Reactor schemes in stations and substations

Current-limiting reactors are placed at chosen points of a station so that the short-circuit current is limited and a fault in one part does not collapse the voltage of the whole station. The main schemes are below.

1. Generator reactor scheme

Reactor in series with each generator, between the generator and the bus.

  G1      G2      G3
 [X]     [X]     [X]
  |       |       |
 =+===+===+===+===+=  bus
      |       |
   feeders

• Protects the generator against faults beyond it.
• Disadvantage: full load current always flows, so constant voltage drop and loss; a feeder fault still lowers the whole bus voltage. Now seldom used, as modern machines have high reactance.

2. Feeder reactor scheme

Reactor in series with each outgoing feeder.

  G1      G2
  |       |
 =+===+===+===+=  bus
     [X]     [X]
      |       |
   feeder   feeder

• A feeder fault is limited by its own reactor; the bus voltage stays nearly normal, so other feeders are not disturbed.
• Disadvantage: no protection against bus faults; constant drop and loss in each feeder.

3. Bus-bar reactor schemes

The bus is divided into sections, each with a generator; sections are joined through reactors. In normal operation little current passes between sections, so losses are small.

(a) Ring system: each section connected to the next through a reactor, forming a ring.

  G1          G2          G3
 =S1===[X]===S2===[X]===S3=
  |                        |
  +----------[X]-----------+

A fault on one section is fed by the other generators only through reactors. Each section is fed from both sides, so it is more reliable than a straight in-line arrangement.

(b) Tie-bar system: each section is connected through its own reactor to a common tie-bar.

 =S1=    =S2=    =S3=   sections
 [X]     [X]     [X]
  |       |       |
 =+=======+=======+=  tie-bar

Fault current from any other section passes through two reactors in series, so each reactor can be about half the value needed in a ring system. New sections are added easily. It needs an additional bus-bar.

Comparison