200HP Pump motor, Start & Stop currents.

[11bgrunt]

A water supply company reported a tripped 400A breaker and unbalanced motor run currents. Nothing was obvious and a recorder was added at the 500kVA padmount transformer. The 200HP motor is the only load. This motor is on a soft start. That motor is a Nidec Vertical Hollow Shaft, Stock, 200 HP, 1780 RPM, HO200V2SLH, 460 V, 60, H445TPA.
The motor starting current average is 775A. The run average is 225A. When the motor shuts off, current goes to 650A and then falls to zero.
Is this because it is moving water?
The water supply company will be rolling their phases to help determine source or load issue. Plant is six years old with no problems. The cause of the 400A breaker tripping is still unknown. Pump starts from tank demand, so the start/run times do vary during the day.
I want to understand the high stopping currents.
Thanks,

 

[don_resqcapt19]

A water supply company reported a tripped 400A breaker and unbalanced motor run currents. Nothing was obvious and a recorder was added at the 500kVA padmount transformer. The 200HP motor is the only load. This motor is on a soft start. That motor is a Nidec Vertical Hollow Shaft, Stock, 200 HP, 1780 RPM, HO200V2SLH, 460 V, 60, H445TPA.
The motor starting current average is 775A. The run average is 225A. When the motor shuts off, current goes to 650A and then falls to zero.
Is this because it is moving water?
The water supply company will be rolling their phases to help determine source or load issue. Plant is six years old with no problems. The cause of the 400A breaker tripping is still unknown. Pump starts from tank demand, so the start/run times do vary during the day.
I want to understand the high stopping currents.
Thanks,

That sounds like some type of ramp to stop setting, with the water running back down the well pipe trying to spin the motor backwards. I believe some soft starts have such a function. I have done some VFDs for deep wells, but we had them set for coast to stop on shut down, and not ramp to stop.

 

[Dzboyce]

The only time I will use ramp to stop on a lineshaft turbine pump, is its feeding into an uphill pipeline. Then we will ramp the pump down to reduce water hammer.

 

[tom baker]

Is there a pump control valve? How is the soft start programmed for stopping?

 

[petersonra]

don't most wells have foot valves to prevent water from flowing backwards?

 

[don_resqcapt19]

don't most wells have foot valves to prevent water from flowing backwards?

The industrial deep wells I worked on did not those at the well. There were valves like that before they connected to the water tower, but they still always had the full vertical column and some distance of horizontal piping that would back flow. We had anti-re-start timers to prevent the pump from attempting to start within five minutes of being stopped. These had 14 or 16" shafts about 1200 feet deep with the pump sitting around 450' deep, and 8" discharge piping.

 

[Dzboyce]

don't most wells have foot valves to prevent water from flowing backwards?

A submersible pump with a motor on the bottom of the bowls normally has a check valve at the pump andvthe column pipevstays full of water

A line shaft turbine pump has the motor on top of the ground. It rotates a lineshaft that extends the full length of the column pipe to rotate the turbine pump assembly. The deepest ive set one this style is 1,050 feet deep, with a 700 hp vertical hollow shaft motor. This style has a check valve at the surface with air vents. The column pipe drains down to the static water level every time the pump stops.