Autotranformer starter for motor?

[stephena]

Does anyone have a diagram that would show an autotransformer used to start a motor? Or a webpage that explains it in detail would be helpful. Thank you.

 

[augie47]

here's one:

 

[Jraef]

There are a few different versions, but the type most people use now, such as the one depicted in augie47's post, is called a "Korndorfer Method Autotransformer Starter", named for the engineer that came up with it just after the turn of the previous century. An older design was what is referred to as "open transition" meaning that for a brief moment there is no power going to the motor and unfortunately some people still use it because the control circuit is simpler. That caused massive transitions spikes that in turn created headaches. I had a really old one take down an entire lumber mill once. Korndorfer came up with this way of keeping power on the motor, a "closed transition", that avoided those problems. It's what most people use now and what you get when you buy a factory build RVAT starter from any of the major makers. Someone created this wiki page for it a few years ago, it does a pretty nice job of explaining it. Fewer and fewer people use this old technology now because of size and expense, so it's good that someone documented in.

http://en.wikipedia.org/wiki/Korndörfer_autotransformer_starter