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A three-phase, 11 kV, 50 Hz, 2 pole, star connected, cylindrical rotor synchronous motor is connected to an 11 kV, 50 Hz source, Its synchronous reactance is 50 Ω per phase, and i t s st at or resistance is negligible. The motor has a constant field excitation. At a particular load torque, its stator current is 100A at unity power factor. If the load torque is increased so that the stator current is 120 A, then the load angle (in degrees) at this node is _____________.
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- – 48 to – 46
- 41
- 51
- 132
Correct Option: A
Ef = Vt – Ia × S
| = | kV - j100 × 50 | |
| √3 |
= 6350 – j5000
| Ef | = √(6350)² + (5000)²
= 8082.23
Now, (Ia × S)2 = Ef 2 + Vt 2 – 2Ef Vt cos δ
(120 × 50)2 = 8082.232 + 63502 – 2 × 8082.23 × 6350 × cos δ
∴ δ = – 47.27°
