1500-\mathrm{MVA} 20-\mathrm{kV}, 60-\mathrm{Hz}

three-phase generator is connected through a

1500-\mathrm{MVA}

20-\mathrm{kV} \Delta / 500-\mathrm{kV}

Y transformer to a

500-\mathrm{kV}

circuit breaker and a

500-\mathrm{kV}

transmission line. The generator reactances are

\mathrm{X}_{d}^{\prime \prime}=0.17, \mathrm{X}_{d}^{\prime}=0.30

, and

\mathrm{X}_{d}=1.5

per unit, and its time constants are

\mathrm{T}_{d}^{\prime \prime}=0.05, \mathrm{~T}_{d}^{\prime}=1.0

, and

\mathrm{T}_{\mathrm{A}}=0.10 \mathrm{~s}

. The transformer series reactance is 0.10 per unit; transformer losses and exciting current are neglected. A three-phase short-circuit occurs on the line side of the circuit breaker when the generator is operated at rated terminal voltage and at no-load. The breaker interrupts the fault 3 cycles after fault inception. Determine (a) the subtransient current through the breaker in per-unit and in kA rms; and (b) the rms asymmetrical fault current the breaker interrupts, assuming maximum dc offset. Neglect the effect of the transformer on the time constants.

Repeat Example 7 V=4kV,X=3Ω\mathrm{V}=4 \mathrm{kV}, \mathrm{X}=3 \OmegaV=4kV,X=3Ω , And R=1Ω\mathrm{R}=1 \OmegaR=1Ω

Essay

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Repeat Example 7 $\mathrm{V}=4 \mathrm{kV}, \mathrm{X}=3 \Omega$ , And $\mathrm{R}=1 \Omega$

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