The following are the symmetrical components of phase B current: Positive Sequence Component = \(10\ \text{cis}\ 45^\circ\), Negative Sequence Component = \(20\ \text{cis}\ (-30^\circ)\), Zero Sequence Component = 0.5 + j0.9. Determine the positive sequence component of Phase A.
A\(20\ \text{cis}\ (-195^\circ)\)
B\(10\ \text{cis}\ 195^\circ\)
C\(10\ \text{cis}\ (-195^\circ)\)
D\(10\ \text{cis}\ (-30^\circ)\)
#42📜 EE Pre-Board August 2012📘 PowerhouseEasy
In an electric system the available short circuit MVA is 600 MVA. What is the Thevenin’s equivalent reactance at 34.5 kV?
A1.984 Ω
B1.587 Ω
C2.561 Ω
D0.046 Ω
#43📜 EE Pre-Board August 2012📘 PowerhouseEasy
A balanced delta connected load draws 100 A line current from a balanced 3 phase supply. Determine the zero sequence components of the currents.
A−50 − j86.6
B50 − j86.6
C0
D86.6 + j50
#44📜 EE Pre-Board August 2012📘 PowerhouseMedium
A 13.8 kV distribution line has a Thevenin’s equivalent impedance of 2.63%. If a phase to phase fault occurs between phase B and C, determine the fault current at 10 MVA base.
A13,000 A
B7,950 A
C5,300 A
D15,900 A
#45📜 EE Pre-Board August 2012📘 PowerhouseEasy
A 150 MVA, 13.8 kV, Y-connected, \(3\Phi\), 60 Hz alternator is operating at rated voltage and at no load when a three phase fault occurs at its terminals. If the subtransient reactance of the alternator is j0.2 pu, calculate the current at the instant the fault occurs.
A10,460 A
B18,117 A
C6,040 A
D31,380 A
#46📜 EE Pre-Board August 2012📘 PowerhouseEasy
This is the least prevalent shunt fault among transmission and distribution lines.
ALG
BLL
CLLG
DLLL
#47📜 EE Pre-Board August 2012📘 PowerhouseHard
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?
Aj0.6039 pu
Bj0.6667 pu
Cj0.8241 pu
Dj0.8663 pu
#48📜 EE Pre-Board March 2013📘 PowerhouseEasy
In an electric system the available short-circuit MVA is 600 MVA. What is the Thevenin’s equivalent reactance at 34.5 kV?
A1.14 ohms
B2.29 ohms
C1.98 ohms
D1.32 ohms
#49📜 EE Pre-Board March 2013📘 PowerhouseHard
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.
A\(100\angle -300^\circ\)
B\(100\angle 120^\circ\)
C\(100\angle -60^\circ\)
D\(300\angle 240^\circ\)
#50📜 EE Pre-Board March 2013📘 PowerhouseEasy
A generator rated 600 kVA, 2,400 V, 60 Hz, 3-phase, 6-poles and wye-connected has 10% synchronous reactance. If a three-phase fault occurs at its terminals, what will be the short-circuit current?
A1,428 A
B1,443 A
C1,532 A
D1,435 A
#51📜 EE Pre-Board March 2013📘 PowerhouseHard
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?
A\(13.4\ \text{cis}\ (-32.2^\circ)\)
B\(10.2\ \text{cis}\ 240^\circ\)
C\(12.27\ \text{cis}\ 208.4^\circ\)
D\(12.27\ \text{cis}\ (-31.6^\circ)\)
#52📜 EE Pre-Board March 2013📘 PowerhouseMedium
A 15 MVA, 34.5 kV / 6.24 kV transformer is connected at an infinite bus. The percent impedance of the transformer is 2.5%. What is the current at the 34.5 kV side for a three-phase fault at the 6.24 kV side?
A25,000 A
B5,000 A
C55,500 A
D10,000 A
#53📜 EE Pre-Board March 2013📘 PowerhouseMedium
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 ground fault.
A8.132 A
B7,516 A
C6,275 A
D2,091 A
#54📜 EE Pre-Board August 2013📘 PowerhouseEasy
When a line to ground faults occurs, the current in a faulted phase is 100 A. What is the zero sequence current in this case?
Azero
B33.3 A
C66.6 A
D100 A
#55📜 EE Pre-Board August 2013📘 PowerhouseEasy
The positive, negative and zero sequence reactances of a 20-MVA, 13.2 kV synchronous generator are 0.3 pu, 0.2 pu and 0.1 pu, respectively. The generator is solidly grounded and is not loaded. A line to ground fault occurs on phase a. Neglecting all resistances, determine \(I_{a1}\).
A−j5 pu
B−j1.67 pu
C−j2.87 pu
D−j3 pu
#56📜 EE Pre-Board August 2013📘 PowerhouseMedium
The per unit reactances of a synchronous generator are \(X_d = 1\), \(X_d' = 0.35\) and \(X_d'' = 0.25\). The generator supplies a 1.0 per unit load at 0.8 power factor lagging. Calculate the voltage behind the subtransient reactance.
A1.79 pu
B1.24 pu
C1.17 pu
D1.59 pu
#57📜 EE Pre-Board August 2013📘 PowerhouseMedium
Three unbalanced 3-phase currents are given as follows: \(I_a = 10\angle -30^\circ\) A, \(I_b = 0\) and \(I_c = 10\angle -150^\circ\) A. Find \(I_{c1}\).
A\(3.34\angle 150^\circ\) A
B\(3.34\angle -150^\circ\) A
C\(3.34\angle 210^\circ\) A
D\(3.34\angle -135^\circ\) A
#58📜 EE Pre-Board August 2013📘 PowerhouseEasy
A generator rated 600 KVA, 2,400 v, 60 HZ , 3-phase, 6-poles and wye- connected has 10% synchronous reactance. If a three-phase fault occurs, what will be the short circuit current?
A1,443 A
B1,532 A
C1,435 A
D1,426 A
#59📜 EE Pre-Board August 2013📘 PowerhouseHard
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.
A\(300\angle 120^\circ\)
B\(300\angle -60^\circ\)
C\(300\angle 240^\circ\)
D\(100\angle -30^\circ\)
#60📜 EE Pre-Board August 2013📘 PowerhouseEasy
The per unit impedance of a circuit element is 0.30. If the base KV and base MVA are halved, then the new value of the per unit impedance of the circuit element will be,
