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MGVCL Exam Paper (30-07-2021 Shift 1)
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The necessary equation to be solved during the load flow analysis using Fast-Decoupled methid is given below:

where B' and B'' are formed using the imaginary part of the bus admittance matrix Ybus, n is the total number of buses in the system, m is the number of voltage regulated buses. The size of matrix B' is

∆P/|Vi|= -B' ∆δ

∆Q/|Vi| = -B'' ∆|Vi|

where B' and B'' are formed using the imaginary part of the bus admittance matrix Ybus, n is the total number of buses in the system, m is the number of voltage regulated buses. The size of matrix B' is

∆P/|Vi|= -B' ∆δ

∆Q/|Vi| = -B'' ∆|Vi|

In FDLF method,

B' corresponds to susceptance of unknown of PQ and PV bus

Order of B' matrix is = (n -1)*(n - 1)

Where n is total no. of buses.

Order of B'' = (n - m - 1)*(n - m - 1)

MGVCL Exam Paper (30-07-2021 Shift 1)
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Insulation Power Factor testing on an oil-filled transformer is not helpful in determining ___

A form of AC testing that applies voltage and measures the leakage/loss current of electrical insulation.

It is a type of insulation testing used to evaluate the integrity of electrical insulation.

MGVCL Exam Paper (30-07-2021 Shift 1)
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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.

The ratio of full load current to short circuit current = 1/5

Xsc = j/(1/5)

External reactance required = j*((1/5) - 0.05))

= j*0.15 pu

Full load current = (30*1000)/(√3*11)

= 1574.6 A

Per unit reactance = j*0.15 = (I*Xr)/V

j*0.15 = (1574.6*Xb)/((11/√3)*1000))

= 0.60 ohm

MGVCL Exam Paper (30-07-2021 Shift 1)
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The normal percentage bias setting of differential relay used for transformer protection will be

In bias differential protection for transformer,

There are two basic settings required to setup the percentage biased differential protection.

1. Minimum pickup

2. The slope.

The minimum pick-up covers the transformer magnetizing current typically 1-4% of transformer rating.

A pick up of 0.2 to 0.3 times the TAP is recommended for general cases.

The slope is defined by determining the potential sources of differential current.