3 phase quarry pump

[alanmcm]

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.

 

[benji]

Can,t wait to see how this thread runs ,

 

[Lonespark]

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

 

[westward10]

Can,t wait to see how this thread runs ,

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.

 

[GMES]

Professionally is the answer you are searching for.

 

[alanmcm]

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?

 

[westward10]

This is true assuming you have winding continuity. As the cable is new you need to look at the motor.

 

[Darkwood]

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?

 

[alanmcm]

This is true assuming you have winding continuity. As the cable is new you need to look at the motor.

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.

 

[Lucien Nunes]

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

 

[alanmcm]

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?

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

 

[westward10]

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.

 

[David Prosser]

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 ?

 

[alanmcm]

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 ?

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.

 

[alanmcm]

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.

thanks very much, I will check at the pump itself once its lifted out.