Improvements in Safety Devices for Alternating Electric Current Power Systems.
Year: 1896

page_text: Date of Application, 14th Apr., 1896-Accepted, 16th May, 1896
COMPLETE SPECIFICATION.
Improvements in Safety Devices for Alternating Electric Current
Power Systems.
I, JAMES DEVONSHIRE, Secretary of The British Thomson-Houston Limited,
of 38 Parliament. Street, Westminster, London (a communication from abroad by
Ernst J. Berg, Electrical Engineer, of Schenectady, in the State of New York,
United States of America) do hereby declare the nature of this invention and in
what manner the same is to be perforined to be particularly described and ascertained
in and by the following statement:-
My invention relates to alternating electric current power systems, particularly
those operated by polyphase currents; and has for its object to provide for such
systems a safety device adapted to prevent accidents when for any reason the power
supply is interrupted on one of the lines.
It is well known that after a motor has attained speed in a polyphase system of
distribution, if one of the lines be disconnected for any reason, the motor then acts
Such a motor is
either as a synchronous or an induction single-phase motor.
incapable of reversal of leads. In many cases it is desirable to preserve this capacity
for immediate reversal; this is particularly true on electric railway lines, where
emergencies may demand that the car shall be reversed to bring it to a quick stop.
It is to provide especially for cases of this class that I have devised my present
invention, which consists briefly in means for supplying an interposed electro-motive
force of displaced phase to the motor, such means being brought into operation by
an interruption of the supply in either of the circuits. The motor is then con-
tinuously operated as a polyphase machine, and becomes capable of reversal by
reversing two of the leads, acting much like a continuous current motor under
similar circumstances.
The accompanying drawings are diagrams illustrating embodiments of my
invention,
Fig. 1 showing the apparatus in its normal operation, and
Fig. 2 the operation in an emergency, requiring the application of my invention.
The particular means which I have illustrated to carry out my invention consists
of a switch so arranged as to interpose between the two remaining mains of the
three-phase system (which acts as a single phase system when the third main is
disconnected or the power fails in that main), means for obtaining a displaced
phase; I have illustrated the combination of an inductance and resistance in series
between the mains and a connection from the third terminal of the motor to a point
between the inductance and resistance. With this arrangement I combine an
"emergency switch," as I prefer to call it, by which, if one of the trolleys should
fly off in the system illustrated, the contacts of the switch would be closed, and the
inductance and resistance would be connected in, as presently to be described. The
switch is operated by balanced magnets, so that when the supply fails its operation
becomes automatic. It is manifest that this is the preferred method, inasmuch as
it does not demand attention from the motorman; for it, however, I may substitute
manually actuated devices without departing from the spirit of my invention.
Referring now to the drawings, A is the field of the motor, B is its armature, the
machine being represented as a three-phase induction motor of the type now well
known; a, b are the trolley lines; T1, T2 are the trolleys; M, M' are the balanced
magnets referred to, in each of which one coil m' is in the ground circuit, and the
other coil m of each magnet respectively is in one of the trolley circuits. The

page_text: switch S is controlled by the magnet M in the circuit of the trolley T, and
the switch S' by the magnet M'. I is an induction coil and R is a resistance. As
illustrated in Fig. 1, neither one of the switches is closed, and the circuit is in normal
operation, the motor running as a three-phase machine."
Referring now to Fig. 2, the same letters indicate like parts, but the switch S¹
in this figure is closed, and the trolley T2 is represented as off the wire b. In this
case the coil m of the magnet M' is dead, and the coil m in the ground circuit is
energized, the terminal of the coil 3 of the field A of the motor being perma-
nently connected to ground. The circuit in this case is from the trolley T
through the coil m of the magnet M to the coil 2 of the motor field, thence
dividing, going through the coil 3 of the motor field and the coils m', m¹ of the
magnets M, M' to ground. The motor roil 1 is connected, as will readily be seen,
by means of the circuits from the switch S', between the trolley T and the ground
as follows; Passing from the trolley T' to the right, and thence to the upper contact
of the switch St, through the inductance I to the center contact of the switch, thence
to the line of the trolley T2, and thence to the coil 1 of the motor. The other
connection is from the ground circuit, the lower contact of the switch St, throngh
the resistance R to the center contact of the switch, and the third terminal of the
motor. It will be seen that the effect of the interpolated inductance and resistance
in the line is to take to the coil 1 of the motor an electro-motive force of dis-
placed phase, thus adapting the motor to still operate as a three-phase polyphase
electric motor. It is to be understood that suitable combinations of inductance,
resistance and capacity, may also be employed to obtain the objects of this invention.
I have not illustrated any particular form of controller for the motor, because these
are of various types, and the particular type selected is unimportant. It is of course
Decessary that the controlling device should be capable of reversing two of the leads
of the motor, but it is otherwise unimportant what its construction may be. Such
a controller is diagrammatically illustrated at K in the drawings.
I have also not further illustrated the operation of the switch S, inasmuch as its
effect is the same as that of the switch S¹, except that it operates upon the coil 2 of
the motor field. It is manifest that, as the third coil of the field is grounded
permanently, it is unnecessary to interpolate a switch in that lead; but if there
were three metallic conductors, another switch might be used without departing
from my invention, its construction and operation being the same as that of those
already described.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed as communicated to me
from abroad I declare that what I claim.is:
1. In an alternating electric power system, power lines supplying polyphase
currents, a motor actuated by such supply lines, and means for supplying to the
motor an electro-motive force of phase displaced from that of either of the lines,
such means operated by a failure of current from one of the supply lines.
2. In an alternating current power system, polyphase supply lines, a motor
connected with all of the said lines, means for supplying to the motor an electro-
motive force of phase displaced from that existing between any pair of the polyphase
lines, and switches for bringing such means into operation.
3. In an alternating current power system, polyphase supply lines, a motor
actuated therefrom, means for supplying to the motor an electro-motive force
of a phase displaced from that of either of the lines, switching mechanism for
bringing such means into operation, and automatic means for controlling the
switching mechanism, the automatic means being actuated by the failure of current
in one of the lines.
4. In an alternating current electric railway, polyphase supply lines, a motor
actuated thereby having some of its terminals connected to the supply lines, and
some to ground, inductance and resistance arranged in a normally disconnected
auxiliary circuit, and switching mechanism for connecting the inductance and

page_text: resistance between one of the lines and the ground, and connecting a terminal of the
motor between the inductance and resistance.
5. In an alternating current electric railway, polyphase supply lines, a motor
actuated thereby having some of its terminals connected to the supply lines and
some to ground, inductance and resistance arranged in an auxiliary circuit, and
automatically actuated switching mechanism for connecting the inductance and resist-
ance between one of the lines and the ground, and connecting a terminal of the
motor between the inductance and resistance.
6. In an alternating current electric railway, polyphase supply lines, a vehicle
making travelling contact therewith, a motor thereon actuated from the lines, an
inductance and a resistance in the auxiliary circuit, switching mechanisms for
bringing the inductance and resistance into circuit between either of the supply lines
and ground and connecting a terminal of the motor between the two, and a balanced
magnet operating each of the switching mechanisms, each magnet included in a
circuit between the motor and the supply line; whereby upon the failure of the
current in either of the supply lines, an electro-motive force of displaced phase is
supplied to the motor automatically, thus continuing to operate it as a polyphase
motor.
Dated this 14th day of April 1896.
For the Applicant,
J. C. CHAPMAN,
70 Chancery Lane, London, W.C., Chartered Patent Agent.