Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
I've been troubleshooting a pump for the last couple of days that intermittently quits. I did get the pump working again but don't understand some of my meter readings.
Its a 480v submersible, I'm guessing around 60HP just by the amp readings. The problem is B phase runs about 9-10 amps lower than A/C, despite shifting motor leads one phase over. Here's my readings, I verified with 3 different meters and used the meter that was the closest average of all three to do all the testing with.
Pump Off:
a-b 495
b-c 492
a-c 501
a-gr 247
b-gr 247
c-gr 429
Pump On(measured at T leads):
a-b 486
b-c 482
a-c 491
a-gr 242
b-gr 242
c-gr 419
Motor runs about 83 amps on A/C and about 73 amps on B phase.
Did a voltage drop test across the starter/breaker combined and only read about .2 ohms on all phases.
Megged it, and had .8 megaohms at 1000volts on all 3 motor leads. Which seems exceptionally low, but isn't the first time a submersible has ran just fine with this low of a reading.
The problem ended up being the programmable O/L relay was set for a 7% current unbalance and was dropping the motor out. I turned it up to 20% to have some single phase protection still but don't understand why the pump is so unbalanced? The problem isn't following the motor leads, so I assume it's an incoming power issue. But the voltage is so close, I wouldn't think it'd make a 10 amp difference?
Any ideas?
Its a 480v submersible, I'm guessing around 60HP just by the amp readings. The problem is B phase runs about 9-10 amps lower than A/C, despite shifting motor leads one phase over. Here's my readings, I verified with 3 different meters and used the meter that was the closest average of all three to do all the testing with.
Pump Off:
a-b 495
b-c 492
a-c 501
a-gr 247
b-gr 247
c-gr 429
Pump On(measured at T leads):
a-b 486
b-c 482
a-c 491
a-gr 242
b-gr 242
c-gr 419
Motor runs about 83 amps on A/C and about 73 amps on B phase.
Did a voltage drop test across the starter/breaker combined and only read about .2 ohms on all phases.
Megged it, and had .8 megaohms at 1000volts on all 3 motor leads. Which seems exceptionally low, but isn't the first time a submersible has ran just fine with this low of a reading.
The problem ended up being the programmable O/L relay was set for a 7% current unbalance and was dropping the motor out. I turned it up to 20% to have some single phase protection still but don't understand why the pump is so unbalanced? The problem isn't following the motor leads, so I assume it's an incoming power issue. But the voltage is so close, I wouldn't think it'd make a 10 amp difference?
Any ideas?
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