In electrical power systems, circuit breakers play a crucial role in protecting equipment and ensuring the stability of the grid. However, improper operation of breakers can lead to major faults and unsafe conditions. One critical issue in breaker operation is multiple closing attempts before clearing a fault. This can occur due to a continuous closing signal to the closing coil. To prevent this situation, the anti-pumping scheme comes into play. The anti-pumping mechanism ensures that the breaker closes only once per closing command. It cannot reclose, even if a continuous closing command passes from the remote or local closing switch. Let us break down how this scheme works, using the provided control circuit diagram as an example.
Anti-Pumping Scheme Circuit Diagram
The diagram represents a part of a DC control circuit designed for closing a circuit breaker. It focuses on an anti-pumping relay to prevent unintended repeated operations.
DC Supply and Remote Close Operation
Here, the DC Supply provides the required power for control operations. The Remote Close terminal sends a closing pulse from the remote control panel. A TNC switch or a closing push button attached to the remote control panel generates the remote close signal.
Local and Remote Selection
The operator uses the Local Remote Switch to select either local or remote operation. When set to the Remote position, the switch connects the closing control path to the Remote Close circuit. When set to the Local position, it connects the closing control path to the positive DC supply bus of the circuit breaker.
The operator manually operates the TNC Switch (Trip-Neutral-Close Switch) to close the breaker locally.
Auxiliary Switch Function
The mechanism of the circuit breaker includes a fitted Auxiliary Switch. When the CB closes, all the parallel NO (Normally Open) contacts close, and all parallel NC (Normally Closed) contacts open. Conversely, when the CB opens, all the parallel NO contacts open, and all parallel NC contacts close.
Role of NC Contact in Closing Path
One of these NC (Normally Closed) contacts is connected in the closing circuit path. It ensures that the breaker is open before any closing action is attempted. This means the Auxiliary NC contact of the circuit breaker in the closing path serves an important role. It ensures that the breaker can only close when it is already in the open position.
The Limit Switch (NO – Normally Open) ensures that the breaker is in the correct mechanical position before closing. The Limit Switch NO contact will close only if the Closing Spring is fully charged.
Anti-Pumping Relay Circuit Details
The Anti-Pumping Relay (AP) is connected in parallel with the closing circuit. There is an Auxiliary NO Contact in series with the Anti-Pumping Coil. An AP-NO (Normally Open) contact of the Anti-Pumping Relay lies in parallel with the auxiliary NO contact.
The Anti-Pumping Coil gets energized only through the series Auxiliary NO contact during circuit breaker (CB) closing operations. An AP-NC (Normally Closed) contact of the Anti-Pumping Relay also lies in the closing circuit path. Initially, this contact remains closed and allows the closing command to reach the Closing Coil.
How the Anti-Pumping Scheme Circuit Works
If we observe carefully, we’ll notice that all the contacts in the closing circuit remain closed when the circuit breaker (CB) is open and the spring is fully charged. When the operator presses the Remote Close switch or operates the Local TNC switch, current flows through the circuit and energizes the Closing Coil. This action closes the breaker, causing all the auxiliary NO contacts of the breaker to switch to a closed state.
As a result, the AP relay activates through its series Auxiliary NO contact. It then opens its AP-NC contact in the closing path, cutting off power to the Closing Coil and blocking further closing attempts. If the operator holds the closing command continuously or sends multiple commands quickly, the AP relay prevents repeated operations.
Once energized, the Anti-Pumping Coil closes the AP-NO contact in its own circuit. This action latches the Anti-Pumping Relay until the operator releases the Remote Close switch or the Local TNC switch.
Importance of the Anti-Pumping Scheme
Without an anti-pumping mechanism, continuous closing signals could cause the closing coil to overheat, leading to damage. Additionally, uncontrolled multiple closing attempts during faults could create instability in the power system and increase the risk of breaker failure during critical operations. By implementing an anti-pumping relay, the circuit ensures:
Conclusion
The anti-pumping scheme is a simple yet vital protection feature in circuit breaker control circuits. By ensuring that the breaker closes only once per command, it prevents unwanted repeated operations, reducing the risk of damage and improving system reliability. This mechanism is essential in all modern high-voltage circuit breaker designs and plays a key role in maintaining stable and efficient power system operations.