A generator-transformer unit is connected to a line through a circuit breaker. The unit ratings are: Generator: 10 MVA, 6.6 kV; , and Transformer: 10MVA, 6.9133kV, reactance0.08pu The system is operating no load at a line voltage of 30 kV, when a three phase fault occurs on the line just beyond the circuit breaker' Find (a) the initial symmetrical rms current in the breaker’(b) The maximum possible DC off-set current in the breaker, (c) The momentary current rating of the breaker

A generator-transformer unit is connected to a line through a circuit breaker. The unit ratings are: Generator: 10 MVA, 6.6 kV; , and Transformer: 10MVA, 6.9133kV, reactance0.08pu The system is operating no load at a line voltage of 30 kV, when a three phase fault occurs on the line just beyond the circuit breaker' Find (a) the initial symmetrical rms current in the breaker’(b) The maximum possible DC off-set current in the breaker, (c) The momentary current rating of the breaker

Power System Analysis and Design (MindTap Course List)

6th Edition

ISBN:9781305632134

Author:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Publisher:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Chapter9: Unsymmetrical Faults

Section: Chapter Questions

Problem 9.4MCQ

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For the circuit shown, if a symmetrical three-phase fault occurs in node 2, determinea. The short-circuit current in all three phases. b. The voltage at node 1 during the fault.c. The current in generator 1 during the fault. Neglect the prefault currents and consider the reference voltage of the system at 10√3 ??.
Problem #2: A transformer is fed from a 100 MVA, 18 kV generator via a 5-cycle breaker. Generator reactance are: X"F18%, X'=25%, Xe=120%. A three-phase fault occurs at the load side of the breaker when the transformer was unloaded. Find: A)The sustained short circuit current in the breaker. B) Initial symmetrical rms current in the breaker. C) Maximum de short circuit component in the breaker.
Problem #2: A transformer is fed from a generator via a 5-cycle breaker. Generator reactance are: X"=18%, X'=25%, Xe=120%. A three-phase fault occurs at the load side of the breaker when the transformer was unloaded. Find: A)The sustained short circuit current in the breaker. B) Initial symmetrical rms current in the breaker. C) Maximum dc short circuit component in the breaker.
Q5: A generator is connected through a transformer to a synchronous motor. Reduced to the same base, the per unit subtransient reactances of the generator and motor are 0.15 and 0.35, respectively, and the leakage reactance of the transformer is 0.1 per uint. A three-phase fault occurs at the terminals of the motor when the terminal voltage of the generator is 0.9 per uint and the output current of the generator is 1 per unit at 0.8 power factor leading. Find the subtransient current in per unit in the fault, in the generator, and in the motor. Use the terminal voltage of the generator as the reference phasor and obtain the solution (a) by using the internal voltages of the machines and (b) by using Thevenin's theorem.
estion 9 The fault current level of a circuit breaker used in a transmission line with phase voltage 2.2 kV and breaking capacity 50 MVA is yet ......kA. vered -ked out of Flag question estion 10 The voltage between lines in a transmission line is the maximum value of the sine waveform. yet vered Select one: -ked out of O True Flag question O False
