IEEE C37.11 for circuit breaker control circuits requires the anti-pump
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.
Thus, the circuit breaker closes, but if the close signal is maintained, the close circuit has an open contact in the circuit, preventing further close operations as long as the close signal is maintained.
The anti-pump function is a very important feature of control circuits. Without the anti-pump function, if the user connected a maintained contact in the close circuit, and the circuit breaker were closed into a fault current, the protective relays would cause an immediate trip action, but the maintained contact in the close circuit would initiate closing (again) into the fault.
Also 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. The requirements as elaborated in the standard are:
- If a closing operation is in progress, and a tripping signal (either mechanical or electrical) is received, the circuit breaker shall react as follows:
- 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 that 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.