Improvements in Safety Devices for Dynamo Electric Machines.
Year: 1898

page_text: Date of Application, 20th Sept., 1898-Accepted, 10th Dec., 1898
COMPLETE SPECIFICATION.
Improvements in Safety Devices for Dynamo Electric Machines.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of this
invention (which has been communicated to us from abroad by Edward M. Hewlett,
residing at Schenectady, County of Schenectady, State of New York, United States
of America, Electrical Engineer), and in what manner the same is to be performed
to be particularly described and ascertained in and by the following statement:-
In the operation of dynamos running in multiple, which is in modern practice
the only method in use of employing a number of machines upon the same load,
it becomes necessary to regulate the terminal voltage of the different generators
to substantial equality, of course considering the character of the machines, the
different circuit resistances, etc. It is well known that if the speed of the dynamo
is increased, the terminal voltage rises; under some circumstances, as when a
large load is suddenly thrown off the station (for instance, in a power-station,
when a number of stationary motors are shut down at noon or in the evening;
or in a lightning station, when the lights in business houses or dwellings are extin-
guished in large numbers), the engine or other prime mover may race, at least
until its speed is controlled either by the regulator or by hand. In such a case,
the terminal voltage will rise with such rapidity that the machine may take
practically all the load on the station, and in some cases, such as that of a large
direct-driven generator, may even for a time try to drive the other machines as
motors. The possible disastrous consequences are readily perceived.
To a less degree a similar trouble might arise with a single dynamo if its prime-
motor should race. This may happen from the causes already pointed out; it
is peculiarly liable to occur in operating electric railways, where it is impossible
In large systems,
to prevent the simultaneous starting and stopping of many cars.
this generally averages up, so that a fair constancy of load is attained; but in
interurban work, where trains of greater weight use more current at starting, or
Here the injurious
on smaller roads, the fluctuations of load are more severe.
effects upon the dynamo are rather mechanical than electrical, arising from the
high speed; though it is manifestly undesirable that the machine should be
operated at an excessive voltage, for which its insulation is insufficient.
To provide for the difficulties here briefly indicated there has been devised an
apparatus which combines the functions of a speed-governor and a circuit-
interrupter in such a way that a desired maximum speed it will not only open the
electric circuit, preventing damage to the dynamo, but will also stop the supply
of power to the prime-mover so that the speed is immediately and greatly reduced.
By this arrangement, danger of injury, electrical or mechanical is very much
reduced and practically eliminated.
It
The invention is illustrated in the drawings annexed as being applied to a
steam-engine, in a form in which it is has been practically used with success.
may be utilized with other prime movers, such as water-wheels, though in that
particular case it is well to shut off the power gradually, rather than suddenly,
for well-known reasons. The modification necessary for attaining this end will
be obvious to one skilled in the art.

