# Transmission of 3phase output power of solar

Registered Users Posts: 21 ✭✭
Hello,

I have a 3 phase pump of 17.5 Hp. And we are planning to install solar module of 15 KWp for the pump. Its rated current is 32.5 Amp. But the problem is the distance between the pump controller and the pump is about 830 meter. We are using vfd pump controller which locates near to solar module. Can anyone please help me to find the exact way of power transmission. Which type of wire should i use and what is the size of wire. I need this with calculation. So if anybody knows about it then please help me with this.

I am guessing you are in Nepal? And the motor is rated at 380-415 VAC (50 Hz)?

And what is the rating of the VFD? Guessing, that it may be around ~565 VDC input minimum?

In general, you want to send the highest voltage the longer distance (the 565 VDC Vmp-array voltage?). Also, VFD's (many times) may not like to send power down long cable runs (VFD's are usually some form of square or modified square wave, which can cause wiring to ring with the inductive load of the motor).

Size of wire in US Gauge... If you want 3% voltage drop, with single phase (DC) wiring of 2,739 feet with an estimated current of (15,000 watts / 565 VDC 26.5 amps

https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.4066&voltage=565&phase=dc&noofconductor=1&distance=2379&distanceunit=feet&amperes=26.5&x=70&y=12
1 AWG copper:
Voltage drop: 15.63
Voltage drop percentage: 2.77%
Voltage at the end: 549.37

https://www.calculator.net/voltage-drop-calculator.html?material=aluminum&wiresize=0.2557&voltage=565&phase=dc&noofconductor=1&distance=2379&distanceunit=feet&amperes=26.5&x=54&y=17
2/0 Aluminum
Voltage drop: 15.49
Voltage drop percentage: 2.74%
Voltage at the end: 549.51

Of course that is in US measurements. In metric:

G Number Ø [Inch] Ø [mm] Ø [mm²]
6⁄0 = 000000 0.580 14.73 170.30
5⁄0 = 00000 0.517 13.12 135.10
4⁄0 = 0000 0.460 11.7 107
3⁄0 = 000 0.410 10.4 85.0
2⁄0 = 00 0.365 9.26 67.4
1⁄0 = 0 0.325 8.25 53.5
1 0.289 7.35 42.4
2 0.258 6.54 33.6
3 0.229 5.83 26.7
4 0.204 5.19 21.1
This is a very rough estimate--And lots of guesswork. I do not know what standards you have for wiring in your region, and if you will bury the cable, put the cable in conduit/pipe, or on poles.

This is not a "trivial" installation... You need a power engineer familiar with your type of application and/or some help from the VFD company.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 29 ✭✭

OK kcbiibk,
Here is a rundown for you.

15KW, 32.5 amp, 3p indicates you are using 337 volts.
830 meter = 2722 ft or approx 1/2 mile

Starting with an allowable voltage drop of 5%;
this allows 16 volt drop in the line.
At 32.5 amp this would be a total of 0.492 ohm or 0.181 ohm per 1000 ft.
But since the electricity must travel both ways we must half this value
giving an allowable conductor resistance of 0.091 ohm per 1000 ft.

This indicates 0 gage Cu wire or 00 Al wire to keep voltage drop below 5% at full power.
But 0 gage Cu is not a standard size.
Even if you could find it, it would be very expensive.
2 gage is readily available but would result in approx 8% voltage drop.
00 Cu (also available) would result in 4% voltage drop.

But because of the high price of Cu these jobs are usually done with Al.
A good choice would be 2 gage Al which would result in 7% voltage drop at full power.
Any decent 3p submerged motor will have no prob at 7% voltage drop.

I recommend the wire be buried.
This is the best lightning protection you can get.
The distributed capacity of a buried cable stops voltage spikes
and will tend to suppress any ringing.

There is no start up surge when using VFDs and 3p.
Set your ramp up for some 5 seconds and your start up current will be less than the run current.

Best wishes

18 Kw PV;  2000 AHr FLA Bat; 12 Kw Inverter;  20 Kw Kohler, LP, low speed, double muffled,   Home built, ground coupled heat pump, VFD enabled;  Leaf
• Registered Users Posts: 29 ✭✭
kcbiibk,