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Publication numberUS2006997 A
Publication typeGrant
Publication dateJul 2, 1935
Filing dateMay 16, 1931
Priority dateMay 16, 1931
Publication numberUS 2006997 A, US 2006997A, US-A-2006997, US2006997 A, US2006997A
InventorsLingal Harry J
Original AssigneeWestinghouse Electric & Mfg Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Circuit breaker control system
US 2006997 A
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Description  (OCR text may contain errors)

y 2, 3 H. J. LINGAL 2,006,997

CIRCUIT BREAKER CONTROL SYSTEM Filed ma 16, 1951 2s 5%. 375 F 3I\ 35 9/1 35*: -2]

I9 I Q 32 29 i- 17 19 .90

WITNESSES: INVENTOR 5,24 Harry J LinyaL J W v I v A'IFRN Y Patented July 2, 1935 UNITED STATES PATENT OFFICE CIRCUIT BREAKER CONTROL SYSTEM Harry J. Lingal, Wilkinsburg, Pa., assignor to Westinghouse Electric & Manufacturing Company, a. corporation of Pennsylvania Applic ation May 16, 1931, Serial No. 537,780

19 Claims.

My invention relates to apparatus for controlling the operation of circuit breakers and. more particularly to solenoid closing mechanisms for circuit breakers.

An object of my invention is to provide a circuit-breaker-closing mechanism which may be operated from a source of alternating-current energy and which shall be simple and rugged in its-design.

Another object of my invention is to provide a copper-oxide rectifier for supplying direct current to operate a circuit-breaker-closing solev noid from a source of alternating current.

A further object of my invention is to provide a circuit-breaker-closing mechanism of high efficiency and low cost because of the fact that both the rectifier and the solenoid have a shorttime current-carrying capacity much greater than their continuous current-carrying capacity.

When it is necessary that a circuit-breaker closing mechanism be operated from a source of alternating-current energy, it has been the prior practice to utilize an alternating-current motor mechanism to operate a centrifugal device to close the circuit-breaker. Such an alternating-current motor mechanism is expensive and has large space requirements and a great number of moving parts which operate at high speeds. This makes the apparatus subject to excessive wear and difficulties due to dirt and corrosion, and also requires the use of delicate bearingshaving fine adjustments. By using a direct-current solenoid which is supplied from an alternating-current line through a copper-oxide rectifier, a much more desirable closing mechanism is provided at a much reduced cost.

The duty cycle of a circuit-breaker-closing mechanism is such that it is operated only for a very short period of time in order to close the breaker and is entirely idle for a large part of the time. operating winding which has a large short-time current-carrying capacity. When such a winding is to be energized from a source of alternating current, it is desirable to have a rectifying device which has a similar current-carrying capacity. It has been found that a rectifier of the contact type, such as-a copper-oxide rectifier, has this desirable characteristic. This makes possible the use of a smaller closing coil and a smaller rectifier than would otherwise be the case.

In use, the time during which the closing coil is energized is only a fraction of a second, so that a much heavier current may be sent through This makes possible the use of an the coil for this'short time than would be feasible if the coil had to be energized continuously. In actual practice, it has been found that the current-carrying capacity of the closing coil may be ten times its continuous current-carrying capacity.

Copper-oxide rectifiers are most desirable for use in combination with such closing coils; since their short-time current-carrying capacity may be as high as thirty times their continuous current-carrying capacity. The use of a copperoxide rectifier for supplying direct-current energyfor a circuit-breaker-closing coil is thus very desirable since they are each capable of carrying a heavy current for the short time during which the coil is energized to close a circuit breaker.

While it might be possible to use a thermionictube rectifier for energizing a circuit-breakerclosing coil, this is not desirable because the maximum current-carrying capacity of a thermionic tube has a-definite limit, since the current carried by the tube can never exceed the electronic emission from the hot cathode, so that, to use a thermionic tube for such an application, it would be necessary to use a tube having a normal capacity large enough to carry the heavy currents for the short time that is required. A tube rectifier is also less satisfactory for this purpose because it is less rugged and employs a glass enclosure which is subject to breakage.

These objects and advantages will be more apparent from the further description of the particular embodiment of my invention illustrated in the single figure of the drawing, which is a diagram of apparatus and circuits embodying my invention.

