Factor Affecting Transient Stability

It has been seen that transient stability is greatly affected by the type and location of a fault, so that a power system analyst must at the very outset of a stability study decide on these two factors. Following are few methods of improving the transient stability limit of a power system.

Methods of its Improvement

1. Higher inertia constant of the machine:  

From swing equation , accelerating power the acceleration of the rotor is inversely proportional to the moment of inertia of the machine. Hence, higher the moment of inertia of the machine the slower will be the change in the rotor angle of the machine and thus will allow a longer time for the operation of the breaker to isolate the fault before the machine passes through the clearing angle.

2. By increasing the system voltage: With the increase in system voltage maximum power P_max is increased due to which machine is allowed to rotate through large angle before if reaches the critical clearing angle which results in greater critical clearing time and the probability of maintaining stability.
3. By reducing the transfer reactance: Use of parallel lines etc. as discussed earlier increases P_max resulting in increase in transient stability limit as mentioned above.
4. By using high neutral grounding impedance in systems where stability is of prime importance.
5. By using high speed circuit breakers.
6. By using high speed excitation systems.
7. By using single pole switches.
8. By using autoreclosing units.
9. By using automatic voltage regulators (AVRs).