Faults

Determine the symmetrical components of the line current in line 'a' if one of the in phase impedance of its delta-connected load connected across lines 'ca' is removed. The delta load with impedance of \(10 \angle 0^\circ\) ohms per phase is supplied from a 220 volts, 60 cycle, 3-phase. Assume a phase sequence of a-b-c.

A star-connected balanced load takes 75 A from a balanced 3-phase, 4-wire supply. If the two supply lines of the fuses are removed determine the symmetrical components of the line currents after the fuses are removed.

A 20 MVA, 13.8 kV, 60 Hz, three-phase synchronous turbo alternator has a positive, negative and zero sequence reactances of 0.25, 0.35 and 0.15 respectively. If lines b and c are short-circuited, determine the subtransient fault current in line b. Assume the alternator is operating at no load and at rated voltage with the neutral of the alternator solidly grounded.

Two 3-phase transformers are connected in parallel at the primary as well as at the secondary sides. One is rated 10 MVA, 34.5/13.8 kV and 4% impedance while the other is rated 7.5 MVA, 34.5/13.8 kV and 5% impedance. The primary tapping point has a 3-phase short circuit MVA of 1000 MVA. Determine the fault current delivered to a 3-phase fault at the secondary side bus bars.

A generator is rated 100 MVA, 15 kV, it is Y-connected, solid grounded and is operated at rated voltage at no-load and is disconnected from the rest of the system. Its positive and negative sequence reactances are each 0.10 p.u. and its zero sequence reactance is 0.05 p.u. Calculate in ohms of inductive reactance to be inserted in the neutral connection of the generator to limit the fault current for a single line to ground fault to the fault current of a symmetrical three-phase fault.

In a short circuit analysis, the positive, negative and zero sequence impedances are 0.20 pu, 0.20 pu and 0.25 pu, respectively, using a base MVA of 50. Estimate the fault current on the faulted lines if a double line to ground fault at the 138 kV level occurs.

A 15 MVA, 6,600 V, 60 Hz, Y-connected synchronous alternator has a positive, negative and zero sequence per unit reactance of 0.20, 0.20 and 0.10 respectively. The neutral of the generator is grounded through a reactor with a per unit reactance of 0.05 based on the generator rating. If a double line to ground fault occurs at the alternator terminals, estimate the current that flows in the reactor.

The secondary side of 5 MVA, 34.5/13.8 kV, 3-phase transformer is connected to a bus bar served by a 20 MVA, 13.8 kV, 3-phase alternator. The primary side of the transformer is tapped from an infinite bus. Estimate the fault current delivered to a 3-phase fault near the common bus bar. The transformer and alternator have 4% and 7.5% reactance, respectively.

Given the one line diagram as shown, determine the current delivered by generator A when a three-phase fault occurs at point P.

Given the one-line diagram as shown, determine the reactance of the limiting reactor x in order to limit the three-phase symmetrical fault power at point P to 400 MVA.

A generator of 50 MVA, 4 kV, \(X_d'' = 25\%\) and a transformer of 50 MVA, 4.2 kV delta/115 kV wye grounded, operating on the 3.8 kV tap, where \(X_T = 10\%\), are to be connected into a single equivalent reactance. What is the single equivalent reactance on a 100 MVA, 110 kV base?

In a 3-phase, 4-wire system, the current in line a has \(I_{a1} = 220\angle 0^\circ\) A and \(I_{a2} = 100\angle 60^\circ\) A. The current through the neutral conductor is \(300\angle -60^\circ\) A. Find the line current \(I_b\) in amperes.

If the loads of a wye-connected transformer are \(I_a = 10\ \text{cis}\ (-30^\circ)\), \(I_b = 12\ \text{cis}\ 215^\circ\) and \(I_c = 15\ \text{cis}\ 82^\circ\), what is the phase b positive sequence component?

In a 3-phase, 4-wire system, the current in line a has \(I_{a1} = 200\angle 0^\circ\) A and \(I_{a2} = 100\angle 60^\circ\) A. The current through the neutral conductor is \(300\angle -60^\circ\) A. Find the line current \(I_b\) in amperes.

The sequence components of the line A current are as follows: \(I_{a0} = 14.13\angle 17.34^\circ\) A, \(I_{a1} = 708.26\angle -31^\circ\) A and \(I_{a2} = 2.98\angle 10.06^\circ\) A. Find the line current \(I_b\) in amperes.

A synchronous generator having a subtransient reactance of 0.15 pu and operating at 5 percent above its rated voltage supplies a synchronous motor having a 0.2 pu subtransient reactance. The motor is connected to the generator by a transmission line and a transformer of total reactance 0.305 pu. A sudden three-phase short circuit occurs at the generator terminals. Determine the per unit subtransient fault current.

A synchronous generator having a subtransient reactance of 0.15 pu and operating at 5 percent above its rated voltage supplies a synchronous motor having a 0.20 pu subtransient reactance. The motor is connected to the generator by a transmission line and a transformer of total reactance 0.305 pu. A sudden three-phase fault occurs at the generator terminals. Determine the per unit subtransient fault current.

The sequence components of the phase c current of a 3-phase system are as follows: \(I_{c0} = 0\), \(I_{c1} = 18.4\angle 88.4^\circ\), \(I_{c2} = 3.23\angle 48.2^\circ\). Find the phase b current in amperes.