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A 220 V, 15 kW, 1000 rpm shunt motor with armature resistance of 0.25 Ω , has a rated line current of 68 A and a rated field current of 2.2 A. The change in field flux required to obtain a speed of 1600 rpm while drawing a line current of 52.8 A and a field current of 1.8 A is
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- 18.18% increase
- 18.18% decrease
- 36.36% increase
- 36.36% decrease
Correct Option: D
| = | × | ||||
| N2 | Eb2 | φ1 |
Ra = 0.25;
Ia = 68 – 2.2 = 65.8A;
Ia2 = 52.8 – 1.8 = 51A
| ∴ | = |  |  | × | |||
| 1600 | 220 - 51 × 0.25 | φ1 |
| ⇒ | = 0.6364 | |
| φ1 |
| ∴ % decrease = | × 100 | |
| φ1 |
| = | | 1 - | | × 100 = 36.36 % decrease | |
| φ1 |
