1000volt deep well motors 3

[ashtree]

We are working through the issues on installing 1000 volt motors on well pumps at about 350 metres (1100 feet ) below ground. We have to go to 1000v because of the cable size required to limit the voltage drop at 400volts is so large that we cant fit the pump and the cable down the well. These are motors in the 110kw range.

These motors would likely be on VFDs which open up some real challenges but there does not seem to be consensus around which is the best spot to mount the step up transformer:

1) Use a standard voltage VFD and boost after the VFD fitted with some serious sine wave filters, or
2) Step up to 1000volts pre VFD and obtain or specially engineer a 1000 volt VFD.

It seems that both options are possible.
There are limited options for the 1000 volt VFDs off the shelf and at least one standard voltage VFD manufacturer modifies a seemingly standard drive to take 1000 volts. From a spares and redundancy viewpoint this would seem to be the worst option.
The step up transformer after the VFD will possibly have some similar issues and there are obviously efficiency and harmonics etc issues with the arrangement.

I would be interested in hearing anyone's experience or opinion on either of these or other options that i might not know about.

 

[LittleInch]

1000V seems to be a mining speciality. Maybe do the reverse and find some motors which match more common VFD supplies?

As 1000V is the cut off between low and medium/ high voltage rry looking for 975V VFDs?

 

[LionelHutz]

A step up after will eliminate almost all of the PWM waveform being applied to the motor. There is no need for sinewave filters. That is the direction I would go.

There is at least one company doing similar and they even step up to a voltage a fair bit higher than the motor rated voltage to account for the voltage drop in the cables. For example, they might use 1350V out of the transformer which drops to 1000V by the time it reaches the pump. It's been a while since I've seen their info, but I don't believe they actually made it clear there was a step up transformer after the VFD in their sales literature.

 

[jraef]

A bespoke VFD “modified” to handle 1000V would be a nightmare in terms of spares, replacements and repairs. Low voltage drives stop at 690V, 1000V is considered medium voltage (for drives), ehere designs typically start at 2300V. So to handle 1000V, there would have to be a custom design of a 2300V drive, and depending on what your line voltage is, you are likely looking at a custom transformer no matter what. So I would rather have a standard off the shelf LV drive fed by a normal LV source and a custom transformer at the well head than a custom drive AND a customer transformer.

A custom transformer is simple to do and, if designed right, will not be a component with a high failure rate to worry about.

 

[waross]

Same voltage with filters, or step up after the VFD. The VFD acts as the filter.
I have seen two methods used on different wells on the same well pad.
In both cases the filter or transformer was mounted beside the VFD enclosure.
When a the VFD voltage matched the motor voltage a filter was used.
For higher voltage motors, a 480 Volt or 600 Volt VFD was used and an adjacent transformer stepped up the voltage to 4160V for the motor.
A transformer after the VFD acts as an effective filter.
Tip, go to 4160V and use standard components and motors.
*memory fails on the exact voltages.

 

[edison123]

"The VFD acts as the filter".

How?

why not go for a 690 V motor of same size? standard VFD and reduced cable size.

 

[waross]

The VFD acts as the filter".

How?

Read it as;
"A transformer after the VFD"
eg: 480 Volt supply.
480 Volt VFD.
On the output of the VFD, a 480 Volt to 4160 Volt transformer.

 

[EdStainless]

Transformer after the VFD.
You need to use good transformers.
We did this with 800-3200V submersibles.
And for us 1000' was shallow, we would often work over 10,000'