Screw compressor MPCBs keep failing , Please Help !!

[Mohammedi Seddik]

Hello ,

i'am facing a screw compressor breaker issue , lately a lot of power interuption hapens and the breaker trips when it hapens , but now the breaker don't even work, its 3 ph + N 630A MPCB but we only use the 3 phases output, its runing a 250 Kw compressor AC motor in Delta/star, here is the MPCB parameters set in the attachments, i checked the compressor circuit and motor and it doesn't look like there is a problem in it, so are those interuptions the reason for those MPCBs keep failing , and if yes can you explain why ? thank you

note : this hapened with more than just one breaker, and with two compressors so i don't think its a bad breaker or a compressor problem.

 

[Cadgey123]

Have you got any control circuitry diagrams or any information on the compressor?
Very vague description to guess what would be the cause so far.

 

[Pete999]

scQUOTE="Mohammedi Seddik, post: 1369902, member: 107957"]Hello ,

i'am facing a screw compressor breaker issue , lately a lot of power interuption hapens and the breaker trips when it hapens , but now the breaker don't even work, its 3 ph + N 630A MPCB but we only use the 3 phases output, its runing a 250 Kw compressor AC motor in Delta/star, here is the MPCB parameters set in the attachments, i checked the compressor circuit and motor and it doesn't look like there is a problem in it, so are those interuptions the reason for those MPCBs keep failing , and if yes can you explain why ? thank you

note : this hapened with more than just one breaker, and with two compressors so i don't think its a bad breaker or a compressor problem.

View attachment 41405[/QUOTE]
Is the MPCB on start up or during the normal running, maybe an idea to put a data logger on the mains, as you say you get a lot of outages at your location, what are the screw compressors, running, A/C plant?

 

[Mohammedi Seddik]

Thank you Pete999 for replying,
the compressor supplys our machinery with compressed air , the current can reach 360A when in load versus 250A during unloading, and it runs with no problems until some power intruptions hapens and the breaker start to act weird, someimes it gives all 3 phases , sometimes one phase is lost , one theory i thought about is sometimes the power inteurption is so fast that the compressor don't even stops however i sense a speed decrease in the compressor motor , maybe the problem is that during those really fast intruptions the 250 kw motor draw a lot of current for it to regain its speed when its runing in delta causing a huge current demande, i forget to tell you that sometimes those compressor display an alarm of current overload 999.9 like in the picture.

 

[Cadgey123]

Sounds like the power interruptions are your problem and not the compressor or breaker.

 

[ipf]

Are you temporarily losing a phase?
Regular single phasing will cause overload problems with the breaker, and resultant damage. Not just with the breaker, either.

 

[Mohammedi Seddik]

yes Cadgey123 sounds like that , but what i need is an explanation of how those interuptions may damage breakers.

 

[Mohammedi Seddik]

ipf , this phase lost is mesured after the failure of the breaker , i don't quit know if the phase is lost or decreased when the compressor is running.

 

[Pete999]

Thank you Pete999 for replying,
the compressor supplys our machinery with compressed air , the current can reach 360A when in load versus 250A during unloading, and it runs with no problems until some power intruptions hapens and the breaker start to act weird, someimes it gives all 3 phases , sometimes one phase is lost , one theory i thought about is sometimes the power inteurption is so fast that the compressor don't even stops however i sense a speed decrease in the compressor motor , maybe the problem is that during those really fast intruptions the 250 kw motor draw a lot of current for it to regain its speed when its runing in delta causing a huge current demande, i forget to tell you that sometimes those compressor display an alarm of current overload 999.9 like in the picture.

View attachment 41406

Personally, I am thinking the MPCB can't cope with the sudden loss of voltage however miniscule, i think you may need to contact the power supplier and explain your difficulties.
I don't know the possibilities but if it was in a country with a stable supply, (and even those can be subject to power outages) a "No break set up may be the answer" it's very difficult to give a remedy to your supply problems from a remote location.
But as the Machinery is large and expensive, would you not consider a survey of the structure of the supply for a trail period, before you go to the expense of installing a no break set up. it may be expensive in the short term, but with s decent set upthe costs should be recovered fairly quickly, and ensure a decent run of the machinery, these are my thoughts from a far, but you will be better placed to come to a conclusion that suits all concerned.

 

[LeeH]

You could send the MPCB back to Schneider and ask them if they would do an autopsy.

Depends on how friendly you are with the local Merlin rep.

I agree with the above, likely to be outages causing the problem. I’d like to know if you ever resolve this.

 

[Pete999]

yes Cadgey123 sounds like that , but what i need is an explanation of how those interuptions may damage breakers.

As I explained the MPCBs may not be able to accept frequent outages, hence my post suggesting a backup system to avoid this.

 

[Pete999]

You could send the MPCB back to Schneider and ask them if they would do an autopsy.

Depends on how friendly you are with the local Merlin rep.

I agree with the above, likely to be outages causing the problem. I’d like to know if you ever resolve this.

The OP is in Algeria, having worked overseas for many years,( although your idea is a good one) it may not be as simple as it sounds, I overcame the problems with unstable supplies by installing the no break syste, it worked vert well the customer was impressed 100% of the time.

 

[Rocboni]

I agree with the theory of frequent power loss causing the issue, possibly because when the motor looses power inertia takes over threfor it is acting like a generator and backfeeding the MCPB, when power is restored the motor needs to synchronise back in phase with the supply which can mimic a short circuit which is possibly what the MCPB is picking up on.

If your just loosing a phase then obviously the breaker will trip a it’ll be drawing more current on the remaining phases.

 

[Bobster]

I agree with the theory of frequent power loss causing the issue, possibly because when the motor looses power inertia takes over threfor it is acting like a generator and backfeeding the MCPB, when power is restored the motor needs to synchronise back in phase with the supply which can mimic a short circuit which is possibly what the MCPB is picking up on.


If your just loosing a phase then obviously the breaker will trip a it’ll be drawing more current on the remaining phases.

A loss of phase or drop in voltage will cause the MPCB to trip with it's thermal characteristics. As it's designed to. It won't damage it.

They are also designed to clear a fault a lot higher in magnitude than MCB's or MCCb's usually between 65kA to 100kA.

A spike in voltage however could (i've not checked the specs of the MPCB) cause damage to the sensing coils in the MPCB if it's an electronic type.

 

[Rocboni]

Can we get the part number of the MPCB, it could be a standard MCCB

 

[Mohammedi Seddik]

Can we get the part number of the MPCB, it could be a standard MCCB

here it is :

 

[LeeH]

That is an MCCB FYI.

 

[Mohammedi Seddik]

Can we get the part number of the MPCB, it could be a standard MCCB

here it is :

 

[Mohammedi Seddik]

That is an MCCB FYI.

So do you think using this with a 250kw motor is a wrong idea ??

 

[LeeH]

I can only presume the compressor being such a large one is on a skid with its own control circuit? If so I cannot see a problem as it will have its own overload protection and that MCCB is just protecting the cable to the compressor.

I can only suggest replacing it with some motor rated HRC fuses and see if they a more robust solution.

But without seeing it everyone is guessing.