SEL 351S Relays

[hidalgoe]

Hello:

We recently replaced our old main substation electromechanical relaying system with a SEL 351S/351A system. The 351A relays are for feeder protection and the 351S relays serve as main secondary breakers.

Our substation consists of 2ea power transformers (69kV/12.47kV, 15/20MVA ABB) feeding a dual lineup with a tie breaker. Each lineup has six feeders (12.47kV).

Each transformer has S&C Trans-Rupters on the primary side (with a Basler relay system for overcurrent protection)

We have to come up with 27 (UV), 59 (OV) and 81 settings for the 351S relays. I am hesistant to recommend settings based on the settings we had for the electromechanical over/undervoltage protection.

Any ideas, folks.

Thank you kindly in advance

 

[dpc]

These modern multi-function relays generally have more functions than would ever be used on a single application.

First, determine what functions are really necessary. The fewer functions enabled, the fewer nuisance trips you will experience. The 351 is a complicated relay - it really helps to keep it as simple as possible, at least initially.

If you decide you need undervoltage, overvoltage, 81O/U or whatever, the setting criteria will be no different than it would be for electromechanical relays. If you can provide additional information regarding your system, you'll probably get a lot of advice on settings. The 81 settings certainly must be coordinated with other frequency and load shedding relaying you have in the system.

 

[hidalgoe]

dpc:

We have no load shedding scheme implemented at this time or other frequency relaying

When I set the old 27/59 electromechanical devices I had access to time-voltage curves, but with the 351S I have not been able to locate any.

Yes, I would appreciate advice on settings for this advanced circuit breaker.

What other information do I need to post?

Thank you,

hidalgoe

 

[davidbeach]

I'd suggest you consult your local SEL Field Application Engineer. I've found them to be quite helpfully and knowledgeable.

 

[stevenal]

Your 351S time-voltage curve is flat. Use the output relay word bit in question to start a timer if you wish, but inverse curves are not possible. With multiple pickups available, you could effectively create a stepped curve.

 

[dpc]

What are your trying to accomplish with the over/undervoltage functions? I guess that's the main question.

As stevenal said, the 27/59 functions in the 351 are definite time, not inverse time. But you can have two levels with different time delays.

 

[rbulsara]

So what is the question? You need someone experienced in setting relays and familiar with the project requirements.

Rafiq Bulsara

http://www.srengineersct.com

 

[jghrist]

The 351A relays are for feeder protection and the 351S relays serve as main secondary breakers.

What is meant by "main secondary breakers"?

 

[hidalgoe]

rbulsara:

I appreciate your concern.

I have over 35 years of experience as a PE and power systems engineer. I have done projects for small and large industrial plants and for colleges, universities, hospitals and a few medium sized utilities.

My motivation was obtaining advice on a relay I am not familiar with since I was very much pressed for time.

Having read your considered and timely responses (and other colleagues responses) to varied electrical problems, I thought it would be proper to seek your advice.

However, I am grateful for your frankness.

Respectfully,

Hidalgoe,

 

[rbulsara]

hidalgoe:

Cool! In that case, dpc already answered it.


Rafiq Bulsara

http://www.srengineersct.com

 

[hidalgoe]

davidbeach,dpc,jghrist,stevenal:

I called a colleague who was familiar with the SEL 351S and discussed this relay's multi-functionality. We came to the conclusion that what I need is separate OV/UV protection; a relay that will provide the time-voltage characteristics that I want for OV/UV protection.

Thank you all for your help and consideration.

Respectfully,

hidalgoe

 

[dpc]

hidlgoe,

I can't imagine why this would be necessary. You've never explained the purpose of the UV/OV protection, so it is difficult to comment on specifics. But whatever floats your boat. Good luck.