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Recent content by eeprom

  1. eeprom

    Inexplicable motor failures

    Electeicpete, No worries. I very much appreciate the input. I care more about solving the problem than being right. In fact I would be more then happy to solve the problem and still be wrong. The motor amps were measured at the motor with a clamp on ampeg. Reading rms. I've used it many...
  2. eeprom

    Inexplicable motor failures

    The motor has already been replaced. If the new motor has the same issues with loading we'll know soon. If the new motor trips, then we have a relay problem, but given that this problem occurs on both pumps, I think the most likely problem is that the vfds haven been allowed to run too...
  3. eeprom

    Inexplicable motor failures

    ElectricPete, Let me ask further...If I add the current vectors on the motor loaded, assuming the phase angles are 120 apart, the residual ground current was 60A. If that imbalance scales to starting current, the measured ground current would be 300A or more. There is a ground fault relay on...
  4. eeprom

    Inexplicable motor failures

    The motor load was determined by flow and pressure. The voltage imbalance was 2 volts at 480V. The current imbalance percentage was the same loaded and unloaded. The voltage imbalance loaded was 2 volts at 480V. The motor was replaced because it was overloaded at far less than full load. It...
  5. eeprom

    Inexplicable motor failures

    Waross, What works the toaster test reveal? Just a higher resolution impedance test? Also, what's an acceptable phase current imbalance? I would expect less than 2% variation from average current.
  6. eeprom

    Inexplicable motor failures

    That's exactly what it seems to be. I would need to do a surge test, and I don't have tools for that. The motor is going to the shop
  7. eeprom

    Braking Resistor Protection

    Braking resistors are usually protected by thermostats that trip the drive. This is pretty common
  8. eeprom

    Inexplicable motor failures

    I have traced this down to phase imbalance, I think. The loaded motor is drawing 634, 591, 587 A, and the voltages are within 2 volts. As far as I can tell, the only reason for imbalance would be winding differences. I believe that the reason the motor is tripping is that the ground fault...
  9. eeprom

    Inexplicable motor failures

    The voltage is 480V, three phase. I cannot run the drives, that's why the motors are running in bypass. The drive on the motor in question has blown fuses, presumably due to the same motor failure that has caused the main breaker to trip. The other motor is in service, in bypass, and cannot...
  10. eeprom

    Inexplicable motor failures

    Heavyside, the current is being measured at the motor disconnect. Waross, I don't have drawings so I've been tracing things out by hand. The VFDs have some sort of filtering on them, I can't tell if it's upstream or downstream. There are 6 fuses in the VFDs, which I am assuming go to two...
  11. eeprom

    Inexplicable motor failures

    Hi, I have two pumps, both 500 Hp, running on VFDs or across the line in bypass mode. Both motors have a history of failing windings. Both motors are inverter rated. There are no RTDs on either. Both motors are within 150ft of their VFDs, and neither motor is using VFD cabling. Both motors...
  12. eeprom

    Synchronizing solar,wind, and grid

    The idea of rectifying the grid is an interesting idea. The you have a bus with three dc inputs and one AC to the loads. No more synchronization is needed.
  13. eeprom

    Synchronizing solar,wind, and grid

    I think we are overthinking this. The renewables will act in parallel to the grid. Think of it as a local source with the option of running as an island. The building loads will be served by the grid and by the renewables. If there's enough renewables, then the meter registers 0kW from the...
  14. eeprom

    Synchronizing solar,wind, and grid

    stevenal, Thanks for your reply. The renewables will be sufficient to run all three buildings, not just critical loads. I have been looking into hybrids, and I do agree that this is the hardware needed.
  15. eeprom

    Synchronizing solar,wind, and grid

    No. Maybe I was not clear. The relay will open and close the breaker. There are three buildings all to be powered by solar and wind whenever possible. There will be two inverters running all the time, one for solar and one for wind. The inverters will each be load connected into a main...
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