Trip Unit Testing Question

[cslater]

We are installing a set of 208V switchgear with electronic trip breakers. We brought in a testing company to test all of the breakers, and to set the timing.

Our direction was to set the Long Time trips at 1.0 and all other settings at minimum. However, there was a misunderstanding, and the Long Time setting was also set at a minimum (0.4).

Clearly this won't work, because our breakers will now trip at 400A rather than 1000A as required.

My question is this: Are the secondary injection tests they performed on the trip units still valid if we adjust the Long Time pickup to 1.0, or should they be retested?

 

[rbulsara]

Our direction was to set the Long Time trips at 1.0 and all other settings at minimum.

That is not good.

However, there was a misunderstanding, and the Long Time setting was also set at a minimum (0.4).

That is even worse!

Get someone experienced in design, system analysis and coordination study to review your electrical system.

Rafiq Bulsara

http://www.srengineersct.com

 

[cslater]

We are working on getting a coordination study done, but need something functional in the mean time. My understanding is that the only "risk" of having all other settings at a minimum is nuisance trips. Are there other risks?

 

[rbulsara]

Nope, if you are OK with nuisance trips. It just shows what happens when a structural engineer plays electrical engineer.

Rafiq Bulsara

http://www.srengineersct.com

 

[cslater]

I'm actually a licensed Civil and Mechanical who was doing a lot of work in the Structural field when I signed up and now can't figure out how to change my "type".

Someday soon I hope to get my Electrical license - so that I can be clueless in three fields.

They need to change the site so I can have my ID say "cslater (Clueless)".

Thanks for the help rbulsara. Appreciate it.

 

[rbulsara]

You are welcome, clslater!

You can change your "type" by emailing to the site management using the "contact us" at the bottom of this page.

Btw, I am clueless about many things too and I engage professionals in those field to do their job. I respect profession of other trades as much as I do mine.

Rafiq Bulsara

http://www.srengineersct.com

 

[dpc]

Are the secondary injection tests they performed on the trip units still valid

Ideally, you would re-test the breakers and trip units at the new settings. But in reality, these type of changes (not this extreme normally) are commonly made without re-testing. If it on an interim basis while a complete coordination study is being completed, I'd be OK with it, since it has been verified that the trip units and breakers are functional and within tolerances for one group of settings.

But the NETA folks may not agree.





David Castor

http://www.cvoes.com

 

[rbulsara]

While secondary injection test may remain valid, secondary injection method by itself is not sufficient to begin with, as it does not test the entire breaker assembly, including the sensors, etc.

Primary injection method is the the proper testing. I would use secondary injection method for subsequent changes like these.

I agree that minor tweaks are OK, without retesting.

Rafiq Bulsara

http://www.srengineersct.com

 

[alehman]

Minor tweaks are OK if the application is not critical. I recently had a case where one of the switch positions on the trip unit didn't work correctly so what we thought was a setting of 1.0 actually tripped at 0.5 when tested. That sort of thing is rare though.

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

 

[Zogzog]

As Rbulsa pointed out a secondary injection test does nto test much, only the trip unit itself. A seconday injection test does not meet the ASNI or NETA testing requirements. So I assmue the "testing company" you brought in is not NETA certified or was required to follow ANSI/NETA specs for the job. Seconday injection testing usually screams "Low bidder".

As far as testing at different settings, no real rule on this, settings are changed all the time, but the most likely failure for most trip units (No idea what type you have) is to fail to the minimum setting, so if you tested them at the minimum set points you really don't know if they work or not. And with secondary injection testing you don't know if your CT's are functioning.

 

[cslater]

Just to clarify, it's a good testing company that is being used. As it was explained to me, some portion of their testing was done via primary injection and some via secondary. I believe the trip characteristics were tested via secondary.