Replacement rheostat for synchronous motors

[mmt019]

I have six M-G sets from the 1940's where the synchronous motor utilizes a motor operated rheostat. The field voltage is 250VDC. The rheostats are in old and in need of replacement (or repair). I have not been able to locate a manufacturer for rheostats. I have tried Ohmite, Cutler-Hammer, and G.E. but none manufacture these. I have read that SCR's are supposed to be the replacement for rheostats since there are no moving parts. What are my options regarding rheostats? Am I just out of luck and need to look at SCRs? How do you replace an SCR in place in place of a rheostat? Who are the manufacturer's for SCRs?

 

[nic00b]

We have replaced most of our rheostat's (mag amp control). We used a company called LPC components.

 

[Skogsgurra]

SCRs are the standard rheostat replacement. But, even if standard and simple, they are not as simple as a motorized rheostat.

There's another option that works very well and also is as simple as can be. That is a motor driven Variac plus a rectifier. It runs much cooler than a rheostat. But you still have the motor and the gear that need some maintenance.

You can also use a "Squariac" with a rectifier. The Squariac* is a transformer with multiple taps that are switched with relays that are closing on voltage zero and opening at current zero for "unlimited" relay life and zero arcing and interference. We have used a transformer with ternary windings for good resolution and a minimum of relays.

*That's what we call it to distinguish it from a Variac, which is round.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.