Chapter 7: Q18MCQ (page 464)
Besides a blast of air/gas, the arc in a circuit breaker can be elongated by _____.
The arc in the circuit breaker can also be elongated by a magnetic force.
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Can superposition be applied in power-system short-circuit studies for calculating fault currents?
(a) Yes
(b) No
Oil can be used as a medium to extinguish the arc in circuit breakers.
(a) True
(b) False
The reactance that plays a role under steady-state operation of a synchronous machine is called _____.
A typical fusible link metal in fuses is _____, and a typical filler material is _____.
A 1000 MVA,20 kV, 60 Hz , three-phase generator is connected through a 1000 MVA, 20 kV,, Y transformer to a 345 kV circuit breaker and a 345 kV transmission line. The generator reactances are per unit, and its time constants are . The transformer series reactance is 0.1per 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 three cycles after fault inception. Determine (a) the sub transient 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.
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