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I'm working in a 2 X 10MW captive power. I want to know about the protective relay co-ordination in between generator, generator transformer and feeders. It also noted that the generation voltage is 11kv, transmission voltage is 33kv, generator full load current is 722A and the rating of GT is 12.5MVA, 11/33KV.

Responding to TK Sarkar’s 07-Mar-08 (00:05) query... I do not know of a definition presented by any recognized technical organization, so I will revert to what I was taught by Professors JL Blackburn and GD Rockefeller, in the Newark,(NJ) School of Engineering, ca 1957! The two were instrumental in transforming (excuse the pun) relay coordination (once just an art-form) into a scientific-discipline (but, in my view still more art-form than discipline.) Folowin is excerpeted from the "Introduction and Genera Philosopies" chapter of their text, "Silent Sentinels" used in their courses:

"Protective relays are a form of active insurance. By their application in all parts of a power system, trouble is quickly determined and action initiated to isolate damaged sections. A well-designed and efficient protective system should have:

1. Reliability – A system adequately and dependably ready for all types of trouble.

2. Selectivity (or coordinated) – Maximum continuity of service through isolation of only the trouble(d) part of the system.

3. Speed – Minimum fault time (duration) and equipment.

4. Simplicity – Minimum equipment and circuitry.

5. Economy – Maximum protection at minimum cost."

Over the course of my experience I added the following:

6. Backup – Additional protection should be employed as a secondary line of defense to clear a fault.

Sarkar, a search of like-topics in the Control List archives should reveal that there is no quick nor simple way to learn about relay-coordination! But, hopefully, I have correctly interpreted your query. If not, let me know!

Regards, Phil Corso, PE (cepsicon@aol.com)