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50 Hz generator is delivering 50% of the power that is capable of delivering through a transmission line to an infinite bus. A fault occurs that increases the reactance between the generator and bus to 500% before the fault. When the fault is isolated, the maximum power that can be delivered is 75% of the original maximum value. The critical clearing angle for the condition is desired, will be
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- 67.44°
- 70°
- 50.4°
- none of these
Correct Option: A
Let Pm is maximum power that can be delivered.
∴ Pm sin δ0 = 0.5 Pm
or δ0 = 30°
During fault the resistance is 500% of the value
before the fault r1 = 0.2, r2 = 0.75
| δc = cos-1 | |
| r2 - r1 |
But 0.5 Pm = 0.75 Pm sin δm
or δm = 41.8&deh;
= 180 – 41.8
= 138.2° = 2.412 radian
| ∴ δc = cos-1 | |
| 0.55 |
= cos-1 (0.383) = 67.4°