b) A fault occurs at bus 4 of the network shown in Figure Q3. Pre-fault nodal voltages throughout the network are of 1 p.u. and the impedance of the electric arc is neglected. Sequence impedance parameters of the generator, transmission lines, and transformer are given in Figure Q3, where X and Y are the last two digits of your student number. jX(1) j0.1Y p.u. jX2)= j0.1Y p.u. jXko) = j0.1X p.u. V₁ = 120° p.u. V₂ = 120° p.u. (i) (ii) 0 jX(1) = j0.2 p.u. 1 jx(2) j0.2 p.u. 2 jX1(0) = j0.25 p.u. jXT(1) jXT(2) 종 3 j0.1X p.u. JX3(1) j0.1Y p.u. j0.1X p.u. JX3(2) j0.1Y p.u. jXT(0) j0.1X p.u. JX3(0)=j0.15 p.u. 0 = x = 1, jX2(1) j0.2Y p.u. V₁=1/0° p.u. jX(2(2) = j0.2Y p.u. jX2(0) = j0.3X p.u. = V3 = 120° p.u. Figure Q3. Circuit for problem 3b). For example, if your student number is c1700123, then: y = 7 = = jXa(r) = j0.13 p.u., jXa(z) = j0.13 p. u., and jXa(o) = j0.12 p. u. Assuming a balanced excitation, draw the positive, negative and zero sequence Thévenin equivalent circuits as seen from…
b) A fault occurs at bus 2 of the network shown in Figure Q3. Pre-fault nodal voltages throughout the network are of 1 p.u. and the impedance of the electric arc is neglected. Sequence impedance parameters of the generator, transmission lines, and transformer are given in Figure Q3, where X and Y are the last two digits of your student number. JX20 /0.1X p.u. jXa2) 0.1X p.u. JX20 j0.2Y p.u. V,= 120° p.u. V, 120° p.u. V, 120° p.u. jX4-70.2X p.u. jX2 j0.2X p.u. jX o 0.2Y p.u. jXncay J0.25 p.u. jXna J0.25 p.u. 3 jXno0.3 p.u. jXTu) /0.2Y p.u. jXra j0.2Y p.u. - j0.2Y p.u. Xp-10.1X p.u. jXa j0.1X p.u. jXp0)- j0.05 p.u. 0 Figure Q3. Circuit for problem 3b). For example, if your student number is c1700123, then: jXac1) = j0.22 p.u., jXac2) = j0.22 p.u., and jXaco) = j0.23 p. u. X-2 Y=8 (iv) Determine the short-circuit fault current for the case when a phase-to- phase fault occurs at bus 2.
Data obtained from a short circuit test on a 132 kV 3-phase circuit breaker with earthed neutral are as follows: -the power factor fault was 0.3. -the recovery voltage was 0.75 of the full line value. -the breaking current was symmetrical. -the restriking transient had a natural frequency of 1600 Hz. Estimate the rate rise of the recovery voltage. Assume that the fault is grounded.
Q2. The single-line diagram of a simple three-bus power system is shown in Figure-2. Each generator is represented by an emf behind the sub-transient reactance. All impedances are expressed in per unit on a common MVA base. All resistances and shunt capacitances are neglected. The generators are operating on no load at their rated voltage with their emfs in phase. A three-phase fault occurs at bus 3 through a fault impedance of Zf = j0.19 per unit. (i) Using Th'evenin's theorem, obtain the impedance to the point of fault and the fault current in (ii) Determine the bus voltages per unit. ) j0.05 j0.075 j0.75 2 j0.30 j0.45 Figure-2: Single line diagram of the power system network for Q2 3
Fill in the blanks 1. Grounding is connecting …….. of electrical equipment to earth. 2. When a …………………………….… fault occurs on an ungrounded neutral system, the potential of the healthy phases rise to the line voltage. 3. The method of reactance grounding is not used because of ……………………… appearing under fault conditions. 4. The cosine of the angle between the ………………………………………. and the ………………………………...…… is called the sending end power factor. 5. The AC power delivered to a load is equal to ………........
6. A 3 phase fault occurs at point F as shown in figure. Determine the critical clearing anglefor the system. The generator is delivering 1.0 p.u power under prefault conditio
A 15,000 KVA, 6.9 KV generator, star connected has positive, negative and zero sequence reactances of 0.25, 0.25 and 0.08 p.u. respectively. A reactor of 0.06 p.u. reactance on the generator rating is placed in the line from neutral to ground: A double line to ground fault occurs at the terminals of the generator when it is operating at its rated voltage and unloaded. Find the unitial r.m.s. line and ground wire current for a solidly grounded fault, and also the voltage to ground of the unfaulted line. (UPSC-1975) Ans: 1-1,-4970 A; I, 5480 A; V. 69.7 KV