A star connected 3-phase 10 MVA, 6.6 kV alternator is protected by circulating current protection, the star point being earthed via a resistance r. Estimate the value of earthing resistance if 85 % of stator winding is protected against earth faults. Assume an earth fault setting of 20 %. Neglect the impedance of the alternator winding

A star connected 3-phase 10 MVA, 6.6 kV alternator is protected by circulating current protection, the star point being earthed via a resistance r. Estimate the value of earthing resistance if 85 % of stator winding is protected against earth faults. Assume an earth fault setting of 20 %. Neglect the impedance of the alternator winding

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

Chapter3: Power Transformers

Section: Chapter Questions

Problem 3.26MCQ: In per-unit equivalent circuits of practical three-phase transformers, under balanced thr-phase...

See similar textbooks

Similar questions

Three single-phase two-winding transformers, each rated 3kVA,220/110volts,60Hz, with a 0.10 per-unit leakage reactance, are connected as a three-phase extended autotransformer bank, as shown in Figure 3.36(c). The low-voltage winding has a 110 volt rating. (a) Draw the positive-sequence phasor diagram and show that the high-voltage winding has a 479.5 volt rating. (b) A three-phase load connected to the low-voltage terminals absorbs 6 kW at 110 volts and at 0.8 power factor lagging. Draw the per-unit impedance diagram and calculate the voltage and current at the high-voltage terminals. Assume positive-sequence operation.
Three single-phase, two-winding transformers, each rated 450MVA,20kV/288.7kV, with leakage reactance Xeq=0.10perunit, are connected to form a three-phase bank. The high-voltage windings are connected in Y with a solidly grounded neutral. Draw the per-unit equivalent circuit if the low-voltage windings are connected (a) in with American standard phase shift or (b) in Y with an open neutral. Use the transformer ratings as base quantities. Winding resistances and exciting current are neglected.
The direct electrical connection of the windings allows transient over voltages to pass through the auto transfonner more easily, and that is an important disadvantage of the autotransformer. (a) True (b) False
In per-unit equivalent circuits of practical three-phase transformers, under balanced thr-phase operation, in which of the following connect ions would a phase-shifting transformer come up? (a) Y-Y (b) Y- (c) -
Determine the positive- and negative-sequence phase shifts for the three- phase transformers shown in Figure 3.36.
What are the conditions for the parallel operation of 1-phase transformers?
2- Draw and explain the phasor diagram for two transformers in parallel.
Consider the three single-phase two-winding transformers shown in Figure. 3. The high-voltage windings are connected in Y. (a) For the low-voltage side, connect the windings in A, and label the terminals a, b, and c in accordance with the American standard. (b) Relabel the terminals a', b', and c' such that VAN is 90° out of phase with V₂'b' for positive sequence. DI H₂ Figure. 3: Three-Winding Transformer
A three phase star connected, 1500 kVA, 13 kV alternator has an armature resistance of 0.9 ohm and a synchronous reactance of 8.0 ohms. When carrying rated load voltage, calculate the generated voltage per phase at loads of a. Unity P.F. b. 0.8 lagging P.F. c. 0.8 leading P.F. d. Calculate the voltage regulation for each loads and determine best regulation.
i need the answer quickly
Two identical three-phase Alternators A and B share equally a load of 10 MVA at 33 KV and 80% lagging power factor. The synchronous reactance of each generator is 4 ohms per phase and the armature resistance is negligible. Alternator A has its field excitation adjusted to carry a25 amperes at lagging power factor. What is the current delivered by Alternator B ?
Connect three single-phase transformers in Y-Y, with subtractive polarity, so that the line-to-line voltages on the primary are 30 degrees delayed to their respective line-to-line voltages on the secondary. It should show each step that is needed to make this connection (example: the phasor diagram) and should show the final connection of the three transformers including the polarity markings. Assume phase A on the primary is terminal "H1".