MGVCL Exam Paper (30-07-2021 Shift 1)
A transformer designed for operation at 60 Hz supply is working at 50 Hz supply system without changing its voltage and current ratings. Compared to the full load efficiency at 60 Hz, the full load transformer efficiency at 50 Hz.

increases marginally
remains unaltered
decreases marginally
increases by 30%

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MGVCL Exam Paper (30-07-2021 Shift 1)
Determine maximum permissible load which a 15 MVA, ONAN cooled transformer to IS : 2026 can take for 6 hr, if the initial load on it was 12 MVA. The weighted ambient temperature is 20˚C. Assume the permissible load kVA as a fraction of rated kVA is 1.25.

12 MVA
18.75 MVA
15 MVA
9.6 MVA

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MGVCL Exam Paper (30-07-2021 Shift 1)
In underground cables, the electrostatic stress is ___ at contactor surface and ___ at the sheath.

zero, minimum
minimum, maximum
zero, zero
minimum, maximum

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MGVCL Exam Paper (30-07-2021 Shift 1)
___ is the rms value of the total current comprising the AC and DC components of the current in the circuit breaker pole at the instant of contact separation.

Symmetrical breaking current
Asymmetrical breaking current
Symmetrical short circuit current
Making current

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MGVCL Exam Paper (30-07-2021 Shift 1)
Determine the ohmic value of the current limiting reactor per phase external to a 30 MVA, 11 kV, 50 Hz, three phase synchronous generator which can limit the current on short circuit of 5 times the full load current. The reactance of the synchronous generator is 0.05 pu.

0.805 Ω
0.605 Ω
0.305 Ω
0.405 Ω

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