11 kw 2pole motor burnt out connected in star
11 kw 2pole motor burnt out connected in star
(OP)
Hi
I have had 2 11 kw 2 pole pumps burn out at the same time.
Both had a converter starters and were found to be connected in star.I have wired the replacements in delta and run no problem.
The motors were 400 v delta 660-690 star.
The manufacturer is insisting that the connection in star would not cause them to burn out but as I understand running at 400 v in star is running undervoltage and not only would the the torque be reduced but this would cause increased temperatures in the windings.
Any technical info to give to the manufacturer would be usefull
regards
speeddial
I have had 2 11 kw 2 pole pumps burn out at the same time.
Both had a converter starters and were found to be connected in star.I have wired the replacements in delta and run no problem.
The motors were 400 v delta 660-690 star.
The manufacturer is insisting that the connection in star would not cause them to burn out but as I understand running at 400 v in star is running undervoltage and not only would the the torque be reduced but this would cause increased temperatures in the windings.
Any technical info to give to the manufacturer would be usefull
regards
speeddial





RE: 11 kw 2pole motor burnt out connected in star
Cannot understand why your supplier/manufacturer says what he says - does he think you were running them with no load?
RE: 11 kw 2pole motor burnt out connected in star
The motor performance with under voltage is complex, since the rotor slip will increase, and the speed will drop reducing some of the load but the motor runs close to the breakdown torque area, this condition reduces the impedance seen by the line and the line current demand increases.
RE: 11 kw 2pole motor burnt out connected in star
I am curious as to why your OL relay did not drop out the starter. It is probably because the OLR was wired into the circuit as if it were Delta, so when you connected in Star it was only seeing 57% of the motor current. Make sure you check that out.
"Venditori de oleum-vipera non vigere excordis populi"
RE: 11 kw 2pole motor burnt out connected in star
The two motors were each driven by its own inverterdrive.
The motors were delivered pre wired and set up by a major manufacturer and commissioned by them. Unfortunately the commissioning engineer failed to notice the motors had been wired in star.After 1 year both motors burnt out at the same time resulting in the closurer of a sizeable factory for half a day.
As a result,the claim is also sizeable. The manufacturer agrea's that they should have been wired in star but insists that this would not have caused the motors to burn out -hmmmm
RE: 11 kw 2pole motor burnt out connected in star
I will however deny any of this in a court of law!
"Venditori de oleum-vipera non vigere excordis populi"
RE: 11 kw 2pole motor burnt out connected in star
If it comes to proving who's right and who's wrong - I suggest that you bring in spare motors and connect everything as it was when they were commissioned. Make sure that you can make a fast replacement once the motors burn out.
If the manufacturer does not agree to do this experiment, then he has (indirectly) admitted that such a situation is not good for the motors. Costs? Yes, but - as you say - there are substantial claims. And the one that loses the "bet" has to pay it all.
I would love to hear if he agrees to such a test.
RE: 11 kw 2pole motor burnt out connected in star
"Venditori de oleum-vipera non vigere excordis populi"
RE: 11 kw 2pole motor burnt out connected in star
Electrical measurements (current, kW etc) did not indicate any problem. However the no-load currents were only about 15% of the rated FLC. Some experts around advised me that normally no-load current of a motor, 2 or 4-pole, should be roughly around 33% of FLC.
I removed one of these motor and opened it in the workshop and found the rotor surface had some blue colour indicating that some overheating had occured.
I contacted the manufacturer directly and raised the possibility that the motor nameplate could have been wrongly indicating as Star connected. The reply from manufacturer was positive, confirming that the motor windings should have been connected in Delta. In admitting their mistake, they send us new nameplates and give us 2 new motors free of charge. Eventhough we had to pay import taxes for the new motors, we accept them graciusly as spares.