Power Systems T...

At a 220 kV substation of a power system, the 3-ϕ fault level is 4000 MVA, and single-line to ground fault level is 5000 MVA. Neglecting the resistance and the shunt susceptances of the system.

The positive sequence driving point reactance at the bus is _____ (in ohms)

Determine the fault current in a system following a double line to ground short circuit at the terminals of a star connected synchronous generator operating initially on an open circuit voltage of 1.0 pu. The positive, negative and zero sequence reactance of the generator are, respectively j 0.35, j 0.25 and j 0.20 and the star point is isolated from ground.

A 20 MVA, 6.6 kV generator with X^’’_d = 10%, X^’_d = 20% and X_d = 100% is connected through a circuit breaker to a transformer. It is operating on load when a short circuit occurs between breaker and transformer.

The sustained short circuit current through breaker is

A 50 Hz turbo generator is rated 50 MVA, 22 kV. It is Y-connected and solidly grounded and is operating at rated voltage at no load. It is disconnected from rest of the system. Its reactance are X^’’ = X₂ = 0.15 and X₀ = 0.05 pu.

Inductive reactance in ohms to be inserted in the neutral connection of the generator to limit the sub transient line current for a single line to ground fault to that of a 3-phase fault.

A 3 phase generator, an open circuit, is excited to give a voltage of 2200 V between lines. The absolute values of the fault currents for various type of faults are:

i) 3-phase fault: 127 A

ii) L-L fault: 129.5 A

iii) LG fault: 190 A

The zero-sequence reactance of the generator is _________ (in Ω).

A 100 MVA, 11 kV, 50 Hz turbo generator is having a symmetrical fault at its terminal. The short-circuit capacity is 500 MVA. The neutral of the alternator is grounded through a reactance of 0.05 pu. The zero-sequence reactance of the generator is 25% of its positive-sequence reactance and the negative sequence reactance is equal to the positive sequence reactance. The short-circuit capacity for a line to ground fault is _____ MVA