page_text: In the drawings Fig. 1 is a side elevation of an embodiment of the invention
applied to the steam-chest of an engine; Fig. 2 is a diagram of circuits including
a proper circuit-breaker; Fig. 3 is a diagrammatical illustration of a number of
machines in a power house, employing the invention.
The
A is the steam-chest of an engine, and B is the main steam-pipe; D is the usual
throttle valve for cutting off the supply of steam; C is another valve shown as a
balanced flap-valve, under the control of the governor I. It is connected to the
governor by a bell-crank C¹ and a rod C attached to the bell-crank E. To the
other arm of the bell-crank E is fastened the weight G, sliding upon the stud G+',
and provided with a detent G². A rod F with lock-nuts furnishes a means for
adjusting the throw of the weight G, and the stroke of the crank E.
detent G bears upon a latch H¹. The rod H is connected at one end to the latch,
and at the other end is a slotted link h, in which slides the pin k, upon one arm of
the bell-crank lever K, the other arm of which is attached to the rod I, controlled
by the governor I. The set-screw serves to adjust the point at which the pin
will cause the device to act. A belt L connects the governor with the engine shaft,
not illustrated. In operative relation with the valve C is the switch M, consisting
of a switch blade m connected by a rod M' with an arm of the bell-crank lever E.
A contact m¹ is in the path of the switch-blade m.
In Fig. 2 the generator N is shown in diagram, connected between the bus-bars.
In the lead from the generator to the negative bus is the circuit-breaker O; a
minute description is unnecessary, particularly as it forms no part of the present
invention, in operating which some other type of circuit breaker might be used.
It is provided with main terminals p, p, and a bridging terminal P, withdrawn by
the spring P¹ when the latch R is tripped by the armature R¹. The latter is con-
trolled by the series coil Q. To these parts there is added in the present invention,
the shunt coil Q', preferably, because most conveniently, acting upon the same
armature. The circuit of this coil is controlled by the switch M, and is con-
nected so that it also is opened by the circuit-breaker when the latter "blows,"
opening the circuit of the switch M.
In Fig. 3 the three generators N, N1, N2, are illustrated with their respective
engines, all supplying common busbars. Each of these generators is provided
with its own circuit-breaker O, and an auxiliary switch M; the apparatus being
simply a duplication of the construction shown in Fig. 1 and 2.
The operation of the parts is as follows: as long as the engine A is running
below a certain maximum speed, the governor rotates without effecting the
switch M or the valve C¹; but when the speed rises beyond the maximum desired,
the pink strikes the adjusting screw h¹ in the end of the slot h, pulls the bar H,
and trips the latch G2. The weight G then drops and closes the valve C,
shutting off steam from the engine. At the same time the switch blade mis
drawn across the contact m³, closing the circuit of the shunt coil Q¹, and opening
the circuit-breaker.
Having now particularly described and ascertained the nature of our said inven-
tion (as communicated to us from abroad) and in what manner the same is to
be performed, we declare that what we claim is:-
1. The combination with an electric generator, a prime-mover driving the
generator, a governor for the prime-mover, and means controlled by the governor
for interrupting the circuit of the generator.
2. The combination with an electric generator, a steam-engine driving the
generator, a governor for the engine, and means controlled by the governor for
interrupting the circuit of the generator when the engine tends to race.
3. The combination with a dynamo and a prime-mover, which drives said
dynamo, for a mechanism electrically connected with said dynamo and mechani-
cally connected with the governor of the prime mover whereby upon an excessive
speed being attained, the governor acts to automatically stop the prime mover and
cut the dynamo out of circuit.

page_text: 4. In an electric generating station, a number of dynamos in an electric circuit,
in combination with one or more engines for driving them, one or more engine
governors, and a mechanism or mechanisms connected therewith and electrically
connected with a source of current, whereby, upon the engine racing, the governor
will operate said mechanism to automatically cut off the power supply, and cut
out the dynamo or dynamos from the circuit.
5. The combination with a dynamo, and a circuit-breaker in circuit therewith,
of an engine driving the dynamo, a mechanism electrically connected with the
dynamo and controlling a valve for the engine, a weight connected with the
mechanism, and mechanism controlled by the governor of the engine normally
holding the weight; whereby the governor of the engine normally holding the
weight; whereby, upon the engine obtaining excessive speed, the governor will
act to drop the weight and operate the mechanism connected therewith to stop
the engine, operate the circuit-breaker and cut the dynamo out of circuit.
6. In an electric generating station, generators electrically connected through a
work circuit, a circuit-breaker for each generator, branch circuits connecting a
coil upon each circuit-breaker with a source of current and a normally open switch
in each branch circuit; in combination with an engine, a governor, a cut-off
valve, and mechanism connecting the governor with the switch and the cut-off,
whereby when the engine races, the cut-off and the circuit breaker are simul-
taneously operated.
THE BRITISH THOMSON-HOUSTON CO. LTD.
A. R. MONKS,
Director.
ALFRED CLEMENTS,
Assistant Secretary.