- Reaction score
- 291
Ive had a amusing days fault finding today, Found several faults but have come out of it asking more questions than I have answers.
So Me and a colleague go to this AHU that keeps tripping for unknown reasons, The pannel has been canabalised and the inverter and motors covers are removed but everything appears to be there.
So we started it up and stood there for 20 mins as the thing runs fine, Slightly puzzled we were about to put all the covers back on when it trips out the 63A breaker.
So starting it up again we clamp each phase finding that L1 is pulling no current and the other 2 are pulling 55A, So this firstly puzzles us as again the motor is spinning fine?
So we test voltage from L1 of the panels incomers, through the breaker, contactor & OL, isolator to inverter no problems, Outgoing of inverter also fine.
But still no current being pulled on L1 and the motor still spinning away merrily.
Is this something to do with the inverter??
So going back to the panel and having a poke around I hear some nice buzzing sounds coming from the internal MG board, Followed up by a nice puff of smoke from one of the breakers (but not the one for the supply fan I am concerned about).
So I take the breakers off and find that several of the bus bar connections are broken and burnt.
So after sourceing a replacement I decide to test the motor to check that its all ok before I go any further.
Meter the windings and IR test them to each other and earth all ok, Its at this point I realise another problem.
The motor had been wired in Star but according to the rating plate it is Delta.
Now I replaced the board (allthough not powered up yet) and intend to finish the job tommorow.
But can anyone explain to me how a motor wired wrongly with only 2 phases pulling current but with voltage accross all 3 run fine for 20 mins before tripping the breaker and not taking out the overload?
Ime assuming it must me something to do with the inverter but its got me puzzled.
Its not helped by the fact that everything has been canabalised!
Thanks muchly
So Me and a colleague go to this AHU that keeps tripping for unknown reasons, The pannel has been canabalised and the inverter and motors covers are removed but everything appears to be there.
So we started it up and stood there for 20 mins as the thing runs fine, Slightly puzzled we were about to put all the covers back on when it trips out the 63A breaker.
So starting it up again we clamp each phase finding that L1 is pulling no current and the other 2 are pulling 55A, So this firstly puzzles us as again the motor is spinning fine?
So we test voltage from L1 of the panels incomers, through the breaker, contactor & OL, isolator to inverter no problems, Outgoing of inverter also fine.
But still no current being pulled on L1 and the motor still spinning away merrily.
Is this something to do with the inverter??
So going back to the panel and having a poke around I hear some nice buzzing sounds coming from the internal MG board, Followed up by a nice puff of smoke from one of the breakers (but not the one for the supply fan I am concerned about).
So I take the breakers off and find that several of the bus bar connections are broken and burnt.
So after sourceing a replacement I decide to test the motor to check that its all ok before I go any further.
Meter the windings and IR test them to each other and earth all ok, Its at this point I realise another problem.
The motor had been wired in Star but according to the rating plate it is Delta.
Now I replaced the board (allthough not powered up yet) and intend to finish the job tommorow.
But can anyone explain to me how a motor wired wrongly with only 2 phases pulling current but with voltage accross all 3 run fine for 20 mins before tripping the breaker and not taking out the overload?
Ime assuming it must me something to do with the inverter but its got me puzzled.
Its not helped by the fact that everything has been canabalised!
Thanks muchly