US3454831A

US3454831A - Quick-opening,low cost,current limiting circuit breaker

Info

Publication number: US3454831A
Application number: US617148A
Authority: US
Inventors: Henry G Willard
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1967-02-20
Filing date: 1967-02-20
Publication date: 1969-07-08
Anticipated expiration: 1986-07-08
Also published as: GB1182955A

Description

y 3, 1969 G. WILLARD 3,454,831

QUICK-OPENING LOW COST CURRENT LIMITING CIRCUIT BREAKER Filed Feb. 20, 1967 Sheet of 2 I l|8 FIGI I -72W F ':'\'IIMIII\A\I\VI\\'IV L -l| I I g1 n" 1 I I E2 T I I I I2 I4 I I I I m. him. I [I3 III) I 1 I3 '7) VAPORIZABLE CONDUCTOR 460 TYPE CURRENT LIMITER '5 L m 0 A D,

I8 I nfl-hlj I P DIVERTER l--- I I I I v i J l I Z,. A. L- A .J

III] III] l VAPORIZABLE CONDUCTOR L TYPE CURRENT LIMITER -I6o L 0 I5 IGI) A f INVENTOR HEN/W G WILLARD BY WW C 7 ATTORNEY July 8, 1969 F. RUSCHE 3,453,831

METHOD OF FORMING AND DRIVING THIN WALL PIPE PILE AND BOOT Filed Jan. 25, 1968 Sheet #3 of 2 FIG. 5E

mvsmozz FREDRIC RUSCHE a v M I ATTORNEY United States Patent 3,454,831 QUICK-OPENING, LOW COST, CURRENT LIMITING CIRCUIT BREAKER Henry G. Willard, Wethersfield, Conn., assignor to General Electric Company, a corporation of New York Filed Feb. 20, 1967, Ser. No. 617,148 Int. Cl. H02h 3/08 US. Cl. 317-11 5 Claims ABSTRACT OF THE DISCLOSURE A quick-opening low cost current limiting circuit breaker comprising a solenoid actuated mechanically operable contactor mechanism having a set of physically separable contacts connected in series circuit relationship with a source of electric potential. The solenoid actuated contactor mechanism is adjusted to open the supply circuit to a load automatically upon the occurrence of an overload above a predetermined rated value. A current limiter of the vap-orizable conductor type is connected in series circuit with the physically separable contacts and is designed to carry a larger overcurrent than the solenoid actuated contactor mechanism. The current ratings of the solenoid actuated contactor mechanism and the current limiter are such that upon the occurrence of an overload condition, the solenoid actuated contactor mechanism is actuated first to commence current interruption by physically separating its contacts. Thereafter the current limiter is acuated to assist in extinguishing the are normally established between the physically separated contacts upon being opened under load current carrying conditions, and simultaneously limits the current that can flow through the circuit breaker to a predesigned low value.

Background of the invention This invention relates to a quick-opening, low cost current limiting circuit breaker.

More particularly, the invention relates to a quickopening, low cost circuit breaker employing standard parts which is reliable in operation and, by reason of its quick-opening characteristic, both limits the current flow during, and cuts short the normal arcing period associated with the opening of the circuit breaker so as to greatly increase its operating life.

A circuit breaker is a control device normally connected in an electric power supply circuit to interrupt power flow through the circuit upon the occurrence of an abnormal or overload condition. Such abnormal or overload condition generally is exemplified by either an overcurrent or an overvoltage condition, and can result in damage to the equipment being supplied, as well as damage to the components of the power supply circuit if it is not interrupted within a short time period. From the foregoing description it will be appreciated that one essential characteristic of a satisfactory circuit breaker is that it be relatively quick acting. This characteristic is necessitated by the fact that the shorter the time period that an overload condition is allowed to eXist, the less likelihood there is that damage will occur, It is also desirable that a circuit breaker limit the value of the overload current allowed to flow through the device. Further, it is desirable that the breaker be relatively low cost, reliable in operation and have a relatively long operating life.

It is therefore a primary object of the present invention to provide a new and improved quick opening, low cost circuit breaker which employs standard commercially available components arranged in a new circuit breaker configuration in a manner so as to rapidly limit overcurrents and shorten the arcing period normally associated with opening of the breaker contacts under load current carrying conditions. As a consequence of the limited current and shortened arcing period the operating life of the breaker is extended and its reliability in operation improved.

