Question

With fault clearing time, the transient stability of a power system
1. increases
2. decreases
3. first increases and then decreases
4. first decreases and then increases

Answer 1

Correct Answer - Option 2 : decreases

• The critical clearance time of a fault is related to maximal fault duration for which the system remains transiently stable.
• Transient stability means the ability of a power system to experience a sudden change in generation, load, or system characteristics without a prolonged loss of synchronism.
• To maintain transient stability, a power system fault must be cleared quickly enough so that the fault on transient remains inside the stability boundary.
• With fault clearing time, the transient stability of a power system decreases. The critical clearing time exceeds, stability is lost by generators losing synchronism.

Transient stability of the system can be improved by

• Increasing the system voltage
• Increase in the X/R ratio
• ​Using high-speed governors on machines
• High-speed circuit breakers help to clear the fault as quickly as possible
• By turbine fast valving
• High-speed excitation
• Use of auto re-closing breakers
• Some of the other ways to improve the transient stability are by employing lightning arresters, high neutral grounding impedance, single pole switching, quick Automatic Voltage Regulators (AVRs).