Letters

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Dear PAC World,
Regarding the article "Disturbance Analysis in Brazil – Grid Procedures and Infrastructure" published in the June’s 2013 edition, the name (Marco Antonio Fernandes Ramos) and his biography as one of the authors of the article, has been omitted.

Jorge Miguel Ordacgi Filho
Brazil

PAC World:
Dear Jorge and Marco,
We sincerely apologize for the omission, and here is Marco's biography and photo:

Marco Antonio Fernandes Ramos was born in 1966 in Rio de Janeiro, Brazil.
He graduated in Electrical Engineering in 1992 at the Santa Ursula University,
and received his Master of Sciences in Electric Engineering degree from the Catholic University of Rio de Janeiro in 2002. Since 1993 he has worked at FURNAS Centrais Eletricas S.A. as a Protection Engineer. Marco has participated in the development of the FURNAS´s Oscillography System, and today he is manager of the Division of Protection Analysis.

Dear PAC World,
I read Torsten Schierz's article on testing generator protection systems in the March 2013 PAC World issue with great interest.

I would add a comment on testing the negative phase sequence element. It appears Torsten is suggesting using a balanced negative phase sequence injection to test this element. This cannot occur in the real world. In fact it is not negative phase sequence, but reverse rotation positive phase sequence. If injecting, these currents pre fault voltages required to not cause operation of the accidental energization protection would also need to be reversed.

Some relays when presented with a reverse rotation positive phase sequence current think they are on a reversible pump machine, and automatically implement a reverse rotation function.

A better option for testing a negative phase sequence element is to inject a phase to phase current. This is the worst naturally occurring negative phase sequence event. It also contains a positive phase sequence component. Negative phase sequence current does not exist by itself in the power system. A positive phase sequence current is also present. For a phase to phase injection the value of negative phase sequence current is the phase current divided by the square root of three.

If there is a transformer in the overall differential zone, to avoid operation of the differential element a 2:1:1 current must also be injected on the HV current transformer input to the protection system.

Terry Foxcroft
Snowy Hydro, Australia

PAC World:
Dear Terry,
Thank you for your comments. We hope that Torsten, as well as our readers from around the world will continue the discussion that you started.

pac world
Editor in chief: dr. Alexander Apostolov (USA)
Editors: Christoph Brumer (Switzerland), Yana St. Clair (USA)
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BeijingSifang June 2016