GB1569778A

GB1569778A - Vacuum circuit breaker control circuit

Info

Publication number: GB1569778A
Application number: GB3855/77A
Authority: GB
Original assignee: Brush Switchgear Ltd
Current assignee: Brush Switchgear Ltd
Priority date: 1977-01-31
Filing date: 1977-01-31
Publication date: 1980-06-18
Also published as: JPS5396475A; NL7704310A; ZA771956B

Description

(54) VACUUM CIRCUIT BREAKER CONTROL CIRCUIT (71) We, BRUSH SWITCHGEAR LIMIXI-D, a British Company, of Loughborough, Leicestershire, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a method of controlling a vacuum circuit breaker and a control circuit therefor.

Normally, on opening the contacts in a vacuum circuit breaker, the arc which will be produced on opening the contacts will be quickly extinguished due to the vacuum provided within an enclosure containing the contacts. In the event of failure of the vacuum circuit breaker occurring due to loss of vacuum, or for another reason, arcing would continue beyond a normal extinguishing period with the results that an external short circuit fault in a circuit protected by the vacuum circuit breaker would not be interrupted by the vacuum circuit breaker and the vacuum circuit breaker itself could be damaged.

Usually one or more back-up circuit breakers would be provided. whereby in the event of failure of the vacuum circuit breaker to operate correctly, the short circuit would be cleared by the or one of the back-up circuit breakers. However, provision should be made to protect the vacuum circuit breaker from damage in the event of failure of its own interrupters.

Devices have been proposed to monitor the degree or presence of vacuum in a vacuum circuit breaker but such devices would be less reliable than the vacuum-circuit breaker itself and could lead to spurious and unwanted interruptions of a circuit including a vacuum circuit breaker with a vacuum monitoring device.

An object of the invention is therefore to provide an alternative method of controlling the operation of a vacuum circuit breaker when its interrupting capability is impaired and a control circuit therefor.

It is a unique feature of the vacuum circuit breaker that in the event of its failure to interrupt a short circuit current as a result of continued arcing due to loss of vacuum or other reason, that the continued arcing will for a period of time be contained within the enclosure containing the contacts. This is because the contacts are of an extremely robust construction and are separated by a gap of approximately 8-12 mm. As arc energy is a function of arc length the energy will be limited by the width of the gap between the contacts and so erosion and volatalisation of the metal of the contacts would take place comparatively slowly. For any particular design of vacuum circuit breaker there is a roughly predictable time (typically about 0.2 second) of permissible arcing before internal heating within the enclosure results in permanent damage to the circuit breaker.

As a vacuum circuit breaker can safely withstand this short period of arcing without being damaged, it is possible to produce a control circuit which can detect quickly whether the vacuum circuit breaker has functioned correctly and if not to take appropriate corrective action within the permissible arcing period. This is not possible with other types of circuit breaker, e.g., oil or air circuit breakers, because they do not have the ability to withstand an extended arcing period.

According to the invention, a method of controlling a vacuum circuit breaker includes the detection of a continuing current after the interrupter contacts of the vacuum circuit breaker have opened and the initiation after a predetermined time of continuous current flow of a closing circuit command to effect the reclosure of the interrupter contacts of the vacuum circuit breaker within a permissible arcing time.

Reclosure of the interrupter contacts, in accordance with the method as set out in the immediately preceding paragraph, immediately prevents further arcing continuing and immediately removes the possibility of damage to the circuit breaker. Reliance for clearance of the short circuit would thus be removed from the vacuum circuit breaker and placed on a back-up circuit breaker in the circuit being controlled. In the event of normal arc extinguishing within the predetermined response time of current detection, there would be no current flowing after the predetermined response time and thus there would be no command to reclose the interrupter contacts.

The invention also provides a control circuit for performing the aforesaid method of controlling a vacuum circuit breaker and comprises a current-responsive relay in series with the interrupter contacts of the vacuum circuit breaker and operable after a predetermined period of energisation by continuous current flow to effect reclosure of the interrupter contacts of the vacuum circuit breaker within the permissible arcing time.

A typical control circuit in accordance with the invention is illustrated in the accompanying drawing.

