100 % stattor earth fault protection

What relay are you using? Where are you reading 95% and 100% stator earth fault protection? Do you have differential protection? Are you using directional ground scheme for generator?

dear sir

thanks for nice reply.

we are using ABB make RAGEK raly for stator earth fault protection of generator .this relay have two stage for earth fault protection.stage one for 95 % and stage two for 100 % earth fault protection.differantial protection is differant thing and we also have the diff. protection for generator and same is covered under REM543 ABB make relay. also directional ground scheme is here .plese tell me about 95 %and 100% stator earth fault protection

regards

suresh kumar paliwal

Common practice in most countries is to earth the generator neutral

through a resistor. The current through the neutral point resistor will normally

be 5 - 10 A when subjected to the rated phase to earth voltage. For

generators with step-up transformer, a neutral point voltage relay with

typical setting 5 % of generator phase voltage will provide earth-fault protection

for 95 % of the stator winding. It also covers the generator bus,

the low-voltage winding of the step-up transformer and other ancillaries

galvanically interconnected with the stator winding.

An earth-fault close to the neutral point of the generator will not give sufficient

neutral point voltage to activate the neutral point voltage (95 %)

relay. Generators which produce about 1 % or more third harmonic voltage

under all service conditions, can have the entire stator winding,

including the neutral point, protected using a scheme which combines the

neutral point voltage function (95 % relay) and a third harmonic undervoltage

function. Under normal service, typically 40 - 60 % of the generated

third harmonic phase voltage will appear across the neutral point

resistor and will activate the third harmonic voltage relay. If an earth-fault

occurs close to the neutral point, the third harmonic voltage drops to a low

value and the undervoltage relay operates. The relay must have a filter

which prevents the fundamental frequency neutral point voltage from

affecting the third harmonic voltage function.

The 100 % stator earth-fault protection can also be used for generators

with unearthed neutral. The third harmonic voltage between the neutral

point and earth will increase compared to generators with earthing resistor

and the third harmonic undervoltage (100 %) function can cover a larger

part of the stator winding. However, in case of an earth-fault in the high

voltage (HV) network, the zero-sequence voltage transferred to the stator

circuit via the capacitance between the HV and LV windings of the stepup

transformer increases compared to generators with neutral point resistor.

The voltage setting or the time delay of the generator neutral point

voltage (95 %) relay must then be increased to get selectivity against

earth-fault relays on the HV side.

Follow this link for detailed info..

http://library.abb.com/GLOBAL/SCOT/SCOT296.nsf/VerityDisplay/108DF8A9ABA23809C1256E4E0054CBBB/$File/1MRK504006-UEN-1-en_Users_Guide_RAGEK_100__and_95__stator_earth-fault_protrection_for_generators.pdf

Dear Sirs,

I am new to the protection world. How can I learn about 95% and 100% stator earth fault protections based on low frequency injection? I have tried to read it from internet but alas, i could not figure out the circuit, how does the 20Hz freq generator, filter unit help, where it is injected, what is the feedback signal etc.

All I know about 100% stator E/F protection is that the voltage generated between the neutral point to the 5% of the winding is very less during an earth fault which will be undetected by the 95% Stator E/F relay, Hence we use a Low freq injection or Third harmonic protection scheme. At present I want to study about the low freq injection schme w.r.t REG316 Relay which uses some hardware like REX010, 011 etc.

Help solicited,

Abbs