Mainswitch fuse overheating

[Eire79]

Hi guys.
I have an ongoing problem with a compressor 166kw variable speed permanent magnet motor. I came across a main Sw fuse upstream from the motor which was extremely how over 100 degrees Celsius and on L 3 which blew fuse. I changed fusecarrier and female recepable whichfuse carrier pins enter to make circuit thinking that possible cause was high resistance at switch . Moving forward a few days same problem has arrised and while I was off site a transformer tripped one day along with the incommer to the main distribution panel feeding the compressor, maybe a coincidence but cause of trip has not been identified either . Also since totally new 400 a main Sw fuse has been installed it still seams to be operating at a high temp and I fear the issue will surface again . Notes to add currents on phases are In the region of 270 to 330 amps per phase I notice a 60 A difference between phases and also the company that supplied the compressor recently changed a stator which has been the only change in layout. I'm going to give the whole system a good going over tomorrow and see can I find any issues . Any advise by members greatly appreciated.

 

[James]

Check the phase voltages for any differences.
It may highlight why you have a difference in current.
I would normally expect the current readings to be much closer to equal than what you are reporting.

Could there be another load on that circuit, just on 1 phase?

I am thinking
Driers
Fans
Aux heaters etc.

 

[Eire79]

Iv done some investigation this morning 'll send a picture of the results . The Sw overheating is aprox 7mtrs upstream of the compressor all terminations checked ok with temperatures at terminals as attached. The main distribution panel is another 20mtrs upstream and has temp of 40 to 45 degrees Celsius , so I'm wondering why closest Sw is overheating so much almost double temp .could it be harmonics etc

 

[James]

Not quite sure about your cable arrangement
Are you running 300A down a 50mm cable?

Also, your supply voltages seem a bit on the low side.

 

[Risteard]

Not quite sure about your cable arrangement
Are you running 300A down a 50mm cable?

Also, your supply voltages seem a bit on the low side.

Perfectly normal supply voltage in Ireland. Obviously we've harmonised on 400/230, but the south used to be 380/220.

Also I read it as there are parallel conductors for the supply.

 

[James]

Perfectly normal supply voltage in Ireland. Obviously we've harmonised on 400/230, but the south used to be 380/220.

Also I read it as there are parallel conductors for the supply.

Agreed, just was not sure exactly what had a parallel supply and what had a single.

Do you normally calculate what the increase in current will be for large motors when running at a reduced voltage?

 

[Eire79]

It's one area in plant with 380 due to tapping on traffo as rest of site is 230 400. Their is about 10 traffo on site here. The plate on comp is rated 380 400 v either way.

 

[davesparks]

Not quite sure about your cable arrangement
Are you running 300A down a 50mm cable?

Also, your supply voltages seem a bit on the low side.

It says parallel 4x50mm, so I'd assume there's 2x50mm for each line

 

[Eire79]

Correct yes 2no 4x50 sq

 

[Darkwood]

Is there any magnetic circulating currents creating excessive heating, have the cables been glanded through metal enclosures correctly?

A pic of the offending switch may be good,

 

[Eire79]

Few pictures to look at plus thermal image . It's up on 100 degrees Celsius again

 

[Risteard]

I take it some of this installation is quite old given the red/yellow/blue & black cable? I mean it's not even brown/red/yellow & blue.

 

[Eire79]

Correct id say 45 to 50 yrs . I personally think it's a harmonics problem as a main incoming mccb tripped other day also at 1600A plus the Rmu feeding 10kv to traffo went also.

 

[Strima]

That appears to be hotter where the cable terminates into the ring crimp on L3, have you tried re-terminating?

 

[James]

Strima you beat me to it!
Just what I was thinking