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  1. alanmcm
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    alanmcm Regular EF Member

    Location:
    Belfast
    Latest fact finding mission for you gurus to help me learn about

    Todays problem was a quarry pump not running, guy went out and meggared the cable and pump and found one of the two 10mm cables was down on the black phase. So while cable was ordered up and being delivered he was called elsewhere. So I was asked to sort the cable and connect up and test. Cable connected, insulation resistance test showed no faults everything cleared to earth. So got the quarry manager to do the startup procedure on the generator and control gear and it tripped straight away. So I done a bell test between the phases to make sure I joined the correct cable and found between grey and brown it belled, but nothing on the black phase. This was the same on both cables that on each cable brown and grey had continuity but nothing on the black. I expected to have continuity between all phases as the pump is connected delta, but having nothing on the black phase and its clear to earth is puzzling. Daylight beat me so have to wait til tomorrow when a crane will come and lift the pump out. could it be possible that the lead has blown off the terminal block? I never checked the resistances between phases so not sure if its balanced, I will do tomorrow. It was close to 6pm and pitch black so didn't get the chance to try and start the pump without it being connected, as it would be the biggest indication. Am I missing anything obvious?

    The pump is a 20kw pump with float. DOL, used to be a star delta starter so two 10mm cables were kept in place incase it was reverted back to this.
     
  2. benji
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    benji Electrician's Arms

    Location:
    north east
    Can,t wait to see how this thread runs ,
     
  3. Lonespark
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    Lonespark EF Member

    Location:
    Scottish highlands
    I would first check pump supply ie fuse/mcb make sure was getting 3 phase and all mcb /fuse working then check continuity at control gear ie contactor /over load were belling out between from top to bottom then same on any isolator then teat windings on motor to me it's sounds like motor
     
  4. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    No advise then?
    Bit confused here when you say no continuity to the black. How did you do it by linking out the ends of the cable.
     
  5. GMES
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    GMES Chief Gorilla Staff Member Trusted Advisor

    Professionally is the answer you are searching for.
     
  6. alanmcm
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    alanmcm Regular EF Member

    Location:
    Belfast
    The ends should be linked through the links on the motor terminal block. Control gear all ok, I have disconnected the pump about 15m away from it in the bottom shelf control panel. Theres only 3 wires going over so its linked out delta on the motor terminal block, I can bell between brown and grey but when I go on black to brown/grey nothing happens. If the links are in place then it should surely bell on the black as well?
     
  7. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    This is true assuming you have winding continuity. As the cable is new you need to look at the motor.
     
  8. darkwood
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    darkwood It's all about Gmes Staff Member Electrician's Arms

    Location:
    West Yorkshire
    Im thinking this is all mis-diagnosed by chance when you doing the continuity checks, was the motor connect at the other end and so might it be the case you have a winding down as oppose to a damaged cable.

    What exact tests were done?
    What sequence were they done in?
    What results did you get and what led you to believe the cable was the issue following these results?
     
  9. alanmcm
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    alanmcm Regular EF Member

    Location:
    Belfast
    The cable from the bottom shelf to the pump hasn't been replaced its one of the supply cables that had a fault originally. I'm leaning towards a fault in the pump itself, possibly caused by the pump running on two phases for a period of time. Ill know more in the morning time. Thanks for the responses.
     
  10. Lucien Nunes
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    Lucien Nunes Mercury Arc Rectifier Trusted Advisor

    Location:
    London
    So to paraphrase your original post: Delta-wired pump motor with only three core cable to panel (although a second 3-core cable is physically present from when it was previously wired for Star-Delta starting). Original cable showed insulation fault to earth on black phase and was replaced. New cable has no faults to earth but "something - not specified" trips immediately when energised. Continuity test via cable to motor shows continuity between brown and grey but neither to black.

    Well yes it does sound like something is seriously adrift in the motor. Or there is more to that cable fault than meets the eye; has it all been replaced or only a section of it? Could the original cable fault have been mis-diagnosed and this problem already existed? Was the motor checked between removing the old cable and fitting the new? Fish it out...

    E2A Hah, posts crossed with the above, all thinking along similar lines
     
  11. alanmcm
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    alanmcm Regular EF Member

    Location:
    Belfast
    I tested the cable doing an insulation resistance test. The only way to do that was to disconnect the cables from the pump as they were paralleled and would have led to the same fault on both cables. So when testing each cable for insulation resistance to earth, I found one of the cables was reading 0.06 ohms on the black phase, brown and grey were clear. These cables go to isolators on the middle shelf, which were switched off so as to check up to that point. I tested from the middle shelf back to the control gear at the top and they were clear on all tests. Once connected up to the new cable I tested insulation resistance to earth across phases with the pump disconnected and it passed. I tested the pump lead and pump to earth and it passed insulation resistance tests. So I got the pump powered up and it tripped immediately.

    I thought perhaps something wasn't switched on or I had something touching to earth so checked connections and colours and made sure everything was ok and didn't find anything wrong. So proceeded back to the bottom shelf to the pump panel and belled between the phases and could only go between brown and grey and not through black. Which leads me to here :)
     
  12. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Check windings tomorrow it could have been "single phasing" which has now done for the other windings which would not necessarily indicate a fault to earth.
     
    Last edited: Dec 15, 2016
  13. DAvid Prosser
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    DAvid Prosser Regular EF Member

    Location:
    UK
    I bet in your mind the set up is really clear but a quick sketch could be worth a thousand word here as I'm not even sure what you mean by "back to the bottom shelf".

    Also just out of intrest due to your statement "checked connections and colours" what voltage is the pump ?
     
