10 Questions You Should to Know about 3 phase inverter

Post by sbrownian » Tue Mar 16, 12:10 am

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Don58 wrote: &#;

Mon Mar 15, 5:32 pm

sbrownian wrote: &#;

Thu Mar 11, 2:36 pm

There are isolation transformers out there that you can hook to 208 and they will output 230 with a center tap, which will re-create the neutral and give you the added benefit of fully isolating the Outback gear from whatever is also on the incoming feed. The higher the kva, the more $ you will spend.

There are isolation transformers out there that you can hook to 208 and they will output 230 with a center tap, which will re-create the neutral and give you the added benefit of fully isolating the Outback gear from whatever is also on the incoming feed. The higher the kva, the more $ you will spend.

Isn't that 208 across two legs that have a 120deg phase difference? Does this mean it will work with a 120deg phase difference so long as the resulting voltage is high enough? The transformer can't correct for phase unless I'm missing some fundamental.

Isn't that 208 across two legs that have a 120deg phase difference? Does this mean it will work with a 120deg phase difference so long as the resulting voltage is high enough? The transformer can't correct for phase unless I'm missing some fundamental.

It doesn't correct for phase differences, it creates an entirely "new" isolated sinewave.

Think of it as one primary winding across two phases. With no reference to neutral or another phase, all the primary winding "sees" is the differential voltage impressed upon it from the two phases. Remember, NO reference to neutral, or the other "leg." The voltage "change" is happening at a 60hz rate.

That voltage is magnetically coupled to two secondary isolated windings, (or one center tapped winding,) that has more turns than the primary, giving the voltage a "boost" (and reducing the available current.)

If left isolated, you now have two 120v outputs on the secondary.

If you connect the "negative" of one winding to the "positive" of the other, you have created a new "neutral" at that junction, and you will measure 240v from the "positive" of one winding to the "negative" of the other. (Look up transformer "phasing.")

Like the primary, the secondary winding has NO direct connection to the [Edit: rest of the] three phase system, and no "reference" to measure to.

By nature, a single winding is a 180 degree device..

You only get 120 degrees when you actually have an alternator that has three separate windings staggered correctly on the stator, and the proper magnetic field to excite it with. (Yeah, I know, there are all kinds of tricks with multiple transformer windings in LARGE rectifier stacks to produce 6 to 12 phase stuff for things like 10s of megawatt cruise ship drives and phase shift tricks with electronics, etc.)

It doesn't correct for phase differences, it creates an entirely "new" isolated sinewave.Think of it as one primary winding across two phases. With no reference to neutral or another phase, all the primary winding "sees" is the differential voltage impressed upon it from the two phases. Remember, NO reference to neutral, or the other "leg." The voltage "change" is happening at a 60hz rate.That voltage is magnetically coupled to two secondary isolated windings, (or one center tapped winding,) that has more turns than the primary, giving the voltage a "boost" (and reducing the available current.)If left isolated, you now have two 120v outputs on the secondary.If you connect the "negative" of one winding to the "positive" of the other, you have created a new "neutral" at that junction, and you will measure 240v from the "positive" of one winding to the "negative" of the other. (Look up transformer "phasing.")Like the primary, the secondary winding has NO direct connection to the [Edit: rest of the] three phase system, and no "reference" to measure to.By nature, a single winding is a 180 degree device..You only get 120 degrees when you actually have an alternator that has three separate windings staggered correctly on the stator, and the proper magnetic field to excite it with. (Yeah, I know, there are all kinds of tricks with multiple transformer windings in LARGE rectifier stacks to produce 6 to 12 phase stuff for things like 10s of megawatt cruise ship drives and phase shift tricks with electronics, etc.)

Guys &#;

Many thx for all yr ideas and suggestions.

Safety is a concern so I do not want to remove covers and probe 400+ volts.

The ground mount PV array (114 panels) & inverter is 100 metres from the house. Between the array and the house is an outdoor heated swimming pool with an ASHP in situ but not yet plumbed or wired. Extension leads are not really feasible.

There will be 3 x emonTx&#;s - at the inverter, in the pool plant room and at the grid supply meter (house). The site has wifi coverage.

Contact us to discuss your requirements of 3 phase inverter. Our experienced sales team can help you identify the options that best suit your needs.

When I open the cabinet at the ground mount PV array, I&#;m faced with 3 unidentified cables from the inverter to the smartgen meter.
Here will be an emonTx (with 3 phase firmware) serially connected to an RPi running emoncms plus 3 CT&#;s and a pulse counter on the smartgen meter.
There is also a 13 amp socket outlet (for the ac/ac adapter) connected to one phase but I know not which. See picture &#;

From an earlier forum exchange with Robert, I understand that at the inverter/smartgen meter, the PF will be close to 1.
Also I assume the power on each phase will be close to equal when generating &#; correct?
The inverter itself has an LCD panel showing what is currently being generated in total.
Once up & running, I envision applying a simple correction factor (based on smartgen meter pulses) to the phase powers as shown by the emonTx.

So my trial & error questions &#; if I clip all 3 CT&#;s to one live cable &#; what emonTx powers will be indicated if the selected live is not nominal phase 1 (ac/ac adapter phase)?
What will I see if by chance the selected live is nominal phase 1? Is this a way of identifying nominal phase 1?

If so I&#;d then be left with 2 x unidentified phase live cables and 2 x CT&#;s. I could try hooking both CT&#;s to each of these phase lives in turn &#; what powers would I see? If one were negative would this be the final clue?

To complicate matters, the installation is at my son&#;s place an hour&#;s drive away and I&#;m spending days trying to set up emon gear in my single phase home with no PV where I&#;ve made an experiment with an emonTx running 3 phase firmware.

I clipped 2 CT&#;s to my one live phase (making sure they were in same direction orientation). One CT was in CT1 input and the other in CT2. The house consumption was 500 watts approx but varying as indicated by CT1 PowerL1. Then I boiled a kettle &#;

CT1 PowerL1 watts
CT2 PowerL2 minus watts (at the same sampling instant)

I switched the second CT into CT3 input, rebooted the emonTx and boiled another kettle &#;

CT1 PowerL1 watts
CT3 PowerL3 watts (at the same sampling instant)

Is this data in any way helpful or relevant?

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