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.
As to the operation of the system in general, the current may be
developed by single-phase, two-phase, or three-phase generators,
and supplied to the transformer substations just as it was formerly
supplied to the rotary converter substations. Only a single phase
is used on any section of the trolley line. The voltage on this
transmission line will depend upon the existing conditions, and can be
figured out like any other problem in power transmission.
[Illustration: Truck Complete with Single-Phase Motors and Contact
Shoes.]
Three-phase generators would ordinarily be used, as less copper is
required to supply a given amount of power. The common frequency is 25
cycles per second. At the transformer stations, the voltage is then
stepped down to that required on the trolley, which may be 2,000,
3,300, 6,600, or even 11,000 volts. While we cannot speak yet of a
standard voltage, 3300 seems to be finding considerable favor. The
voltage for which the motors are wound is 200 or 250, the General
Electric motors using the former voltage, and the Westinghouse the
latter. When operating on alternating current the motors are connected
in parallel, and when running on direct current they are connected
in series. Motors have been constructed from 50 to 225 horsepower,
and there is no apparent reason why larger ones could not be made to
operate with equal satisfaction.
[Illustration: Magnetic Speed Indicator.]
Among the roads in this country which are either using, or planning to
use single-phase current, may be mentioned the Ballston-Schenectady
line, which was one of the first systems to be equipped and has
been in successful operation for some time. This road uses the
alternating-current motor developed by the General Electric Co. The
motors are adapted for operation on the 2,000-volt alternating-current
trolley between cities, and on the standard 600-volt direct current
in Schenectady. They are wound for 400 volts, and are operated in
series on the 600-volt direct current. The frequency used is 25 cycles.
Current is supplied by an overhead trolley, no feeders being used.
A second road of importance is one in Georgia between Atlanta and
Marietta, which is 15 miles in length. This uses the Westinghouse
equipment. The current on the trolley is 2,200 volts and 25 cycles. It
is transmitted at a voltage of 22,000.
Another road of importance is the Indiana and Cincinnati interurban
line, 41 miles in length, which has been in operation on regular
schedule since July 1st, 1905. For 37 miles the road is operated
from alternating current, and for 4 miles, from direct current. Four
75-horse power motors per car are used, capable of a maximum speed of
65 miles per hour.
[Illustration: Armature Quill.]
The Bloomington, Pontiac and Joliet Electric Railway is a single-phase
road equipped with General Electric apparatus, and has maintained a
regular schedule over a distance of more than 10 miles since March,
1905.
The plans are now being laid for a single-phase road, which will run
south from Spokane, Washington, a distance of 150 miles. The current
on the transmission line is 45,000 volts, which is stepped down to
6,600 on the trolley. The car will be capable of operating on current
from a 6,600-volt alternating, a 700-volt alternating, or a 575-volt
direct-current supply.
Perhaps the most important move which has been made in the direction
of single-phase traction thus far is the decision of the New York, New
Haven, and Hartford road to establish a long-distance passenger traffic
on the single-phase system. According to the latest plans this road
will operate between the Grand Central Depot and Woodlawn, N. Y., over
the terminal tracks of the New York Central road, on direct current
taken from the trolley. From Woodlawn, N. Y., to Stamford, Conn., the
road will be operated on the single-phase system.
[Illustration: A Pair of Drivers with Single-Phase Motor Mounted upon
Quill.]
The equipment is being supplied by the Westinghouse Co. The current
is generated by revolving-field type turbine-driven alternators.
The armatures are designed for either three-phase or single-phase
connection. The current is generated at 25 cycles and 11,000 volts,
being delivered directly to the trolley, and thence to the cars,
without the intervention of any transformers. The double catenary
suspension from messenger wires is used to support the trolley. The
locomotives are each equipped with four 200-H. P. gearless motors,
designed to operate on 235-volt alternating current and 275- to
300-volt direct current. The armature is not mounted on the shaft
direct, but is built upon a quill through which the axle passes with
about ⅝-inch clearance all around. There is a flange at each end of
the quill from which seven pins project and fit into the hubs of
the driving wheels. On the direct-current part of the line, current
is delivered to the car through eight collecting shoes from a third
rail. On the alternating-current section, current is delivered through
two pantograph bow trolleys. On the direct-current section the
series-parallel method of speed control is used, current being fed
directly to the motors which are connected two in series permanently
and the series-parallel control is applied to the motors in groups of
two. The alternating-current speed control is accomplished by six taps
from an auto-transformer for the corresponding running points. The cars
weigh 78 tons and are capable of a speed of 60 to 65 miles per hour.
The electro-pneumatic unit-switch type of control is used. At each
end of the cab is a master controller from which the main controller
is operated. Several locomotives can be operated together on the
multiple-unit system, if desired.
[Illustration: Six-Unit Switch Group, Single-Phase System.]
The Washington, Baltimore and Indiana single-phase road is the latest
in the field, contracts having been placed very recently. The current
will be transmitted at 33,000 volts and 25 cycles, then being stepped
down to 6,600 volts on the trolley. The road will be 60 miles long and
will be equipped with General Electric apparatus. Four 125-H. P. motors
capable of operating on either alternating current or direct current
will be used, and the cars will be capable of a speed of 60 miles per
hour.
