Faults

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

Given three unbalanced three-phase voltages:
\(V_a = 150 + j0\text{ V}\)
\(V_b = -90 - j120\text{ V}\)
\(V_c = -120 + j90\text{ V}\)
Determine \(V_{a1}\).

The three-phase unbalanced currents are:
\(I_a = 10\text{ cis }(-30^\circ)\)
\(I_b = 0\)
\(I_c = 10\text{ cis }150^\circ\)
Find the negative sequence current of phase a.

Given the following currents:
\(I_a = 60 + j0\text{ A}\)
\(I_b = -36 - j48\text{ A}\)
\(I_c = -48 + j36\text{ A}\)
Solve for the negative sequence component of \(I_a\).

The three-phase unbalance currents are:
\(I_a = 10\text{ cis }(-30^\circ)\)
\(I_b = 0\)
\(I_c = 10\text{ cis }150^\circ\)
Find the zero sequence current.

The sequence currents of phase a current are as follows:
Zero sequence current = \(14.13 \angle 17.34^\circ\)
Positive sequence current = \(2.98 \angle 10.06^\circ\)
Negative sequence current = \(708.26 \angle -31^\circ\)
Determine phase a current.

The sequence components of phase a current are:
Zero sequence component = \(0.47 + j1.49\)
Positive sequence component = \(18.4\text{ cis }(-31.6^\circ)\)
Negative sequence component = \(3.23\text{ cis }168.2^\circ\)
Determine the phase b current.

The sequence components of phase a current are:
Zero sequence = \(0.47 + j1.49\)
Positive sequence = \(18.4\text{ cis }(-31.6^\circ)\)
Negative sequence = \(3.23\text{ cis }168.2^\circ\)
Determine the phase c current.

A 5 kVA, 2400-120/240 volt distribution transformer when given a short circuit test had 94.2 volts applied with rated current flowing in the short-circuited wiring. What is the per unit impedance of the transformer?

A 3-phase, 375 kVA, 480 V, 50 Hz, wye connected alternator has an equal positive and negative sequence reactance of 10%. Find the symmetrical fault current, if a 3-phase fault occurs at the alternator terminals.

A generator rated 600 kVA, 2400 V, 60 cycles, 3-phase, 6-poles and wye-connected has 10% synchronous reactance. If a three-phase fault occurs, what will be the short circuit current?

At a certain location in an electric system, the available fault MVA is 400 MVA. A 15 MVA, 34.5 kV/6.24 kV, 2.5% impedance, wye-wye grounded transformer is installed at that location. Determine the short circuit MVA at the secondary side of the transformer.

A 100 MVA, 22 kV synchronous turbo generator has positive and negative reactances of 0.20 p.u. and a zero sequence reactance of 0.05 p.u. The neutral of the generator is grounded through a reactor of 0.242 ohm. Determine the ratio of the subtransient current for a single line to ground fault to the subtransient current for a three-phase fault. Assume the generator is operated without a load and at rated voltage.

The reactance of a three-phase alternator is 8 percent. If the alternator is rated 25 MVA at 13.25 kV output voltage, line to phase, solve for the magnitude of the fault current generated when a short circuit occurs between 2 phases at the terminals.

A 3-phase, 375 kVA, 480 V 50 Hz, wye connected alternator has an equal positive and negative sequence reactance of 10%. Find the unsymmetrical fault current, if a 2-phase fault (line to line) occurs at the alternator terminals.

A 5 MVA, 13.8 kV / 480 V, 5% impedance transformer is tapped at 13.8 kV line where the Thevenin's equivalent impedance is 1/2 ohm. Determine the fault current at the primary for a three-phase fault at the secondary.

At a certain point of the system network the positive, negative and zero sequence impedances are 0.25 p.u., 0.25 p.u. and 0.3 p.u. respectively. The base MVA is 100. The voltage level at that point is 34.5 kV. Determine the zero sequence current for a one line to ground fault.

In a short circuit study, the positive, negative and zero sequence impedance are 0.25 pu and 0.25 pu and 0.3 pu, respectively. The base MVA is 100. Determine the fault current for a three-phase fault at the 115 kV level.

A 3-phase 220-V Y-connected alternator has a synchronous impedance of \(0.15 + j2\) ohms per phase. The alternator is connected through a short transmission line whose impedance per wire is \(2 + j1\) ohms to a Y-Y connected transformer bank whose total equivalent impedance referred to the secondary (high side) is \(50 + j86.6\) ohms. A three-phase load is connected from the secondary side of the bank through a transmission line whose impedance is \(50 + j75\) ohms per wire. If a symmetrical three-phase fault occurs at the load side, how much is the current will flow to the alternator windings. Assume the bank has a transformation ratio of 1:10.

Three single-phase transformers each rated 50 kVA, 2400 volts primary 277 volts secondary, four (4) percent impedance have their primaries connected in delta and their secondaries in wye. Calculate the fault current drawn if a short circuit occurs between two phases at the secondary terminals.