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Discussion Starter · #1 ·
Can anyone either explain to me or direct me to a webpage that explains the theory of operation of a Star Delta wound motor?
I understand that they basicly are set up to change the way they are wound during startup to allow for lower starting amps and then a timer switches them to the normal operation mode.
I want to get a better understanding so I know how to troubleshoot them when I have a machine that has a problem. I feel very comfortable with normal 3phase motor starters but I dont know where to start with Star Delta.
 

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I believe its a relay controller to allow the motor to start up as a star motor then it switches it to delta. Starting a delta motor it wants to jump instantly to full speed, which takes serious amperage, starting a star motor allows a softer start.

Its been a while since I studied electrical but I think a star is connected to one single point at one end of the coil and the delta is directly between phases.

If you run into one I'd search long and hard for a wiring diagram of the controller first. A mistake could get real expensive real fast!
 

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Discussion Starter · #4 ·
Well
thanks for the link. It is inetersting site with good info but I have to admit I dont feel enlightened yet. Though I did learn a few things like that there should be pause while contactors switch. I wonder now how long that pause should be. Also not sure how many contactors we are looking at. It seems to me I remember at least 3 contactors in the first one I was trying to figure out.

Unfortunatly any of the larger compressors I get in that come from Germany seem to have these types of starters. I think they are probably better in the respect that they start with less starting amps and probably less torque stress and wear as they start at a lower speed and then kick into full speed which would allow the oil pump to get a pressure up a bit and the splash oil part of the system to splash more oil around. But I dread the day I have to troubleshoot a machine that has something wrong with one of these control systems.
Now if a compressor wont start I can check the supply voltage, Push in the contactor manualy and if the motor starts then I know I have a control problem which is mostly checking which switch is not letting voltage thru to the closing coil(Or closing coil is burnt) With the star delta I cant just bump start the motor and see that the High amp stuff is fine or not.
 
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