auto transformer

[ghelectricaloz]

I have been given the task of connecting 110 kW motor to auto transformer starter that had previosly ran this motor, at a different site with a different generator. I tested the control circuit and measured 277 V (3 phase) in the startup condition, and 415V in the run condition. Thinking this was working fine I connected the motor, on startup the star contactor (KM1) burnt out and the motor barely moved. This new generator is 140kVA, we knew this would be borderline to run the motor. On inspection found the star contactor was actually wired in a delta configuration, contrary to the drawings supplied. All other diagrams I can find seem to be the same (star connection in startup of KM1). Is the genie underpowered? why is KM1 connected in Delta? Mechanical load seems free. I need to get this plant running, help would be awesome, cheers GH

 

[Jraef]

You are mixing your terminologies so it is impossible to ascertain what you have. An Autotransformer starter is a completely different type of starting method from a Star-Delta starter. Please define exactly which one you have.

In either case, 140kVA is way too small of a generator to start a 110kW motor, with or without reduced voltage starting of any sort. You still need current; no AC motor with a load connected will start with much less than 200% current, and even then it would need to be an extremely light load. The only way you will be able to accelerate that motor with that generator is with a VFD, or if the motor is the only load, disable the generator's governor and allow the motor to drag the generator down, then the engine will bring them both up together (but that is not guaranteed to work).

 

[ghelectricaloz]

reply re autotransformer

reply re autotransformer

Cheers,
Definately is autotransformer starter, drawings in panel and all other drawings I have seen the 'star' contactor (KM1) i am referring too is to connect the auto transformer centre taps in to star, literally terminals commoned up to create a star point, it is the first contactor energised and electrically interlocks out KM3 DOL contactor. KM2 is pulled in through NO contacts of KM1 and applies power to autotransformer and motor starts with reduced voltage. after a time KM1 is de-energised and KM3 is energised to run the motor DOL The autotransformer loses power as KM2 has dropped because of KM1 dropping out. The part that makes me curious is that the KM1 was not actually wired with links from T1 to T2 to T3 as described, but links where installed from L1 to T2, L2 to T3, and L3 to T1. Do you know why this might be? thanks for your info on the genie size, thought this might have been the case, I am thinking now that this could be the problem. cheers GH