An extra 3-phase Utility, How much will it cost?

Re: An extra 3-phase Utility, How much will it cost?

He will have to call his utility... In residential areas, there may not be three phase power available...

In those cases, there are several methods of running three phase equipment... One of the simplest is to wire up two wires of a three phase motor (rotary converter) to a single phase circuit... Run the two wires + the third wire from the 3 phase idler motor to the three phase lathe/mill/grinder/etc... Wrap a cord around the three phase idler motor and give it a pull (like starting a gasoline lawn mower). Then turn on the single phase power.

The 3 phase idler motor will generate "good enough" third leg to run pretty much any 3 phase motor out there...
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There are a few details (a "Y" wound 3 phase motor is supposed to be better as a "generator". The idler motor should be 2x the horsepower of the load it is running).

If you are running a CNC mill/lathe--run the single phase digital electronics on the "real" 240 VAC power.

-Bill

Re: An extra 3-phase Utility, How much will it cost?

I am not the guy to answer that question--perhaps somebody else here can...

But 240 VAC (split phase 120/240 VAC) is the standard in homes.

In California, light industrial parks (i.e., office complexes), single/3 phase 208 / 120 VAC is probably more common (from what I have seen).

You probably have get the address and utility service information to find out what is already present--and talk with the utility about how they would want the connection/what connections they would support...

Be prepared to pay a connection charge if you want to do something that is not already there (i.e., a full three phase connection instead of an open delta, etc.)...

It probably will be a bit of an adversarial issue (getting information, right power, not getting extra charges) as utilities are typically dragged into GT solar.

Also, I would guess the payment / net metering plans are quite different (from what little I have read) between residential (and typically 10kW or less) GT system vs commercial (and over 10kW-100kW) GT connected systems.

The 208 vs 240 VAC system differences should not be that big of issue (compared with the rest) and you probably need to be prepared for either.

Please let us know what you find out.

-Bill

Re: An extra 3-phase Utility, How much will it cost?

A VFD is, basically, a variable frequency 3 phase converter, which is connected to a three phase motor.

So, instead of hitting the motor with full voltage and 3 phase 60 Hz power... They can start with a frequency much closer to zero (and a lower voltage?)--and gently bring the motor up to full speed (or programmed speed if different than full speed).

Everything has losses--So, if you have a 5kW inverter, you may need 10-20% more power to run it.

Also, not everything pulls current from an AC line "in phase" which a clean current wave form. A resistor (or filament light bulb) take the current as a sign wave, in phase with the voltage sine wave... This is the "best" an AC circuit can perform... Cos 0 degrees = 1.0 or the Power Factor = 1.0

Many devices (motors, electronics, florescent/arc type lamps, etc.) don't take the AC current in phase with the voltage (it is a bit like either standing off to the side of a car with a rope and pulling "forward"--only a part of the rope strain is actually moving the car forward--the rest is wasted pulling the car sideways---Or like instead of pulling on the rope with steady force--you jerk the rope. You need stronger rope to have an equivalent pulling power).

For AC electrical power--a PF of 0.6 is very common. That means that a 1,200 watt whatever at 120 volts really used:

• Power = 1,200 watts * 1/120 volts * 1/1.0 PF = 10 amps
• VA = 1,200 Watts * 1.0 PF = 1,200 VA
• 1,200 watts * 1/120 volts * 1/0.6 PF = 17 amps
• 1,200 watts * 1/0.6 PF = 2,000 VA

In terms of power from the battery bank--both take ~1,200 watts... However with a PF=0.6 there is more current required to operate the motor/etc. -- therefore heavier wire required, more wasted heat, etc. Or--more or less the equivalent hardware required to run a 2,000 watt load with poor power factor.

Power Factor Correction is becoming more common now--but you need to be really careful and be sure not to overload the inverter/generator with loads, by wattage, should work fine--But by VA (KVA / Volts * Amps) would overload the power source.

The above is a lot of hand waving and very quickly degrades into lots of ugly vector math/trig... I will quickly be over my head--but we can continue with some more info/links if you wish.

-Bill