ion implanter isolation transformer

[leoliu]

Does anybody here know this type of transformer. It is delta/wye , 208v/208v, 10kva. But the neutral point of secondary is connected to a 100kV DC point? Why the neurtal point is connected like that? Strange to me. Any opinion?

 

[alehman]

One guess -
Vacuum tubes have a heating element called a filament which in some applications needs to operate at a high potential to function as an electron emitter. The most common example of this today is the magnetron in a microwave oven. A transformer supplies low voltage for the filament with the secondary winding being insulated for high voltage with respect to ground. A high voltage DC supply is applied to one of the two filament terminals to make it act as an emitter.

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

 

[leoliu]

Thanks, alehman. I still don't understand several things. Is the DC source different form that for isolation transformer? Why the DC voltage need to be connected to the neutral point?

 

[alehman]

The DC source is external to the transformer. Sometimes it is derived from a elecrically separate winding on the same transformer. Don't know why it's connected at the neutral.

 

[waross]

A 10 KVA 208/208 Volt transformer that can withstand 100,000 volts DC floating on the secondary is outside of my experience. I suspect that the connection is to the low side of the HV DC source.
yours

 

[alehman]

It would no doubt be a special transformer to withstand the high DC voltage.