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.
How does a differential protection relay work?
Definition: The relay whose operation depends on the phase difference of two or more electrical quantities is known as the differential protection relay. It works on the principle of comparison between the phase angle and the magnitude of the same electrical quantities.
How the generator is protected against unbalanced loading?
This causes the over heating of the rotor and thus the rotor damage. Unbalanced stator currents also damage the stator. Negative sequence filter provided with the over current relay is used for the protection against unbalance loading.
What is differential protection of alternator?
Differential protection of alternator or Merz-Price circulating current protection system is a only protection system that protects alternator stator from burning through at least 80% of it. … There are two types fault might occur in a alternator stator, namely phase to phase fault or phase to ground fault.
What type of relay is best suited for generator protection?
With the size and voltage output of generators increasing, this form of protection is becoming essential for all generating units. The recommended relay is the high impedance relay having a setting range of 10-40% of rated current.
What are the generator protections?
With increasing size and voltage of the generator, this form of protection is becoming essential for all large generating units.
- Stator Earth Fault Protection. …
- Rotor Earth Fault Protection. …
- Unbalanced Stator Loading Protection. …
- Protection against Stator Overheating. …
- Low Vacuum Protection.
What is the purpose of differential protection?
One of the most important protection in power system is differential protection. It is used to protect the electrical equipment against internal fault such as internal winding short circuit or bus bar phase to phase short circuit, inter turn short, winding puncture etc.
Why is differential protection used?
Differential protection schemes are mainly used for protection against phase-to-phase fault and phase to earth faults. The differential protection used for power transformers is based on Merz-Prize circulating current principle.
What is the drawback of differential over current protection?
The main drawback of differential overcurrent protection is the difference in the magnetic conditions of the iron-cored CTs which may cause false operation of the relay at the time of an external fault.
What is differential protection scheme?
Differential protection is a unit-type protection for a specified zone or piece of equipment. It is based on the fact that it is only in the case of faults internal to the zone that the differential current (difference between input and output currents) will be high.
How do you protect a generator from overload?
Stay within the output rating of your generator and turn off all non-essentials, such as multiple televisions, dishwashers and washing machines. This will stop your generator from overloading and also conserve fuel. The holiday lights and video games can wait until power is completely restored.
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.
What is differential fault in generator?
Differential protection for a generator is mainly employed for the protection of stator windings of generator against earth faults and phase-to-phase faults. The stator winding faults are very dangerous, and it causes considerable damage to the generator.
What is the difference between differential protection of transformer and generator?
There is no difference. Differential protection is differential protection. … Any internal fault inside the stator winding is cleared by mainly differential protection scheme of the generator. The differential protection is provided in the generator by using longitudinal differential relay.
What is percentage differential protection?
The percentage differential relay is designed to operate the differential current in terms of its fractional relation with actual current flowing through the circuit. It is used to protect the system under Current transformer saturation, unequal CT ratios, nuisance trip etc.