1E Motor Thermal Overload - Outage Question

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mityeltu

mityeltu

Senior Member
Location
Tennessee
OK, I have been on the phone with Schneider Electric (Square-D) and frankly I find their technical assistance to be just about as useful as a third nipple.

We have some thermal overloads that are being qualified by a third party for a 1E application at our nuke site. The thermal overloads have been failing due to resistance measurements of the units. I don't think they are testing them correctly.

The data that they sent stipulates that the nominal resistance is at 20? C. They do not list the temp during the testing. I suspect that there is a compensation factor (similar to that for cables) to be applied to these units, but square-d doesn't want to help me for some reason. I think they don't like nuclear.

Anyway, is there anyone here who can supply the calc for motor thermal overload unit ambient temperature resistance compensation?

I know what at least one person will say, why not just tell them to supply this information and provide proof that the units were measured at 20?C or that the temp was compensated during measurement. Valid point, but for my own edification and to have my barrel loaded before I call I would like to know.

Thanks.
 
B

BJ Conner

Senior Member
Location
97006
IT's a NUKE

IT's a NUKE

Your asking for certification of performance for equipment that is essential to the safe shut down of a nuclear power plant.
The process ( testing, documentation, Quality program implimentation, etc etc. ) is expensive and probably not what your going to get on the phone.
Who built, tested, and cetified your original MCCs?
A manufacture is not going to take on the libility of supplying a component for a nuclear power plant.
Good Luck.
 
zog

zog

Senior Member
Location
Charlotte, NC
I would think the documentation for qualification under thier appendix B program would require ambient tempature to be recorded and correct for, in fact I am shocked it was not.

While overloads are not my thing, I don't see why tempature correction would be any different than the normal correction values.
 
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J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Have you looked at page 16-128 of Schneider Electric's Digest 175?
It contains a procedure for calculating trip current ratings of their overload relays for applications at other than 40?C. However, this may not be the same procedure used to 'certify' or test the performance of these devices.

According to NEMA ICS2-222, from at least back in 1994, overload relay tests shall be conducted in an ambient temperature of 40?C +/- 1?C. The overload relay shall be at equilibrium with the ambient before testing.
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
The industry standard for testing and labeling OLRs is performance based on heating, of the mass of the thermal unit, at 40?C not on resistance at 20?C. I find it totally plausible that there are no official compensation tables.
 
mityeltu

mityeltu

Senior Member
Location
Tennessee
Right, I found the compensation curve, but I can't correlate the test data with anything. I have a table of nominal resistance values for the thermal overloads apparently compiled by square-d (their name is on it, but no one at square-d will confirm the data). This chart stipulates that the data is for 20?C.

This is part of the problem. If my third party tester is not compensating for the temperature (no one will tell me and it is not indicated on the test report - infuriating), then part of the reason the units are failing outside a +/- 10% range could be because the units are not being tested against the proper temp. Again, at this point I have no way of verifying ANY data.

The last rub is that these overloads could affect my voltage drop at the terminals of my motor. I was informaed a little while ago that we have had to remove the overloads on some motors because the voltage drop per ETAP was too large - I personally find this laughable due to the enormous safety factors that I find built into our model.

Never the less, I was hoping that someone here had a formular for temp correction of thermal unit resistance similar to the one I have for temp correcting cable resistance.

Anyone? Anyone?

Bueller? Bueller?
 
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