Car Framing — Car Weights — Car Painting.

+Line Construction+ Page 73

Overhead Construction — Trolley-Wire — Clamps and Ears — Span Wires — Brackets — Feeders — Section Insulators — High-Tension Lines — Third-Rail System — Conduit Systems — Contact Plow — Current Leakage — Track Construction — Girder Rail — Trilby Groove Rail — Shanghai T-Rail — Common T-Rail — Track Support — Ballast — Joints (Welded, Cast-Welded, Electrically Welded, Thermit-Welded) — Bonding and Return Circuits — Feeder Systems — Block Signals — Electrolysis and Its Prevention.

+Power Supply and Distribution+ Page 98

Direct-Current Feeding — Booster Feeding — Alternating-Current Transmission — Interurban Distribution — Power-House Location — Alternating-Current Generators — Double-Current Generators — General Plan of Power Stations — Switchboards — Generator D. C. Panels — Starting Up a Generator — Feeder Panel — Alternating-Current Switchboards — High-Tension Oil-Switches — Storage Batteries in Stations — Three-Phase Motors — Single-Phase Motors.

+Operation of Electric Railways+ Page 115

Power Taken by Cars — Road Tests of Cars — Economy in Power — Sliding and Spinning Wheels — Testing for Faults — Bond Testing — Motor-Coil Testing — Grounds — Burn-Outs — Defects of Armature Windings — Sparking at Commutator — Failure of Car to Start — Open-Circuit Tests — Short-Circuit Tests — Fuse-Blows — Armature and Field Tests for Grounds — Reversed Fields — Car Repair Shops.

+The Single-Phase Electric Railway+ Page 137

Commutator Type Single-Phase Motor — Advantages and Disadvantages of Single-Phase System — Lines in Operation.

+Index+ Page 149

[Illustration: HEAVY-DUTY CROSS-COMPOUND CONDENSING ENGINE, DIRECT CONNECTED TO 1,500 K.W. RAILWAY GENERATOR.

St. Louis Transit Company’s Power House. Fulton Iron Works.]

ELECTRIC RAILWAYS.

PART I.

The general name “electric railway” is applied to all railways employing _electric motors_ to supply power for the propulsion of cars. On all electric railways in commercial use to-day, the electric motor is used to furnish power to the driving wheels of the car or locomotive, the electric motor being the most efficient known means of transforming electrical into mechanical energy.

Electric railways are usually classified according to the methods by which current is supplied to the moving car. Thus, where an overhead trolley wire is used, as on the great majority of electric railways, the term _trolley road_ is applied. Where an insulated steel rail is laid alongside the track rail for supplying current, as on the “elevated” roads in America and on a few interurban roads, the term _third-rail road_ is used. Where, as on the street railways of a few large cities, the conductors are placed in a conduit underneath the surface of the street, and current is taken by means of a plow or shoe running in the conduit, the name _electric-conduit railway_ is most commonly applied. There are also a few systems using conductors buried beneath the pavement, and having contact buttons or sections of conductor rail on the street surface, which sections are supplied with current by automatic electromagnetic switching apparatus as the car passes, but which are normally dead and harmless. The overhead trolley and the third-rail systems are by far the most common.

A further general classification of electric railways has recently been made because of the introduction of alternating-current railway motors. The great majority of electric railways employ direct-current motors. Where alternating-current motors are used, the road is spoken of as one using single-phase alternating-current motors or three-phase alternating-current motors, as the case may be.

All electric railway systems in commercial use are operated on an approximately constant potential or voltage, and the various electric motor cars operating on the system are connected across the lines in parallel. The most common practice is to utilize the rails and ground as one side of the circuit, and the overhead trolley wire or “third rail” as the other side, as in Fig. 1. The trolley wire or third rail is, of course, thoroughly insulated from the ground. The positive poles of the generators at the power house are usually connected to the trolley wire, and the negative poles to the rails and ground. The various electric motor cars, being connected in parallel or multiple between the trolley wire and the ground, draw whatever current is necessary for their operation. Where the conduit system is used, both sides of the circuit are insulated from the ground, and the contact shoe or plow collects current from two conducting rails in the conduit, one of these conducting rails being positive and the other negative. A double-trolley system is also in use to a limited extent. In this system, both the positive and the negative sides of the circuit are insulated from the ground, one trolley wire being positive and the other negative.

