I don’t think a determination of the actual harmonic content from the ERCOT Benchmark data is feasible at the moment. However, the approach I took was to look at the GIC magnitudes for our equipment in the case data and see where there might be elevated DC. Some of our transformers had only a couple of amps DC flowing through them; these areas will not be an issue. As DC current increases, harmonics will increase. From a protection perspective, I know that microprocessor based relays only operate on the fundamental frequency and not the harmonic content, so in most cases* microprocessor-based protection systems will be fine.


Electromechanical relays may or may not be OK. Most EM differential relays (ABB HU, GE STD, GE BDD for example) have harmonic blocking built into them, and since the dominant harmonic of a GIC event is the second, these relays probably* won’t misoperate. Unfiltered EM relays (such as the time-overcurrent CO9) do include the harmonic content and will “measure” higher than the actual fundamental and would be more likely to mis-operate. I’d like to get my hands on a negative sequence relay, as I anticipate issues with those also because of the phase-shift construction that won’t work correctly at non-fundamental frequencies.


What I’d suggest would be to first look at the DC current magnitudes, and then look at the generator protection system to see what type of relaying is in use, and whether or not that relaying incorporates filtering. I can’t give a “rule of thumb” other than what I found from the IEEE K-11 Working Group (“The Effects of GIC on Protective Relaying”, IEEE Transactions on Power Delivery, Vol. 11, No. 2, April 1996): “GIC levels below 30 A have no noticeable effect on the power system.” Better safe than sorry, though.


Best regards,




*In protection there are exceptions to everything. For example, a neutral conductor with heavy harmonics can have 70A with only 15A fundamental and may not be protected properly by a filtered relay.


Andrew K. Mattei, P.E.

Supervisor, Electrical Engineering Design

Brazos Electric Power Cooperative



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From: Planning Geomagnetic Disturbance Task Force <[log in to unmask]> On Behalf Of Rake, Stewart
Sent: Thursday, February 21, 2019 8:34 AM
To: [log in to unmask]
Subject: Re: PGDTF Agenda for the February 26th meeting




Will the determination of harmonics from the benchmark GMD event will be discussed at the February 26th meeting?  Several of the generators I have been in contact with concerning the attached market notice are unclear how to determine what ERCOT is requesting.

This may have been covered in a previous meeting.  If so, any information you could share would be appreciated.


Stewart Rake

Luminant Compliance

Office:  (214)875-8091

Cell:  (903)436-0134


From: Planning Geomagnetic Disturbance Task Force <[log in to unmask]> On Behalf Of Aster Amahatsion
Sent: Wednesday, February 20, 2019 2:16 PM
To: [log in to unmask]
Subject: PGDTF Agenda for the February 26th meeting




PGDTF members,

Attached is the agenda for February 26th PGDTF meeting updated based on comments received.



Aster Amahatsion

2019 PGDTF Chair


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