transformer isolation?

[zlast]

I have a question concerning tranformers. I recently removed the mounting ears from a large laminated core transformer. The ears were attached with 4 large bolts, which were insulated from the transformer body by nylon shoulder washers. Curious as to this construction I took another smaller transformer (different manufacturer) and removed one of the mounting ears. ON the smaller transformer the bolts retaining the mounting ears were ALSO encapsulated by nylon shoulder washers. However, the mounting ears are not electrically isolated from the laminated body of the transfomer (confirmed via continuity test). So, knowing that engineers do things for a reason...why are the nylon shoulder washers used if the mounting ears are not electrically isolated from the body of the transformer? The bolts retaining the mounting ears may be electrically isolated, why is this a concern? As allways thanks for your time and expertise!

Z

[gmphadte]

First of all, the laminations in a transfomer are insulated and do not contact each other.

If the bolts were not insulated, there is a possibility that it will make contact with all the laminations, which will increase the eddy current loses. The shoulder washer will keep the bolt in the air through the laminations' holes. The ears themselves are in contact with the outer lamination only and are mostly 2 separate plates on each side

Hope that answers your Q.

Gajanan Phadte