In general, the illustrated embodiment of my invention comprises a circuit breaker I, a rectifier 3, a control switch 4, a rectifier-circuit relay 5, a control relay 1 and a source of alternating- ,current energy 9.

The circuit breaker l includes a pair of stationary contacts II which are connected in the main-line circuit l3l5. The circuit between contacts II is closed by a conducting bridging member I! which is, actuated from opened to closed position by a toggle mechanism IS.

The circuit breaker is biased to open-circuit position by means'of a spring 2| and is moved to closed position by an electromagnet comprising an armature 23 and a closing coil 25.

When the breaker has been moved to closed position, it is latched closed, against the spring 2|, by means of a latch 21 which engages a projection 29 of the closing mechanism.

The circuit breaker is opened by a tripping coil 32, which releases the latch 21 from the projection 29. The tripping coil 32 may be connected to a manual tripping switch or it may be controlled by the electrical conditions of the main circuit by any of the well known tripping schemes.

An auxiliary switch 36, comprising contacts 3|33 and a bridging member 35, is operated by the closing mechanism to complete the circuit between the contacts 3 |-33 when the breaker is in its closed position.

While the circuit breaker is shown as being directly connected to the closing mechanism, it should be understood that the closing mechanism may be of the well known trip-free type, so that the breaker may be tripped open without movement of the closing solenoid. In such case, the auxiliary switch would be placed to be operated by the closing mechanism rather than by the circuit breaker.

The closing coil 25 of the solenoid is connected to terminals 36 and 38 of the direct-current side of the rectifier 3 through conductors 3'|-39. The rectifier 3 comprises four stacks of rectifier disks 4|,.42, 43 and 44' connected to give full-wave rectification when alternating current is impressed across the terminals 4|49. The rectifier 3 is of the dry-disk contact type and preferably comprises alternate disks of copper, each having a copper-oxide surface on one side thereof, and lead washers for making electrical contact with the disks. Such rectifiers have the property of being able to conduct large currents for short periods of time because the metal disks have large capacity to absorb the heat generated, without damage to the rectifier. Another desirable characteristic of such a contact rectifier, when used with a circuit-breakerclosing mechanism, is that it has a negative temperature coelficient of resistance so that the resistance to the passage of current through the rectifier in the forward direction decreases as the temperature of the rectifier is increased. This is desirable since copper, such as is used for the winding of the closing solenoid, has a positive temperature coefiicient of resistance. This means that, as the resistance of the closing coil increases with increase of temperature, the resistance of the rectifier decreases, thus tending to keep the total resistance uniform. This is desirable since a constant number of ampere turns is obtained to close the circuit breaker under different temperature conditions. This is important since the solenoid and rectifier are subject to fluctuations in temperature over a wide range, because of heating by the heavy current, and to ambient temperature changes which may vary from -40 F. to +120 F, 1 V V The rectifier 3 is energized from the alternating-current source 9 through a transformer 5|, from terminal 52, through'conductor 53, contacts 55 and 51 of the rectifier-circuit relay 5, across which the circuit iscompleted by a conducting bridging member 59, through conductor 6|, to an adjustable resistance 63 which is connected to terminal 49. There is an important advantage obtained due to the fact that the contacts of the rectifier-circuit relay 5 are in the alternating-current circuit of the rectifier rather than in the direct-current circuit. This makes it possible to use lighter and less expensive materials for the contacts of the relay 5 without decreasing the life of the contacts. The alternating-current circuit can be opened with much less damage to the contacts than can the direct-current circuit, since theenergy stored inductively in the solenoid is discharged into the direct-current circuit through the copper-oxide contact rectifier and not into the alternating-current circuit. The relay contacts, therefore, do not have to interrupt a large induced current such as they would if connected in the direct-current circuit of the rectifier.

The resistance 63 is provided in order to vary the alternating-current voltage which is supplied to the rectifier and provides means for compensating for the aging of the rectifier. The adjustable rheostat also provides means for varying the direct-current voltage which is impressed upon the closing coil 25 in order to obtain the proper speed of operation of the closing mechanism. A fuse 65 is provided in the alternatingcurrent circuit between terminal 41 of the rectifier and terminal 50 of the transformer 5| for protection against abnormal currents.

