LV BREAKER TEST PROBLEM - PRIMARY INJECTION

[EMT01]

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 question, may test okay on one or more tests and then fail on any given function. We then re-test and it may pass or it may not.

This is what we experienced this week on a single breaker... We had one test bad on INST.(day 1); then on day 2 (in the presence of the customer) it failed on Long-Time and passed on all other tests; day 3 (today) in the presence of a forensic engineer it passed on all tests. We then tested four additional breakers and all had some sort of failure on LT, ST, INST, or GFP. These were intermittant failures that we could not get to repeat.

The bottom line is that the breakers are inconsistent in their failures and these failures are seldom repeatable. Square D is not acknowledging a problem, but one another project (a few months ago) a Square D service technician used (8) different trip units in order to get (3) breakers functioning without any problem.

If someone would like additional information about our testing process, test results, other experience, etc. please let me know. Does anyone else have similar experience with these breakers? Any help would be appreciated.

 

[dpmac]

Please provide more information regarding the trip unit type and model. In addition, are you using a Square D Secondary Test Set in conjunction with the Primary Injection testing. If so, which model test set?
Thank you.

 

[EMT01]

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 defeat thermal memory, GFP and other functions, as necessary.

(2) Different Primary inj. Test Sets - Multi-Amp CB7150 w/ Mac 20 Controller; Multi-Amp CB8160

Our procedure is document the breaker NP info; pull the rating plug (per instruction manual); perform megger tests, contact resistance tests; replace rating plug; connect sec. inj. test set; defeat thermal and GFP; perform trip unit pick-up test and verify pick-up @ 105-120% (per instructions); then proceed with Primary Current testing.

Hope this helps. Please let me know if you need something else. Thanks.

 

[rbulsara]

That's very high failure rate for any mfr. Especially for masterpacts. I would say change the test set or the "tester" (testing technician) or both! And see what happens.

 

[Zogzog]

There sure have been a lot of masterpact issues on this forum lately.

I have also seen high failure rates on Masterpact breakers but not nearly that high. 57 of 107 is insane.

 

[oldfieldguy]

Could the trip units be responding incorrectly due to non-sinusoidal waveform outputs from the high-current test sets?

I remember that being a problem with some early solid-state protective relays and the MultiAmp SR-51 and SR-76 test sets.

old field guy

 

[dpmac]

Wow.

We just completed (today) a couple of projects utilizing the same breakers, trip units, secondary test sets and procedures. Only difference is the primary injection tests set mfg (but the controls were MAC 20). There would be no problem with non-sinusoidal waveform outputs on those model Multi Amp test sets your using.

We tested over 100 (New) breakers tested the same way as you are and not a single problem with any test or function.

Your not using the same cable on the Secondary Inj. Test Sets - SQD #S33595 are you? Any chance you damaged that cheesy trip unit cable connector and are missing a pin or two or they are stuck retracted? (I hope its not damaged, Square D is very proud of that cable: List price is $795.00)

We have probably tested 300 of this style breaker/trip unit in the same fashion over the past few months and I must say we had minimal if any problems at all. I am incredibly curious as to whats going on here. You have to get Square D on board. I will ask our regional guy if there is any issues he knows about.

 

[dpmac]

Other questions: Did the Secondary Test Set ever come up with a problem or discrepancy right off the bat when you plug it in? In other words did it ever say the trip units were defective? Did it ever come up with a discrepancy regarding the rating plug? For example you have a 4000A RP installed but the secondary test says says its a 1600A or something else? We have seen this happen but the breaker still tested on all phases and functions. The defective rating plug caused the trip unit to default to a lower value. It was defective, but consistent. Not the case with your situation.

 

[EMT01]

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) different high-current sets; (6) different secondary injection sets; and have had (5) different techs perform / witness the testing; and (1) forensic engineer (former NETA board member and testing company owner).

OLDFIELDGUY:
I don't think so, becasue almost 50% work perfectly.

DPMAC:
We have found that the cables (all of them) have to be inserted perfectly. A LITTLE MORE INFO... If the cable was not connected correctly the test set will trip the breaker in approx. 0.04 seconds. Our experiences have been way too much delay (like 5-10X too long) or no trip at all, until the test was terminated that is. ALSO, WE CHECKED THE CURRENT DISPLAY ON THE TRIP UNITS (those with local ammeter) AND FOUND THE TEST SET AND BREAKER TO BE READING THE SAME CURRENT (within 1% or so). As far as the rating plug issue, I'd have to say we haven't seen a problem, but even if it did occur that would mean the breaker would trip sooner rather than later or not at all.

EVERYONE:
The first project had (102) breakers and right at 50% failed. The trip units were made in China. I was wondering if maybe they had two lines of manufacture and there was an internal circuit assembly problem, because when the Square D Technician came out to the last job-site he brought some trip units and the customer spec'd spare trip units with each piece of gear, so there were (8) total on-hand when Square D showed up. We (and Square D) used all (8) trip units in order to get (2) breakers functioning correctly.

 

[rbulsara]

Whatever it is, there something more to this what appears. But that is not here nor there. Good Luck.

