GATE 2014 EE (EE1) – Question 49
A synchronous generator is synchronized to an infinite bus with lamps connected as shown. Bus phase sequence is R–Y–B, and generator terminals are R′–Y′–B′. Lamps become dark sequentially L_a,L_b,L_c. The incoming generator’s phase sequence and frequency are ______.
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Correct answer: (A) opposite sequence, higher frequency
Explanation
Each lamp connects corresponding bus and generator terminals. Equal phase sequences would make all three voltage differences vary together, so sequential darkness indicates opposite phase sequence. For the reversed sequence, increasing relative generator angle makes the dark conditions occur at0°,120°,240°for La,Lb,Lc. Thus the incoming frequency is higher and phase sequence opposite: **A**.