In case of MV system ( 3.3kV onwards to 33kV) voltage between phase and earth is high. Also capacitive charging current is not large enough to compensate the same, so is likely to be excessive. Hence resistance is connected between neutral to ground connection. Current through neutral is limited to 100-400 Amperes.

Restricting the earth fault current / current through neutral Although all the component of power system at MV level are rated at full MV system fault level, for instance: •, • Cables, • Bus ducts, • Rotating machine winding, etc. Than what is getting protected by restricting the earth fault current/current through neutral? The neutral of transformer or generator are grounded through impedance, the principal element of which is resistance. This method is used when the earth fault current would be too large if not restricted (e.g.) MV Generators.

1.3 Zones and types of Protection system 1.3.1 Zones of Protection system • An electric power system is divided into several zones of protection. Each zone of protection, contains one or more components of a power system in addition to two circuit breakers. Inversion, bilinear. Complex Integration: Line integrals in the complex plane, Cauchy's. To acquire skills to understand all types of control components. Examples of PDF, Transformation of Random Variables. Rao, 'Switchgear Protection and Power Systems', Khanna Publishers.

Here, a resistor is connected intentionally between the neutral and earth. This is to limit the earth fault current. Winstep xtreme torrent. The reasons to limit the earth fault current The reasons to limit the earth fault current are: 1.

In rotating electrical machines like motors and generators, if the earth fault current is high, as in the case of solid earthing, the core damage would be high. To limit the damage to the core, machine manufacturers allow only a limited ground fault current. This is given in the form of a core damage curve. A typical value would be 25A-100A for 1 second. This value is used as a guide in selecting NGR and setting stator earth fault relays in generator protection. Winding damage in rotating electrical machines is not of serious concern (Though windings are rated for full fault level).

The repairs to winding damages can be done by the local re-winder. But, in case of core damage, repairs cannot be carried out at site.

The machine has to be sent back to the manufacturer’s works for repairs thus resultingin prolonged periods of loss of production. Since rotating electrical machines are not present in voltage levels from 22kV onwards, these systems are usually solidly grounded.

X0/X1 ratio of the system also decides type of neutral earthing. If the corresponding X0/X1 ratio falls under that predefined range. It is a choice between to weather to deal with higher voltage or higher current while under short circuit. Effectively earthed lowers the over voltage limit of the healthy phases while another phase is short circuited to earth. But the ground fault current is very high.