MANAVKUMAR SAMJAYKUMAR BHAVSAR_ASSIGNMENT 1_CVG6320

1. The subscript d in the generator subtransient reactance refers to: 1. Generator impedance 2. If the available fault current slightly exceeds the breaker published 2. Generator 3. Direct axis 4. 1 and 2 reactance interrupting rating, then it is safe to use the breaker. 1. True | 2. False 3. Maybe 3. The rms symmetrical fault current times an asymmetry factor K, is equal to the ac fault current. | 2. False 4. The most common fault on a 3-phase power system is: 1. True 3. Maybe | 2. DLG 3. L-L 1. SLG 5. All rotating and non-rotating load impedances are usually included in a power system fault study 1. True 2. False 3. Мaybe

Please solve Q1(C) ONLY. Q1(A) is for reference.

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.

The sequence components of the fault current are as follows: Ipositive = j 2 p.u., Inegative = - j0.5 p.u. and Izero = -j 1.5 p.u. The type of fault in the system is 1. Three phase fault 4. Double line fault 2. Single line - to- ground fault 5. Three phase to ground fault 3. Double line to ground fault

3. The per unit values of positive, negative and zero sequence reactances of a network at fault are 0.08, 0.07 and 0.05 respectively. Determine the fault current if fault is line-to-line-to-ground. [j 16 p.u.]

If the source impedance at a 13.2 kV distribution substation bus is (0:5 + 1:5) Q per phase, compute the RMS and maximum peak instantaneous value of the fault current, for a balanced three-phase fault. For the system (X/R) ratio of 3.0, the asymmetrical factor is 1.9495 and the time of peak is 7.1 ms (see Problem 1). Comment on the withstanding peak current capability to which all substation electrical equipment need to be designed. Problem 1 Consider the expression for i(f) given by i(t) = v21ms [sin(@t-0-)+ sin 0,.eR/X)] where ez = tan-1 (WL/R). (a) For (X/R) equal to zero and infinity, plot i(f) as a function of (wf). (b) Comment on the DC offset of the fault current waveforms. (c) Find the asymmetrical current factor and the time of peak, tp, in milliseconds, for (X/R) ratios of zero and infinity.

Q.3 When a line-to-ground fault occurs, the current in faulted phase 'a' is 100A. The zero-sequence current in phase 'c' is r

Q2: A generator supplies motor through a star-delta transformer. The generator is connected to the star side of transformer. A fault occurs between the motor terminals and the transformer. The symmetrical components of the rubtransient current in motor and transformer toward the fault as table below laz(per unit) j2.0 lao(per unit) j3.0 las (per unit) Motof toward the fault Transformer toward the -0.8-j2.6 0.8-j0.4 j1.0 fault Assume X-X,- X2 for both the motor and gencrator. Describe the type of fault. Find (a) the prefault current, in line a, (b) the subtransient fault current in per unit and (c) the subtransient current in each phase of the gencrator in per unit. Gén. Motor