[Illustration: Fig. 1.]

[Illustration: Fig. 2. Railway Motor.]

Further discussion of the matters just outlined will be taken up in the succeeding pages.

CAR EQUIPMENT.

MOTORS.

The voltage most commonly employed by electric railways is 500 to 600; and the motors are 500-volt direct-current series-wound motors, designed especially for railway service. The electric railway motor must be dustproof and waterproof because of the position it occupies under the car. For this reason electric railway motors are made in the form of a steel case (Fig. 2), which entirely surrounds the field-magnet poles and takes the place of the yokes or frames that support the fields on stationary motors. Cast steel is the material now usually employed for railway motor cases and fields, on account of its mechanical strength and its high magnetic permeability. The four poles project inwardly from the case, as seen in the open motor case, Fig. 3, which is that of a Westinghouse No. 69 motor.

[Illustration: Fig. 3. Railway Motor. Upper Field Raised.]

Railway motors have usually four poles because this permits of a symmetrical and economical arrangement of material around the armature, and hence permits the motor to be placed in the small space available on the car truck. Two-pole motors have been used in the past, but they were not as compact as the four-pole type.

=Characteristics of Railway Motors.= The curve sheet, Fig. 4, for the Westinghouse No. 69 motor represents in general the characteristics of all direct-current railway motors.

The figures for each curve are found with names corresponding to the curve to which they apply, at each side represented by vertical distance on the sheet. The amperes, represented by the horizontal distance, are marked at the bottom, and apply in common to all the curves.

The tractive effort at different current consumption is represented by a line curving upwards somewhat. This shows that the tractive effort increases, in a proportion greater than directly, as the current increases.

The torque required in starting may be many times greater than that necessary to maintain the car at full speed. The series-wound motor, therefore, furnishes this great starting torque more economically than a shunt-wound motor the torque of which is proportioned to the current. This feature of the series-wound motor makes it especially adapted to street railway work.

[Illustration:

WESTINGHOUSE No. 69 RAILWAY MOTOR 500 VOLTS

GEAR RATIO, 14 TO 68. WHEELS, 33″

CONTINUOUS CAPACITY, 25 AMPERES AT 300 VOLTS, OR 23 AMPERES AT 400 VOLTS.

Fig. 4. Characteristic Curves of Railway Motor.]

The efficiency curve shows the motor to have an efficiency of about 83 per cent with gears. Much other information may be obtained by a proper study of the curves. The fields are worked near the point of magnetic saturation. This economizes metal and space and is also an advantage because of the fact that when so worked the armature reactions have very little effect on the fields. The neutral points between fields are consequently shifted very little and it is therefore not necessary to shift the brushes when the motor is reversed.

[Illustration: Fig. 5. Armature Winding.] General Data on Street Railway Motors.

=Armature Winding.= The armature winding is what is commonly known as the series or wave winding, shown developed in the paper on Direct-Current Dynamos. This winding is shown in Fig. 5, which is an end view of an armature and commutator. In the figure, however, the armature is shown with a much smaller number of slots than a railway armature should have in practice. One reason for the employment of the wave or series winding on railway motor armatures, is that with this winding no cross-connections are necessary when only two brushes are used, and these two brushes may be placed 90° apart in a convenient and accessible position. Another reason is that the current, in flowing from one brush on the commutator to another, must always pass through the magnetic field of all four of the motor poles. This makes it impossible for any unbalancing of the magnetic circuit to cause more current to flow through one portion of the armature than is flowing through another portion. In a railway motor it has been found quite possible to have one pole or pair of poles exerting a greater magnetic attraction on the armature than another pair, owing to differences in the iron and differences in the clearance between the armature and pole pieces, which differences cause more magnetic lines of force to flow from some pole pieces than from others. With the lap-armature or the ring-armature winding, since the various portions of the armature under different poles are in parallel with one another, any difference in the magnetic flux between different poles will cause a different amount of current to flow in the various paths through the armature.

