Reactors Fault current limiting

Single-or three-phase Single-phase reactors are used in the neutral circuit either to limit the ground fault currents or as arc-suppression coils (Section 20.5). Similarly, three-phase reactors are used for three-pha.se applications. 

Figure 27.9 Use of current limiting reactor, (1) to limit the fault current, or (2) to limit inrush current during a capacitor switching...

These are meant to limit the ground fault current and are used between the neutral of the system and the ground. They are single-phase and may be short-time rated, otherwise they are the same as the current limiting reactors (Figure 27.12). Their ratings can be calculated by... 

Reactors are indnctance coils and the name reactor is used to imply their use for limiting fault current. Current limiting is often achieved by adding reactance into part of the power system. Reactors perform this fnnction economically. 

Saturable reactors to limit the enclosure currents and reduce the fault level and losses caused by it. 

The high impedance is usually a resistance chosen to limit the earth current to about 20 mA. A current detector is used in conjunction with the resistance to raise an alarm if a line-to-earth fault occurs. A zig-zag transformer, or reactor, is sometimes used with three-wire supplies such as used in drilling rigs and emergency systems. It is specially designed and internally connected to create a very low zero sequence impedance to earth currents. Therefore, the current is limited only by the resistance of the neutral earthing resistor. Some special purpose earth current alarm systems are available that inject a small DC current into the three-phase system, which is used to identify the actual location of the fault. 

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