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5/25/2009: As a follow-up to this problem, we took some breakers that we had already tested to a well respected NETA firm in the Chicago area for re-testing and also testing of some virgin breakers. We had them re-test (2) Masterpacts with the 6.0A trip unit (PRI. INJ.). One tested OK and the...

DPMAC: LTD @ 300% has gone up tp 15X longer than published trip time and we have terminated the test. The same goes for other functions. Once the breaker "cooks" for this amount of time the breaker will usually fall within the curve on the next attempt, but if not by the third or fourth...

TROSEPE: The breakers are drawout and ground-fault is defeated with the secondary test set. The secondary test set has been connected to every breaker we have tested to provide power to the trip unit. There does not appear any pattern to the failures. I WOULD LIKE TO GET A LITTLE MORE...

OK guys...I'm too new to the posting thing, so I'm going to lump this together. RBULSARA: This failure rate is over two different projects, to-date. The high-current test sets are not yet due for re-calibration. The test sets work fine with all other breakers testes. We have used (2)...

Breakers are Masterpact ANSI Rated NW & NT 800-4000AMP Frame To date, we have had a total of 57 failed NW & NT breakers of 107 tested using Primary Injection. (5) Different Trip Units: Micrologic 5.0, 5.0A, 5.0P, 6.0A, 6.0P (6) Different Secondary Inj. Test Sets - SQD #S33595 - Used to...

We have recently tested numberous Square D Mastpact NW & NT circuit breakers and are having a 50+% failure rate, when performing primary current injection tests. All other tests are OK (insulation resistance, contact resistance, Trip Unit pick-up). We are finding that the breakers, in...

Don't forget that when topping off fluid, verification of the fluid could be necessary in the event the gauge is out of calibration. Sometimes it is necessary to adjust the float rod after taking an actual measurement of the fluid level. Also, be sure to make sure if the unit has a N2 blanket...

I wouldn't typically untank a three-phase power transformer for a moisture related problem. However, it depends upon several factors; size; criticality of the feed; accessibility; etc. If the unit is significantly beyond the IEEE / ANSI limits for in-service oil you may want to: 1.) Repair...

Assuming the level is OK and the fluid is mineral oil, then I would look at the oil quality test results (specifically moisture content). If moisture is elevated, then look to the acid neutralization number and if also elevated (.20 or higher for this class of XFMR) then sludge may be forming...

apowerengr, The bank is actually a Wye-Delta. The general consensus, for a 2%Z transformer is + or - .1%Z on the nameplate or about a 10% variance. I will look again at the GE & ABB manuals I have and see if I've missed something. Thanks.

Can anyone point me to an IEEE or ANSI standard that addresses the maximum variation in transformer impedance for a three-phase delta connected bank? I cannot seem to find a definitive answer, but rather some generalities (such as + or - 7.5%). I have a client who recently lost two...