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A 3 – φ supply, 5 kW induction motor has a power fact or 0.75 lagging. A bank of capacitors is connected in delta across the supply terminals and power factor raised to 0.9 lagging. kVAR rating of the capacitors connected in each phase, will be _________ kVAr
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- 0.663 kVAr
- 66.3 kVAr
- 663 kVAr
- 660.3 kVAr
Correct Option: A
p.f., cos φ1 = 0.75
⇒ φ1 = cos–1 (0.75) = 41°24'
and tan φ1 = tan 41°24' = 0.8819
Final power factor, cos φ2 = 0.9 (lagging)
⇒ φ2 = cos–1 (0.9) = 25°50'
and tan φ2 = tan 25°50' = 0.4843
Motor input, P = 5 k watt.
Efficiency, η = 100% (assuming)
Leading kVAr supplied by the condenser bank
= P (tan φ1 – tan φ2)
= 5 (0.8819 – 0.4813)
= 1.99 kVAr.
Rating of capacitors connected in each phase
| = | = 0.663 kVAr | |
| 3 |