The relay 5, which controls the supply of energy to the rectifier 3, is actuated by a winding 6'! which is connected from a tap 69 to give any desired voltage from the transformer 5|, through contactsll and 13 of relay I and contacts 11 and I9 of control switch 4, to terminal 52 of the transformer by conductor 53. The operating circuit of relay 5 includes contacts '||'|3 of the control relay 1 which are normally closed by means of a bridging member 8|. relay, 1 is also provided with a second pairof contacts 83 -85, the circuit across which is closed by a bridging member 81 when the operating winding 89 is energized.

The winding 89 is connected from the tap 69 of the transformer 5| to contact from which the circuit is completed either across contacts 3| and 33 of the auxiliary switch 30 on the circuit-breaker-closing mechanism and conductor 9|, or contacts 83 and 85 and conductor 92, to conductor which is connected, through contacts '|||9 of the control switch 4 and conductor 53, to terminal 52 of the transformer.

The control u In order to actuate the circuit breaker to thus completing the operating circuit of relay 5 from conductor 53, across contacts II and 19 of the control switch 4 and contacts II and 13 of control relay 7, to energize winding 61 to move the bridging member 59 to complete the alternating-current side of the rectifier circuit across contacts 55 and 51. This closes the circuit from conductor 53, through the alternating-current side of the rectifier, to the other side of the transformer 5| and causes 'a direct current to flow, through conductors 31 and 39, to the closing coil 25 which actuates the armature 23 to move the circuit breaker to closed position.

The operation of the closing mechanism moves bridging member 35 of the auxiliary switch 30 to complete a circuit across contacts 3| and 33, which causes current to flow through conductors 53, 90 and 9| to the operating winding 89 of cont ol relay 1, thus causing the opening of the alternating-current side of the rectifier circuit at contacts '|||3 and the closing of the shunt circuit including contacts 8385. This arrangement provides means for opening the alternating-current supply circuit to the rectifier 3 to deenergize the closing coil 25 as soon as the armature 23 has moved to closed position, thus preventing the continued energization of the closing coil 25 by reason of the holding of the control switch 4 closed after the closing coil has performed its function of operating the closing mechanism. This prevents the burning out of the closing coil and rectifier due to their being energized for a long time, thus making practical the use of a closing coil and a rectifier which have a short-time current-carrying capacity much greater than their normal current-carrying capacities.

The closing of the shunt circuit, including contacts 83 and 85 of control relay 7, by bridging member 8'! completes a circuit in parallel with the contacts 3i and 33 so that if the circuit breaker latch should be tripped to the open position because of abnormal electrical conditions of the main circuit when the attempt is made to close the circuit breaker, the control relay 1 will remain electrically locked in its energized condition after the auxiliary switch has once been closed to keep the operating circuit of relay 5 open at contacts H and 13, thus keeping the winding 61 deenergized so that the alternatingcircuit breaker, resulting in the circuit breaker being repeatedly opened and closed. It is thus seen that, if the control switch 4 is held closed, the circuit breaker will be closed only once and that it is necessary to open the control switch before the circuit breaker can be closed again.

While the rectifier-circuit relay 5 and the control relay 1 are shown as being energized from the alternating-current source 9 through the transformer 5i, it should be understood that they may be of a type to be operated by direct current either from a direct-current source or by means of a rectifier from a source of alternating cur rent.

It is thus seen that a control scheme is provided which is most desirable for use in connection with a closing coil of a circuit breaker which is supplied with direct current from a copper- .oxide rectifier, since the control circuits prevent the continuous energization of the closing coil 25, thus making possible the use of both a closing coil and a contact rectifier which have the capacity to carry a large current such as is needed to close a circuit breaker without the excessive heating of either the closing coil or the rectifier and preventing damage to either the closing coil or the rectifier because of this heavy current being kept on continuously.

While I have illustrated and described a particular embodiment of the invention, it should be understoodthat numerous modifications of this apparatus may be used, and that the scope of my invention is not to be limited except as is indicated by the following claims.

I claim as my invention:

1. In electrical apparatus, a circuit interrupter having contacts connected in a main power circuit, electrically operated actuating means for said circuit interrupter, and a rectifier having a short-time current-carrying capacity several times greater than its continuous current-carrying capacity for energizing said actuating means, alternating current energy supply means for said rectifier having such voltage that the current flow through said rectifier when said actuating means is energized is several times greater than the continuous current-carrying capacity of said rectifier means for connecting said actuating means to said energy supply and means for breaking said connection after a short interval of time.