========+======+=====+=====+======+======+======+======+========+=========+=======+==========+=========+=====+======= Type of |Horse |Amp- |Speed|Total |Slots.|Cond- |Commu-| Weight |Armature | Gears |Commutator| Pinion |Dia- |Length. Motor. |Power.|eres.|Full |Field | |uctors|tator |complete|Complete.| and | Bearing. |Bearing. |meter| | | |Load.|Turns.| | per |Bars. | with | |Casing.| | |Arma-| | | | | | | slot | | Gears. | | | Inches. | Inches. |ture.| --------+------+-----+-----+------+------+------+------+--------+---------+-------+-----+----+----+----+-----+------- General | | | | | | | | | | | | | | | | Electric| | | | | | | | | | | | | | | | 51 | 82 | | 640 | 56 | 37 | 12 | 111 | 3875 | 953 | 338 | 3 | 5¾ | 3¼ | 8¼ | 16 | 10½ 52 | 27 | | 640 | 155.5| 29 | 24 | 87 | 1725 | 357 | 265 | 2½ | 6⅜ | 2¾ | 7¾ | 11 | 9 57 | 52 | | 470 | 110 | 33 | 18 | 99 | 2972 | 704 | 340 | 2⅝ | 6⅜ | 3¼ | 8¾ | 14 | 12 55 | 160 | | | | 47 | 6 | 141 | 5415 | 1550 | 490 | 3¼ | 7½ | 3¾ |11 | | 67 | 40 | | | 110 | 37 | 18 | 111 | 2385 | 595 | 385 | 2⅝ | 6⅛ | 3 | 8 | | 54 | 25 | | | | | | 115 | 1831 | 395 | 285 | 2½ | 6 | 2¾ | 7¾ | | 74 | 65 | 113 | | 70.5| | | | 3534 | 845 | 415 | 3⅛ | 6¾ | 3⅝ | 8¾ | | --------+------+-----+-----+------+------+------+------+--------+---------+-------+-----+----+----+----+-----+-------

--------+------+-----+-----+------+------+------+------+--------+---------+-------+-----+----+----+----+-----+------- Westing-| | | | | | | | | | | | | | | | house | | | | | | | | | | | | | | | | 68 | 40 | | | | 55 | 12 | 109 | 2280 | 505 | 330 | 2¾ | 6¾ | 3 | 7¾ | 14 | 8 69 | 30 | | | | 35 | | 105 | 1950 | 385 | 330 | 2¾ | 6 | 2¾ | 7 | 13 | 6¾ 76 | 75 | | | | 39 | | 117 | 3840 | 505 | 860 | 3¼ | 8 | 3½ | 9 | 16½ | 56 | 55 | | | | 39 | | 117 | 3000 | 315 | 720 | 3 | 7½ | 3¼ | 8½ | 14 | 12 50c| 150 | | | 144 | 55 | 6 | 115 | 5550 | 1500 | | | | | | | 49 | 35 | | | 114 | 59 | | 117 | 1925 | 438 | 327 | 2¾ | 6 | 2¾ | 7½ | 13⅝ | 6½ --------+------+-----+-----+------+------+------+------+--------+---------+-------+-----+----+----+----+-----+-------

By reference to the winding diagram given in Fig. 5, it may be noted that a complete circuit through two coils ends at the segment adjacent to the one from which the start was made. It may also be noted in the table of motor data that all of the armatures have an odd number of segments and an odd number of slots. It is absolutely necessary in a wave winding to have an odd number of segments. Otherwise the winding could not be made symmetrical and the circuit through two coils be made to return to a segment adjacent to that from which the start was made. With equal spacing between the top and bottom leads of the two coils, an even number of segments would make the circuit return either on the segment from which the start was made or two segments from it.

The first drum-wound street railway motor armatures had as many slots in the armature as there were coils and segments. The great number of slots necessarily made the teeth very thin and consequently weak. This is very objectionable as sometimes the armature bearings wear away, allowing the face of the armature to drag on the pole pieces and thin teeth are bent out of shape.

Armatures are now almost entirely constructed with either two or three coils to a slot. When two coils are used in each slot with an odd number of slots an even number of coils results. If these were all connected to the commutator an even number of segments would be necessary. As this is not possible with a wave winding, one of the coils is “cut out.” The ends are cut short and taped and it is termed a “dead” coil. This makes the winding somewhat unsymmetrical, all the coils not bearing the same angular relation to the commutator segments to which they are connected. This difference is, however, not great enough to affect the operation of the machine.

