ort-circuit occurs at its terminals. The fault MVA and fault

Does an open- operation, the kVA rating compared to that of the original thr-phase bank is (a) 2/3 (b) 58 (c) 1

Draw three transformers for each of the different three-phase connections. That is, draw three transformers and then make the connection, eg star-star, then redraw three transformers and make another three-phase connection, and so on until all four combinations of three-phase connections are made.

(iv) none of above 64. A 50 Hz, 11 kV, 3-phase alternator with earthed neutral has a reactance of 5 ohms per phase and is connected to a bus-bar through a circuit breaker. The distributed capacitance upto circuit breaker between phase and neutral is 0.01 µF. The peak re- striking voltage across the contacts of the breaker is

2) 9.2Three - 25 KVA single-phase transformers are connected in delta – delta. One of the transformers has been defected. What is the maximum real power that the transformer bank can deliver at a power factor of 0.8?

A 110 MVA, 13.8 kV, three phase alternator will have a per phase nominal impedance of

A generator supplies a motor through a Y-A transformer. The generator is connected to Y side of the transformer. A fault occurs between the motor terminals and the transformer. The symmetrical components of the subtransient current in the motor flowing toward the fault are: I =-0.8- j2.6pu I =-j2.0pu I =-j3pu From the transformer toward the Fault: I = 0.8– j0.4pu I? =-j1.0pu 1 = Opu Assume X =X,=X, for both the motor and the generator. (a) Describe the fault type and find the prefault current, if any, in line a. (b) Determine the subtransient fault current in per unit. (c) Calculate the subtransient current in each phase of the generator in per unit taking into consideration the phase shift of the Y-A transformer.

In order to avoid difficulties with third-harmonic exciting current, which three-phase transformer connection is seldom used for step-up transformers between a generator and a transmission line in power systems. (a) Y- (b) -Y (c) Y-Y

Even though the fault current is not symmetrical and not strictly periodic, the rms asymmetrical fault current is computed as the rms ac fault current times an asymmetry factor, which is a function of _______.

Tutorial 1.7 The three-phase ratings of a three-winding transformer are: Primary Y-connected, 66 kV, 24 MVA Y-connected, 13.2 kV, 12 MVA Secondary Tertiary A-connected, 2.3 kV, 4 MVA Neglecting resistance, the leakage impedances are: Zps Zns = 6% on 24 MVA, 66 kV base Zpt = 8% on 24 MVA, 66 kV base Zst = 7% on 12 MVA, 13.2 kV base Find the per-unit impedances of the per-phase equivalent circuit for a base of 24 MVA, 66 kV in the primary circuit. {Ans: j 0.0; j 0.06; j 0.08}