INDEX
Air brakes, 56
Air compressors, 57
automatic governor for, 57
Westinghouse, 58
Alternating-current generators, 105
Alternating-current switchboards, 110
Alternating-current systems, 113
single-phase motors, 114
three-phase motors, 113
Alternating-current transmission, 99
Armature coils, 8
Armature leads, 9
Armature tests for grounds, 133
Armature winding, 5
defects of, 124
mistakes in, 126
Automatic governor for air compressors, 57
Ballast, 85
Bearings of railway motors, 13
Block signals for electric railways, 94
Bond testing, 120
Bonding and return circuits, 88
Booster feeder, 98
Brackets, 75
Brake leverages and shoe pressure, 54
Brake rigging, 53
Brake shoes, 64
Brush holders, 10
Brushes, 10
Burn-outs, 123
Canopy switch, 39
Car, failure of to start, 127
Car bodies, 67
Car circuit breaker, 39
Car construction, 67
Car equipment, 3
Car heaters, 34
electric, 34
hot-water, 36
Car painting, 72
Car repair shops, 134
Car weights, 72
Car wheels, 51
Car wiring, 37
Cast-welded joints, 87
Coefficient of friction, 65
Common T-rail, 84
Commutator type single-phase motor, 139
Compressors, 57
Conductivity of steel rail, 80
Conduit systems, 81
contact plow, 82
cost of, 82
current leakage, 83
Contact plow, 82
Contact shoes, 45
Controller construction, 19
Controller notches, 27
Controller wiring, 20
Controllers, 16
Cost of power, 119
Couplers, 66
Current required to heat cars, 35
Current leakage, 83
Defects of armature windings, 124
Direct-current feeding, 98
Double-current generators, 105
Drawbars, 66
Economy in power, 118
Electric car accessories, 39
canopy switch, 39
car circuit breaker, 39
contact shoes, 45
fuses, 41
lamp circuits, 43
lightning arresters, 41
trolley base, 44
trolley poles, 44
trolley harp, 45
trolley wheels, 44
Electric cars, road tests of, 117
Electric heaters for cars, 34
Electric railway, 1
Electrically welded joints, 87
Electrolysis, 95
prevention of, 97
Feeder panel, 110
Feeder systems, 92
Feeders, 75
Field coils, 8
Field tests for grounds, 133
Four motors, 19
Fuse blows, 130
Fuses, 41
Gearing, 12
G. E. electric brake, 61
G. E. train control, 29
Generator, starting up, 108
Generator D. C. panels, 106
Generators, 105
Girder rail, 83
Grounds, 123
High-tension lines, 77
High-tension oil switches, 111
Highway crossings, 80
Hot-water heaters for cars, 36
Insulators, third rail, 79
Interurban railway, system of distribution for, 101
Joints for rails, 86
Lamp circuits, 43
Lightning arresters, 41
Locating defects in motor and controller wiring, 128
Location of
power houses, 101
third rail, 79
Lubrication of railway motors, 13
Magnetic blow-out, 26
Maximum traction trucks, 51
Momentum brakes, 59
Motor leads, 9
Motor suspension, 14
Motor-coil testing, 121
Motors, 3
as emergency brakes, 63
of the New York Central electric locomotive, 15
Multiple-unit control, 29
Oil switches, high tension, 111
Open-circuit tests, 128
Opening cases for inspection, 10
Overhead construction, 73
brackets, 75
feeders, 75
high-tension lines, 77
section insulators, 76
span wires, 74
trolley wire, 73
trolley-wire clamps and ears, 73
Potter third-rail shoe, 46
Power
cost of, 119
economy in, 118
taken by cars, 115
Power house location, 101
Power stations, general plan of, 105
Power supply and distribution, 98
Railway motors
bearings, 13
brushes, 10
characteristics of, 3
gearing of, 12
lubrication of, 13
Rate of retardation in braking, 66
Resistance of track, 91
Resistances, 38
Return feeders, 92
Reversal of motor, 26
Reversed fields, 133
Rheostat control, 17
Road tests of electric cars, 117
Sectional insulators, 76
Series-parallel control, 17
Shanghai T-rail, 84
Short-circuit tests, 130
Single trucks, 48
Single-phase electric railway, 136
Single-phase motors, 114, 139
Sleet on trolleys and third rails, 46
Sliding and spinning wheels, 119
Span wires, 74
Sparking at the commutator, 127
Sprague multiple-unit system of control, 29
Steel car framing, 71
Storage air brakes, 58
Storage batteries in stations, 113
Street railway motors, general data on, 6
Supplementary return feeders, 92
Swing bolster trucks, 49
Switchboards, 106
alternating-current, 110
Switches, third rail, 79
Swivel trucks, 48
T-rail, 84
Thermit welding, 88
Third rail, 79
advantages in operation, 80
Third rail
conductivity of, 80
cost of, 80
highway crossings, 80
insulators for, 79
location, 79
switches, 79
Three-phase motors, 113
Track brakes, 63
Track construction, 83
Track resistance, 91
Track sanders, 65
Track support, 85
Transmission systems, efficiency of, 101
Trilby groove rail, 84
Trolley base, 44
Trolley harp, 45
Trolley poles, 44
Trolley wheels, 44
Trolley wire, 73
Trolley-wire clamps and cars, 73
Trucks, 46
maximum traction, 51
single, 48
swing bolster, 49
swivel, 48
Type L controllers, wiring of, 24
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