Reactor function and ring bus-bar scheme

Function of reactor

A current-limiting reactor is a coil with high inductive reactance and negligible resistance. It limits the short-circuit current to a value that circuit breakers can interrupt, localises the fault so that the rest of the bus keeps its voltage, and reduces mechanical and thermal stress on equipment.

Ring type bus-bar reactor scheme

The bus-bar is split into sections, one generator per section, and adjacent sections are joined through reactors so that the sections form a closed ring. Feeders are taken from each section.

      G1            G2            G3
      |             |             |
  ==[S1]===[X]===[S2]===[X]===[S3]==
    |  |          |  |          |  |
    |  feeders    feeders     feeders
    |                              |
    +-------------[X]--------------+
         (reactor closing the ring)

Working:

• In normal operation each generator mainly feeds the load on its own section. Only small balancing currents flow through the reactors, so their voltage drop and power loss are small.
• When a fault occurs on a feeder of, say, section S2, generator G2 feeds it directly, but G1 and G3 feed it only through the reactors. The fault current from the other sections is therefore limited.
• The faulty section is fed from both of its neighbours, each through its own reactor, so the fault current coming from the rest of the system is split between two reactors.

Advantages:

• Good fault-current limitation with low losses in normal running.
• A fault is confined to one section; the voltage on the other sections stays fairly high.
• Each section is supplied from both directions, so supply is more reliable than in a plain series (in-line) scheme.

Disadvantages:

• More reactors and a more complex layout than the simple series bus-bar scheme.
• Load sharing between sections depends on the loads being balanced.