Summary of the invention In practicing the invention, a new and improved quickopening, low cost circuit breaker is provided having the above set forth characteristics and comprises a solenoid actuated mechanically operable contactor mechanism having a set of physically separable contacts connected in series circuit supply relationship with a load and a source of electric potential. The solenoid actuated contactor mechanism is adjusted to automatically open the supply circuit to the load upon the occurrence of an overload above a predetermined rated value. A current limiter of the vaporizable conductor type is connected in series circuit with the physically separable contacts and the load with the current limiter being capable of carrying a larger overcurrent than the solenoid actuated contactor mechanism. The current ratings of the solenoid actuated contactor mechanism and the limiter are such that upon the occurrence of an overload condition, the solenoid actuated contactor mechanism is actuated first to commence current interruption by physically separating its contacts. Thereafter the current limiter is actuated to rapidly limit the current to a predesigned low value and assist in extinguishing the are normally established between the physically separated contacts upon being opened under load current carrying conditions, and simultaneously limiting the current that can flow through the circuit breaker to a predesigned limited value.

Other objects, features and many of the attendant advantages of this invention will be appreciated more readily as the same becomes better understood by reference to the following detailed description, when considered in connection with the accompanying drawings.

Description of the drawings In the drawings, like parts in each of the several figures are identified by the same reference character, and:

FIGURE 1 is a schematic circuit diagram of a new and improved quick opening, low cost, current limiting circuit breaker constructed in accordance with the invention;

FIGURE 2 is a characteristic curve illustrating the current versus time operating characteristic of the circuit breaker shown in FIGURE 1; and

FIGURE 3 is a schematic circuit diagram of a modified form of a quick opening, low cost, current limiting circuit breaker constructed in accordance with the invention.

Description of the preferred embodiments FIGURE 1 is a schematic circuit diagram of a quickopening, low cost, current limiting circuit breaker constructed in accordance with the invention. The circuit breaker shown in FIGURE 1 comprises a solenoid actuated, mechanically operable contactor mechanism formed by a pair of physically separable contacts 11a, 11b and 12 and a solenoid actuating winding 13. The dash dot line shown at 14 indicates that the solenoid actuating winding 13 operates to open the movable contact 12 so that it no longer forms a closed electrically conducting path through the fixed contacts 11a, 11b. The mechanically operable contactor mechanism may comprise a conventional commercially available low cost magnetic contactor arrangement such as that described on page 39 of the textbook entitled Controllers for Electric Motors by James and Markle, published by the McGraw-Hill Book Company, copyrighted 1945. While any kind of mechanically operable contactor can be employed, it is preferred that the contactor have the conventional magnetic, blow out coil and are chute arrangement such as is described in the above mentioned reference text. Additionally, it is desired that the contactor be designed in a manner such that the circuit can be actuated by manually closing the movable contact 12 on the fixed contacts 11a and 11b. Thereafter should an overcurrent condition occur, the increased current above design rating flowing through the solenoid winding 13, causes the movable contact 12 to be opened, thereby physically separating the contact 12 from the fixed contacts 11a and 11b and interrupting current flow through the contacts. Such magnetically operable contactors are available commercially from a large number of manufacturers such as the General Electric Company at a cost ranging from one dollar up depending upon the design of the contactor. Alternatively, the mechanically

operable contactor mechanism

11a, 11b, 12 and 13 may comprise a thermally actuated switching arrangement utilizing bimetallic elements, or may comprise a combined magnetic-thermal actuated mechanism such as that disclosed in US. Patent No. 3,117,203 to be described more fully hereinafter. If a combined magnetic-thermal actuated contactor mechanism such as that disclosed in US. Patent 3,117,203 is employed, its current carrying characteristics are preferably adjusted to be in accordance with the teaching of this disclosure.

