Series capacitors are used in transmission line to compensate for the line inductance. These capacitors are connected in series with the lines. Series Capacitors increase transmission capacity and increase system stability.
Series capacitors also help reduce voltage drops. However care must be taken when designing series capacitors. Series capacitors can increase the fault levels in the system. They can also cause overvoltages when the system is lightly loaded.
Ferro Resonance can occur if the value of the system capacitance and the inductance is close to the resonance value.