2. In electrical apparatus, a circuit interrupter including a contact for controlling a main power circuit, means for biasing said contact to open'-' circuit position, latching means for holding said contact in closed-circuit position, electrically operated actuating means for closing said contact against said biasing means, a source of alternating current, a contact rectifier for supplying energy from said source of alternating current for operating said actuating means, and means responsive to said contact reaching closed-circuit position for cutting ofi said supply of energy.

3. In electrical apparatus, a circuit interrupter including a contact for controlling a main power circuit, means for biasing said contact to opencircuit position, latching means for holding said contact in closed-circuit position, a direct current operated actuating means for closing said contact against said biasing means, a source of alternating current, a contact rectifier, means for connecting said rectifier to said source of alternating current and to said actuating means,'

and means for disconnecting said rectifier from said source of alternating current assoon as said moving contact has moved to closed-circuit position.

4. In electrical apparatus, a circuit interrupter including a contact for controlling a main power circuit, means for biasing said contact to opencircuit position, latching means for holding said a contact in closed-circuit position, a direct-current solenoid mechanism for closing said contact when energized for only a short interval of time, means for causing a fiow of current through said solenoid several times greater than its continuous current-carrying capacity, said means including a contact rectifier having a short-time current-carrying capacity several times greater than its continuous current-carrying capacity, and means for connecting said contact rectifier to a source of alternating current for only a short interval of time.

5. In electrical apparatus, a circuit interrupter including a contact for controlling a main power circuit, biasing means for moving said contact to open-circuit position, means releasable to cause said biasing means to move said contact to opencircuitposition, a direct-current solenoid mechanism operable to close said contact in a short interval of time, means for causing a flow of cur- I rent through said solenoid several times greater than its continuous current-carrying capacity, said means including a contact rectifier having a short-time current carrying capacity several times greater than its continuous current-carrying capacity, means for connecting said rectifier to a source of alternating current, and means actuated as soon as said contact has reached,

closed position for disconnecting said contact rectifier from said source of alternating current.

6. In electrical apparatus, a circuit interrupter including a contact for controlling a main power circuit, means for biasing said contact to opencircuit position, latching means for holding said contact in closed-circuit position, electrically o'perable to cause movement of said contact from closed-circuit position to open-circuit position even though said control element may be held in said position to cause energization of said actuating means to close said contact.

'7. In electrical apparatus, a circuit interrupter including a contact for controllinga main pow- ;er circuit, means for biasing said contact to opencircuit position, la "hing means for holding said to cause movement of said contact from closedcircuit position to open-circuit position even though said control element may be held in said position to cause energization of said actuating means to close said contact, and means preventing reenergization of said actuating means until said control element has been moved out of said position to cause energization of said actuating means to close said contact.

8. In electrical apparatus, a circuit interrupter including a contact for controlling a main power circuit, biasing means for moving said contact to open-circuit position, means releasable to cause said biasing means to move said contact to opencircuit position, a direct-current'solenoid mechanism operable to close said contact, a source of alternating current, a contact rectifier for supplying energy to said solenoid from said source of alternating current,-means including a control element movable to one position to cause the energization of said solenoid through said contact rectifier to close said contact, and means operable to cause said releasable means to cause said movable contact to move to open-circuit position even though said control element may be held in said position to cause the energization of said solenoid to close said contact.

9. In electrical apparatus, a circuit interrupter including a contact for controlling a main power circuit, biasing means for moving said contact to open-circuit position, means releasable to cause said biasing means to move said contact to open-circuit position, a direct-current solenoid mechanism operable to close said contact, a source of alternating current, a contact rectifier for supplying energy to said solenoid from said source of alternating current, means including a control element movable to one position to cause the energization of said solenoid through said contact rectifier to close said contact, and means operable to cause said releasable means to cause said movable contact to move to open-circuit position even though said control element may be held in said position to cause the energization of said solenoid to close said contact, and means preventing reclosure of said contact by said solenoid until said control element has been moved out of saidposition to cause the energization of said solenoid to close said contact.

