Odd distribution voltage
Odd distribution voltage
(OP)
I need to install a distribution system to provide 138/80 vac 3 phase voltages into a vacuum test chamber. I am looking for alternatives for a method of producing this voltage from the more typical distribution voltages (208, 240 & 480).
Also, I am looking for an economical source of GFI circuit breakers for 80 vac single phase. I have confirmed that conventional 120 vac GFI's will not work at the 80 vac level.
Also, I am looking for an economical source of GFI circuit breakers for 80 vac single phase. I have confirmed that conventional 120 vac GFI's will not work at the 80 vac level.






RE: Odd distribution voltage
Maybe a 3:1 stepdown wired as a buck(opposing voltage)autotransformer, an appropriately sized unit that transforms 12.5 kV to 4160 should work wired to 208/120.
The High Voltage unit might be expensive but maybe you can find one surplus somewhere.
GE puts out a little book about their HV transformers that shows the connections.
As to the GFI's Those will probably have to be custom made but maybe you could try getting the parts from a Variable Frequency Drive since they use a lower voltage at lower frequencies.
Good Luck, -Dan76
RE: Odd distribution voltage
RE: Odd distribution voltage
1. 240VAC 3phase may produce 138VAC 3phase over 240Vdelta/240Vstar transformer where 138VAC is phase to neutral voltage on the secondary 240Vstar.
2. Once you have 138V 3phase another transformer 138Vstar/138Vstar will produce 80V 3phase in the secondary star winding with neutral.
RE: Odd distribution voltage
Point 1.
Primary 240Vdelta (preferred) or 240Vstar
Secondary 138Vstar (138Vdelta has less convenient grounding)
Point 2.
Primary 138Vdelta (preferred) or 138Vstar
Secondary 80Vstar (80Vdelta has less convenient grounding)
RE: Odd distribution voltage
So that leaves me still with the challenge to find an economic source of GFI's. A company called Bender in Exton, PA has offered me several options not including anything comparable in price or simplicity to the "garden variety" of receptacles and circuit breakers seen in any supply house. I have soecifications from several manufacturers which state that their 120 vac units will work down to 80 - 85 % of nominal but that doesn't help me.
RE: Odd distribution voltage
Maybe you could open up a commercially available 120V GFCI receptacle or circuit breaker and replace the existing series-connected line resistor with a lower value to get satisfactory reduced-voltage operation.
Of course, doing anything like this would be absolute madness where life-safety or property-protection issues were involved.
RE: Odd distribution voltage
On the GFI modifications, I am not permitted such an option. I need to find something that has the typical UL etc. approvals.
RE: Odd distribution voltage
If a custom transformer turns out to be the solution, and you don't need isolation from the source circuit, an autotransformer might be cost effective.
RE: Odd distribution voltage
RE: Odd distribution voltage
For a custom transformer, specifying something like four 2½% taps FCBN and two 2½% taps FCAN should add only a small cost to the unit.
RE: Odd distribution voltage
Thanks for all the interest.