US3373350A

US3373350A - Apparatus for testing the arc capability of an electrical circuit breaker

Info

Publication number: US3373350A
Application number: US556479A
Authority: US
Inventors: Reece Michael Peter
Original assignee: Associated Electrical Industries Ltd
Current assignee: Associated Electrical Industries Ltd
Priority date: 1962-03-07
Filing date: 1966-06-09
Publication date: 1968-03-12
Anticipated expiration: 1985-03-12

Description

March 12, 1968 M P. REECE Filed June 9, 1966 Cg sou/me CRM i/[A/VS Aug 5%; CM Aid/770K Sc IS R7 A 5 T7 2 rcs I TISI'Cgg/QRL 63 AC. 6

P2 R J- I c4 TG7\:L real R6 f 1 U 2 F1 {W1 a 1P2 COUNT/N6 ME/M S ARC CAPABILITY OF AN ELECTRICAL CIRCUIT BREAKER INVENTOR MICHAEL PETER REECE ATTORNEYS United States Patent C) 3,373,350 APPARATUS FQR TESTING THE ARC CA- PABILITY F AN ELECTRICAL CIRCUIT BREAKER Michael Peter Reece, London, England, assignor to Associated Electrical Industries Limited, London, England, a British company Continuation-impart of application Ser. No. 261,283, Feb. 27, 1963. This application June 9, 1966, Ser. No. 556,479 Claims priority, application Great Britain, Mar. 7, 1962, 8,315/62 4 Claims. (Cl. 324-28) ABSTRACT OF THE DISCLQSURE An arrangement for testing the arc interrupting capability of an electrical circuit breaker at rated kilovolt amperes without the expenditure of a corresponding amount of power by means of a first circuit connected to apply a large main test current at low voltage to the arc interrupting contacts of the circuit breaker and a second circuit connected to apply to these contacts a small additional test current followed by a high voltage surge simulating a recovery-voltage transient at the last current zero of the main test current before the arc is interrupted, characterized by the provision of a third circuit which is operable at a preceding current zero of the main test current to apply to the arc interrupting contacts a current pulse which is effective to change the polarity of the current in the are drawn between these contacts sufiiciently rapidly to prevent the arc from being extinguished at such preceding current zero.

This is a continuation-in-part of the application of Michael P. Reece Ser. No. 261,283 filed Feb. 27, 1963 and now abandoned.

The present invention relates to an arrangement for testing electrical circuit breakers.

It is well known that circuit breakers of large capacity can be tested synthetically by using a first circuit to supply a current to the circuit breaker equal to the required large main test current and a second separate circuit to supply a small additional test current followed by a voltage across the circuit breaker equal to the restriking voltage which the circuit breaker will experience in normal operation as it interrupts a large current at a high voltage. It is the restriking voltage which tends to maintain the arc, which appears across the contacts of the circuit breaker during the process of interrupting the current.

By using a first circuit to provide a large main test current at a low voltage and a second circuit to provide the small additional test current and the restriking voltage the test plant rotating machine capacity required for testing the circuit breaker is very much reduced as compared with the capacity required in a testing arrangement in which one circuit is used to provide a large test current at the required high voltage.

If the circuit breaker to be tested in such that more than one half cycle of the main test current occurs during the time taken by the circuit breaker to open and interrupt the arc, it will be necessary to apply the small additional test current followed by the restriking voltage across the contacts of the circuit breaker each time the main test current passes through zero, in order to re-ignite the arc and thereby make the test conditions as similar as possible to the operational conditions.

In known testing arrangements the additional test current and restriking voltage are supplied by discharging a large capacitor and the repeated application of this current and restriking voltage every half cycle of the main test current can be arranged by repeatedly charging and discharging the capacitor. This requires a considerable recharging power and equipment and appreciably increases the cost of the arrangements. Also the auxiliary circuit breaker which is used to interrupt the low voltage test current supply circuit every time the high voltage is applied needs to be more complicated.

