Short Answer:

Transient stability refers to the ability of a power system to remain stable after a large and sudden disturbance such as a short circuit, fault, or sudden loss of generation. To improve transient stability, several methods are used including fast fault clearing, increasing system inertia, using high-speed excitation systems, and adding power system stabilizers (PSS).

Other techniques include the use of series compensation, FACTS devices, and controlled switching. These methods help reduce rotor angle deviations, maintain synchronism among generators, and ensure the system quickly returns to a stable condition after a fault.

Detailed Explanation:

Methods used to improve transient stability

Transient stability is crucial for ensuring that the power system can withstand and recover from major disturbances without leading to system separation or blackout. A disturbance causes the generator rotor to accelerate or decelerate rapidly. If not controlled, it can lead to loss of synchronism. Various engineering and operational methods are applied to improve transient stability and maintain system reliability.

The goal of these methods is to reduce the system’s reaction time, enhance the damping of oscillations, and increase the system’s ability to absorb shocks. These methods can be broadly grouped into design-based and control-based techniques.

Key methods to improve transient stability

1. Fast fault detection and clearing:
   • Reducing the clearing time of faults with fast-acting protection devices helps limit the deviation of rotor angles.
   • Use of high-speed circuit breakers and protective relays ensures quick isolation of faulty sections.
2. High-speed excitation systems (AVR):
   • Automatic Voltage Regulators with fast response improve the system’s ability to handle voltage dips.
   • A quick increase in excitation after a fault boosts electrical output, helping the rotor to decelerate and regain synchronism.
3. Power system stabilizers (PSS):
   • PSS are used along with AVRs to damp out rotor oscillations.
   • They improve small signal stability and support transient stability by controlling excitation based on speed deviations.
4. Increase in system inertia:
   • Synchronous machines with high rotating mass provide kinetic energy to counter sudden speed changes.
   • Higher inertia slows down the rate of frequency change, giving more time for control systems to act.
5. Use of FACTS devices:
   • Flexible AC Transmission System (FACTS) devices such as SVC (Static Var Compensator), STATCOM, and TCSC (Thyristor Controlled Series Capacitor) provide rapid control of voltage and power flow.
   • They improve dynamic response and help in stabilizing rotor angles during and after disturbances.
6. Series compensation:
   • Adding series capacitors in transmission lines reduces line reactance.
   • This improves power transfer capability and reduces the likelihood of instability during high loading conditions.
7. Rescheduling generation and load shedding:
   • Strategically adjusting generator output and shedding non-essential loads during faults can reduce stress on the system.
   • These actions help prevent instability in critical conditions.
8. Controlled switching:
   • Operating circuit breakers or system components at the best possible instant (zero crossing) minimizes disturbance.
   • Controlled switching reduces overvoltages and oscillations caused by sudden changes.
9. System strengthening:
   • Adding new transmission lines or interconnections reduces loading on existing lines and improves overall system stability.

Conclusion:

Improving transient stability involves a combination of fast control actions, smart system design, and real-time response devices. Techniques like fast fault clearing, power system stabilizers, series compensation, and FACTS devices help minimize rotor disturbances and ensure synchronism is maintained. These methods are essential for protecting the system from major failures and keeping the power grid secure and reliable.