10. In electrical apparatus, a circuit interrupter. a direct-current solenoid mechanism for closing said circuit interrupter, a contact rectifier for said direct-current solenoid, a source of alternating current, relaying means including a contact member connected in the alternatingcurrent circuit of the contact rectifier for controlling the connection of said solenoid to said source of alternating current through said contact rectifier, a control element actuable to one position to energize said relaying means to connect said solenoid to said source of alternating current through said; contact rectifier and thereby close the circuit interrupter, means actuated by said circuit interrupter reaching closed position for causing said relaying means to open said contact member and disconnect said solenoid from said source of alternating current, and said relaying means then maintaining said solenoid disconnected from said source of alternating current until after said control element has been moved out of said position to energize said relaying means to close the circuit interrupter.

11. In electrical apparatus, a circuit interrupter, a direct-current solenoid mechanism for closing said circuit interrupter, a contact rectifier for said direct-current solenoid, a source of alternating current, relaying means for controlling the connection of said solenoid to said source of alternating current through said contact rectifier, a, control element actuable to one position to energize said relaying means to connect said solenoid to said source of alternating current through said contact rectifier and thereby close the circuit interrupter, means actuated by said circuit interrupter reaching closed position for causing said relaying means to disconnect said solenoid from said source of alternating current, and means operable to cause said circuit interrupter to move to open position even though said control element may be held in said position to close the circuit interrupter.

12. In electrical apparatus, a circuit interrupter, a direct-current solenoid mechanism for closing said circuit interrupter, a contact rectifier for said direct-current solenoid, a source of alternating current, relaying means for con trolling the connection of said solenoid to said source of alternating current through said contact rectifier, a control element actuable to one position to energize said relaying means to connect said solenoid to said source of alternating current through said contact rectifier and thereby close the circuit interrupter, means actuated by said circuit interrupter reaching closed position for causing said relaying means to disconnect said solenoid from said source of alternating current, and means operable to cause said circuit interrupter to move to open position even though said control element may be held in said position to close the circuit interrupter, and said relaying means then maintaining said solenoid disconnected from said source of alternating current until after said control element has been moved out of said position to energize said relaying means to close the circuit interrupter.

13. In electrical apparatus, a circuit interrupter including a contact for controlling a main power circuit, means for biasing said contact to open-circuit position, latching means for hold ing said contact in closed-circuit position. a direct-current solenoid mechanism for closing said contact when energized for only a short interval of time, means for causing a flow of current through said solenoid several times greater than its continuous current-carrying capacity, said means including a contact rectifier having a short-time current-carrying capacity several times greater than its continuous current-carrymeans to disconnect said contact rectifier from said source of alternating current, and means operable to cause the release of said latching means and the movement of said contact to open-circuit position by said biasing'spring even though said control element may be held in said position to close the contact.

14. In electrical apparatus, a circuit interrupter including acontact for controlling a main power circuit, means for biasing said contact.

to open-circuit position, latching means for holding said contact in closed-circuit position, a direct-current solenoid mechanism for closing said contact when energized for only a short interval of time, means for causing a fiow of current through said solenoid several times greater than its continuous current-carrying capacity, said means including a contact rectifier having a short-time current-carrying capacity several times greater than its continuous current-carrying capacity, a source of alternating current and relaying means for controlling the connection of said contact rectifier to said source of alternating current, a control element actuable to one position toenergize said relaying means to connect said contact rectifier to said source of alternating current and thereby close said contact, means actuated as soon as said contact has reached closed position for causing said relaying means, to disconnect said contact rectifier from said source of alternating current, and means operable to cause the release of said latching means and the movement of said contact to open-circuit position by said biasing spring even though said control element may be held in said position to close the contact, and said relaying means preventing the reconnection of said contact rectifier to said alternating current source and the return of said contact to closed circuit position prior to movement of said control element out of said position to close the contact.

15. In electrical apparatus, a circuit breaker for controlling a main power circuit, means for biasing said circuit breaker to move to opencircuit position, means releasable to cause said circuit breaker to be actuated to open-circuit position by said biasing means, a direct-current solenoid mechanism operable to close said circuit breaker, a source of alternating current, a contact rectifier connected to supply energy from said source of alternating current to actuate said direct-current solenoid mechanism, means inoluding a relay for controlling the flow of current to said direct-current solenoid mechanism, said relay having its contacts connected in the alternating-current circuit to said contact rectifier, means including a control element movable to one position to cause the energization of said direct-current solenoid mechanism to close the circuit breaker, and said releasable means being operable to cause said circuit breaker to be actuated to open-circuit position even though said control element be held in said position to close the circuit breaker.

