shunt reactor

Fixed type
Reactor installed in three-phase networks to increase power factor during off-load or reduced load conditions, reducing losses in the transmission lines (capacitive).
Typically it is installed in the wind farms where variation of the load factor is extended.
It has a fixed rating, connecting to the power line all the time (it can be switched on/off depending on the load).

Variable type (VSR)
They are used to stabilize voltage during load variations in the network system. Power rating is not fixed but can be changed in steps ensuring a more stability of voltage and compensating reactive power when the value of load is changed.