We have a customer that put in a 120/208 3 phase generator and a transformer 120/208 to 120/240 to match our voltage.He is getting funny voltages from the secondary side of the transformer p-p 240 p-n 150s.He has wired the 208 side of the t-former with the neutral connected to the windings.Isnt there a phase shift from 208-240?So the neutral on the 208 side should be frame ground?Do the make an isolation transformer 120/208 - 120/240?Any thoughts?
Transformer
- Thread starter newt
- Start date
- Status
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Lets review: generator 208/120Y w/neutral to transformer 208/120Y w/neutral; so far, so good. Yes, do interconnect the neutrals.
Transformer secondary 240 phase-to-phase, implying a Delta connection. Where are you connecting a neutral on the secondary???
In other words, it sounds like your secondary is floating. Between what two points are you measuring your phase-to-neutral voltage?
Transformer secondary 240 phase-to-phase, implying a Delta connection. Where are you connecting a neutral on the secondary???
In other words, it sounds like your secondary is floating. Between what two points are you measuring your phase-to-neutral voltage?
Last edited:
jtester
Senior Member
- Location
- Las Cruces N.M.
If you ground the neutral on the wye side, it will tend to balance the wye side, the generator side. If you truely have a high leg system, you probably have imbalances which will be a problem with the ground on the wye.
If you eliminate the grounded neutral on the generator side, I don't mean eliminate the generator neutral or ground, just don't tie the transformer neutral to the system neutral, you will have no problems with loads.
That doesn't explain why you are seeing unusual voltages, but will head off a problem.
There is a phase shift between the wye and delta sides, but that wouldn't explain the voltage to neutral that you are seeing either.
Jim T
If you eliminate the grounded neutral on the generator side, I don't mean eliminate the generator neutral or ground, just don't tie the transformer neutral to the system neutral, you will have no problems with loads.
That doesn't explain why you are seeing unusual voltages, but will head off a problem.
There is a phase shift between the wye and delta sides, but that wouldn't explain the voltage to neutral that you are seeing either.
Jim T
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
I would like a better description of what you have conected and where.
Are you backfeeding a transformer?
Is your load three phase? Is it 4 wire?
There is no commonly available transformer with 208Y/120 on one side and 240D/120 on the other side.
In general, when backfeeding a transformer never connect the X0 bushing to the system. This is especially important when using a wye-delta transformer.
Are you backfeeding a transformer?
Is your load three phase? Is it 4 wire?
There is no commonly available transformer with 208Y/120 on one side and 240D/120 on the other side.
In general, when backfeeding a transformer never connect the X0 bushing to the system. This is especially important when using a wye-delta transformer.
- Status