16. In electrical apparatus, a circuit breaker for controlling a main power circuit, means for biasing said circuit breaker to move to opencircuit position, means releasable to cause said circuit breaker to be actuated to open-circuit position by saidbiasing means, a direct-current solenoid mechanism operable to close said circuit breaker, a source of alternating current, a

contact rectifier connected to supply energy from said source of alternating current to actuate said direct-current solenoid mechanism, means including a relay for controlling the flow of current to said direct-current solenoid mechanism, said relay having its contacts connected in the alternating-current circuit to said contact rectifier, means including a control element movable to one position to cause the energization of said direct-current solenoid mechanism to close the circuit breaker, and means including an auxiliary switch actuated by the movement of said solenoid mechanism in closing the circuit breaker for preventing a second closing of the circuit breaker by said solenoid mechanism until said control element has moved out of said position to which it was moved to cause the prior closing of the circuit breaker.

17.-In electrical apparatus, a circuit interrupter including a contact for controlling a main power circuit, biasing means for moving said contact to open-circuit position, means releasable to cause said biasing means to move said contact to open-circuit position, a direct-current solenoid mechanism operable to close said contact, a source of alternating current, a contact rectifier for supplying energy to said solenoid from said source of alternating current, means including a control element movable to one position to cause the energization of said solenoid through said contact rectifier to close said contact, relaying means actuable to control the flow of current to said solenoid, said relaying means including a relay electrically locked in the position to which it moves when energized until said control element has moved out of said position to close said contact to prevent said contact being closed more than once for each movement of said control element to said position to close said contact.

18. In electrical apparatus, a circuit breaker for controlling a main power circuit, means for biasing said circuit breaker to move to opencircuit position, means releasable to cause said circuit breaker to be actuated to open-circuit position by said biasing means, a direct-current solenoid mechanism operable to close said circuit breaker, a source of alternating current, a contact rectifier connected to -supply energy from said source of alternating current to actuate said direct-current solenoid mechanism, relaying vmeans for controlling the flow of current to said direct-current solenoid, said relaying means including a movable contact connected in the altermating-current circuit to said contact rectifier and including a solenoid having means operable after said direct-current solenoid has been operated to close the circuit breaker to electrically lock the solenoid of the relaying means in the positionto which it is moved when energized, a control element for said relaying means movable to one position to cause closing of the circuit breaker, and said solenoid of the relaying means remaining electrically locked-in until said control element has moved out of said position to cause closing of the circuit breaker to prevent the circuit breaker being closed more than once for each movement of the control element to its position to cause closing of the circuit breaker.

19. In electrical apparatus, a circuit breaker having its contacts connected in a main power circuit, means for biasing said circuit breaker to move to open-circuit position, a latch normally holding said circuit breaker against movement by said biasing means,. a direct-current solenoid mechanism operable to close said circuit breaker and stress said biasing means, a source of alternating current, a contact rectifier connected to supply energy from said source of alternating current to actuate said direct-current solenoid mechanism, relaying means for controlling the flow of current to said direct-current solenoid, said relaying means including a movable contact connected in the alternating-current circuit to said contact rectifier and including an actuating solenoid, a control element for said relaying means movable to one position to cause closing of the circuit breaker, means for releasing said latch to cause movement of the circuit breaker to open-circuit position and said movement of the circuit breaker to open-circuit position by said biasing means upon the release of said latch taking place even though said control element may be held in said position to which it is moved to cause closing of the circuit breaker, and means for preventing a second closing of the circuit breaker by said direct-current solenoid mechanism until said control element has moved out of said position to which it was moved to cause the prior closing of the circuit breaker, said preventing means including an auxiliary switch actuated by the movement of said direct-current solenoid mechanism in closing the circuit breaker and including means for electrically locking said actuating solenoid of the relaying means in the position to which it moves when energized until said control element has moved out of said position to which it is moved to cause closing of the circuit breaker.

HARRY J. LINGAL.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2420629 *Sep 28, 1944May 13, 1947Gen Railway Signal CoPower supply for traffic controlling systems
US7148781 *Oct 13, 2004Dec 12, 2006Beausoleil David MLandscape lighting transformer having increased loading features
Classifications
U.S. Classification361/152, 361/194
International ClassificationH01H51/00, H01H51/10
Cooperative ClassificationH01H51/10
European ClassificationH01H51/10