Why reactors are used and their types

Reactors are coils with large inductive reactance and very small resistance. They are used in power systems mainly to limit short-circuit current so that circuit breakers and equipment are not over-stressed, and to localise faults.

Why reactors are used

• Fault current $I_f = V/X$; adding reactance cuts $I_f$ and the fault MVA, so cheaper breakers can be used.
• Keep the voltage on healthy sections from collapsing during a fault.
• Reduce mechanical forces and heating in windings during short circuits.
• Shunt reactors absorb surplus VAr on long, lightly loaded lines.

Types by construction

Types by location (reactor schemes)

1. Generator reactor: in series with each generator. Protects the generator, but is in circuit all the time, so causes constant voltage drop and loss. Modern generators have enough internal reactance, so it is seldom used.
2. Feeder reactor: in series with each outgoing feeder. A fault on one feeder does not disturb the bus voltage much. But it gives no protection for bus faults, and causes drop and loss on each feeder.
3. Bus-bar reactor: connects sections of the bus.
   • Ring system: sections joined in a ring through reactors.
   • Tie-bar system: each section connects through a reactor to a common tie-bar; fault current from other sections passes through two reactors.

Shunt reactor

Connected between line and earth at the end of long EHV lines to absorb charging current and limit the rise of receiving-end voltage (Ferranti effect).