Improvements in Automatic Circuit Breakers.
Year: 1898

page_text: Date of Application, 8th July, 1898--Accepted, 26th Nov., 1898
COMPLETE SPECIFICATION.
Improvements in Automatic Circuit Breakers.
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 in Schenectady, in the County of Schenectady, and State of
New York, Electrical Engineer), and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement: -
This invention relates more especially to the art of running dynamo electric
machines in parallel and is applicable to those cases in which it is desired to operate
machines of different characteristics in multiple on the same circuit. The inven-
tion may, however, be used in any case where it is desired to cut a source of current,.
or a dynamo electric machine of any type, out of circuit when the current through
it is reversed.
For example, it often becomes necessary to run compound wound and
shunt machines in parallel and in such cases difficulties arise, owing to the
difference between the characteristic curves of the machine. The nature of these
curves is too well known to require description. It will, suffice to say that when
machines of the different characters referred to are run in parallel, their respective
electromotive forces will differ at certain values of the load and one of the
machines will, therefore, be run as a motor. By the use of this invention, the
machine which is run as a motor will be cut out of circuit when the difference of
electromotive forces has reached a certain predetermined value.
Another example of a case where this invention is of value is where one or more
rotary converters are used to feed direct current bus-bars. In such a case, a rotary
converter might accidently be disconnected from its source of supply, with the
result that current from bus-bars would then return through the rotary converter
and drive it as a motor.
By the operation of this invention, the rotary converter will then be cut out of
circuit.
The invention consists in general, of a device for causing the circuit of any one
of a number of dynamo electric machines running in multiple and supplying the
same load, to be opened when the electromotive force of that machine reaches a
value which is lower by a predetermined amount, than the electromotive force of
the others. The nature of the invention will be apparent from the following
specification and its scope will be particularly pointed out in the appended claims.
The accompanying drawings show an embodiment of this invention, in which,-
Fig. 1 is a diagram of the circuits;
Figs. 2 & 3 are front and side elevations, respectively, of the relay device, and
Fig. 4 is a detail.
The relay device E is fixed to a suitable device G which may form an integral
part of, or be fixed to, the switchboard. The device consists of a core about which
is a series coil F and a shant coil F. Attached to the upper and lower ends of

page_text: the core, respectively, are arms E¹ and E³. An armature E2 is pivoted at its lower
end to the arm E3 with its upper end in position to be attracted by the arm E¹.
Some selected portion of the magnetic circuit of the relay is of hardened steel, so
as to form a permanent magnet and polarize the relay. It is convenient to make
the armature serve as the permanent magnet, though other parts of the magnetic
circuit might serve as such instead of, or in conjunction with, the armature, as
questions of design may dictate.
An adjustable spring is connected to a downward projection of the armature E²
and acts to urge the upper end of the armature away from the arm E¹. Two
insulated spring contact fingers e², e³, are carried by the armature, as best shown
in Fig. 3. These contact fingers co-operate, respectively, with the contact
points e, e¹. It is required that only one of the contact fingers shall make contact
with its contact point when the armature moves in one direction. To accomplish
this object, each of the contact points is provided with a
of these guards is illustrated in detail in Fig. 4, which should read in connection
deflecting guard. One
with Figs. 2 and 3, and consists, as will readily be seen, of a body portion extending
above the level of the corresponding contact and with a downwardly curved spring
deflector extending below the level of the surface of the contact point. When a
contact finger moves towards one of these deflecting guards it will pass under the
same when moving in one direction, and be forced into contact, momentarily, with
the corresponding contact point; while, on the return movement, the contact finger
will be engaged by the deflector and will pass over the contact point without
engaging the same. The deflecting guard H is arranged with respect to the
contact point e so that the contact finger e² makes contact therewith when falling
away from the magnet core and is prevented from making contact when moving
in the opposite direction. The reverse is the case with respect to the contact
finger e. In the latter case, the deflecting guard H¹ is so arranged that the contact
finger is prevented from making contact with the contact point e¹ when the
armature moves away from the core and is forced to make contact when the
armature moves towards the core.
The relay E is electrically connected with, and operates to trip, a circuit break-
ing mechanism designated in the drawing as C. The circuit breaker has the usual
contacts c, c, with the bridging piece C¹ supported in position by toggle arms
operated by a handle K. A pivoted latch lever c¹ normally locks the toggle in
position to hold the bridging piece against the contacts c, c. The outer end of the
latch lever c is in position to be acted on by either of the solenoid magnets D, D¹,
and is normally retracted by a spring & Upon withdrawal of the latch from its
locking position, the contractile spring C operates to quickly remove the bridge
piece C and break the circuit.
The arrangements of circuits is illustrated in Fig. 1 which, for purposes of
illustration, shows the application of our device to the case where a shunt and
compound wound machine feed the same bus-bars. A and A¹ represent respectively.
a shunt and a compound machine connected to bus-bars a, b. The series coil F of
the relay, and the coil D of the circuit breaker C are connected in series in one
of the main leads of the shunt machine, A. The contact finger e is connected
through the coil D¹ with one terminal of the shunt machine, and the contact e is
connected through the low resistance coil, D, with the other terminal. The
contact el is connected through the high resistance coil F' with one of the bus-bars,
while the co-operating contact finger is connected to the other bus-bar.
The operation of the device is as follows:-
With the parts in the position illustrated, let it be assumed that the machines are
working on points of their characteristic curves so related to each other that each
machine gives out a fair proportion of the total energy delivered. Under these
conditions, the armature E³ remains in position with its upper end against the
arm E. If now the load increases, the compound machine will raise the electro-
motive force at which the current is delivered with the result that the shunt
machine will deliver less current because it will be working on that part of its