Accordingly, it is an object of the present invention to provide a new and improved testing arrangement for electrical circuit breakers.

Another object of the present invention is to provide an arrangement for testing an electrical circuit breaker which avoids the need for supplying the additional test current and restriking voltage for maintaining or re-igniting the arc drawn by a circuit breaker under test as the latter is opened, for each successive current zero of the main test current, except the last, while the main test current is being interrupted.

With the above objects in view the present invention provides an arrangement for testing an electrical circuit breaker comprising a first circuit including an alternating current source and connected to supply a large main test current at low voltage to the circuit breaker under test, an auxiliary circuit breaker connected in said first circuit, a second circuit including a high voltage source and connected to supply a small additional test current followed by a restriking voltage across said circuit breaker under test when said main test current is interrupted by said auxiliary circuit breaker, a third circuit connected to said circuit breaker under test in series with said auxiliary circuit breaker and including current pulse producing means, and control means connected to receive control current derived from said main test current and operable in response to said control current in respect of at least one occasion that the main test current passes through zero during opening of the circuit breaker under test to cause said current pulse producing means in said third circuit to produce a current pulse which, as applied to the circuit breaker under test through said auxiliary circuit breaker, is effective at the zero value of the main test current, to change the polarity of the current in the are being drawn by the circuit breaker under test sufficiently rapidly to prevent the are from being extinguished.

Also, according to the present invention, there is provided an arrangement for testing an electrical circuit breaker of the type which has the characteristic that more than one half cycle of main test current occurs during the time taken by the circuit breaker to open and interrupt an are, said arrangement comprising: a first circuit connected to the circuit breaker under test and including an alternating current source suitable for supplying a large main test current a low voltage to the circuit breaker under test; an auxiliary circuit breaker connected in said first circuit in series with said alternating current source and operable to interrupt the supply of main test current from said alternating current source to the circuit breaker under test a second circuit including a high voltage source and operable to supply a small additional test current followed by a restriking voltage to the circuit breaker under test; isolator means connected in series with said second circuit across the circuit breaker under test; timing control means operable to cause operation of said auxiliary circuit breaker and said isolator means in timed relation to the occurrence of the last half cycle of the main test current during the opening of the circuit breaker under test, whereby to interrupt the supply of main test current from said alternating current source to the circuit breaker under test and to connect said second circuit to the circuit breaker under test; first control means, sensing means for applying to said first control means control signals indicative of each current zero of the main test current during the opening of the circuit breaker under test, said first control means being responsive to said control signals to cause operation of said second circuit in respect of the last half cycle of the main test current before the circuit breaker under test has finished opening; a third circuit connected in series with said auxiliary circuit breaker across the circuit breaker under test; current pulse producing means in said third circuit; and second control means connected to receive control current derived from said main test current and operable in response to said control current in respect of each occasion that the main test current passes through zero during opening of the circuit breaker under test to cause said pulse producing means to produce a current pulse which, as applied to the circuit breaker under test through said auxiliary circuit breaker is effective at the current Zero of the main test current to which it pertains, to change the polarity of the current in the are being drawn by the circuit breaker under test sufiiciently rapidly to prevent the are from being extinguished.

In operation of a testing arrangement according to the invention the current pulse is passed through the circuit breaker under test just before each successive current zero of the main test current before the last while the main test current is being interrupted so as to maintain the arc, and the small additional test current followed by the main restriking voltage is supplied only at the last current zero.

In order that the invention may be more readily understood reference will now be made to the accompanying drawing in which the single figure is a circuit diagram of an arrangement for testing a circuit breaker according to the invention.

With reference to the figure, the testing arrangement there shown comprises a first circuit including an alternating current source I connected in series with a stopper coil SC and an auxiliary circuit breaker ACB. The source I is suitable for supplying a main test current at low voltage to a circuit breaker TCB under test.

