In series line compensation, the degree of compensation is usually in the range of

Question

Examoogle · Accepted Answer

0.3 to 0.8

Explanation: In series line compensation, the degree of compensation (k) is defined as the ratio of the reactance of the series capacitor ($X_c$) to the total line reactance ($X_L$). The typical range for practical power system stability improvement is 30% to 80% (0.3 to 0.8), as values beyond this can trigger subsynchronous resonance (SSR) issues.

Working Principle: The series capacitor compensates for the inductive reactance of the transmission line, effectively shortening the electrical length of the line. By reducing the net series reactance ($X_{net} = X_L - X_c$), the power transfer capability is significantly increased according to the power-angle equation $P = \frac{V_1 V_2}{X_L - X_c} \sin(\delta)$.

Key Formulas: $k = \frac{X_c}{X_L}$ — Definition of degree of compensation; $P_{max} = \frac{V^2}{X_L(1 - k)}$ — Impact of compensation on maximum power transfer

Key Points: Series compensation is used to increase the steady-state power transfer capacity.; It reduces the effective voltage drop across the transmission line.; Higher levels of compensation (>80%) risk Ferranti effect and complex resonance phenomena.; Subsynchronous resonance (SSR) is a critical concern when $k$ is high.

Advantages: Increased power transfer capability; Improved voltage stability and regulation; Improved steady-state and transient stability; Load sharing between parallel lines

Disadvantages: Risk of Subsynchronous Resonance (SSR); Requires complex protection schemes (spark gaps/varistors); High initial cost for high-voltage capacitors

Applications: Long-distance EHV transmission lines; Increasing capacity of existing transmission corridors

Additional Info: The range 0.3 to 0.8 is industry standard; values above 0.8 are rarely used due to protection and resonance complexity.. Option D (0.2 to 0.25) is typically too low to justify the investment cost of series capacitor banks.

Answer: A is correct — The degree of compensation in series line compensation typically ranges between 0.3 and 0.8 to balance power transfer gains with system stability constraints.

Exam Tip: Always remember that series compensation targets the transmission line reactance ($X_L$), while shunt compensation (like SVCs or STATCOMs) primarily targets voltage magnitude ($V$).

Related Questions

Discussion (0)