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T/F: series compensation in EHV lines

Short answer

TRUE. Series capacitors reduce net line reactance, increasing steady-state power limit Pmax = VsVr/(XL(1–k)). This boosts transfer capability on stability-limited long EHV lines.

State whether the following statement is TRUE or FALSE. Justify your answer with a brief explanation: Series compensation may be used in EHV transmission line to increase the power handling capacity of the line.

TRUE.

  • Steady-state power transfer: P=VsVrXLsin⁡δP = \frac{V_s V_r}{X_L}\sin\delta.
  • A series capacitor of reactance XCX_C reduces the net reactance to XL−XC=XL(1−k)X_L - X_C = X_L(1-k), where k=XC/XLk = X_C/X_L is the degree of compensation (normally 25–70%).
  • Hence
Pmax=VsVrXL(1−k)P_{max} = \frac{V_s V_r}{X_L(1-k)}

e.g. 50% compensation doubles the steady-state limit.

  • It also improves transient stability, reduces voltage drop and allows better load sharing between parallel lines.

Limits: risk of sub-synchronous resonance with turbine-generator shafts, and need for over-voltage protection (MOV, spark gap) across capacitors. Series compensation does not raise the thermal limit, so it is useful mainly on long EHV lines that are stability-limited.

✓ Answer checked by Claude Opus 5.5 (high effort)

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