H
holmslaw
..
Any Motor Men Out There?
- Thread starter conny
- Start date
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Hi guys,
thanks again for the responses.
OK, here goes.
F.Port, quite correct it was MΩ not ohms, my mistake.
And yes there is definitely a fault between V1 and W1.
Col, yes ends are marked right, it was a running motor and the leads were already marked, we just checked them and added additional markings as the originals were a bit grubby.
NHA, every repair shop uses a bog standard 1,000v megger, always have done.
LR, if there are shorted turns on any coil, either solely on its own phase or tracking across to one other phase then the resistance of at least one phase will be significantly different to the other two phases.
U1,V1,W1 are the incoming leads.
Holmslaw, sorry mate, not seen a wind-up one in years! (Used to have some good fun with them though ).
OK, today ran through all the tests again and got same results, (obviously). Then I came up with the idea of doing a Hi-Pot test on each individual phase but instead of testing to see if the phase broke down to 'true' earth, i.e. the motor casing I decided to fool it into thinking V1 and W1 was earth by connecting the earth lead to each in turn.
So, using only Lead 1 and earth I connected L1 to U1 and earth to V1. Now I knew there was no short between U phase and V phase or W phase so the Hi Pot shouldn't trip. Ramped it up to 2010V, It didn't trip. Repeated test using U and W phases. No trip. So far so good.
Lead 1 to V phase and earth to W phase should produce a 'Trip Out' as there was a short betwen them according to the megger.
Managed to reach 140V before tripping out, confirming there was a definite short between phases V and W. But this short should have shown up on the 'Surge' test as spikey waves or a fluctuating wave form and it didn't. Hence the puzzle. The manager contacted Whitelegg, the Baker Test manufacturers and their head technician had never heard of this happening. Told him all the tests I had done including the latter ones and he still can't explain why it didn't show up on the 'surge'.
Result is he is coming to the workshop on Thursday with the latest spec tester, (next model up to the one we used from our other branch), and will watch while I run through them all again. He admits he is at a loss as to why this is happening.
Will let you know how it goes on Thursday.
Can I just say how grateful I am for the input of you lads, seems to me you like a challenge with something different from the mundane DI problems you often answer.
Thank you all for your patience with me.
thanks again for the responses.
OK, here goes.
F.Port, quite correct it was MΩ not ohms, my mistake.
And yes there is definitely a fault between V1 and W1.
Col, yes ends are marked right, it was a running motor and the leads were already marked, we just checked them and added additional markings as the originals were a bit grubby.
NHA, every repair shop uses a bog standard 1,000v megger, always have done.
LR, if there are shorted turns on any coil, either solely on its own phase or tracking across to one other phase then the resistance of at least one phase will be significantly different to the other two phases.
Its a typo, the star point is made up of U2,V2,W2.
U1,V1,W1 are the incoming leads.
Holmslaw, sorry mate, not seen a wind-up one in years!
(Used to have some good fun with them though ).OK, today ran through all the tests again and got same results, (obviously). Then I came up with the idea of doing a Hi-Pot test on each individual phase but instead of testing to see if the phase broke down to 'true' earth, i.e. the motor casing I decided to fool it into thinking V1 and W1 was earth by connecting the earth lead to each in turn.
So, using only Lead 1 and earth I connected L1 to U1 and earth to V1. Now I knew there was no short between U phase and V phase or W phase so the Hi Pot shouldn't trip. Ramped it up to 2010V, It didn't trip. Repeated test using U and W phases. No trip. So far so good.
Lead 1 to V phase and earth to W phase should produce a 'Trip Out' as there was a short betwen them according to the megger.
Managed to reach 140V before tripping out, confirming there was a definite short between phases V and W. But this short should have shown up on the 'Surge' test as spikey waves or a fluctuating wave form and it didn't. Hence the puzzle. The manager contacted Whitelegg, the Baker Test manufacturers and their head technician had never heard of this happening. Told him all the tests I had done including the latter ones and he still can't explain why it didn't show up on the 'surge'.