The physically separable contacts 11a, 11b and 12 are connected in series circuit relationship with a load 15 across a source of supply potential whose terminals are shown at 16a and 16b, and which may comprise a source of either direct current or alternating current. A current limiting device 17 is connected in the series circuit comprising the load 15, power supply terminal 16a, 16b and physically separable contacts 11a, 11b and 12. The current limiting device 17 preferably is of the vaporizable conductor type such as that described in US. Patent No. 3,117,203R. L. Hurtle, inventor, entitled Circuit Protective Devices and Circuits issued Jan. 7, 1964, and assigned to the General Electric Company. For a more complete description of the construction and operation of the current limiter device 17, reference is made to this patent. However, for the purpose of the present disclosure it is believed that the following description of the nature and operation of the limiter device 17 will suffice. The current limiting device 17 is a rapidly operable current limiting protective device for power circuits which maintains electrical continuity both during and after its current limiting action. The device comprises a body of strong and inelastic, non-porous, ceramic insulating material having one or more capillary passages formed therein. The capillaries are filled end to end with a vaporizable conducting material which is in contact with terminal members insulated from one another and extending to the outside of the enclosure. The conductive material in the capillaries is capable of carrying a predetermined amount of current without substantial loss or without substantial change in its electrical properties. However, when the device is subjected to excessive currents of a sulficient magnitude to vaporize all or part of the vaporizable conductive material within the capillaries, an extremely high pressure, high resistance steady state are is established in the capillaries which limits and reduces the current flow through the device to some predetermined low level. Upon the overcurrent being removed, the device will cool back down and the vaporizable conductive ma terial in the capillaries will reassume its conducting state so that it is possible for the current limiting device to be cycled through a number of current limiting operations without adversely affecting its operating characteristics in either the normal current conducting mode or the overcurrent mode of operation.

In preferred forms of the invention, it is desirable that a current diverter shown in dotted outline form at 18, be connected in parallel circuit relationship with the current limiter 17. The current diverter 18 preferably comprises a resistor 19 and an inductor 22 connected in series circuit relationship. The resistor 19 could comprise a positive temperature coefficient resistor and for some applications a capacitor could be added to the circuit. In one specific form of the diverter, the resistor had a value of one ohm and the inductor a value of ten microhenries.

During normal operation of the circuit breaker shown in FIGURE 1, the circuit can be placed in operation by manually closing the movable contact 12 on the fixed contacts 11a, 11b of the solenoid actuated mechanically 0perable contactor mechanism. Thereafter for so long as normal load current flows to the load 15 through the power supply terminal 16a, 16b, the circuit will remain in this condition. However, in the event of an overcurrent condition, the overcurrent flowing in the solenoid winding 13 will cause the movable contacts 12 to be actuated so as to physically separate movable contactor 12 from fixed contacts 11a and 11b. This occurs before the current limiter 17 operates due to the fact that the current limiter 17 has a larger current rating, and hence by design can tolerate a larger overcurrent than the solenoid actuator contactor mechanism. Hence, the overcurrent first will actuate the solenoid actuator contactor mechanism causing its movable contact 12 to be physically separated from the fixed contacts 11a, 11b and causing an arc to be formed between the movable and fixed contacts. Because of the existence of this arc, the overcurrent condition will continue until the arc is extinguished. This continued overcurrent condition will thereafter actuate the current limiter 17 which, upon being placed in its vaporized state severely limits the current to a predesigned low value. This predesigned low value is sufiiciently low that it Will no longer sustain the are appearing between the movable contact 12 and the fixed contacts 11a, 11b of the solenoid actuated contactor mechanism. As a consequence this arc will be rapidly extinguished in an extremely short period of time on the order of to 300 microseconds resulting in complete interruption of current flow to the load 15. If it is employed the current diverter 18 assists this operation by diverting some of the current away from the current limiter.

FIGURE 2 of the drawings is a characteristic curve plotting current versus conduction period over a number of electrical degrees of a large half sinusoidal current pulse imposed on the circuit shown in FIGURE 1 of the drawings. The half sinusoidal shaped solid line curve 25 illustrates the character of the prospective overcurrent that could be imposed on the circuit of FIGURE 1 from the available supply, as well as the current which would flow through the load 15 if the circuit were designed to carry currents of this magnitude. The solid line curve shown at 26 illustrates the operating characteristics of the combined 25 amp regulating current limiter and 15 amp solenoid actuated magnetic contactor employed in the circuit of FIGURE 1. From a consideration of curve 26, it will be appreciated that the circuit of FIGURE 1 is effective to almost immediately limit the current to a value of about 1,700 amperes and thereafter terminates current flow within substantially 10 electrical degrees of the imposed half sinusoidal waveshape overload current 25. If the solenoid actuated

contactor

11a, 11b, 12 and 13 by itself were employed to interrupt such an overcurrent, the time that would be required to completely interrupt the current is illustrated by the dotted line curve 27. By comparing curve 27 to curve 26 it will be seen that the time required to accomplish complete interruption is almost four times as long for a conventional mechanically operable contactor mechanism as that required with the instant invention. It might also be noted that while the

contactors

11a, 11b, 12 and 13 operate to immediately limit the current, this is not a required characteristic of the contactor. Even if the current continued to increase after the contactor opened, the regulating current limiter 17 could still drive the current to zero in the short time interval indicated.