The Westinghouse 49 motor is an example of an armature with a dead coil. By reference to the table of motor data it will be seen that this armature has 59 slots. Two coils in each slot would make 118 coils. One of these, however, is cut out, giving 117 segments.

Cutting out a coil can be avoided by putting three coils in each slot.

An odd number of coils results then no matter what the number of slots may be. In the majority of examples given in the table there are three times as many segments as slots. The sides of the slots of modern street railway armatures are straight. The coils are prevented from flying out by bands of wire extending over the tops of the coils around the armature. Steel or silicon bronze wire of about No. 14 gauge is used. Recesses are made in the armature teeth for the reception of these bands so that the wire when wound will come flush with the face of the armature. The bands are usually ¾ to 1½ inches wide. The wires are well soldered together to secure them in place. One trouble experienced with armatures is the slipping off of these bands. The heated armature expands and stretches them. When the armature cools the bands are loose and then often slip off. When they do so the coils fly out by centrifugal force, strike the pole pieces and ground the motor.

[Illustration: Fig. 6. Armature Coil.]

=Armature Coils.= Railway motor armatures are to-day universally constructed with form-wound coils, which are wound on a form of proper shape and carefully insulated before being placed in the armature.

The coils of the smaller motors (those up to 40 or 50 horsepower) are usually wound with round wire. The cotton covering of the wire is depended upon for insulation. To strengthen this, however, the coils after being wound are immersed in an insulating compound and then baked in an oven. The whole coil is usually wrapped with insulating tape (See Fig. 6). The armatures of larger motors have coils made of copper bars. Mica is often placed between and around the bars for insulation, though oiled linen cloth tape cut bias is also employed, especially in repair work.

=Field Coils.= Field coils are so constructed that they may be readily removed should they become grounded or short-circuited. Some makers wind them on a brass shell or form which is slipped over the pole piece. In some motors the field coils are composed of copper ribbon, wound bare, with ribbons of insulating material between the turns. Field coils of wire for the smaller motors, if not wound on shells, are wound on forms and before completion are taped in such a manner that they will hold their shape without being enclosed in a spool. The terminals are brought out where they will be of easy access when the field is in place (See Fig. 7).

[Illustration: Fig. 7. Field Coil.]

=Armature Leads.= In Fig. 3 is seen a completed armature in the motor casing of a Westinghouse No. 69 motor. Since the motors are four-pole, the two sides of any one coil occupy slots 90° apart in the armature coil, as indicated in Fig. 5. The ends of the coils are connected to commutator bars 180° apart. The relative position of the commutator connections of any armature coil can, of course, be varied so as to bring the brushes in the most convenient position in the motor casing. Brushes are always of carbon, and are placed where they can be easily reached from the opening in the motor casing over the commutator.

=Motor Leads.= The reversing of the current through the armature, independent of the field current, to secure reversal of direction of rotation of the armature, makes it necessary that four wires enter the motor. The portions of these wires connected permanently to the motor are termed the motor leads because they “lead out” the current. Sometimes an ordinary two-way connector is used in connecting these leads to the wires of the cable, but often a jack-knife connector is employed to facilitate connecting and disconnecting. Considerable difficulty has been experienced by the wearing away of the insulation of the leads where they rest on the motor shell. To avoid this there has recently come into use a lead protected by a spiral metal covering. =Brushes.= That the motor may operate in either direction equally well, the carbon brushes are placed radially or nearly so. No provision is made for shifting their position relative to the fields. They usually occupy a position equidistant between pole tips. The common types are either ½ or ⅝-inch thick and from 2¼ to 4 inches wide.

[Illustration: Fig. 8. Brush Holder.]

=Brush Holders.= Two methods of securing the brush holders are employed. In Fig. 3, the brush holders may be seen to be secured in position by being bolted through the end of the motor shell. Fig. 8 shows the brushes mounted on a yoke which is secured to the motor shell. The yoke is of wood and provides the necessary insulation. Where the holders are fastened directly to the shell a block and washers of vulcabeston or other insulating material intervene to furnish the insulation between the shell and the holder. In practice the greatest difficulty experienced with brush holders is preventing them from becoming grounded by dirt and carbon dust which collects on the insulation.