EE MCQ

MGVCL Exam Paper (30-07-2021 Shift 1)
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Three equal star-connected inductors take 8 kW at 0.8 power factor when connected to a 460 V three - phase 3-wire supply. If one of the inductor in phase – Y is short circuited, then the line current in phase-Y is ___ Assume RYB sequence.

Here, Y phase is shorted,

Equation of 3-phase power = √3*VL*IL*cosφ

IL = P/(√3*VL*cosφ)

= 8000/(√3*400*0.8)

= 12.55 A

Phase impedance = Vp/Ip

= 460/(√3*12.55)

= 21.16 ohm

cosφ = 0.8, So φ = 37 degree.

Here Impedance of Y phase is shorted,

So, Neutral point and Y phase at same potential,

Three line voltages are given by,

Vry = 460∟0°

Vyb = 460∟120°

Vbr = 460∟-120°

Here N and Y phase at same potential,

Ir = (460∟-120°)/(21.16∟37°)

= -21.7∟83° A

Ib = (-460∟120°)/(21.16∟37°)

= 21.7∟-157° A

Ib = -(Ir + Iy)

= -21.7∟83° + 21.7∟-157°

= 37.6∟53° A

Related Question

MGVCL Exam Paper (30-07-2021 Shift 1)
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Three resistances 750 Ω, 600 Ω and 200 Ω are connected in parallel. The total current is 1 A. Determine the voltage applied.

Equivalent resistance of the circuit, Req = (750|| 600 || 200)

Req = 125 Ω

Current from source = 1 A

Source voltage = 1*125

Source voltage = 125 V