Chapter 7: Q9MCQ (page 463)
Can superposition be applied in power-system short-circuit studies for calculating fault currents?
(a) Yes
(b) No
Therefore, the correct option is (a) Yes.
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As shown in Figure 7.21, a, synchronous generator with is connected through a transformer to a bus that supplies four identical motors. The rating of the three-phase transformer is with a leakage reactance of. Each motor has a sub-transient reactance on a base of .A three-phase fault occurs at point P, when the bus voltage at the motors is.
(a) the sub-transient fault current,
(b) the sub-transient current through breaker A, and
(c) the symmetrical short-circuit interrupting current (as defined for circuit breaker applications) in the fault and in breaker A.
Before proceeding with per-unit fault current calculations, based on the single-line diagram of the power system, a positive-sequence equivalent circuit is set up on a chosen base system.
(a) True
(b) False
Even though the fault current is not symmetrical and not strictly periodic, the rms asymmetrical fault current is computed as the rms ac fault current times an “asymmetry factor,” which is a function of _____.
The amplitude of the sinusoidal symmetrical ac component of the three-phase short-circuit current of an unloaded synchronous machine decreases from a high initial value to a lower steady-state value, going through the stages of _____ and _____ periods.
Besides a blast of air/gas, the arc in a circuit breaker can be elongated by _____.
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