Result is he is coming to the workshop on Thursday with the latest spec tester, (next model up to the one we used from our other branch), and will watch while I run through them all again. He admits he is at a loss as to why this is happening.
Will let you know how it goes on Thursday.
Can I just say how grateful I am for the input of you lads, seems to me you like a challenge with something different from the mundane DI problems you often answer.
Thank you all for your patience with me.
ah well someone has to ask the stupid questions..
often times it's easy to overlook or dismiss out of hand something simple while searching for something you think is a lot more complex..
I've had a guy call me out to fix a bandsaw that kept cutting out.. turns out they'd unplugged it to clean under it and hadn't pushed the plug all the way back in.. so when it moved a bit and pulled the cable to the plug it cut out..
took me all of 30 seconds to figure that out but cost them an hour and a half billable time..
same place, different day, I was sent there to re-connect a motor that they had sent away for re-winding. it was on a conveyor belt for a scratching packing machine.
wired it in, turned it on.. nothing..
measured voltage at the motor, 240V to earth on 2 phases, nothing on the 3rd..
measured at the panel with cables disconnected, 240V to earth on all 3 output terminals..
figured it was the wire so I pulled in a new one..
connected it all up again, still nothing from the motor.. again 240V to earth on 2 phases.. the 3rd phase which I'd just pulled a new wire in for was still at 0..
checked at the panel terminals with the motor still connected, nothing on the terminal this time.. WTF?
traced it back through the panel and it turned out to be a loose screw on the contactor.. tightened it and all was good.. ..
There is no such thing as a stupid question.
As you say, the simplest things are often overlooked.
Talking of bandsaws reminded me of a compressor I had to rewind. No problems, wound it, assembled it, tested it, painted it and customer picked it up himself.
Next day he brings it back saying it blew up when he connected it up. Had a look and terminal block was burnt and sooty. Cleaned out terminal box and fitted new block, tested it, no problem. Next day back again, same problem. Asked him what he was doing he said he had a diagram in the workshop of where to put the wires and when he did it just blew up, twice!
So repeated the change again and tested it. Boss said you take it back and watch how he connects it up. Get there and he proceeds to connect 3 phase leads to star point!
Me "What are you doing?"
Him "Thats where these wires went when I took them off originally."
Me "And where were those 2 little brass strips when you disconnected the wires originall?"
Him "They were on those 3 stumps, you've put them back on the wrong ones."
I said, "I'll connect it up for you and guarantee it will work."He was terrified when I connected it to the 'other stumps' as he put it and stood at the other side of the room when I switched on!
Lo and behold, one motor running perfectly! I even had the direction right!
He got billed for 1 complete rewind and overhaul, 2 repairs and an installation charge.
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you gotta love these people that throw money at you for no real reason though..
went to one place where someone had wired in some new lights that he couldn't get working..
I got there and he showed me what was happening, switch the switch, nothing..
so I asked to look at the CU at which point it dawned on him ( quite visibly ) that he'd forgotten to switch the breaker back on after adding the lights..
went to one place where someone had wired in some new lights that he couldn't get working..
I got there and he showed me what was happening, switch the switch, nothing..
so I asked to look at the CU at which point it dawned on him ( quite visibly ) that he'd forgotten to switch the breaker back on after adding the lights..
Not disputing that he would pick it up between any pair of windings if the instrument was at fault, more to do with the instrument and how effective it is in every day use including using it for motors, installations etc.
Personally I can't see a bog standard Megger IR tester delivering the 500v or 1kv as a pulse as a change in voltage would have a knock on effect on the insulation resistance measurement by also measuring Xc. I'll have to have a play about with my Megger and sillyscope sometime!
Are you going to get the new Baker for free?
Are you going to get the new Baker for free?
That would certainly earn me some brownie points with the boss!!
Somehow I think he'll try and persuade us to buy his version, (around £30,000 I've heard), and maybe give us a discount for part-ex on the old one.
Well we won't be buying the Baker Tester!
