Circuit Breaker Anti-pump Function

What is Anti-Pump?

An anti-pump relay in medium voltage circuit breakers ensures that a single close command results in only one closing operation, regardless of the command's duration.?        

It prevents the circuit breaker from continuously opening and closing if it receives simultaneous open and close commands, or if the close switch is jammed.?

The repeated open and close of the circuit? is known as circuit breaker hunting or pumping.

How does the anti-pump function operate?

On the schematic above, all contacts are shown with the breaker open and the “Close” spring fully charged (LSb open and LSa closed). Initially, when the close switch (CS) is pressed, the Close Spring Release relay (SR) is energized and the breaker closes. The “close” spring is discharged which closes LSb and opens LSa. With LSb closed, the anti-pump relay (Y) closes and is maintained closed by its own contact Y(seal-in).? Parallely, with the LSb contact closed, the spring motor (M) charges the close spring and when fully charged, opens LSb and closes LSa. With LSa closed again, normally SR should be energized but cannot because the NC? contact Y is now open. So if the breaker trips after closing, it will not close again even though CS is still pressed. The breaker will only be able to close again after CS has been released and pressed again.

Trip-Free vs Anti - Pumping

IEEE C37.04 for medium-voltage circuit breakers requires that they be trip-free, which is a condition in which the mechanism is designed such that the tripping or opening function takes precedence over the closing function. Trip-free is a requirement of all medium-voltage circuit breakers, whether stationary mounted or drawout mounted.        

IEEE C37.11 for circuit breaker control circuits requires the anti-pumping function. This requires that when an electrical closing command is issued, only a single closing operation results. This is normally accomplished by incorporating an anti-pump relay in the close circuit. The anti-pump relay is energized at the same time that the close signal is applied. The anti-pump relay is connected so that it seals in as long as the close signal is maintained. The anti-pump relay, when sealed in, opens a contact in the close circuit. The anti-pump function is one of the fundamental requirements for every medium-voltage circuit breaker.        

Trip-Free Requirements for MV Circuit Breaker Per IEEE C37.04?

• If the closing signal and the tripping signal are initiated simultaneously, the circuit breaker contacts are permitted to close or touch momentarily before opening.
• If the closing signal is initiated before the tripping signal is initiated, the circuit breaker contacts are permitted to close or touch momentarily before opening.
• If the trip circuit uses circuit breaker auxiliary switch contacts (52a contacts, closed when the circuit breaker is closed) or other equivalent contacts, the trip coil of the circuit breaker cannot be energized until these contacts in the trip circuit are made. Therefore, the circuit breaker main contacts are permitted to close or touch momentarily before opening
• If the tripping command is initiated mechanically (manually) and held in the actuated position before a closing signal (whether electrical or mechanical) is applied, the circuit breaker main contacts are not permitted to close, even momentarily. If the mechanism design requires, the circuit breaker may discharge stored energy but the main contacts are not permitted to move more than 10 percent of the open gap distance. The dielectric withstand capability of the open gap shall not be reduced, and the main contacts shall assume the fully open position.

Conclusion

The anti-pump function is one way to electrically implement the trip-free requirement on MV circuit breakers.

Authors: Yves Zomebot, PE & Jixil Johnson

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