From a consideration of the above descripion, it will be appreciated that due to the shorter time period allowed for arcing, the deterioration of the contacts as a result of each opening is greatly reduced thus assuring greater reliability in operation as well as greatly extending the operating life of the circuit breaker. Because the circuit breaker arrangement of FIGURE 1 can be fabricated from conventional commercially available elements such as a solenoid actuated contactor mechanism and the regulating current limiter device 17, its cost of fabrication is relatively low in comparison to circuits whch would require specially designed components. Additionally, while the arrangement shown in FIGURE 1 has been described as comprising a separate mechanically operable contactor mechanism and a separate current limiter, the two devices could be incorporated in a single unitary structure such as that described in the Hurtle Patent No. 3,117,203 by appropriate design. Further, while a ampere rated contactor has been combined with a 25 ampere regulating current limiter in the example cited other combinations of rating values clearly are possible to provide any desired combined circuit operating characteristics.

FIGURE 3 of the drawings schematically illustrates a modified form of the circuit shown in FIGURE 1. In the circuit arrangement of FIGURE 3, the actuating winding 13 of the solenoid actuated mechanically operable contactor mechanism is connected in series circuit relationship with a limiting impedance 29 across the load 15. Otherwise the circuit is entirely similar to the circuit arrangement of FIGURE 1 and operates somewhat in the same manner.

In operation, the circuit of FIGURE 3 will sense the voltage developed across the load 15. As long as the voltage developed across the load 15 is normal, load current will be supplied to the load through the closed contacts 11a, 11b and 12. However, in the event of an overvoltage condition being developed across load 15, the winding 13 will sense the overvoltage condition and open the movable contact 12 in the above described manner. Thereafter, the circuit functions in the same manner as described above to quickly interrupt the current flow to load 15.

From the foregoing description it can be appreciated that the invention provides a new and improved quick opening, low cost current limiting circuit breaker which employs standard commercially available components arranged in a new circuit breaker configuration. This new circuit breaker configuration results in shortening the arcing period normally associated with opening of the breaker contacts under load current carrying conditions, and as a consequence of the shortened arcing period, the operating life of the breaker is extended, and its reliability in operation is improved.

Having described several embodiments of a new and improved quick opening, low cost current limiting circuit breaker constructed in accordance with the invention, it is believed obvious that other modifications and variations of the invention are possible in the light of the above teachings.

I claim:

1. A quick-opening low cost current limiting circuit breaker including in combination a mechanically opera'ble contactor mechanism having a set of physically separable contacts connected in series circuit relationship with a source of electric potential, said mechanically operable contactor mechanism being adjusted to automatically open the supply circuit to a load upon the occurrence of an overcurrent above a predetermined rating value, and a current limiter of the vaporizable conductor type connected in series circuit relation with said physically separable contacts, the current ratings of said mechanically operable contact mechanism and said limiter being such that upon the occurrence of said predetermined value, said mechanically operable contactor mechanism is actuated first to commence current interruption by physically separating its contacts and thereafter said current limiter is actuated to limit the current rapidly to a predesigned low value and assist in extinguishing the arc normally established between said physically separated contacts.

2. A circuit breaker according to claim 1 wherein the mechanically operable contactor mechanism is a solenoid actuated contactor mechanism having its solenoid actuating winding connected in a series circuit comprising the physcially separable contacts, the current limiter and the source of electric potential.

3. A circuit breaker according to claim 2 wherein a current diverter is connected in parallel circuit relationship with the current limiter.

4. A circuit breaker according to claim 3 wherein the current diverter comprises a resistor and an inductor connected in series circuit relationship.

5. A circuit breaker according to claim 4 wherein the solenoid actuated contactor mechanism includes a magnetic blow-out coil for blowing out the are normally established between the physically separated contacts upon being opened under load current carrying conditions.

References Cited UNITED STATES PATENTS 2,855,545 10/1958 Beyrard 317-11 3,238,418 3/1966 Heft 317-33 JOHN F. COUCH, Primary Examiner. J. D. TRAMMELL, Assistant Examiner.

US. Cl. X.R.