Autotransformer start

[ptonsparky]

After recent comments that a softstart may not be the best replacement choice for an Autotransfomer start, we decided to investigate the old starter. The motor would just barely turn, if at all, until the run kicked in. T
urns out the starter had worked properly until about 15 years ago. At that time the leads to the "Yellow"100% and "Red" were reversed on one side of the Xfmr. At minimum the 65% start tap was changed to 35% on this side, but I feel the total voltage supplied at start may have been even less because both sides of the transformers are on the same armature. Am I on the right track?

We had never worked on one before and had to learn as they paid. They will still come out several thousand dollars ahead.

 

[frenchelectrican]

Tom.,,

You are on the track with the reduced voltage on the autotransformer starting arrangment.

Most Autotransformer useally have few taps typically are 80%, 65%, 35%, those useally are pretty common taps but i know there are other taps along way.

sometime back back i was working with sawmill that machine have 200 HP motor and did used old style autotransformer starter kinda instering one to use you have to move the lever to " start " postion and hold that for about 5 -10 seconds to get up the speed then move the lever to run postion. and it will stay there until you hit the stop button which it will trip the locking cam or shunt coil to unlock to stop postion.

but they are slowly going out of favour as well senice the VSD or soft start is getting common now.

But you have to keep in your mind many autotransformer starters they are kinda limited to the #'s of start per hour [ they can really build up heat pretty fast if you cycle too much ]

Merci, Marc