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Can 15kW Axpert Inverters Start 9.3kW Submersible Pump?


Kilowatt Power

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This topic of the startup current of a pump crops up repeatedly. Most often it doesn't get resolved from what I can determine.

In this case the pump is 3 phase which is great because we can use VSDs and soft starters to mitigate this peak current during startup. A soft starter is a variable voltage device (as opposed to a VSD which varies both frequency and voltage)

Soft starters are intended to start drive systems that have great inertia. If a drive system cannot be accelerated up to full speed in a few seconds then the startup current must be limited since it is so great (as has been indicated) that it overloads and stresses all wiring and switchgear. But they are also useful when the electrical supply is not able to withstand this transient. It doesn't make sense to provide an inverter with the capacity of a power station since this is not the regular load on the supply.

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10 hours ago, Javi Martínez said:

As you can see start current is 123 A...¿

Actually, the Axperts will output 230 V per phase, so 400 V line to line. So 118 A.

Quote

How many Axperts do you need?

Each phase would need 230 V × 118 A = 27 kVA, so each phase would need 3 inverters, assuming that 5 kVA Axperts really can do 10 kVA per inverter for a second or so. So that's 9 inverters total. The startup current is still lower than I thought, at only 5 x Inom.

5 hours ago, Richard Mackay said:

It doesn't make sense to provide an inverter with the capacity of a power station since this is not the regular load on the supply.

Indeed. The continuous apparent power is going to be around 23.7 A × 230 V = 5.5 kVA, so two inverters per phase would carry it comfortably. That's still 6 inverters though.

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18 hours ago, Kilowatt Power said:

I had this in mind and had even proposed the INVT GD100-011G-4-PV solar pumping inverter with 16S3P Jinko 330Wp panels (total 15840Wp) but the client wants to be able to run the pump at night. Needless to mention, doubling or even tripling the installed 20m3 water storage tank capacity would have been the best route to follow. 

I think after analyzing his water needs, storage plus a smaller surface pump for night time and a smaller solar driven borehole pump during the day is by far the most logical solution.

But if your hands are tied by a dictatorial client present him with the pro and cons (and associated costs) of his options.

The cost of 9 inverters,  ( and the size of battery to run this at night steady state) and knowing that one failure puts him out of business should be enough to tip the scales.

Otherwise give him what he wants, if he's paying and accepts the costs and risks.

 

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10 hours ago, phil.g00 said:

I think after analyzing his water needs, storage plus a smaller surface pump for night time and a smaller solar driven borehole pump during the day is by far the most logical solution.

But if your hands are tied by a dictatorial client present him with the pro and cons (and associated costs) of his options.

The cost of 9 inverters,  ( and the size of battery to run this at night steady state) and knowing that one failure puts him out of business should be enough to tip the scales.

Otherwise give him what he wants, if he's paying and accepts the costs and risks.

 

Yes, I agree, but the question was clear. I don´t know if @Kilowatt Power wants other kinds of advice. 

If I were in that situation, depending on the amount of water per day needed, I would install the next:

 

7-8 Kwp pannel and a 11 KW VFD. I would limit frequency to 40-42 Hz in order to reduce the power needed, being sure that the refrigeration of motor is enough.  Power would be 4-5 kW and flow rate 5 m3/h. 

If it is neccesary, at night, I would feed AC IN in the same VFD whith a pair of Axperts in parallel and an Autotransoformer, 230-400 W 5 KVA, whith the same frequency. Also, an inductance is needed after VFD, since the line is too long. Concerning batteries, 20 kwh LiFePo4 could be enough. 

The autotransformer has two functions, increases voltage, and avoid spikes from VFD to inverter.

 

 

 

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12 hours ago, phil.g00 said:

I think after analyzing his water needs, storage plus a smaller surface pump for night time and a smaller solar driven borehole pump during the day is by far the most logical solution.

 

Good idea! 

I'm not impressed by inverters/UPSs . Too often these are seen to be the answer (after one has given up on the generator option!) But they always seem to disappoint. Way back I also thought that by installing a couple of batteries and an inverter I would be able to keep essential stuff running at my house during power outages. Well the batteries died and then leaked acid in the house so I didn't feel like rushing out and buying another set!

After pondering this universal disappointment that we end up experiencing I concluded that a lot of the backup power solutions are inefficient: e.g. What has made the laptop PC such a success over desktop PCs is not only that its portable but that it can run for hours on its own batteries. It can do this because the manufacturers have done a fine job of creating an efficient package. (If you don't agree with this then do a test of comparing a UPS powering a desktop vs a laptop PC)

This prompted me into developing low voltage backup solutions. The product I make is a low voltage backup unit for broadband internet routers. It works like a charm and keeps your internet going 12hrs (see small print..) but is head and shoulders better than a UPS/inverter solution.

I know nothing about solar driven pumps but as Phil has pointed out maybe these are way more efficient than the AC option and offer a much better solution, even if you have to make a plan to get it to pump at night??

 

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