Why only 95% of the stator winding is protected upon a phase to earth fault?
In case of an earth-fault on the stator winding and no additional fault resistance, the fundamental frequency neutral point voltage is increasing in proportion to the distance of the fault from the neutral point. Hence a voltage relay set to 5 % of the stator phase voltage will protect 95 % of the stator winding.
Is it possible that 100% winding of generator is protected against earth fault how?
It is should be noted that, 100 % of the stator winding cannot be protected in resistance neutral earthing system. How much percentage of stator winding would be protected against earth fault, depends upon the value of earthing resistance and the setting of relay.
Why do you protect the generator against faults?
The main protection provided in the stator winding against phase to phase or phase to earth fault, is longitudinal differential protection of generator. Second most important protection scheme for stator winding is inter turn fault protection.
What are the protective methods used for stator protection of a generator?
Over current relays can not detect the winding temperature because electrical protection can not detect the failure of the cooling system. So to protect the stator against over heating, embed resistance temperature detector or thermocouples are used in the slots below the stator coils.
What is generator differential protection?
1. Generator differential protection (87 G) It is unit type protection, covering the stator winding for phase to phase faults due to breakdown of insulation between stator phase windings. … If CTs of identical ratios are used on neutral and line side of generator, an operating current setting of 20% it can be adopted.
What is stator fault?
Stator faults usually start as inter-turn short circuits. In fact the primary or main cause of the stator faults is insulation degradation which leads to inter-turn short circuits. When an inter-turn short circuit occurs, extremely high currents flowing in the short circuited coil cause the propagation of destruction.
Why are generators earthed?
1. Generator earthing. The neutral point of a generator is usually earthed to facilitate protection of the stator winding and associated system. Earthing also prevents damaging transient overvoltages in the event of an arcing earth fault or ferroresonance.
What is earth fault protection?
It is a safety device used in electrical installations with high earth impedance. It detects small stray voltages on the metal enclosures of electrical equipment. The result is to interrupt the circuit if a dangerous voltage is detected. The EFR is protected against tripping from transients and prevents shock.
What percentage of generator winding can be protected against earth faults through restricted earth fault protection?
Principle of 100% stator Earth Fault protection:
Here the generators with step-up transformer, a neutral point voltage relay (27TN/59N) with typical setting 5 % of generator phase voltage will provide earth-fault protection for 95 % of the stator winding.
What are generator faults?
Your generator protection must have a way to detect generator faults. A fault is any unwanted current flow in an electrical system. Faults can cause all kinds of problems for your generators, including current loss, interruption of power delivery, and damage to the generator due to overheating.
What are the causes of fault in generator?
Common Causes of Generator Failure
- Battery Malfunction. There are several things that can cause your battery to fail. …
- Fuel, Coolant, or Oil Leaks. Fuel leaks often happen due to an issue with the pump system. …
- Low Coolant. Coolant is what keeps your engine from overheating. …
- Air in Fuel System. …
- Poor Maintenance.
What is overcurrent protection generator?
Overcurrent protection uses as back-up protection for protection generators from faults between two windings of stator (two phases of stator). … It is supposed to aid in sensing faults that are electrically close to the generator terminals as there is insufficient fault impedance to maintain the voltage at the generator.
What is the difference between unit and non unit protection?
The main difference between unit and non-unit schemes is that individual non-unit schemes do not independently protect one clearly defined part (or zone) of the system. 3.6. Non-unit protection system (overcurrent protection).
Why over current protection is not necessary for modern generators?
Answer : Over Current protection is not considered necessary for modern alternators because these are capable of withstanding a complete short circuit at their terminals for sufficient time without much over heating and damage.
What is class A protection?
Class ‘A’ protection: This is provided with an external lightning conductor on top of. the building connected through a down conductor to ground. (Earth). This is known as class ‘A’ protection.