The transient stability limit of a power system can be appreciably increased by introducing

Question

Examoogle · Accepted Answer

Series capacitance

Explanation: The transient stability limit of a transmission line is increased by introducing series capacitance because it compensates for the inherent line inductive reactance. By reducing the overall transfer reactance between the sending and receiving ends, the power-angle characteristic is improved, allowing higher power transfer for a given angular stability margin.

Working Principle: The steady-state power transfer capability of a line is defined by $P = \frac{V_s V_r}{X_{eq}} \sin(\delta)$. By placing a capacitor in series with the line, the equivalent reactance $X_{eq} = X_L - X_C$ decreases. This reduction in series reactance directly increases the maximum power transfer limit ($P_{max} = \frac{V_s V_r}{X_{eq}}$) and allows the system to remain stable under transient disturbances by providing a stiffer coupling between the generator and the infinite bus.

Key Formulas: $P = \frac{V_s V_r}{X_L - X_C} \sin(\delta)$ — Power transfer equation with series compensation; $X_{eq} = X_L - X_C$ — Effective reactance of the compensated line

Key Points: Series compensation reduces the effective line reactance ($X_L - X_C$).; It enhances the steady-state and transient stability limits of the power system.; Improves voltage regulation and load division among parallel lines.; Potential risk of sub-synchronous resonance (SSR) must be managed.

Advantages: Increased power transfer capability; Improved transient stability; Better voltage profile control along long lines

Disadvantages: Risk of sub-synchronous resonance (SSR); Requires complex protection schemes (e.g., fast bypass gap protection); Higher installation and maintenance costs

Applications: Long-distance EHV and UHV transmission lines; Inter-area power corridors to increase capacity

Additional Info: Series compensation is expressed as a percentage of line reactance, typically 30% to 70%.. Shunt inductance is used for Ferranti effect control (light load conditions), whereas series capacitance is for power transfer enhancement.. Shunt capacitance is used for local reactive power support (voltage improvement) but does not directly decrease series line reactance.

Answer: C is correct — Introducing series capacitance reduces the line's effective inductive reactance, thereby increasing the power-angle stability limit.

Exam Tip: Always remember: Series elements modify the line's electrical length (reactance), while shunt elements modify the voltage profile at the buses.

Related Questions

Discussion (0)