Transformer issues

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nickelec

Senior Member
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Would anything else but a bad coil cause this transformer to dip significantly in voltage when a load is applied, wile under load one of my phases drops down to about 50-60 volts it should be about 280
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280 volts? Got a clearer picture? How much load? Single phase load or three phase load? What tap settings?
 
Are you measuring HV side with 480 volt applied from a Wye system? Look for a poor connection or blown fuse.

Did you have a typo of 280 vs 208 on the LV side?

What are the currents of each HV phase while no load is connected to the secondary?

Not enough information.
 
50 to 60 volts on one phase is usually a bad or broken neutral connection and that would shift phase voltage under load. The other phase would go high as the neutral point floats. Are you reading a single coil voltage that drops under load, right at the transformer. Or are you reading phase voltage downstream of the Y connection where the neutral could break and float.

The single coil voltage should always maintain the turns ratio to the applied primary voltage, within the transformer rating. If you suspect the bad coil, the ratio of the applied primary voltage to the secondary coil voltage would have to match the other two coil voltages.

Lack of a secondary system bonding jumper would do it.

What does the N to G voltage do when the phase voltage goes to 60.
 
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I was measuring the coil voltage at the transformer itself, when I go back I will check for a brooken or loose neutral connection

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