This circuit breaker TCB under test which is connected between two test terminals T1 and T2 of the testing arrangement, is of the type which has the characteristic that more than one half cycle of the test current occurs during the time taken by the circuit breaker TCB to open and interrupt the arc. The arrangement also comprises a second circuit including a high voltage source V connected across a capacitor C2 in series with a switch S, and a triggered spark gap TG3, an inductance L1 and a capacitor C1 connected in series across capacitor C2. Capacitor C2 is adapted to be charged from the source V through the switch S and to be discharged through spark gap TG3 into L1 and C1 and across the circuit breaker TCB under test by way of an isolator IS so as to supply the small additional test current followed by the restriking voltage for the test, as described above.

Timing control means CM are provided for controlling the operation of the auxiliary circuit breaker ACE and the isolator IS in relation to the operation of the circuit breaker TCB under test. In the known arrangements considered at the beginning of the specification, timing control means such as CM would be required to function every half cycle of the main test current during the time taken by the circuit breaker TCB under test to open and interrupt the arc, in order to operate the auxiliary circuit breaker ACB each such half cycle so as to interrupt the main test current supply while the additional test current and restriking voltage is being applied to the circuit breaker TCB under test from the second circuit through the isolator IS which latter, as a consequence, would also be required to be operated by the timing control means CM each such half cycle. However, with the present invention, this repeated action is avoided, as will be described, and the timing control means CM is required to operate the auxiliary circuit breaker ACE and the isolator IS only for the last half cycle before the circuit breaker TCB under the test opens. The triggering of the spark gap T G3 is controlled by control means comprising current responsive means CRM and counting means CCM in such manner as to cause the spark gap TG3 to be triggered only in respect of the last half cycle of the main test current before the circuit breaker TCB under test has finished opening, so that the small additional current followed by the restriking voltage produced by the second circuit is applied only once to the circuit breaker TCB under test. In order to achieve this control, the counting means CCM, which comprises relay or other counting elements, is connected to receive a pulse from the current responsive means CRM in respect of each current zero of the main test current flowing in a resistor R4, and the counting means CCM is arranged to count these pulses and to produce an output causing triggering of the triggered spark gap TG3 when the resultant count signifies that, for the particular type of circuit breaker TCB under test, the penultimate current zero before this circuit opens has been reached. The current responsive means CRM may be a so-called peaking strip or transformer operated by the magnetic field of the current in resistor R4.

A third circuit is provided for maintaining the arc across the circuit breaker TCB under test at each half cycle of the test current, except the last, as the circuit breaker TCB gradually opens. This third circuit provides a current pulse having a steep front and a long tail which occurs just before the main test current passes through zero. The current pulse is added to the main test current and causes the value of the test current to change rapidly from about 100 amps of one polarity to about 100 amps of the other polarity.

Since the test current thus changes through a zero value very quickly the arc is not extinguished.

The third circuit comprises a capacitor C3 connected in series with an isolation spark gap G2, a resistor R1, which may have a capacitor C6 connected in parallel with it when the circuit breaker TCB under test has shunt capacitors or low value resistors connected across it, a triggered spark gap TG1 means P1 for charging capacitor C3 and a high resistance R5 in parallel with C3 and TGI. By triggering TGl, the capacitor C3 is caused to discharge through G2 and R1 to supply a current pulse through ACE and TCB. The stopper coil SC prevents the current pulse from passing through the current source 1. It will be appreciated that the current pulse is provided by a voltage which may be very much higher than the voltage of the main test current.

The third circuit may also include a self inductance L2 connected in series with the circuit breaker TCB under test and provided with a pulse forming circuit comprising a capacitor C4 in series with a spark gap G3, a resistor R2, at triggered spark gap TG2, means P2 for charging capacitor C4 and a high resistance R6 in parallel with C4 and TG2. When C4 is discharged by triggering TG2 a current pulse fiows through L and produces a sharply peaked current pulse through circuit breaker TCB. This sharply peaked current pulse can be used to boost the current pulse provided by capacitor C3.

