Question:
Resistance switching is used in circuit breaker to:
Resistance switching is used in circuit breaker to:
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Resistance switching is primarily used in Air-Blast and $SF_6$ circuit breakers because their high post-arc dielectric recovery rates make them highly susceptible to current chopping and severe transient voltage oscillations.
Updated On: Jun 25, 2026
- decrease the restriking voltage and increase the severity of transient oscillations
- increase the severity of transient oscillations and the severity of transients
- Reduce the restriking voltage and severity of transient oscillations
- increase the restriking voltage and reducing the severity of transient oscillations
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The Correct Option is C
Solution and Explanation
Concept:
During arc interruption in a high-voltage circuit breaker, a highly energetic transient recovery voltage appears across the separating contacts. If the rate of rise of restriking voltage (RRRV) exceeds the dielectric strength recovery rate of the medium, the arc re-ignites. Resistance switching involves connecting a calculated shunt resistor ($R$) across the main contacts of the circuit breaker. This path alters the natural resonant frequency of the system circuit and provides critical damping to control transient surges.
Step 1: Understand the mathematical transient behavior without resistance switching.
When a circuit breaker clears a short-circuit fault, it behaves as an undamped LC series network. The transient restriking voltage can be expressed as: \[ v(t) = V_m (1 - \cos \omega_n t) \] where $\omega_n = \frac{1}{\sqrt{LC}}$ is the natural resonant frequency. The peak value reaches $2V_m$, causing a severe transient voltage stress across the contacts.
Step 2: Analyze the effect of connecting a shunt resistor (Resistance Switching).
When a resistor $R$ is placed in parallel across the breaker contacts, the circuit becomes a parallel RLC combination during the interruption phase. The characteristic differential equation changes, and its damping factor $\alpha$ becomes: \[ \alpha = \frac{1}{2RC} \] To completely eliminate high-frequency transient oscillations, the circuit should be critically damped. The critical value of resistance required is: \[ R_c = \frac{1}{2} \sqrt{\frac{L}{C}} \]
Step 3: Deduce the physical consequences on restriking voltage parameters.
By introducing this resistance path: 1. A portion of the inductive energy is dissipated as heat across the resistor instead of converting entirely into capacitive electrostatic energy. 2. The peak value of the restriking voltage is heavily attenuated. 3. The transient high-frequency oscillations are damped out, reducing the frequency of oscillation. Therefore, resistance switching effectively reduces both the restriking voltage magnitude and the overall severity of transient oscillations, which corresponds perfectly to Option (C).
Step 1: Understand the mathematical transient behavior without resistance switching.
When a circuit breaker clears a short-circuit fault, it behaves as an undamped LC series network. The transient restriking voltage can be expressed as: \[ v(t) = V_m (1 - \cos \omega_n t) \] where $\omega_n = \frac{1}{\sqrt{LC}}$ is the natural resonant frequency. The peak value reaches $2V_m$, causing a severe transient voltage stress across the contacts.
Step 2: Analyze the effect of connecting a shunt resistor (Resistance Switching).
When a resistor $R$ is placed in parallel across the breaker contacts, the circuit becomes a parallel RLC combination during the interruption phase. The characteristic differential equation changes, and its damping factor $\alpha$ becomes: \[ \alpha = \frac{1}{2RC} \] To completely eliminate high-frequency transient oscillations, the circuit should be critically damped. The critical value of resistance required is: \[ R_c = \frac{1}{2} \sqrt{\frac{L}{C}} \]
Step 3: Deduce the physical consequences on restriking voltage parameters.
By introducing this resistance path: 1. A portion of the inductive energy is dissipated as heat across the resistor instead of converting entirely into capacitive electrostatic energy. 2. The peak value of the restriking voltage is heavily attenuated. 3. The transient high-frequency oscillations are damped out, reducing the frequency of oscillation. Therefore, resistance switching effectively reduces both the restriking voltage magnitude and the overall severity of transient oscillations, which corresponds perfectly to Option (C).
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