Understanding Transient Voltage in Circuit Breakers

Circuit breakers are essential devices used to interrupt fault currents in electrical systems. When a circuit breaker opens, an arc is formed between the separating contacts as the current flows through the ionized air. This arc continues until the current reaches its natural zero crossing.

What is Restriking Voltage?

The voltage that appears across the circuit breaker contacts at or near the instant of current zero is known as the restriking voltage. This voltage is highly transient, meaning it changes very rapidly over a short period. It is an oscillating voltage caused by the interaction of the system inductance and capacitance (L-C oscillations) after the arc is extinguished. The magnitude and rate of rise of the restriking voltage (RRRV) are critical factors in determining whether the arc will re-ignite (restrike) or be successfully extinguished.

Let's look at why the other options are not correct:

• Recovery Voltage: This is the normal frequency (power frequency) voltage that appears across the circuit breaker contacts after the arc has been completely extinguished and the transient oscillations of the restriking voltage have died down. It is essentially the voltage of the system that the breaker is interrupting.
• Arc Voltage: This is the voltage that exists across the contacts during the arcing period itself. It is relatively low compared to the system voltage and depends on the arc length and the current. The question asks about the voltage that appears at or near current zero, during the arcing period, but specifically the transient voltage that appears as the arc is about to be extinguished or just after.
• Rated Voltage: This is the maximum voltage for which the equipment is designed to operate continuously. It is a steady-state system parameter, not a transient voltage appearing across the contacts during interruption.

Based on the definitions, the transient voltage that appears across the contacts at or near current zero during the arcing period, specifically after the arc extinction attempt, is the restriking voltage.