Problem 1 (Computing Critical Clearing Time (CCT) using EAC):
A three-phase 50 Hz synchronous generator is supplying power through pure reactive parallel transmission lines to an infinite bus. The machine is delivering 1.0 per unit power () before a three phase short circuit fault occurs in the system.
The mechanical power is Pm=1.1pu, Eq’=1.1pu and the per unit inertia constant H=10 MJ/MVA. Figure 1 shows the power angle characteristics before, during and after the fault with all values in pu:

Compute:
The steady-state power angle .
The maximum power angle .
The critical clearing angle .
Compute the critical clearing time (in sec).
If the clearance time can be reduced to 120msec, what is the maximum power that this machine can deliver while remaining stable?

Figure 1. The power angle characteristics before, during and after the fault for Question 1 with all values in pu.

Problem 2:
A salient pole synchronous motor is connected to an infinite bus over a short feeder whose impedance is purely reactive. The power-angle curve for transient condition is P’(d’) = 1.3 sin d’ + 0.2 sin 2d’ where the amplitudes are in pu on the machine rated base values. With the motor operating initially unloaded, a shaft load of 0.70 pu is suddenly applied.

Compute the operating torque angle
Assume = 25 degrees and computer areas A1 and A2.
Compute the maximum torque angle that the motor can operate and remain in synchronism with the infinite bus.

Posted: May 3, 2013

2 Electrical Utility Engineering 623-2013, Module 2-Stability, Assignment #2

(before the fault)

(after the fault)

(during the fault)

ted base values. With the motor operating initially unloaded, a shaft load of 0.70 pu is suddenly applied.

Compute the operating torque angle
Assume = 25 degrees and computer areas A1 and A2.
Compute the…