MGVCL Exam Paper (30-07-2021 Shift 2)
Interposing current-transformer (CT) is used in differential protection of a transformer to

minimize the effect of saturation of the main CTs
limit the main CT secondary current
increase the sensitivity of the relay
match the standard ratio of CTs used on both sides of the transformer winding

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MGVCL Exam Paper (30-07-2021 Shift 2)
In the circuit of figure, the switch is closed to position-1 for a long time. At t = 0 the switch position is changed from postion-1 to postion-2. Find an expression for the current i(t).

i(t) = (E/R) cos√(LC) t A
i(t) = (E/R) cos[1/√(LC)]t A
i(t) = (E/R) sin√(LC) t A
i(t) = (E/R) sin[1/√(LC)]t A

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MGVCL Exam Paper (30-07-2021 Shift 2)
The line currents in amperes in phases a, b and c respectively are 500 +j150, 100 – j600 and – 300 + j600 referred to the same reference vector with phase sequence of abc. Find the symmetrical component of currents.

Ia₀ = (100+j50) AIa₁ = (146.41+ j65.47) AIa₂ = (546.41-j165.47) A
Ia₀ = (100+j50) AIa₁ = (546.41+j165.47) AIa₂ = (-146.41-j65.47) A
Ia₀ = (100+j50) AIa₁ = (200+ j107.75) AIa₂ = (200-j107.75) A
Ia₀ = (100+j50) AIa₁ = (546.41+ j165.47) AIa₂ = (546.41-j165.47) A

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MGVCL Exam Paper (30-07-2021 Shift 2)
A generating station having 'n' section busbars each rated at Q kVA with ×% reactance is connected on the tie-bars systems through busbar reactances of b%. Determine the short circuit kVA if a 3-phase fault takes place on one section.

Q[(1/x) - (n+1)/(bn-x)]
Q[(1/x) + (n+1)/(bn-x)]
Q[(1/x) + (n-1)/(bn+x)]
Q[(1/x) + (n+1)/(bn+x)]

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