GATE EE 2014 Set 1 — Question 26
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Power Systems → Fault Analysis → Symmetrical Components
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Question
A 2-bus system and corresponding zero sequence network are shown in the figure.
The transformers and are connected as
Correct answer
(B) [figure]
Solution
Reading the zero-sequence network (b).
- : hangs off the bus-1 side, and there is an open circuit (the pair of dots) between and the line (). has no connection to the reference bus.
- : connects the line to the reference bus, and there is an open circuit between that point and bus 2 ().
- – (one star grounded, the other ungrounded): the ungrounded star gives zero-sequence current no return path, so none flows in either winding. Model: attached to the grounded-star side, open towards the ungrounded side, and no link to the reference bus. This matches , with the grounded star on bus 1 and the ungrounded star on the line.
- –: zero-sequence current can flow in the grounded star because it circulates inside the delta. Model: the star side sees to the reference bus, and the delta side is open. This matches , with the grounded star on the line side and the delta on bus 2.
- (A): every star is ungrounded, so could not give the line a path to the reference bus.
- (C): as – would put a shunt from bus 1 to the reference through ; the network has no such shunt.
- (D): as – would put a shunt from the line to the reference at ; again, none is shown.
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