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A well known and expertise specialist once said: "The best IED maintenance test is not to do it". He had some good reasons in saying this assertion.

Negative-sequence overcurrent relays can be set much more sensitive than phase overcurrent relays.http://files.engineering.com/getfile.aspx?folder=dc203aa7-0552-4bc1-b27d-82e85d7d34d5&file=SEL_Negative-Sequence_Overcurrent_Element_Application_and_Coordination.pdf

Hope this paper helps you.http://files.engineering.com/getfile.aspx?folder=a3a89876-d679-4151-96b2-bb810e43aff5&file=Determining_the_Correct_Connection_Compensation.pdf

¿What to do when the fault current is less than load current?, i.e. ¿how do you protect circuits under these conditions?

Mr. Brooke, look for the attached Application Guide for the SEL-279H reclosing relay handling 2 breakers.http://files.engineering.com/getfile.aspx?folder=9cae5380-3d1f-46c1-8643-42d2ed280196&file=SEL-279H_Application_Guide.pdf

I believe figures in the Schneider Catalogue explain by themselves.

The SEL-311L relay has also 87L and 21P/21G single-pole tripping. Not sure but perhaps you may configure the relay for reclosing purposes as well.

M1337, maybe you can get extra knowledge in reading this paper.http://files.engineering.com/getfile.aspx?folder=bbef1426-fddc-4fc3-8710-b47e3d542a8a&file=SEL_Considerations_Using_High-Z-87B_or_Low-Z-87B.pdf

MBrooke, you can find among SEL Application Guides that identified with number AG95-29, Dated on 20140611, and authored by Armando Guzman, Jeff Roberts, and Karl Zimmerman, Volume I, entitled "Applying the SEL-321 Relay to Permissive Overreaching Transfer Trip (POTT) Schemes. Read pages from 8...

Mbrooke, do not worry about past times, worry about present, and even future, times.

Phase and Ground Distance Relays may support communications-assisted tripping schemes. If applying this Distance Relay to Permissive Overreaching Transfer Trip (POTT) schemes with the assistance of a communications channel, the relay provides high-speed protection for faults anywhere along the...

Look at this link: https://en.wikipedia.org/wiki/Electricity_distribution_companies_by_country Regards

I found this SEL paper useful for your needs. http://files.engineering.com/getfile.aspx?folder=4f4f6acc-69b4-430c-9bcd-91f5076797c6&file=SEL_Today's_Power_Engineering_Shortage_An_Alarming_Problem.pdf

We discovered high resistance faults on 400kV lines when we realized large MW consumption in comparison to MVAR.

Attached you will find the paper "Breaker Failure Philosophies"http://files.engineering.com/getfile.aspx?folder=92f5f65e-0350-4d78-921c-814e2dca54e2&file=SEL_Breaker_Failure_Philosophies.pdf

djr3203 and magoo2 ¡wow! and thousand ¡wows! Now I see, after many years, that a three-phase fault will NEVER be completely symmetrical!

Thanks dpc You mentioned an important point: "But the overvoltage can be controlled". ¿May I ask you how?

Thank you very much for your useful replies. One more question: If this generator were high-resistance grounded, ¿would it be prone to suffer overvoltage conditions?

Criterion that should be taken into account to decide what grounding method are to be used.

Dear colleagues, I appreciate your help in selecting a 3,000KVA mining power transformer regarding its winding-connections, that is, advantages and disadvantages between a delta[34.5kV]/delta[6.9kV] bank or a delta[34.5kV]/star[6.9kV] high-resistance grounded bank. Thank you.