TGl, TG2, which may be Trigatrons, may be triggered by control means in the form of two ferrite rings F1, F2 surrounding the test current carrying conductor and a secondary conductor connected across the current source 1 through a high resistance R3. A current flows in this secondary conductor which leads the test current by approximately and can have allow value as required. The triggering electrodes of TGl, TG2 are connected respectively to windings W1, W2 around the ferrite rings F1, F2 respectively.

The effects of the test current and the secondary current in the conductors passing through the rings F1, F2 are combined and as the value of the test current approaches zero the value of the secondary current will be different and, at one instant, when the value of the test current is about 100 amps, the effects of the test current and the secondary current will be equal and opposite. At this instant a pulse will be produced in each winding W1, W2 which will trigger TGl and TG2. The time of occurrence of this pulse can be selected by suitably selecting the value of the resistance R3.

The resistance R4 can also be used as a shunt for a current measuring or indicating device such as an oscilloscope.

With a circuit as above, TGI and TG2 are triggered just before the value of the test current passes through zero so as to cause the value to pass through zero very quickly and prevent the are from being extinguished. Additional relay or other counting circuits, as represented by the dotted line blocks CR1 and CR2, can be provided for selecting when the triggering pulses are applied to T61 and TG2 so that the current pulse need only be supplied when required.

What I claim is:

1. An arrangement for testing the arc interrupting capability of an electrical circuit breaker at rated kilovolt amperes without the expenditure of a corresponding amount of power, said arrangement including in combination with the circuit breaker to be tested,

(a) an auxiliary circuit breaker,

(b) a source of high alternating current,

(c) means connecting the circuit breaker under test and said auxiliary circuit breaker in series with the high current source,

(d) a high voltage source for applying a small additional test current followed by a simulated recovery voltage to the circuit breaker under test, said auxiliary circuit breaker preventing the imposition of high voltage across said source of alternating current,

(e) a first spark gap connected in series with said high voltage source across the circuit breaker under test, and

(f) first control means responsive to the last current Zero of the current from the current source as applied through the circuit breaker under test during opening thereof to cause breakdown of said first spark gap so that the small additional test current and simulated recovery voltage are applied to the circuit breaker under test,

and said arrangement being characterized by the provision therein of (g) current pulse producing means,

(h) a second spark gap connected in series with said current pulse producing means,

(1) means connecting the circuit breaker under test and said auxiliary circuit breaker in series with the series combination of said current pulse producing means and said second spark gap, and

(j) second control means responsive to a current zero before the last of the current from the current source as applied through the circuit breaker under test during opening thereof to cause breakdown of said second spark gap thereby to cause said current pulse producing means to produce a current pulse which, as applied to the circuit breaker under test, is effective at such current zero of the current from the current source to change the polarity of the current in the are being drawn by the circuit breaker under test sufficiently rapidly to prevent the are from being extinguished.

2. An arrangement as defined in claim 1, wherein said current pulse producing means comprises a capacitor connected in series with said second spark gap and a current charging source connected in circuit with said capacitor for charging the latter, breakdown of said second spark gap as aforesaid causing said capacitor to discharge through the circuit breaker under test, thereby to supply said current pulse.

3. An arrangement as defined in claim 1 wherein said second control means comprises current responsive means operable to produce a pulse each time the current from said current source passes through zero, and counting means for counting the pulses produced by said current responsive means and operable to cause breakdown of said second spark gap at a particular current zero of the current from said current source as determined by the number of pulses received by said counting means.

4. An arrangement as defined in claim 1, including a conductor and a resistor connected in series across said current source, a ferrite ring extending around said conductor and a second conductor which carries the current from said current source as applied to the circuit breaker under test, and a winding extending around said ferrite .ring and connected to said second spark gap, said ferrite ring constituting said second control means and being so magnetisable by currents in said conductors to produce in said winding, as the current from said current source approaches zero value, a control pulse effective to cause said breakdown of said second spark gap.

References Cited UNITED STATES PATENTS 3,064,183 11/1962 Slarnecka 324-28 RUDOLPH V. ROLINEC, Primal y Examiner. E. L. STOLARUN, Assistant Examiner.