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.
A13,501 A
B10,452 A
C12,532 A
D11,953 A
#22
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.
A1.50
B1.25
C1.00
D0.80
#23📜 EE Board October 1992
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.
A0.0233 \(\Omega\)
B0.0225 \(\Omega\)
C0.0376 \(\Omega\)
D0.0325 \(\Omega\)
#24📜 EE Board October 1982
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.
A6704 A
B6135 A
C6808 A
D6458 A
#25
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.
A3890 A
B3906 A
C4510 A
D4180 A
#26📜 EE Board March 1998
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.
A10,500 A
B3,300 A
C4,200 A
D6,050 A
#27📜 EE Board October 1980
A 10 kVA, 110 V, 3-phase, 4-wire, 60 Hz alternator generates 70 volts per phase when excited to give rated voltage at full load. The armature synchronous impedance per phase is 0.2 ohm. What is the current in each phase if the generator terminals are short-circuited?
A350 A
B875 A
C620 A
D534 A
#28📜 EE Board October 1998
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.
A6275 A
B8132 A
C7516 A
D2091 A
#29
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.
A1204 A
B1011 A
C1090 A
D1104 A
#30
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.
A5920 A
B5623 A
C6125 A
D6342 A
#31📜 EE Board March 1998
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.
A3000 A
B2000 A
C2500 A
D3500 A
#32
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.
A22.73 A
B23.66 A
C21.54 A
D24.15 A
#33📜 EE Board April 1984
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.
A2260 A
B2585 A
C2036 A
D2256 A
#34📜 EE Board October 1986
emergency 3-phase generator, 3-wire GM generator is rated 350 kVA, 460 volts, 60 Hz, with a reactance of 8%. Solve for the symmetrical 3-phase short circuit.
A5,321 A
B5,703 A
C5,284 A
D5,491 A
#35📜 EE Board October 1997
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 short at the 6.24 kV side?
A55,500 A
B10,000 A
C5,000 A
D25,000 A
#36📜 EE Board April 1985
A three-phase, 3-wire generator is rated 325 kVA, 480 volts, 60 Hz with a reactance of eight (8) percent. Solve for the fault current delivered by the generator during a 2-phase short circuit at the terminals.
A4232 A
B4462 A
C4012 A
D4156 A
#37
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.
A12,760 A
B18,900 A
C15,340 A
D16,400 A
#38
Determine the minimum rupturing capacity of the circuit breaker as shown, if a three-phase symmetrical fault occurs at point P.
A30 MVA
B20 MVA
C10 MVA
D15 MVA
#39
Given the one line diagram as shown, determine the current delivered by generator A when a three-phase fault occurs at point P.
A172.5 A
B167.1 A
C145.5 A
D198.4 A
#40
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.
