can anyone help out with a problem I have got, We have a 3 phase compressor that is failing to start up, it is on a star delta 3 seperate contactors, when we press to start up the first two contactors start up on slow speed then shuts down on low speed, it is a 400 amp compressor running in parallel with two others, they are fine and the compressor is newly serviced, we are guessing it is an electrical problem as two fitters have told us the starter control is at fault, any suggestions greatfully received? We have had the program checked in the plc that controls the compressors so we are scratching our heads now.
I would doubt the 400 amps on the compressor, what is it doing as you mention there are another two? would need to be some serious kit running those and also the physical size of the compressors would need to be housed in a plant room that would need some footprint, a bit more info is required such as make of compressors, is this as I assume running on a SCADA system and if so are you able to interrogate the SCADA for further info? Also this is a Screwfix forum so luckily you have stumbled across me and there are a few others on here who are industrial sparks, why a Screwfix forum for help?
Thank you for replying, The compressor is a stall that has failed it is a large refrigeration cold stores. I came on here as I use screwfix myself and have tried another forum with no joy. I am a senior engineer and we do have a team of electricians and multi skilled fitters. We have also had an electrician out who says it is a fault with the compressor but we have since proved this theory wrong. The compressor has been off line for a week now and is giving rise for concern so this is I know clutching at straws but any help or pointers would be welcome. The SCADA is wonderware if you are familiar with that? The contactors are 24V 300 Amp rated and are relatively new. First time our team has not been able to solve this so why we are on here. The amperage is 400 Amps and the compressors fully loaded will run at this but as we have 3 of them so as not to run each one at this, generaly sit quite happy ticking over at 198 amps on the panel display, however since losing this one the other two are running much higher at 300 each which will put a lot of strain as they run 24/7. Hope this makes sense to you.
To name a few more top notch sparks on the forum - no particular order Lec Baz Spin London Lee Sparky Rulland Un Sen And loads more - my apologies to those who I have not listed
So I am in the right place at last then, hopefully someone will see the obvious that we are missing, we have come to a brick wall with this as we have tried everything and no joy, the compressor to replace would be in the region of £100k so that would be a last resort.
I take it the star contactor never opens to allow the delta to close? It sounds like it could be a signaling issue, have you checked to see the inputs/outputs to the SCADA are working. I assume it controls the timing of the changeover Has it ever worked since you changed the contactors, although unlikely has the overload relay been set too low?
The contactors were replaced about 12 months ago at a cost of £900 each and the compressor has run ever since, last week it stopped and refuses to start, we got our programmer in who checked all our programs that control the compressors and he says all is well. The overload was checked for working, it is a radio activated relay that controls each compressor, we swapped a known working relay over to test it and still the same.
We are uncertain to how the compressors are controlled as if the duty satisfied signal comes on it drops one of the compressors out until there is a call for duty so that's why we called in our PLC Guru to check the sequencing of the program. The other two compressors are Sabroe but have all worked well together til now.
Just an update on my problem, we have just had our rewinders out to test the motor out for us, he checked the bearings and all connections cable etc and insists the motor is fine. We have had two of our electricians on itand in the control panels most of the day and they are both just saying they don't see why it isn't working, everything is checking out ok but still it isn't running. They checked the contactors and they all check ok and power will run through them when they kick in but its just not kicking in. Total loss at the moment and weather is getting warmer which is a real worry.
I won't lie this is far beyond my area and most common electricians But, if you've had all these people out and you spent so much time trying to find a fault that appears to not be there, have you thought about starting again? As in rebuild the control side of things. I had a similar issue on a roller mill last year everything seemed okay so in the end I had the control panel stripped and rebuilt. They couldn't find anything wrong with old panel but once the rebuilt one was installed it worked fine.
As I said it's beyond me but I assume this is something g that has been designed and built to suit your spec? If so could you not contact the company and get them out? Or have you designed and built it yourself
The system is 30 years old aprox, we have had loads of so called experts who have walked away telling us its the compressor
I think I'd be going down a re-build route. You'd more than likely find as with most old systems a newer one will be much simpler and more efficient. I think you need to way up the costs of having all these people looking at and not sorting it to the cost of a new system. I'm sure someone would find the issue but it's how many sparks do you have to go through to get the right one. Especially as you say the weather's getting warmer and your other machines are running at a much higher output than needed to. This could also cause issues with them
Experts on this sort of stuff are thin on the ground, we have manufacturer trained technicians here who cannot solve it, the problem is the compressor manufacturers went out of business leaving us with only manuals. Spares are still ready available for the compressor but the control wiring is difficult to fathom out. its a mixture of plcs and panels that run it all.
That is our concern at the moment we are panicking now, had quotes to replace the lot a few years ago and was into hundreds of thousands, plus the down time we can ill afford.
Where abouts in the UK are You? There's a few control gear guys on here maybe if your in there location that could come to you
We are based in Grimsby, if anyone can get this compressor running again we will pay well, we cannot have it all ripped out as it is a large scale Ammonia system so cannot be shut down
I think I would get someone in (if you don't have the skills inside) and try a temporary wire in of a timer based star - delta startup, take out the contactor cabling from the current controls and see what happens, if it starts up correctly, then it's your controls, if it fails then it's more likely to be an issue on the power side. One question, have you checked the voltage at startup to make sure you don't have a resistive connection somewhere that when trying to start all 3 motors it drops off
We cannot even pump the ammonia away and clear down any lines until this unit runs without the aid of tankers, and we have 16 ton of it to remove so that in itself is a few weeks to remove at the earliest
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