High Impedance Differential protection 1

[RRaghunath]

Our client uses High impedance circulating current principle for Restricted Earth fault protection and for Busbar protection.
Of late there is discussion with some section of engineers saying we should change with times and low impedance type protection is the order of the day and entire world is after all changing and so on.
As protection engineer, I am conversant with the merits/demerits of high impedance based protection and personally hold the view that unless driven by need, there is no point in changing the protection philosophy just because others are doing and such reasons.
I am also aware low impedance differential protection from ABB (RADSS) was available since 1980s (or even before.

I would like to know the views of the learned members of this forum.
I would also like to see if some one has statistical data as to how many utilities of the world still continue to use the High impedance principle based differential protection.
I know CIGRE collects such data and I am not sure they have done it on this particular issue.

Thanks in anticipation.

 

[REM76]

I know several years ago Siemens was using the high impedance differential bus protection in thier high voltage substation design. This was implemented as a typical design for the new 400 kV substations that were part of the power interconnection projects between the Middle East and Europe. This project is still going and I think the design is still the same.

 

[Marmite]

You might find the attached paper of interest. It discusses the relative merits of high and low impedance REF schemes.
Regards
Marmite

 

[PUNGLU]

It is obvious that technological advancements have enabled manufacturers to come up with relays with less VA requirements. Low impendance differential and REF schemes are gaining popularity but a change from the high impedance could be purely based on economic sense.

From the merits and demerits and cosidering the economic sense vis a vis sensitivity then I don't see why you can decide suddenly to overhaul the scheme.

Unless the relays have deterorited then I think you should maintain the relays. We still use PBOs, TJMs and FACs and they serve well the purposes.....

 

[slavag]

Hi.
Raghun is very, very intresting Q.
About REF HI, Marmite thanks a lot for the document.
Many countries/utilities request REF HI ( I see from time to time projects for ME, India and others).
On other hand, I see utilities at retrofir time disconnect REF HI and used REF LI only, but for the big AT still used REF HI.
BBP, as Rakan said, for the 400kV one and half CB configuration used HI BBP, but as combination of LI and HI
BBP for redandancy.
Lot of new projects in ME and Eroupean contries used only LI BBP, but for the redundancy used two options:
1. two LI BBP or one LI BBP and additional separated LI BFP
is connected to different CT's.
Best Regards.
Slava

 

[slavag]

Good Morning.
I would like add some intresting document about 87T ( diff )
protection. isn't exactly about OP, but..

http://library.abb.com/global/scot/...lementation_of_Negative-Sequence_Currents.pdf

Additional about HI BFP,
RADSS is great protection, but "problem" isn't RADSS, are class Px CT's( we need use same CT ratio on all bays for the BBP HI) and BB replika EM relays. Before 2 years flashover on this relay was reason for serious fault in our area. For RADSS we always need RAICA ( BFP), as separate relay and many times connected to the separated CT core.
I don't say about end-fault protection. Optionality for the bay protective functionality in the BBP.
Economical reason, less wiring, more flexibility is reason for used modern LI BBP instaed perfect HI BBP.
Just my pinion.
Best Regards.
Slava

 

[RRaghunath]

Thanks all for the posts.
Marmite, Thanks for the informative paper on REF protection.

But, I am still looking for some idea as to how many utilities in the world still continue to specify High impedance type REF/Busbar protection!

 

[jghrist]

You might be able to get some information on relative sales of bus differential relays from Schweitzer. They sell both a high impedance SEL-587Z and a low-impedance (current) SEL-487B for bus differential applications. One advantage of the SEL-587Z is cost (about 60% of the 487B).

Schweitzer uses a directional element in their SEL-387 for transformer REF protecdtion.

 

[RRaghunath]

Thanks, jghrist.
AREVA also sells MCAG and MFAC models for High impedance differential protection. They too seem to be doing well.

 

[slavag]

Hi Raghun.
Maybe possible ask your local ABB, Areva, GE, Siemens for the reference list.
Best Regards.
Slava