The super-dooper one the tech guy brought with him was the same as our other branch one. It didn't pick up the fault either!
I ran through all the tests I had done earlier in the week with him programming his machine for each test and it gave exactly the same results as both of our machines. After discussions between the techie, the client, our branch manager, our area manager, (who is a very knowledgeable bloke who worked his way up from the shop floor) and myself the techie stated that he would stake his reputation on the stator being fit to run once assembled.
I then told him about the test I had come up with of using 1 phase as the test phase and the other 2 phases as the 'earth'. He agreed to give it a go but was sceptical of it showing anything wrong.
Result after showing him that doing it this way showed a clear short between V and W phase was a very embarrassed techie!
It was a test not shown in the manual and it had never occured to him to try it. Client asked if he was now going to contact headquarters in America to ask why it didn't pick up the fault on the standard tests, was he going to tell them about this method and would he be recommending that they add it to their instruction manual? Yes, was the answer to all 3 questions!
After more testing and opening up the internal connections a bit more we have come to the conclusion that a damaged thermistor has caused the 2 windings to short out across 1 or 2 turns of the coils. This came to light after we found 6 sets of leads buried down the back of the coil ends with the ends taped up, seems when ever a set 'failed' they cut the leads, insulated them, tucked them out of the way and inserted a new set of thermistors. It came up in the discussions that the clients staff actually megger the thermistors when they are fault finding/routine testing!
Thermistors as some of you may know should never have more than 2.5Vac passed through them yet these guys had wacked 500-1,000v across them at some stage.
Discussions are now taking place to decide who will pay what for the rewind. Think they are going to agree on splitting the cost as; a/ our test equipment didn't pick up the fault and b/ the clients staff may have caused the fault.
All in all a very interesting and informative week or two.
The super-dooper one the tech guy brought with him was the same as our other branch one. It didn't pick up the fault either!
I ran through all the tests I had done earlier in the week with him programming his machine for each test and it gave exactly the same results as both of our machines. After discussions between the techie, the client, our branch manager, our area manager, (who is a very knowledgeable bloke who worked his way up from the shop floor) and myself the techie stated that he would stake his reputation on the stator being fit to run once assembled.
I then told him about the test I had come up with of using 1 phase as the test phase and the other 2 phases as the 'earth'. He agreed to give it a go but was sceptical of it showing anything wrong.
Result after showing him that doing it this way showed a clear short between V and W phase was a very embarrassed techie!
It was a test not shown in the manual and it had never occured to him to try it. Client asked if he was now going to contact headquarters in America to ask why it didn't pick up the fault on the standard tests, was he going to tell them about this method and would he be recommending that they add it to their instruction manual? Yes, was the answer to all 3 questions!
After more testing and opening up the internal connections a bit more we have come to the conclusion that a damaged thermistor has caused the 2 windings to short out across 1 or 2 turns of the coils. This came to light after we found 6 sets of leads buried down the back of the coil ends with the ends taped up, seems when ever a set 'failed' they cut the leads, insulated them, tucked them out of the way and inserted a new set of thermistors. It came up in the discussions that the clients staff actually megger the thermistors when they are fault finding/routine testing!
Thermistors as some of you may know should never have more than 2.5Vac passed through them yet these guys had wacked 500-1,000v across them at some stage.
Discussions are now taking place to decide who will pay what for the rewind. Think they are going to agree on splitting the cost as; a/ our test equipment didn't pick up the fault and b/ the clients staff may have caused the fault.
All in all a very interesting and informative week or two.
to be fair, I would have thought that basic end to end continuity and coil to coil and coil to easth IR testing would be the first thing you did prior to the fancy "ping" testing ( which is what the baker does from your description? or am I not reading it right? )..
Sounds a bit like a TDR for motor circuits to me.
TDR?
time domain reflectometer
yeah, a ping tester..
sends a very short pulse down the wire and sees how long it takes to bounce back....
sends a very short pulse down the wire and sees how long it takes to bounce back....
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