Buck and boost transformer on well pump question

[WarrenG]

Hello to all and thanx for any input on this matter. A customer just had a submerged encased well pump replaced, and also the control/starter box. The well pump requires single phase 230 volts to operate. The customer has a three phase 208/120 volt service. So a single phase 1kva pri 240 sec 32, buck and boost transformer was used to boost the 208 up to about 239 volt. The system worked fine for some time and then the transformer went bad, so they think. So a new exact replica was installed. Now the pump will not work at all. The voltage measured at the pump dissconnect is 239 volts before the pump is turned on. Once the pump is put in the on position, the voltage at the same dissconnect drop to nearly 0 or 7 volts. I did an amp check and amp draw is 0. There is no neutral in this system, its a 2 wire only with ground. I checked all the capacitors, overloads and contactor and wiring in the control box and everything seems fine. Even the coils of the motor were tested and they are within spec. Basically we start with 239 v untill the pump is put in the on position at which time it drops to 0 to 7. Any ideas whats going on here? Thanx for the help.

 

[Electric-Light]

There is likely a blown fuse somewhere or a loose connection between the transformer and the pump

 

[gar]

110503-1352 EDT

A high resistance connection somewhere.

Your boost transformer seems about right in relation to the the nominal voltages you mentioned. I do not know what you mean by a 1 KVA boost transformer. Hopefully this means something like an output current rating of about 1000/32 = 31 A.

You did not mention the power or current rating of the pump. Assuming it is a 2 HP unit and about 2000 VA, then a full load current might be about 2000/230 = 8.7 A.

On this load current assumption the original boost transformer, if from a quality manufacturer, should not have failed, and may not have failed.

You did not mention where the pump disconnect switch is located, I assume it is at the pump.

You need to measure the input voltage to the boost transformer when the pump is turned on. Is it still 208 or whatever it was before the pump was turned on?

Then do the same change of voltage test on the boosted output. If this boosted voltage at the transformer output is still good with and without the pump switched on, then measure the voltage at the input to the pump disconnect for the same two conditions.

This last test you have already done and the voltage drops to essentially 0 V. Thus, the problem is between the AC source voltage and the pump disconnect input. Most likely in the wire or termination points.

.

 

[A/A Fuel GTX]

Sounds like a bad connection that shows up under load.

 

[WarrenG]

Thanx for the quick reply. The x-fmr is mounted next to the source. The well pump is located aprox 60ft away. The dissconnect. Is located at the well along with the control/starter box. I have 230 at the contactor inside the control box. When the contactor pulls in, the voltage drops to 0-7 volts. As I mentioned earlier, I tested all the components inside the control box and they test normal. The well pump s FLC is 28amps, its 5hp. The 1kva xfmr is just the lable rating just like the pri 230v to 32v sec. A buck and boost chart was used to select proper x-fmr size. The only component I was unable to test was this small enclosed relay which has the starter capacitor and run capacitors connected to it. I thought maybe the capacitors were maybe messing with the sine wave of the x-fmr. But that is an un educated guess.

 

[gar]

110503-2132 EDT

You must check the output voltage of the boost transformer added to the AC source, about 239 V. If this does not change substantially when the pump load is enabled, then the problem is between this point and wherever you measured the voltage at the pump end.

.