Answer: Shunt compensation is preferred over series compensation because series compensation has some disadvantages which are discussed below
1. series compensation introduce a subsynchronous frequency, proportional to the square root of the compensation in the system. In some cases, this property may interact with turbo generator shaft and develop high torsional stresses.
2. Switching-in of an unloaded transformer through a series compensated line may produce ferroresonance.
3. Series compensation may lead to meloperations of the protection system leading to unnecessary tripping.
4. high recovery voltage may devolve across the circuit breaker contact due to series compensation.
Series Compensation Series compensation is basically a powerful tool to improve the performance of EHV lines. It consists of capacitors connected in series with the line at suitable locations.
For high voltage transmission line the line capacitance is high and plays a significant role in voltage conditions of the receiving end. When the line is loaded then the reactive power demand of the load is partially met by the reactive power generated by the line capacitance and the remaining reactive power demand is met by the reactive power flow through the line from sending end to the receiving end.