Merlin gerin masterpact problem

[ch427]

Hi all,i have a problem with a merlin gerin masterpact 800amp m08 h1 circuit breaker.
over the weekend the breaker has been randomly tripping with little load on it,the tripping mechanism will indicate a fault and the breaker will discharge
the phases have around 45 amps on them when this happens as the plant it usually feeds is not in operation,the loads on it are heating and lighting circuits etc from local distribution boards
the breaker will reset ok after the trip and then may go on for another few hours before it happens again
ive had issues on these breakers(there are another 2 fitted elsewhere)in the past when weather is bad,a lightning flash has been enough to trip them
im not clued up on them but am sure they dont have ground fault monitoring presesnt,im also sure they were not set up correctly when installed roughly 4 years ago
ive tried to enclose a few photos to see if you can shed any light on the issue
let me know any further details you may need
Thanks

 

[ch427]

another image

 

[parlitu]

First of all, you shoud install a current recorder (if you have one) on all three phase, and let it there until the breaker trip. You will find out the exactly current values (maybe there is a peak value, cause by a load starting, transformer, or motor, or something else) and you will be with one step further to solve this problem. Unfortunetly I did not work with this kind of brekers, so I can't give you more details for the moment, but I will search to find out more.

 

[ScottyUK]

Merlin had a type fault on the earlier ST series tripping units where a component aging problem caused misoperation. It's about ten years ago so my memory is a little blurry: I can't remember if the failure mode was fail-to-trip under fault conditions or the breaker went trigger-happy. I seem to recall the latter. I have not heard of a problem with the STR series, but there's that nagging doubt when it has happened once before.

Of course the tripping unit might be knackered too. There's a test port on the front for a breaker test set to plug in, or you could hire in someone to do a more comprensive test than you can from the test port.


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If we learn from our mistakes I'm getting a great education!

 

[Rodmcm]

Are you sure that they are tripping on protection? Some breaker versions have a permanently energised no volt release which is often used as a tripping coil ( sometimes connected in series to emergency stops and the like ( MG can do both). If it has this then I would check the supply/connections to this circuit.

 

[rbulsara]

ch427:

To me the breaker's Instantaneous setting (I) appears to be set to lowest (most sensitive). Plus I am not sure how other setting fares when plotted on a TCC curve.

For starters set the INST Setting near to highest and then have a testing firm test the breaker and have a coordination review performed by a competent engineer. If this breaker is representative of other breakers in the facility, they would be having much more issues or potential issues.

 

[zaphod1]

I have seen problems in the Square D masterpact similar to this before. If the trip unit fails then the breaker defaults back to a low percentage of its frame rating. This is an easy fix and the trip unit is only a couple of hundred dollars. This may be your problem.

 

[ScottyUK]

Have a look at thread238-126746 and particularly the reply from BigAmp.


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If we learn from our mistakes I'm getting a great education!

 

[ch427]

Thanks for your input,i spoke with the technical dept at merlin gerin today and they were almost positive it was down to the breaker being lightly loaded causing the trips as suggested in that thread
They suggested an engineer visit to re programme the trip unit to sort out the issue,it seems to be quite a common problem

 

[EddyWirbelstrom]

I remember about 15 years ago, the trip unit type STR58U on the Masterpact ACBs are self powered from the internal CTs. However on very low currents the STR58U trip unit would trip if a trip unit power supply module type AD was not included. On higher loads the power supply module is not required.