GB2197491A - Electrical circuit breaker monitoring apparatus - Google Patents

Abstract

The duration of a tripping pulse tpc applied to a circuit breaker tripping coil (4, Fig. 1 not shown) is sensed at terminals 11, 12 of a monitoring unit and is compared with the durations of a plurality of different duration pulses tp1, tp2 from a timing means (I), and an indication of the results of the comparisons given (L2,L3) whereby to monitor the operation of the circuit breaker. <IMAGE>

Description

SPECIFICATION Electrical circuit breaker monitoring apparatus This invention relates to electrical circuit breaker monitoring apparatus, and in particular to such apparatus operative to monitor the times taken for operation of a circuit breaker after receipt of tripping signals.

Experience has shown that electrical circuit breakers such as those used in electrical power supply systems, which are normally closed but which are designed to open on receipt of a tripping signal, may occasionally take an unacceptably long time to open, particularly if they have not been operated for a relatively long period.

Reasons for this are believed to be evaporation of solvents from material used to lubricate the circuit breakers, leaving highly viscous material causing slow operation ; corrosion; and collection of contaminents such as dust.

There is thus a need for apparatus which will monitor the operating times of a circuit breaker, the information obtained being recorded for comparison with expected times so that circuit breaker condition can be assessed and operational history considered following operation under fault conditions.

According to this invention there is provided electrical circuit breaker monitoring apparatus comprising detector means operable to determined the duration of a tripping pulse applied to the tripping coil of an electrical circuit breaker; a timing means triggered by said detection means to provide a pulse of set duration; means to compare the duration of the tripping pulse determined by the detector means with the duration of the set pulse from the timing means; and indicator means operative to indicate whether the tripping pulse is longer than the set pulse from the timing means.

This invention provides monitoring apparatus which can be associated with an electrical circuit breaker to serve to monitor the operation thereof, and in particular to indicate whether the circuit breaker has taken longer than an expected time to operate, thereby indicating a possible fault or probable future difficulties.

This invention will now be described by way of example with reference to the drawings, in which: Figure 1 shows the tripping circuit for an electrical circuit breaker as used in an electrical power supply system; Figure 2 is a circuit diagram of an apparatus according to this invention; and Figure 3 is a timing diagram illustrating operation of the apparatus of Fig. 2.

Fig. 1 shows a series arrangement of a fuse 1, contacts 2 of a protection relay (not shown) serving to effect tripping of a circuit breaker, a normally closed circuit breaker auxillary switch 3 which is opened when tripping (opening) of the circuit breaker is complete, and a tripping coil 4 of the circuit breaker.

On operation of the protection relay the contacts 2 close and the tripping coil 4 is energised by the typically 30V or 1 10V supply. The circuit breaker is thus tripped (opened) and at completion of the tripping operation the switch 3 is opened thus breaking the supply to the tripping coil 4.

Thus, the duration of the pulse across the tripping coil 4 is a reliable measure of the actual time taken for operation of the circuit breaker.

Referring now to Figs. 2 and 3 also, the apparatus have shown operates to compare the pulse (tPC in Fig. 3) across the tripping coil 4 with two pulses (tp1 and tp2 in Fig. 3) of mutually different set duration, and to give an indication if the duration of the tripping pulse exceeds that of one or both of the set pulses.

The pulses are shown in Fig. 3 with different amplitudes for reasons of clarity only. The set pulses are shown as having durations of 150mS and 200mS respectively; these are only typical values the actual value being set in dependence upon the acceptable time for operation of the circuit breaker being monitored.

Referring now to Fig. 2, the circuit here shown comprises input terminals T1 and-T2 for connection across the tripping coil (4 in Fig. 1) of a circuit breaker to be monitored, and a + 1 2V supply terminal. As noted above the voltage across the tripping coil may be 30V or 110V, and this voltage is limited by zener diode Z and resistor R1/1 to 15V for application to a single pole reed relay RL serving as a dection means, which is closed thereby thus connecting the 1 2V supply to one terminal of each of double pole reed relays RL2 and RL3 by way of diodes d1 and d2 respectively.The 1 2V supply is also applied to the bases of transistors Tr1 and Tr2 by way of diodes d2 and d3 and resistor R2, and diodes d1 and d4 and resistor R4, respectively.

The resulting negative going transients at the collectors of Tr1 and TR2 are applied via capacitors C1 and C2, respectively, to trigger the two timing circuits within a dual timer integrated circuit 1(556 CMOS).

The integrated circuit I when triggered generates two+ve pulses (tp1 and tp2 in Fig. 3) the durations of which are determined by the values of resistor R10 and capacitor C3, and resistor R11 and capacitor C, respectively.

These two pulses are supplied from terminals 5 and 9 of the integrated circuit I to the other terminals of the reed relays RL2 and RL3, by way of light emitting diode L2 and resistor R13, and light emitting diode L3 and resistor R14, respectively.

