GB2040573A

GB2040573A - Improvements in electric circuit breakers

Info

Publication number: GB2040573A
Application number: GB7904373A
Authority: GB
Original assignee: Wolff H W
Current assignee: Wolff H W
Priority date: 1979-02-07
Filing date: 1979-02-07
Publication date: 1980-08-28

Abstract

A circuit breaker for a.c. having a fixed contact and a movable contact and automatic means for opening the circuit initiated by a fault or overload in the circuit, characterised by a solenoid with a plunger armature operating directly on the movable contact on the occurrence of an overload current above a predetermined value to open the circuit and simultaneously operate a trip lever to release the automatic means in order to keep the contacts open.

Description

SPECIFICATION Improvements in electric circuit breakers This invention relates to improvements in electric circuit-breakers and more particularly to circuit-breakers for alternating current of the type comprising a fixed contact connected in the circuit, a movable contact which can engage the fixed contact, manual and automatic means for opening the circuit by moving the movable contact from the fixed contact, the automatic means being initiated by a fault or overload in the circuit and operating through electro-magnetic or thermal action.

A thermal magnetic overload unit has been proposed wherein the thermal elelement is adapted to cause disconnection of the circuit on the occurrence of smali sustained overloads, the electro-magnetic element being adapted to cause disconnection on short-circuit.

It has been found however that due to inertia of the circuit-breaker mechanism the current builds up to the half wave maximum before the current can be interrupted.

Conventional overload and short-circuitprotection devices act upon the tripping mechanism of the circuit-breaker, consequent upon which the contacts open. This action requires several milliseconds during which the current has time to rise, and, in the event of an alternating current, to pass through the peak value applicable to the particular circuit conditions, with consequent generation of a substantial amount of thermal energy, which has to be absorbed and dissipated by the circuit-breaker.

It is already known that if the contacts are separated directly upon the occurence of a shortcircuit, i.e. without the intervention of the tripping mechanism the current is interrupted in a substantially shorter time and is thus prevented from passing through its peak value, with consequent considerable reduction of the effect of the short-circuit upon the circuit-breaker, and hence increasing its ability of dealing with such fault conditions. This effect is known as current limiting.

The object of the invention is to provide a current limiting circuit breaker in combination with a circuit-breaker of the type referred to.

According to the invention a circuit-breaker of the type referred to comprises a solennoid with a plunger operating directly on the movable contact of the circuit-breaker on the occurrence of an overload current above a predetermined value to open the circuit and simultaneously operating a trip lever in order to release the mechanism so as to maintain the contacts open.

The invention will be described with reference to the accompanying drawings: Fig. 1 is an elevation of the circuit breaker mechanism in the closed position.

Fig. 2 is a similar view showing the circuit being broken by the current limiting action of an electric solenoid and plunger and showing also the simultaneous release of the mechanism by the action of the plunger on the trip lever.

Fig. 3 is a similar view showing the trip mechanism being actuated by the action of the thermal element.

Fig. 4 illustrates graphically the current limiting effect the mechansim of the circuit breaker is housed in a casing of insulating material, one side of the casing being detachable for the assembly of the mechanism therein.

A terminal a1 is arranged at one end of the circuit-breaker and a second terminal a2 at the other end thereof. The terminal al is directly connected to the fixed contact B and the terminal a2 is connected to the movable contact C through a bimetal strip H, flexible connection F1, solenoid A and flexible connection F2.

The movable contact C is mounted on an arm D provided with a pin d projecting into a slot dl and with a projection d2 engaging the trip lever G. The arm D may be operated manually by a forked lever E being pivotally mounted on the casing, or supporting frame. The arln D is located between the two legs of the lever E and is engaged by the cam like lever formed by legs e and pin el. A spring e2 for biasing the arm D towards the 'open' position -is fixed at one end to the movable contact C forming an articulated extension of the arm D, and at the other end to the lever E.

The moving contact C is provided with an extension C1 engageable by the plunger a3 of the solenoid A upon the occurrence of the energisation of the solenoid A by a current above a predetermined value the movement of the solenoid being in the direction of the arrow X to directly break the contact C. The contact C is thus opened without the intervention of the tripping mechansim. Fig. 2.

A normal tripping action is however still necessary. Otherwise the contact C would reclose immediately upon cessation of the current. Normal tripping of the circuit is also carried out by the plunger a3, the opposite end a4 of which is formed with a flange a5 which engages an arm g on the trip lever G which releases the trip lever from the projection d2 on the arm D, - Fig. 2, the pin d being thereby enabled to move inside slot dl in the direction of arrow Y.

On the occurence of smaller overloads of a value insufficient to operate the solenoid plunger the bimetal strip H operates in known manner to trip the lever G (Fig. 3).

The arrangement thus provides a means of increasing the short-circuit capacity of a small circuit-breaker as described in specification No.

779624 i.e. of increasing its ability to deal with short-circuit currents potentially much larger than those which could have been dealt with by the arrangement described in Specification No.

779626.

