Detail design of solar water pumping

kcbibek310

Can anyone help me to give idea about selecting suitable VFD controller in solar water pumping( 3-phase Submersible pump). And also calculating the size of wire from VFD device to pump. 

mike95490

We need to know the size (HP) of the pump, and the voltage it runs at.

kcbibek310

Suppose the pump is of 3HP and the operating voltage is 415V and the distance between VFD( Controller/Panel) to pump is 100m( Length of cable)

mike95490

Ouch !  That's going to be expensive bag of parts.  Your VFD manual may have some suggested wire gauges for long runs, or they may caution against long runs,  going to have to read the manual
Cheapest controller I can find, is about $900
https://www.grainger.com/product/EATON-Variable-Frequency-Drive-32WP39
Your mileage may vary

kcbibek310

Why it is problem with VFD if we have long cable?

mcgivor

Capacitance becomes an issue when long cables are between the drive and motor, this can be corrected with inductors, but the best solution is to keep the distance between the two as short as possible, the run to the drive is not as critical, so mount the drive at the pump end.

kcbibek310

But i think while selecting the cable length for any motor or pump, we mainly focus on the voltage drop in the cable., isn't it? And i think the value of capacitance can be neglected upto 100m. Can you tell me about it?

mcgivor

The distance between the drive and motor is to be kept as short as possible, naturally the conductors must be sized correctly to account for voltage drop, what you don't want is the drive feeding a motor 100 meters away, even with shielded conductors, it's a little hard to explain but read this link to gain insight. http://www.invertekdrives.com/variable-frequency-drives/problems-with-motors-and-cables-22.aspx

mcgivor

Another point worth considering is if the motor used is rated for use with a frequency drive, the windings must have an insulation rateing higher than the supply voltage, to account for spikes, in the case of 600V motors the insulation rating must be 1000V, premature failure will most likely occur if this is ignored.

jonr

Rarely is it wise to operate right at the limit (100m).  I would locate the VFD (but not the panels) closer to the pump.    If you can't, then use a load reactor.

I assume you are using an inverter to get a steady 415VAC?  That's a shame since the VFD is just rectifying it and then doing similar things.

Solar2

Well guys, three phase motors tolerate high cable losses just great.
That is one of the big reasons for using three phase.
In easy start situations like a submerged pump, the motor will start turning with only 2 volts or so.

Also, I have never had motor voltage breakdown problems with VFDs.
Quite the opposite, the VFD shields the motor from voltage spikes that can come down the line.

Our main well has 1300 ft of wire to it counting the well drop.
It is 2 Hp at 220 V and I am using 12 Ga wire.
No problem at all.
I usually set the VFD for a 3 second ramp up and down.
That way the pump doesn't jerk around during start or stop.

I don't know who calculated the wire tables we sometimes see.
They must have stock in the copper mines.

There is a problem with the cheap VFDs.
If you operate them near the top of their ratings and near 100% duty cycle 
they burn up their capacitors after a year or so.
When powering something like a heat pump which may run near 100% for some months,
it is best to at least double the size of the VFD.
This applies to a AC powered VFD.
If you power them with DC there would be no problem.