Protective Relay

Why?

Transformers may have equipped "volts per hertz" over-excitation relays to protect the transformer from overvoltage at higher than rated frequencies? Is that what you're talking about?

Please specify more about what you'd like to know so we can know what you want better if you'd please

If you have to ask this then I doubt that you are qualified to understand an accurate answer. I recommend you first research the difference between a current sensitive relay and a One D Ten T relay. Don't forget to consider how each of these relays should be used to protect a power generating facility.

For the common protection of transformer and generator Differential protection Relay having # 87 is used (sometimes also referred to as 87GT)

If you want to start doing some research on your own, transformer protection commonly includes such functions as primary and secondary overcurrent (time and instantaneous 50/51), neutral overcurrent (50/51N), ground overcurrent (50/51G), current differential (87T), fault pressure (63), and sometimes directional overcurrent (67), reverse power (32), and even thermal overload (49). The numbers in parentheses are the ANSI standard device designations.

Generator protection gets even more diverse:

Zone Distance or impedance (21)

Volts per hertz or over-excitation (24)

Sync Check (25)

Undervoltage (27)

Reverse power (32)

Loss of excitation / field (40)

Phase current balance / negative sequence overcurrent (46)

Stator Thermal overload (49)

Inadvertent Energization (50/27)

Phase & neutral overcurrent, time & instantaneous (50/51/N)

Voltage-restrained or voltage-controlled overcurrent (51V)

Phase Overvoltage (59)

Neutral Overvoltage (59N)

Fuse Loss detection (60V)

Field Ground (64F)

Stator Ground (64S)

Out of Step (78)

Over / under-frequency (81O/U)

Phase differential current (87)

And more…

Looks like you have some studying to do.

thank u very much to giving me that answer. I know that these relays are ANSI standards. But i m asking where i'll get that details. (working, application). Is any other book is there to read which is mention the all relays application and working. bcoz i have not seen or read 86, 95, 94 etc. relay in any engineering books. If u know then plz tell me.

Get the free download of GE's "The Art & Science of Protective Relaying" to help you understand the principles and functions of protection relays. Go to this link:

http://www.gedigitalenergy.com/multilin/notes/artsci/index.htm

hi peter t

thank you very much for giving me the details.

nice to talk to u. Pls get in touch.