1. A circuit-breaker of the type referred to comprising a solenoid to operate directly on the movable contact of the circuit-breaker on the occurrence of an overload current above a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in electric circuit breakers This invention relates to improvements in electric circuit-breakers and more particularly to circuit-breakers for alternating current of the type comprising a fixed contact connected in the circuit, a movable contact which can engage the fixed contact, manual and automatic means for opening the circuit by moving the movable contact from the fixed contact, the automatic means being initiated by a fault or overload in the circuit and operating through electro-magnetic or thermal action. A thermal magnetic overload unit has been proposed wherein the thermal elelement is adapted to cause disconnection of the circuit on the occurrence of smali sustained overloads, the electro-magnetic element being adapted to cause disconnection on short-circuit. It has been found however that due to inertia of the circuit-breaker mechanism the current builds up to the half wave maximum before the current can be interrupted. Conventional overload and short-circuitprotection devices act upon the tripping mechanism of the circuit-breaker, consequent upon which the contacts open. This action requires several milliseconds during which the current has time to rise, and, in the event of an alternating current, to pass through the peak value applicable to the particular circuit conditions, with consequent generation of a substantial amount of thermal energy, which has to be absorbed and dissipated by the circuit-breaker. It is already known that if the contacts are separated directly upon the occurence of a shortcircuit, i.e. without the intervention of the tripping mechanism the current is interrupted in a substantially shorter time and is thus prevented from passing through its peak value, with consequent considerable reduction of the effect of the short-circuit upon the circuit-breaker, and hence increasing its ability of dealing with such fault conditions. This effect is known as current limiting. The object of the invention is to provide a current limiting circuit breaker in combination with a circuit-breaker of the type referred to. According to the invention a circuit-breaker of the type referred to comprises a solennoid with a plunger operating directly on the movable contact of the circuit-breaker on the occurrence of an overload current above a predetermined value to open the circuit and simultaneously operating a trip lever in order to release the mechanism so as to maintain the contacts open. The invention will be described with reference to the accompanying drawings: Fig. 1 is an elevation of the circuit breaker mechanism in the closed position. Fig. 2 is a similar view showing the circuit being broken by the current limiting action of an electric solenoid and plunger and showing also the simultaneous release of the mechanism by the action of the plunger on the trip lever. Fig. 3 is a similar view showing the trip mechanism being actuated by the action of the thermal element. Fig. 4 illustrates graphically the current limiting effect the mechansim of the circuit breaker is housed in a casing of insulating material, one side of the casing being detachable for the assembly of the mechanism therein. A terminal a1 is arranged at one end of the circuit-breaker and a second terminal a2 at the other end thereof. The terminal al is directly connected to the fixed contact B and the terminal a2 is connected to the movable contact C through a bimetal strip H, flexible connection F1, solenoid A and flexible connection F2. The movable contact C is mounted on an arm D provided with a pin d projecting into a slot dl and with a projection d2 engaging the trip lever G. The arm D may be operated manually by a forked lever E being pivotally mounted on the casing, or supporting frame. The arln D is located between the two legs of the lever E and is engaged by the cam like lever formed by legs e and pin el. A spring e2 for biasing the arm D towards the 'open' position -is fixed at one end to the movable contact C forming an articulated extension of the arm D, and at the other end to the lever E. The moving contact C is provided with an extension C1 engageable by the plunger a3 of the solenoid A upon the occurrence of the energisation of the solenoid A by a current above a predetermined value the movement of the solenoid being in the direction of the arrow X to directly break the contact C. The contact C is thus opened without the intervention of the tripping mechansim. Fig. 2. A normal tripping action is however still necessary. Otherwise the contact C would reclose immediately upon cessation of the current. Normal tripping of the circuit is also carried out by the plunger a3, the opposite end a4 of which is formed with a flange a5 which engages an arm g on the trip lever G which releases the trip lever from the projection d2 on the arm D, - Fig. 2, the pin d being thereby enabled to move inside slot dl in the direction of arrow Y. On the occurence of smaller overloads of a value insufficient to operate the solenoid plunger the bimetal strip H operates in known manner to trip the lever G (Fig. 3). The arrangement thus provides a means of increasing the short-circuit capacity of a small circuit-breaker as described in specification No. 779624 i.e. of increasing its ability to deal with short-circuit currents potentially much larger than those which could have been dealt with by the arrangement described in Specification No. 779626. CLAIMS

1. A circuit-breaker of the type referred to comprising a solenoid to operate directly on the movable contact of the circuit-breaker on the occurrence of an overload current above a predetermined value to open the circuit.

2. A circuit-breaker as in claim 1 in which the movable contact is operated directly by the plunger of an electric solenoid operating simultaneously on a trip mechanism for the movable contact to maintain the movable contact open.

3. A circuit-breaker as in claims 1 and 2 in which the movable contact is opened by the operation of the bimetalic strip on the trip mechanism when the overload current is below the predetermined value for operating the solenoid.

4. A circuit-breaker for electric circuits substantially as described with reference to the accompanying drawings.

4. A circuit-breaker as in claims 1 to 3 in which the movable contact is operated directly by the plunger of an electric solenoid operating simultaneously on a trip mechanism for the movable contact to maintain the contact open.

5. A circuit breaker for electric circuits substantially as described with reference to the accompanying drawings.

New claims or amendments to claims filed on 1 sot November 1 979 Superseded claims 1, 2, 4 and 5 New or amended claims :- 1. A current limiting electric circuit-breaker of the type referred to comprising a first terminal directly connected to the fixed contact, a second terminal coupled to the moving contact through a bimetal strip, a flexible connection, a solenoid and a second flexible connection, the moving contact being operated on an overload by excitation of the solenoid to operate a plunger therein to engage an extension on the moving contact to directly open the circuit, all in combination with a lever pivoted on the casing engage by a forked lever also pivoted on the casing and in contact with an arm carrying a pin movable in a slot in the casing with a projection on the arm engaging a trip lever pivoted on the casing which aliows a spring on the plunger to bring this later into engagement with the extension on the movable contact to open the circuit, and a lever pivoted on the casing and acting on a forked lever also pivoted on the casing to allow the pin of the arm to travel in the slot under the action of a biasina spring to prevent the automatic reclosing of the circuit after having been operated by an overload.

2. A circuit-breaker as in claim 1 in which the movable contact is operated directly by the plunger of the electric solenoid operating simultaneously on a trip mechanism for the movable contact to maintain the movable contact open.