page_text: characteristic corresponding to a higher electromotive force. Upon continued
increase of load upon the bus-bars the load on the compound machine will increase
and the load on the shunt machine will decrease, until a point is reached where the
current is reversed through the shunt machine and it runs as a motor. The
current through the coil F is normally in a direction to magnetize its already
polarized core, but, upon reversal of current through the shunt machine, the
current passes through the coil F in the opposite direction. When the reversed
current reaches a certain predetermined value, the core is magnetized sufficiently
to permit the armature, under the tension of the spring e, to move away from the
core into the position shown in dotted lines in Fig. 2.
will,
As the armature moves towards its dotted position the contact finger
momentarily, touch the contact point e, thus completing the circuit from the
positive bus-bar through the shunt coil D', on the circuit breaker C, to the contact
finger e, to the contact point e and through the coil F back to the negative bus-
bar. The core of the coil D' being thus energized trips the latch c¹ of the circuit
breaker C which then opens the circuit of the machine A.
It
If now,
It is desirable that before the circuit breaker C be closed, the relay should be
put into condition to act in case the current should again immediately reverse.
is manifest, that if current should be sent through the series coil F, the core
should be magnetized so as to hold the armature in its normal position, then if this
cannot be done without closing the circuit breaker C, there is provided an
additional coil F adapted to be connected in shunt with the mains.
the armature be moved from its dotted line position (Fig. 2), to the full line
position shown in Figs. 1 and 2, the contact e² will pass under the guard H¹
and touch the contact e¹, thus completing the circuit through the coil F to the
minus bus-bar and magnetizing the core of the coil F. The armature E³ will
then remain attracted. If now, the circuit breaker be closed, it will remain closed
so long as the conditions are proper for normal running, but as soon as the current
reverses, it will open again.
The tension of the spring may be so adjusted as to give the desired degree of
sensitiveness to the relay. The stiffer the spring, the more readily does the device
act. Ordinarily, it is not desirable to have the circuit opened for every momentary
shift of current; the relay is, therefore, so polarized as to hold the armature
attracted with a slight, or somewhat in excess of the pull of the spring. In the
case of a rotary converter, it is ordinarily preferred to have the pull of the spring
adjusted so that it is nearly equal to the attraction of the armature, at the time
when there is no current in the coil F; this ensures prompt opening of the circuit
if the current reverses.
Having now particularly described and ascertained the nature of our said
invention (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 of dynamo electric machines in multiple, a circuit breaker
in the lead of a given dynamo, a polarized relay, and a circuit controlled by the
relay and including a coil upon the circuit breaker.
2 The combination of a number of dynamo electric machines of any desired
type, supplying a work circuit in multiple, and a polarized relay for controlling a
circuit breaker for opening the circuit of any given machine, when its current is
reversed.
3 The combination of a circuit breaker having an overload or series coil, a shunt
coil, and a polarized relay controlling the circuit of the shunt coil, either the shunt
or the series coil acting to open the circuit breaker.
4 A relay device for opening the circuit breaker upon reversal of current, com-
prising a coil in series in the lead to the bus-bars, a polarized magnetic circuit
including an armature, and contacts co-operating by movement of the armature, to
complete a circuit including a coil on the circuit breaker.
5-A relay device comprising a polarized core, an armature, a series coil, a shunt

page_text: coil, and contacts respectively operated by the opening and closing of the armature,
one set of the contacts controlling the circuit of the coil on the circuit breaker,
the other the circuit of the shunt coil on the relay.
6-A relay device comprising a polarized magnetic circuit including an
armature, a series coil in the lead to the bus-bars, a shunt coil in an independent
circuit, and means for closing the independent circuit, so as to repolarize the core of
the relay independently of the series coil after the core has been demagnetized by
reversal of current in the latter.
7 An automatic circuit breaker having a fixed and a movable contact, with a
guard over one of them so arranged that one contact touches the other as the switch
moves in one direction, but not during the reverse movement.
8-An automatic circuit breaker comprising fixed contacts, movable contacts,
and guards over some at least of the fixed contacts, permitting the movable
contacts to touch said fixed contacts when passing in one direction but not in
the other.
9 An automatic circuit breaker for a dynamo electric machine, comprising a
circuit controlling device operative upon reversal of current and a circuit breaker
controlled by said circuit closing device and acting to open circuit said dynamo
electric machine.
10 An automatic circuit breaker comprising a circuit closing device operative
upon reversal of current, and an independently actuated circuit breaker controlled
by said circuit closing device.
11-An automatic circuit breaker comprizing a polarized relay and a
mechanically actuated circuit breaker controlled by said polarized relay.
Dated this 8th day of July 1898.
THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED.
A. R. MONKS,
Managing Director.
ALFRED CLEMENTS,
Assistant Secretary.