 

[trosepe]

EMT01,
Are these fixed mounted circuit breakers or draw out? If fixed mounted; you need to be be sure some of the primary injection current is not being shunted to ground through the main bonding jumper in the switchboard. One side of the output transformer on the CB175 is grounded and if the system transformer is close; depending on how and where you connect your test cables, enough current can be shunted away from the circuit breaker under test to affect the results. It will change with every connection giving you the inconsistent results you are seeing. If these are draw out, need more info.

By any chance do these circuit breakers have neural ground fault CT's in the switchboard? That is another issue I can go over if you respond yes.

 

[dpmac]

trosepe stated: "Are these fixed mounted circuit breakers or draw out? If fixed mounted; you need to be be sure some of the primary injection current is not being shunted to ground through the main bonding jumper in the switchboard. One side of the output transformer on the CB175 is grounded and if the system transformer is close; depending on how and where you connect your test cables, enough current can be shunted away from the circuit breaker under test to affect the results. It will change with every connection giving you the inconsistent results you are seeing. If these are draw out, need more info."


I was giving this thought also but his comment: "ALSO, WE CHECKED THE CURRENT DISPLAY ON THE TRIP UNITS (those with local ammeter) AND FOUND THE TEST SET AND BREAKER TO BE READING THE SAME CURRENT (within 1% or so)." led me to think this would not be the case.

 

[trosepe]

I just spoke with an associate that had a similar situation with primary injection testing of Masterpact drawout circuit breakers. He said they had to common the load side stabs of the circuit breaker under test, connect one side of the test set output to line side of A phase and connect the other side of the test test to line side of B&C phases. This due to the circuit breaker responding to injection through a single phase with inconsistent trip results. After this set up was employed; all was well. The test set up described was for A phase and of course for B phase you connect one side of test set to line side B and the other to the line side of A&C etc.

 

[alehman]

trosepe,
That's very strange. I wonder how they decided to do the testing like that.

Alan
----
"It’s always fun to do the impossible." - Walt Disney

 

[trosepe]

They found that unless all three phases had current, the trip units would not operate properly. It makes sense that a self powered trip unit may need all three phases with current. GE Versa Trip needs current through two phases to operate properly. The thread indicated these circuit breakers had ground trip functions. If there is not current on at least two phases, it would see that current through a single phase as a ground fault event.

 

[dpmac]

trosepe said: "They found that unless all three phases had current, the trip units would not operate properly. It makes sense that a self powered trip unit may need all three phases with current. GE Versa Trip needs current through two phases to operate properly. The thread indicated these circuit breakers had ground trip functions. If there is not current on at least two phases, it would see that current through a single phase as a ground fault event."

I believe this type of testing arrangement would apply if no secondary test set was available. The secondary test set is required to defeat the GF function (and other things) and allows for single phase testing when performing primary injection tests. In addition, the secondary test set provides power to the trip unit when performing primary injection tests. I hope this helps.

 

[trosepe]

dpmac,
You are right if it was done properly. It seems something may be a bit off with the test procedures to have such a high failure rate. Been in the business a long time and I have not experienced or heard of a failure rate this high. What do you think.

 

[dpmac]

trosepe:

I agree there is something afoot.

EMT01:

Is there any pattern as to trip unit type or breaker size failures ? For example, do you see a larger percentage of failures in the trip units with voltage monitoring capabilities (those with "P" designation)? This may indicate that rating plugs may damaged during insulation resistance testing. Are you sure they are being removed during insulation resistance testing?

You said the failure mode was excessive trip times. Are only the "wide" frame breakers showing this behavior? "Wide" frame are larger frame size breakers with 4 poles per phase, (2 line and 2 load) Are your people aware that primary injection can only be performed on the "inside poles" as The CT's are only on one of the two poles associated with each phase.

Please keep us posted on this situation

 

[trosepe]

EMT01,

What is the rating, impedance of your test power source? Is it a generator? How long are the input cables to the test set and what size are they?

 

[EMT01]

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 INFORMATION FROM YOU ABOUT THE BREAKER TEST CONNECTIONS YOU MENTIONED. Was a secondary test set being used and if so, what part number. Secondly, did they have any breakers "pass" beforehand, remember that we had alomst half pass the first time without any issues?

EVERYONE: A little more info... The high-current test set is and always has been connected to permanent power (no generator). We are testing the breakers in our shop. We are using hard bus (no cables) for connection to the breaker stabs.

All of the rating plugs were removed prior to meggering. I read in the Sqaure D manual that only the "P" & "H" trip units require removal of the rating plugs (section 10 of Masterpact manual), so in theory even if we hadn't removed the rating plugs from the 5.0 and 5.0A they should be unaffected.

HERE'S A LITTLE MORE NEW INFORMATION:
Once a function of the breaker has been determined to be "out of the curve" and the test terminated, the breaker will "improve" on an immediate retest until it eventually falls within the curve. This may take one more test, but for 95% of the breakers this requires no more than (3) tests total. Additionally, 97% of the breakers will eventually pass on all tests. We have re-tested a few of the breakers again on the following day and had different trip functions fail and end up going through the same process again, until the breaker passes all tests again.

Basically, these breakers are inconsistent and if our testing is correct, represents a real danger to the customer from both a protection stand-point and safety (especially arc flash).