Which device is used in substations to improve the power factor?

Option 3 : Synchronous condenser

Synchronous condenser:

• A synchronous condenser is used to improve the power factor.
• It delivers leading reactive power in the system which decreases the reactive power demand from the supply, thus increasing the power factor of the substation.

Synchronous reactor:

• It improves the overvoltage condition at the receiving end of the transmission line.
• It absorbs excess reactive power available, thus decreasing the overvoltage condition.

Series inductor:

•  Series reactors are used as current limiting reactors to increase the impedance of a system. 
• It is used to protect the system against voltage surges.

Series capacitor:

• The addition of a capacitor in the line decreases the reactance of the system.
• Thus the power transfer capability of the system increases.
• It also increases the stability of the system.