Restriking Voltage Across Breaking Contacts

When a circuit breaker operates to interrupt current, especially in AC circuits, an arc is often formed between the separating contacts. The circuit breaker must extinguish this arc to successfully break the circuit. After the arc is extinguished, a voltage appears across the gap between the contacts.

Understanding the Voltages

Let's look at the voltages that appear across the breaking contacts during and after the interruption process:

• Arc Voltage: This is the voltage that exists across the contacts while the arc is present and conducting current. It is typically a relatively low voltage that sustains the arc.
• Restriking Voltage: This is the transient voltage that appears across the circuit breaker contacts immediately after the arc current is interrupted (i.e., at the instant of arc extinction). It is a result of the sudden release of energy stored in the inductance of the circuit and the presence of capacitance (like stray capacitance and grading capacitances) in the system. This voltage oscillates at a high frequency and can reach peak values significantly higher than the system voltage. The rate of rise of this voltage (RRRV) is crucial for successful circuit interruption.
• Recovery Voltage: After the transient oscillations of the restriking voltage have died down, the normal power frequency voltage across the contacts is established. This voltage is called the recovery voltage. It is essentially the system voltage that appears across the open circuit breaker.

The question asks for the voltage that appears across the breaking contact specifically "at the instant of arc extinction". Based on the definitions, this corresponds to the beginning of the transient period when the Restriking Voltage appears and starts oscillating across the contacts.

Therefore, the voltage that appears across the breaking contact at the instant of arc extinction is called the Restriking Voltage.