Referring to the drawing, a current transformer or sensor 2 for energising a relay 3 is included in the control circuit of the vacuum circuit breaker 1. The current trans former 2 and the relay 3 are normally outside the evacuated enclosure containing the interrupter contacts of the vacuum circuit breaker 1. The relay 3 may have a high or low current setting according to requirements and has a contact 4 which is normally open and is self-resetting to the open position and is connected in series with a contact 8 which is moved on closure of the contact 4 to operate an indicator that the closure of the contact 4 has occurred. The contact 4 is closable after a time delay and is arranged in a control circuit to effect re-closure of the interrupter contacts of the vacuum circuit breaker 1 when arcing continues beyond a prescribed period of time.The control circuit contains a solenoid S of a contactor 6 which when energised effects energisation of a solenoid 7 which effects re-closure of the interrupter contacts of the vacuum circuit breaker 1. In a typical arrangement if the vacuum circuit breaker 1 fails to interrupt the current in any of the phases, then the relay would operate to effect closure of the contact 4 after say 0.02 second and the closure of the contactor 6 followed by the reclosure of the interrupter contacts of the vacuum circuit breaker 1 by the solenoid 7 would be completed in say 0.12 second. Thus if the permissible arcing time of the vacuum circuit breaker is at least 0.2 second, reclosure would be safely achieved before thermal failure of the vacuum circuit breaker could develop.

The closure of the contactor 6 may also operate an indicator or alarm contact 9.

WHAT WE CLAIM IS: 1. A method of controlling a vacuum circuit breaker including the detection of a continuing current after the interrupter contacts of the vacuum circuit breaker have opened and the initiation after a predetermined time of continuous current flow of a closing circuit command to effect the reclosure of the interrupter contacts of the vacuum circuit breaker within a permissible arcing time.

2. A control circuit for performing the method according to Claim 1 comprising a current-responsive relay in series with the interrupter contacts of the vacuum circuit breaker and operable after a predetermined period of energisation by continuous current flow to effect reclosure of the interrupter contacts of the vacuum circuit breaker within the permissible arcing time.

3. A control circuit as claimed in Claim 2 in which the current-responsive relay includes a current transformer or sensor in series with the interrupter contacts of the vacuum circuit breaker.

4. A control circuit as claimed in Claim 2 or 3 in which the current-responsive relay is arranged to close a normally-open contact which when closed effects operation of a contactor to effect re-closure of the interrupter contacts of the vacuum circuit breaker, said normally-open contact being closable after the current-responsive relay has been energised for said predetermined period.

5. A control circuit as claimed in Claim 4 in which said normally-open contact is also connected to operate a first indicator to indicate whether said normally-open contact is open or closed.

6. A control circuit as claimed in Claim 4 or 5 in which a further normally-open contact is arranged to be closed when the contactor closes, said further normally-open contact, when closed, effecting operation of a second indicator or an alarm.

7. A control circuit for a vacuum circuit breaker substantially as described herein and shown in the accompanying drawing.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. contacts of the vacuum circuit breaker within a permissible arcing time. Reclosure of the interrupter contacts, in accordance with the method as set out in the immediately preceding paragraph, immediately prevents further arcing continuing and immediately removes the possibility of damage to the circuit breaker. Reliance for clearance of the short circuit would thus be removed from the vacuum circuit breaker and placed on a back-up circuit breaker in the circuit being controlled. In the event of normal arc extinguishing within the predetermined response time of current detection, there would be no current flowing after the predetermined response time and thus there would be no command to reclose the interrupter contacts. The invention also provides a control circuit for performing the aforesaid method of controlling a vacuum circuit breaker and comprises a current-responsive relay in series with the interrupter contacts of the vacuum circuit breaker and operable after a predetermined period of energisation by continuous current flow to effect reclosure of the interrupter contacts of the vacuum circuit breaker within the permissible arcing time. A typical control circuit in accordance with the invention is illustrated in the accompanying drawing. Referring to the drawing, a current transformer or sensor 2 for energising a relay 3 is included in the control circuit of the vacuum circuit breaker 1. The current trans former 2 and the relay 3 are normally outside the evacuated enclosure containing the interrupter contacts of the vacuum circuit breaker 1. The relay 3 may have a high or low current setting according to requirements and has a contact 4 which is normally open and is self-resetting to the open position and is connected in series with a contact 8 which is moved on closure of the contact 4 to operate an indicator that the closure of the contact 4 has occurred. The contact 4 is closable after a time delay and is arranged in a control circuit to effect re-closure of the interrupter contacts of the vacuum circuit breaker 1 when arcing continues beyond a prescribed period of time.The control circuit contains a solenoid S of a contactor 6 which when energised effects energisation of a solenoid 7 which effects re-closure of the interrupter contacts of the vacuum circuit breaker 1. In a typical arrangement if the vacuum circuit breaker 1 fails to interrupt the current in any of the phases, then the relay would operate to effect closure of the contact 4 after say 0.02 second and the closure of the contactor 6 followed by the reclosure of the interrupter contacts of the vacuum circuit breaker

1 by the solenoid 7 would be completed in say 0.12 second. Thus if the permissible arcing time of the vacuum circuit breaker is at least 0.2 second, reclosure would be safely achieved before thermal failure of the vacuum circuit breaker could develop.