Circuit Breaker

A 50 Hz 3-phase alternator with grounded neutral has an inductance of 1.6 mH per phase and is connected to the bus-bars through a circuit breaker. The capacitance to earth of the circuit between the alternator and the circuit breaker is $0.0032\,\mu\mathrm{F}$ per phase. Due to a short on the bus-bars the breaker opens when the rms value of the current is 8000 A. Determine the following (i) frequency of oscillation (ii) Active recovery voltage (iii) time for maximum RRRV and (iv) maximum RRRV.

In a short circuit test on a 132 kv, three phase system, the breaker gave the following results. Pf of the fault is 0.4, recovery voltage is 0.9 of full line value and the natural frequency is 16 KHz. Determine the rate if rise of restriking voltage in following cases.

i) Assume that symmetrical fault is grounded.

ii) Assume that symmetrical fault is not grounded.

In a 220 kV system the reactance and capacitance up to the location of circuit breaker is $8\,\Omega$ and $0.025\,\mu\mathrm{F}$, respectively. A resistance of $600\,\Omega$ is connected across the contacts of the circuit breaker. Determine the following: (i) Natural frequency of oscillation, (ii) Damped frequency of oscillation, (iii) Critical value of resistance which will give no transient oscillation and (iv) The value of resistance which will give damped frequency of oscillation, one-forth of the natural frequency of oscillation.