Using Step-up Transformer with LV VFD

I'll go for option 1, Boss.

I would consult with some VFD manufacturers who offer both voltage ranges, getting performance and price comparisons. I suspect, but don't know, that Option 1 is better. Please let us know what you discover.

Saving cost may be a factor to consider. Also consider that MV motors have lower initial torque than LV motors, in general.

That' a non-issue with a centrifugal pump as the load presents zero torque to the motor at blast-off, Boss.

True, but the pump has not yet been specified as centrifugal, even if it probably is a multistage version.

Probably.

The initial operation of a centrifugal pump depends on the torque of the motor and the starting torque required by the pump. Head and gate position are two more factors when choosing the pump.

The motor/pump is the same, regardless of the option he takes.

There's only one real consideration. The cost.

If you have 3.3KV available use that and a VSD.
If only LV is available use a LV pump and VSD.

I can't see the sense of stepping up the O/P voltage of a VSD.

This looks to be a case of:
"We've bought this, how do we get it to work?"

500 meters of low voltage cable to a 275kW motor might swing the decision.

Fair point but I'd still be taking a close look at the costings.

All valid and pertinent points have been requested or discussed so far. On general principles, I support Crabtree's first idea of a medium VFD without a transformer, just on the basic principle of less parts are usually better.

I do have a few questions for the OP. What is the longitude and latitude of this motor and what color is the bearings and the motor housing?

My apologies. With so many recent postings providing nothing but useless information, I felt I could ask for some useless information.

I hope everyone is having a good weekend.

Sorry-

Late night calculations weren't so good. 500m = 1,638 ft. Therefore distance is 3* stated. 1,638ft of #4 or #2 wire. Cost of wire is therefore at least $100.00, most likely more, and the total cost at least $70,000!

Good Luck, Old Salt,

GA anyhow. OP had better verify figures, if he doesnt he's not doing his job lol.

LongintheTooth-

Yes! Just like me, he probably made a mistake on the first go around. His will be much more expensive than the cost of a line of pencil lead about a foot long.

Thanks!

Good Luck, Old Salt

As I understood motor would be in the well, VFD and the transformer would be on the ground level. That means the cable is not a factor. The key point is the transformer and transformers do not prefer to work in a wide range of frequency or transforming extreme low frequencies needs special - expensive - transformer.

I definitely recommend the medium voltage VFD.

I understand your point, but cable definitely is a very important factor, the higher the voltage, the lower the current, thus a smaller wire gauge can be used, saving a whole lot of money.

Name plate data of the motor? Volts, amps, HP

Supply voltage from the high line or generator?

Type of pump & number of stages, plus HP required per stage

Flow rate required?

Type of cable you are considering using?

Once you have given all that data then can your question be answered...

Failing that.. call a pump company who will design a completion for you

Nice thought, how many times do we get information to give a real answer?

I would go with the medium VFD. The transformer may not do very well with fluctuating frequency.

There is no benefit to installing LV equipment where MV equipment can be used.

LV applications result in a significantly larger equipment footprint, much larger power conductors/cable, and a significant amount of added weight.

All of these items add up to increased difficulty and higher cost for maintenance.

I would opt for the MV VFD.

The economics of this will in all likelyhood point you to a LV drive and step up transformer. For a 275kw motor (368HP), a MV Drive will cost you in the neighborhood of $125-$140K. Most, if not all, of the MV drive mfg.s have the 1000 HP MV drive as their smallest frame. You are pretty much paying for a 1000HP drive when you buy one for 368HP. A 400HP LV drive will run closer to $25-$30K. Add in harmonics mitigation on the input side and a long lead filter or sine wave filter on the output side and you'll be in the $50-$60K range. (Harmonics mitigation and a good output waveform are pretty standard with MV drives.) Add in the step up transformer to get this to 3300V +/- and your total will almost certainly be less than $100K. In fact, a good multi-tap step up transformer is the way to go as it allows you to adjust for depth and voltage drop based on lead length and wire size.

This is done all the time in the deep well water business in the US, and similarly in deep well oil production (see Schlumberger) all the way up to 2000HP +.

If your pump is gong to run for a significant amount of time, there are also additional losses though the output transformer that result in increased energy consumption. In addition, if you have a primary voltage of let's say 11kV, then you need a significantly larger (physically) primary transformer for supplying the 400V for the LV VFD, and the I squared R losses in that transformer will be higher as well. If it were me, I would go for the MV drive.

The only unmentioned benefit to a LV drive option would be the familiarity factor of the people who need to work on it. In some areas, special qualifications are necessary to work on any MV equipment and if your on-site people do not have that (or are afraid of MV in general), it means bringing in outside contractors whenever work needs to be done.