Relay Coordination Study? 1

[mfische]

I am a younger, inexperienced electrical engineer, and have been asked to (at my job) look into requirements of a relay coordination study. I am aware of what a relay coordination study is, but do relay coordination studies (to be accepted by inspectors or utility companies) need to be stamped by a professional engineer ? Or is there ever a scenario in which a non PE (but has his FE and a BS in Electrical engineering) can perform a study?

Thanks!

 

[Sharpie8]

I expect where you are working will dictate this. You need to provide more information as National and local regulations can vary.

 

[oldfieldguy]

There are herds of third-party engineering firms who will undertake this task for you. If you have a previous study, it will help.

If you're in USA, you'll do well to get this and an arc-flash study done at the same time.

old field guy

 

[mfische]

I am wanting to perform a relay coordination study so that my company can save money by not going to a third party engineering firm. I am an engineer myself, but don't have a PE yet.

That being said, this is a question in general.. there isn't a specific job or location I am trying to do a study for yet. I have found some articles that mention a typical relay coordination study comes down to One-line diagram (showing conductor, transformer, and other ratings of motors etc), Short-circuit study, current scale selection (show the time coordination is achieved), and other information as well.

My questions about this boil down to two:

1) Are most jurisdictions going to mandate an relay/protective coordination study be signed/sealed by a registered PE?
2) Are there certain items inspectors are always going to want to see with a coordination study? (Like one-line, characteristic curve, etc)

Thanks for any help

 

[tinfoil]

It depends on Location.

Here in Ontario, utility-owned substations with a largest voltage <50kV require engineers seal, whereas >50kV does not (don't ask, its a long story).
Customer-owned facilities need a seal when first built, but not necessarily when being upgraded or updated.

Next province over in Quebec or Manitoba, no seal is required, but one must follow 'good utility practices'.

So I do not think that there can be a 'general' answer.

 

[tomatge]

Personally I'm a little nervous about this thread. You say that you are "a younger, inexperienced electrical engineer" and "am aware of what a relay coordination study is" - which suggests to me that you haven't actually done one or even truly appreciate what's involved or at stake.

If you do this and get it wrong then there are two likely outcomes when the protection scheme is needed to do what it's there for and doesn't work properly:

1. More widespread indiscriminate tripping on the network, greater disruption, loss of customers etc., or:
2. What should trip doesn't, risking damage to plant, equipment or even personnel.

I don't think that many utilities would thank an inexperienced engineer for such an outcome because he felt like having a go at it himself and save the utility a bit of cash!

 

[mfische]

Hahaha!!! Okay.. Got it.. Thanks for "advice". Im sure you know everything also. hahaha

 

[alehman]

mfische,
Please take tomatge's advice to heart. I think it would be fine if you would work with an experienced engineer on this, but relay settings are not something to undertake on your own. You may understand the principles involved, but there are many nuances and "gotchas" that present opportunities for serious error.

Alan
The engineer's first problem in any design situation is to discover what the problem really is. Unk.

 

[mfische]

Alehman, Thanks.. I appreciate it. And I agree with you. I know this is a big deal, and have found that out the more I researched. Thanks for the advice!

 

[Desrod2]

mfische: protection coordination is a balance between safety and operating cost. You can set relays with very safe settings but you will get a lot of unwanted trips causing losses in production and your boss might not like that. On the other side you might put too much emphasis on production and neglect safety...and if there is a problem I hope you won't have to explain why someone might not return home from work or why half the plant is out of commission!
We are based in Canada, Quebec and we perform protection coordination studies for various clients. By law, such work is to be performed by registered engineers with proper professional insurance coverage.
I would recommend that you first acquire experience before performing studies in house. Doing protection work in house is a good practice since you will have first hand information and could then redo your coordination and arc flash studies when there is any changes. If there is no other eng. in house, you can hire external firms for coaching or require to work with them on a couple of studies. We do a lot of expertise transfer with our clients.

Hope this helps!
Daniel D

 

[mfische]

Thanks Daniel! Awesome advice. I agree.. I need the experience and I figured I needed it. I just wanted to know what the limits were. Thanks again for your help!

 

[ScottyUK]

Bear in mind that there is rarely one single 'right' solution, although there are countless thousands of wrong ones. A lot of knowing which solutions are good ones comes as a result of trying to figure out why someone else's scheme didn't work the way it was intended to. Setting relays is as much an art as it is a science, that is to say that there is a lot of judgement required as well as some calculation.

 

[Zogzog]

Bear in mind that you may not save any money, you will want a software package to do this and they can be tens of thousands of dollars. Farming this out to a specialist firm is usually the more economical solution.

Also there is the PE issue, several people asked about your location as that will determine if a PE is required.

 

[oldfieldguy]

Before the days of ETAP, etc., there was log-log paper and calculations with slide rule or calculator. These methods still work, although they are time-consuming, but rather inexpensive. You can find and print the log-log paper from the Internet.

Possession of the tools, whether software or paper, is only a small part of the process. Gathering system data is a second. Putting the two together, if you've never done one before, is time to get expert assistance. this applies for either method, hand or software.

old field guy

 

[HamburgerHelper]

There are a lot of things done with relay settings that you need experience to understand. There are a lot of things that you can do but you shouldn't even though you can. There is always a fight between security and selectivity. Security being that the fault is tripped out quickly and selectivity being the proper amount of the system was tripped out to isolate the fault. Industrial customers often don't care if their equipment has lost life due to not tripping a fault out quickly. More emphasis is placed on not interrupting the process with a misoperation. Utility relay settings tend to be tighter since more emphasis is placed on protecting the equipment. At SEL, the joke in training was answers to protection questions begin with "it depends..." There pros and cons to any application and each application has its own priorities.

 

[davidbeach]

Security is making sure the relay doesn't trip when it shouldn't and dependability is making sure that the relay trips every time it should. They are at opposite ends of a continuum and you can not maximize both at the same time. The relay settings and programming need to be just exactly as complicated as necessary but not any more.

 

[HamburgerHelper]

I used the term security wrong like David pointed out. What I meant to say was speed vs security/accuracy.

http://www.cdeep.iitb.ac.in/nptel/E...System Protection/digital_protection/lec4.pdf

 

[arrehman1]

I have seen coordination studies stamped by PE's in the state of Washington, USA.

Check the following IEEE standard for coordination study: IEEE Std 242-2001, IEEE Buff Book. All the good information/advise in this post is discussed in detail the Buff book.

Good luck!

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