    Last edited: Dec 15, 2016
  14. alanmcm
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    alanmcm Regular EF Member

    Location:
    Belfast
    the pump is a 3 phase 415v setup.
    Top shelf - generator and control gear
    Middle shelf - 32a plug and isolator arrangement, 2 x 32a isolators for each 10mm cable going down and 16a for float.
    Bottom shelf - pump and pump panel.
     
  15. alanmcm
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    alanmcm Regular EF Member

    Location:
    Belfast
    thanks very much, I will check at the pump itself once its lifted out.
     
  16. Marvo
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    Marvo Gender Confused Staff Member

    Location:
    South Africa
    Is the generator supply fused?

    If the original cable fault took out only one of the supply fuses then the two remaining phases might have damaged one of the motor windings.

    Disconnect the motor and test it for winding resistance. Remove any links and megger test between windings if you can as well.

    The pump motor is almost certainly damaged but before you reconnect after repairs or replacement make sure it has effective protection against two-phasing.
     
  17. alanmcm
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    alanmcm Regular EF Member

    Location:
    Belfast
    Good thinking Ill put in place a phase detection relay if there isn't one already, I'm thinking there isn't. Once its lifted out ill test more effectively, my welly boots just aren't made for wading through the water to get to the pump.
     
  18. Marvo
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    Marvo Gender Confused Staff Member

    Location:
    South Africa
    With mine pumps we always get a crane to drag it/lift it onto dry ground. Quarry pumps would be similar.

    I witnessed one of the maintenance guys on a mine get killed whilst working on a pump in a slurry pit one time so think safety and not just electrical safety, assess and manage risks from all places, especially upstream.
     
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  19. darkwood
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    darkwood It's all about Gmes Staff Member Electrician's Arms

    Location:
    West Yorkshire
    Thanks for the reply Alan wasn't been funny in any way but knowing the sequence of events can save many a guess work and hopefully give better advice
     
  20. alanmcm
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    alanmcm Regular EF Member

    Location:
    Belfast
    Didn't take any offence from it, I love learning and find asking a forum of highly qualified and experienced people is better than just trying to muddle through it. Means I can learn different safe techniques and methods to get the result I'm after and to improve the safety. I'm not the most experienced but I'm getting there, slowly but surely and safety is paramount in this line of work.

    I appreciate all the replies and the patience trying to understand what I'm trying to ask.
     
  21. timbobelfast
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    timbobelfast Electrician's Arms

    Location:
    Belfast
    I would be checking the windings. Sounds like one set is O/C.
    Also check your Isolator does't have a Pole O/C as well!
     
  22. benji
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    benji Electrician's Arms

    Location:
    north east
    Probably got nothing to do with fault but would 10mm be ok with the starting current , if not you could parallel both cables
     
  23. LankyWill
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    LankyWill Electrician's Arms

    Location:
    Northants
    Just from a learning perspective, how do you test a motors windings? what results are you looking for?
     
  24. Marvo
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    Marvo Gender Confused Staff Member

    Location:
    South Africa
    If you can remove the links you'd test that all three windings are equal resistance and that their resistance is per manufacturer spec if info is available. You'd also megger test between each of the 3 windings to ensure there is no breakdown of the insulation between them.
     
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  25. alanmcm
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    alanmcm Regular EF Member

    Location:
    Belfast
    Test the windings to earth using an insulation resistance tester. Test between each line to earth and expect quite high readings, over 1M ohm is acceptable but I wouldn't like to walk away from a motor knowing the motor is close to that. Then remove links and go between each line and test for resistance and make sure the windings are balanced.
     
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  26. alanmcm
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    alanmcm Regular EF Member

    Location:
    Belfast
    There is 2 10mm cables coming down and are paralleled together.
     
  27. LankyWill
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    LankyWill Electrician's Arms

    Location:
    Northants
    cheers mate
     
  28. alanmcm
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    alanmcm Regular EF Member

    Location:
    Belfast
    Went in yesterday morning and disconnected the pump from the circuit and tested the cables again for insulation resistance and all OK. Got the quarry operative to start it up, with the pump disconnected, and it didn't trip. Tested voltages and all were fine. So pump at fault. Didn't get a chance to get at the pump as the crane lifted one out and dropped a new one in and the old one was whisked away for repair. When it returns I'll ask what the fault was as I would like to know.

    Thanks for all the help and advice.
     
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  29. darkwood
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    darkwood It's all about Gmes Staff Member Electrician's Arms

    Location:
    West Yorkshire
    It had a winding out, so was 2phasing when when you fired it up from what you put, I think we all picked up on that early on when you explained things, what I don't understand is the 'guy' you said had left this to you because he was elsewhere, (I understand you're on your ladder of learning so aimed at him) this was a basic test procedure and he got it wrong, I think if he cannot nail a basic one like this then he shouldn't be undertaking the work in the first place, It makes me wonder if he's trying to do engineering work off the back of his 17th quals and no formal electrical engineering training or any specific motor diagnostic and repair knowledge at least your training in the correct area for this stuff .... some questions need asking here when you see him next as this has cost the company that runs the site extra down time, it may not be an issue on this site but any other it could be a production hit in the thousands of pounds?
    We are always happy to help out but your colleague should have easily diagnosed this one with the correct basic test procedures, have a chat with him next time you see him and please explain to him what was wrong and enjoy taking the credit at his expense ;).
     
    Last edited: Dec 17, 2016
  30. timbobelfast
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    timbobelfast Electrician's Arms

    Location:
    Belfast
    Think I know the quarry site and the electrical contractor. This is basic fault finding for any industrial electrician. The site manager should be calling a meeting!
     
    • Like Like x 1
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