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The total load taken from an a.c. supply consists of
A- a heating load of 15 kW
B- a motor load of 40 kVA at p.f. 0.6 lagging
C- a load of 20 kW at p.f. 0.8 lagging
A capacitor is connected in parallel with load and p.f. raised to unity. The kVAR rating of the capacitor should be
  • a)
    112 kVAR
  • b)
    92 kVAR
  • c)
    55 kVAR
  • d)
    47 kVAR
Correct answer is option 'D'. Can you explain this answer?
Verified Answer
The total load taken from an a.c. supply consists ofA- a heating load ...
The parallel loads draw a total reactive power of 47 kVAR lagging. In order to raise the p.f. to unity, the capacitor should supply leading reactive power of 47 kVAR.
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The total load taken from an a.c. supply consists ofA- a heating load ...
Solution:

Given,

Heating load = 15 kW

Motor load = 40 kVA at a power factor of 0.6 lagging

Load = 20 kW at a power factor of 0.8 lagging

To improve the power factor to unity, a capacitor is connected in parallel with the load.

Let the kVAR rating of the capacitor be X.

Now, the total load on the supply after connecting the capacitor in parallel will be:

15 kW + 40 kVA at a power factor of 1 (as kVA = kW/Power factor) + 20 kW at a power factor of 1

= 75 kVA

The total current drawn by the load before connecting the capacitor is:

I = Power/Voltage

For the heating load:

I1 = 15 kW/230V = 65.22 A

For the motor load:

I2 = 40 kVA/(0.6 x 230V) = 120.97 A

For the load:

I3 = 20 kW/(0.8 x 230V) = 108.7 A

Total current before connecting capacitor = I1 + I2 + I3 = 294.89 A

The total current after connecting the capacitor in parallel will be:

I = Power/Voltage

For the heating load:

I1 = 15 kW/230V = 65.22 A

For the motor load:

I2 = 40 kVA/(1 x 230V) = 173.91 A

For the load:

I3 = 20 kW/(1 x 230V) = 86.96 A

Total current after connecting capacitor = I1 + I2 + I3 = 326.09 A

Now, the reactive power supplied by the capacitor is given by:

Q = P*tan(arccos(PF))

Where, PF is the power factor after connecting the capacitor.

For a power factor of 1, the reactive power supplied by the capacitor is zero.

So, the total reactive power required to improve the power factor to unity is:

Q = S*tan(arccos(PF))

Where, S is the apparent power of the load.

S = 75 kVA

PF = cos(arctan(0.6)) = 0.8 lagging

Q = 75*tan(arccos(0.8)) = 47.03 kVAR

Therefore, the kVAR rating of the capacitor should be 47 kVAR.
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The total load taken from an a.c. supply consists ofA- a heating load of 15 kWB- a motor load of 40 kVA at p.f. 0.6 laggingC- a load of 20 kW at p.f. 0.8 laggingA capacitor is connected in parallel with load and p.f. raised to unity. The kVAR rating of the capacitor should bea)112 kVARb)92 kVARc)55 kVARd)47 kVARCorrect answer is option 'D'. Can you explain this answer?
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The total load taken from an a.c. supply consists ofA- a heating load of 15 kWB- a motor load of 40 kVA at p.f. 0.6 laggingC- a load of 20 kW at p.f. 0.8 laggingA capacitor is connected in parallel with load and p.f. raised to unity. The kVAR rating of the capacitor should bea)112 kVARb)92 kVARc)55 kVARd)47 kVARCorrect answer is option 'D'. Can you explain this answer? for SSC 2024 is part of SSC preparation. The Question and answers have been prepared according to the SSC exam syllabus. Information about The total load taken from an a.c. supply consists ofA- a heating load of 15 kWB- a motor load of 40 kVA at p.f. 0.6 laggingC- a load of 20 kW at p.f. 0.8 laggingA capacitor is connected in parallel with load and p.f. raised to unity. The kVAR rating of the capacitor should bea)112 kVARb)92 kVARc)55 kVARd)47 kVARCorrect answer is option 'D'. Can you explain this answer? covers all topics & solutions for SSC 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for The total load taken from an a.c. supply consists ofA- a heating load of 15 kWB- a motor load of 40 kVA at p.f. 0.6 laggingC- a load of 20 kW at p.f. 0.8 laggingA capacitor is connected in parallel with load and p.f. raised to unity. The kVAR rating of the capacitor should bea)112 kVARb)92 kVARc)55 kVARd)47 kVARCorrect answer is option 'D'. Can you explain this answer?.
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