As we’ve discussed within the previous articles about the protection of transformers and transmission lines. Nowadays the fashionable electrical power systems contains several parts e.g. alternators, transformers, station bus bars, transmission lines and other equipment. it’s become necessary to guard every and every a part of the electrical power grid from the faults which can occur sooner or later. it’s very profitable by using protective relays for the improper behavior of the system. which may be detected by the sensitive relays easily. the foremost serious faults on the alternators which require attention on the immediate basis are the stator winding faults. the essential system for the protection of alternators is that the differential relay scheme because the differential nature of measurement makes the system far more sensitive and reliable than other protective systems.
An alternator is an electrical generator that converts energy to electricity within the sort of AC .
The generating units, especially the larger ones are only a few in numbers but high in individual cost and most other equipment. Therefore it’s desirable to stay of these equipment safe and guarded from damaging faults. Here we are getting to discuss some faults which can occur within the alternators.
Failure of prime-mover:
When the input to the first cause fails, the alternator runs as a electric motor and draws some currents from the provided supply. This condition is named “inverted running”.
Failure of a field:
The chances of field failure are very undoubtedly very rare. But if it occurs it cannot damage the alternator.if the alternator runs without providing field supply. The faulty alternator are often easily separated manually and not provide automatic system from separation.
This type of fault occurs mainly thanks to the partial breakdown of the winding insulation or thanks to overload on the availability system. Sometimes overcurrent protection for alternators makes no sense thanks to the subsequent reasons.
1) within the modern days, the alternator windings are with high impedance in order that they stand an entire short at their terminals for sufficient time then It are often easily separated manually.
2) The disadvantage of using overload relay for cover of alternators is that such a protection might disconnect the alternators from the bus bars on momentary troubles outside, it disturbs the continuity of power supply to the consumers.
The main explanation for over speed may be a sudden loss of the high amount of load disconnecting from an alternator. So for that purpose, a mechanical centrifugal device is mounted on the driving shaft to trip the most valve of the first cause when dangerous over speed occurs.
The field excitation system is extremely neat nowadays in order that it cannot provide overvoltage but overvoltage may occur thanks to over speeding of a major mover. Overspeeding of alternators reason may be a sudden loss of an enormous amount of load disconnection. If some system is installed on the moving shaft of the alternator then It are often controlled easily.
Unbalanced loading means different phase current within the alternator. the various current condition occurs in alternator thanks to earth or fault between phases. Unbalanced loading if it’s allowed to persist it can burn the windings or may damage the mechanical fixings.