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GATE 2019 EE – Question 62

Power Systems · Principles of over-current, differential, directional and distance protection; Circuit breakers · 2 marks · Numerical answer

In a 132 kV system, the series inductance up to the point of circuit breaker location is 50 mH. The shunt capacitance at the circuit breaker terminal is 0.05 $\mu$F. The critical value of resistance in ohms required to be connected across the circuit breaker contacts which will give no transient oscillation is ________.

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Correct answer: 500

Explanation

A parallel resistance across the breaker gives no oscillation when it is at or below the critical value $R=\frac12\sqrt{\frac LC}=\frac12\sqrt{\frac{50\times10^{-3}}{0.05\times10^{-6}}}=\frac12(1000)=500\ \Omega$.