If one or both of the pulses from the integrated circuit I applied to the reed relays RL2 and RL3 has subsided before the contact of reed relay RL1 has opened, that is before operation of the circuit breaker is completed, then one or both of the reed relays RL2 and RL3 will become latched due to the 1 2V sup ply applied to their contacts as shown, and thus one or both of the light emitting diodes L2 and L3 will remain energised and lit.

Thus, the diodes L2 and L3 will serve to indicate that the circuit breaker has taken longer than either one or both of the times set by the pulses (tp1 and tp2 in Fig. 3) from the integrated circuit I, the possibility of a problem thus being indicated. The diodes L2 and L3 will remain lit until the reed relays RL2 and RL3 are reset by an operative with a permanent magnet, irrespective of any subsequent operation of the monitored circuit breaker.

The circuit includes a third light emitting diode L1 connected in series with resistors R5 and R,2 between the 12V supply and earth, which diode is lit to indicate that the circuit is operational.

Apparatus as described above can be relatively cheap and thus one such apparatus can be permanently associated with a circuit breaker to effect monitoring thereof, this being preferable to the known method in which portable monitoring equipment is carried by an operative from circuit breaker to circuit breaker.

As shown, the reed relays RL2 and RL3 can be provided with output terminals T3, T4 and T5, T6, respectively, which are connected on closing of the relay, and to which other indicator means, for example means to transmit an indication to a remote location such as a central monitoring station, can be connected.

Although the apparatus described above has an independent 12V supply, sufficient power for operation of the apparatus can be obtained from the pulse applied to terminals T1 and T2 (the tripping coil pulse) by the use of a rapidly chargeable (a few milliseconds) energy store charged by the tripping coil voltage. The energy stored would be sufficient for operation of the circuit for the duration of the largest set pulse (tp2 in Fig. 3) (say 500mS), the light emitting diodes RL2 and RL3 being replaced by non-volatile memories such as latching relays which could subsequently be interrogated.

With such apparatus the set pulses would not commence until sufficient energy had been obtained from the tripping pulse, say after 5mS, and thus such a time delay would have to be built into the circuit and allowed for in the comparison operation. Such a modified apparatus would not be permanently energised, and has the further advantages that it would require only two connections (T1 and T2), and less circuitry than the apparatus shown in Fig.

2.

Although in the apparatus described above the time taken for operation of the circuit breaker is compared with two set times, it will be appreciated that circuitry providing only one or three or more set times can be pro vided if less or more detailed monitoring is required.

Claims (12)

1. Electrical circuit breaker monitoring apparatus comprising detector means operable to determine the duration of a tripping pulse applied to the tripping coil of an electrical circuit breaker; a timing means triggered by said detection means to provide a pulse of set du ration; means to compare the duration of the tripping pulse determined by the detector means with the duration of the set pulse from the timing means; and indicator means operative to indicate whether the tripping pulse is longer than the set pulse from the timing means.

2. Apparatus as claimed in Claim 1, in which the timing means is operative to provide a plurality of mutually different duration set pulses, the comparison means serving to compare the duration of the tripping pulse with that of each of the set pulses, and the indicator means serving to indicate the duration relationship between the tripping pulse and each of the set pulses.

3. Apparatus as claimed in Claim 1 or Claim 2, in which the detector means comprises a reed relay connectible across the tripping coil of the electrical circuit breaker.

4. Apparatus as claimed in any preceding claim, in which the timing means is an integrated circuit with an associated resistor/capacitor network or networks set to determine the duration of the or each set pulse.

5. Apparatus as claimed in any preceding claim, in which the comparison means comprises an individual latching reed relay for the or each set pulse, the detector means serving to effect application of a voltage to one terminal of the or each latching reed relay for the duration of the detected tripping pulse, and the set pulse or a respective one of the set pulses from the timing means being applied to the other terminal of the or each latching reed relay, a latching reed relay becoming latched only if the voltage is present at its one terminal after the set pulse at its other terminal has ended.

6. Apparatus as claimed in any preceding claim, in which the indicator means comprises a respective light emitting diode associated with the or each set pulse from the timing means.

7. Apparatus as claimed in any preceding claim, including a source of electrical power serving for operation of the apparatus.

8. Apparatus as claimed in any preceding claim, including a light emitting diode which is lit to indicate that the apparatus is functional.

9. Apparatus as claimed in any one of Claims 1 to 5, including an energy store arranged to be charged by the voltage of the tripping coil of the electrical circuit breaker, and thereafter provide the electrical power necessary for operation of the apparatus.

10. Apparatus as claimed in Claim 9, in which the indicator means comprises non-volatile memory means.

11. Apparatus as claimed in Claim 9 or Claim 10, including delay means operative to effect triggering of the timing means a set time after response of the detector means to a tripping pulse, the set time serving to ensure adequate charging of the energy store for operation of the apparatus, and the set time being allowed for in the comparison operation.

12. Electrical circuit breaker monitoring apparatus, substantially as hereinbefore described with reference to the drawings.