×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Gen./Transformer Differential Prot.

Gen./Transformer Differential Prot.

Gen./Transformer Differential Prot.

(OP)
Can anyone suggest a differential relay for a Generator and its step up transformer. One set of differential CTs are on the neutral side of the 13.8kV generator and the other set is on 115kV Bus of a step-up transformer. So the zone of protection includes both Gen. and Transformer. Which relay (Make and Model) will be best suited for this application?

RE: Gen./Transformer Differential Prot.

ABB's REG670 can provide an overall differential function in addition to stator differential. I assume this is an additional protection function and not in lieu of the stator differential relay: you will not have enough sensitivity to adequately protect the stator if you have to use a biased diff relay to accommodate the GSU tapchanger.

RE: Gen./Transformer Differential Prot.

I have had experience with the SEL 700G in a similar application. There was not a tap changer on the GSU.

SEL 700G

RE: Gen./Transformer Differential Prot.

A bit more information from the OP about his intended application would help. wink

RE: Gen./Transformer Differential Prot.

(OP)
Both the Generator (13.8kV, 160MVA) and Step-up Transformer (13.8/115kV, 166MVA) have their dedicated differential protection. The overall differential protection is named as "Gen. Step-up Transformer Overall Differential Protection".

RE: Gen./Transformer Differential Prot.

(OP)
@ScottyUK

In my application, there is a tap changer on 115kV side for GSU transformer. Does it makes difference for Differential Protection? Because I believe the tap changer variation will be compensated in the relay settings for differential protection.

RE: Gen./Transformer Differential Prot.

A biased differential relay allows a larger imbalance current to flow without tripping the relay as load current increases. This is probably the most common type of differential relay used in transformer protection. In contrast a stator differential relay usually has a very low setting which is independent of load current.

If you use a biased scheme I don't think you will be able to achieve as low a setting and the protection afforded to the machine will be reduced. The cost of an additional relay is likely to be a few thousand pounds or dollars, to protect a machine worth perhaps 1000 times as much.

RE: Gen./Transformer Differential Prot.

"Both the Generator (13.8kV, 160MVA) and Step-up Transformer (13.8/115kV, 166MVA) have their dedicated differential protection. "

I see this as added protection as back up to the primary units. If you can live with lower sensitivity if it is a back up unit (high slope / second slope) settings most modern relays will satisfy your initial requirements. You will want to also pay attention to the CT's for matching performance and lead length / burden issues for a run that long. What you don't want is your back up protection to nuisance trip for a through fault, due to saturation issues. On a 160 MVA unit that could be quite a distance between the Gen Neutral CTs and the Transformer HV side or HV breaker, if you choose to further extend the back up protection to cover the breaker.

RE: Gen./Transformer Differential Prot.

Thanks smallgreek, I missed the first of the two consecutive posts from burntcoil. blush. I agree with your comments.

RE: Gen./Transformer Differential Prot.

Possible use any transformer differential protective terminal, if it's only overall differential protection.
If you need also back-up protection to generator protection, a good style for such application use protective terminals like to ABB REG670/REG650, Alstom P34x, Siemens 7UMx.

In your case, a best way use same terminal as exist transformer differential, less spare parts :).

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources