Using Extended Variables to Monitor Multiple Phase Power


#1

I use a Generac Neurio energy monitor to record my PV production and my power consumption on each phase of my house power. I upload the data from my Neurio to PVOutput using a Pi 3B running Debian OS through the Crontab function which runs my task every five minutes and uploads the data through the PVOutput’s API.
This is the output so far today.

The Delta Energy is the kWh used for the last 5 minute reporting period. During the early morning hours the only things running are the “always on” items which draw power when idle such as the TVs and computer peripherals or kitchen appliances. The refrigerator shows on phase A and a freezer in the garage shows on phase B. Spikes are usually kitchen appliances. I have chosen to display PV production on this graph and have turned off three items normally displayed which appear grayed out.
There are other energy monitors available which can be utilized in this manner. People with three phase power might also be interested in a way to monitor all phases for consumption. In that case you would need a monitor capable of monitoring three phase power.
Kudos to PVOutput for providing the ability to construct this display.


#2

This might seem like a rather a dumb question ( so someone should ask it & I feel eminently qualified to do so ) but do you only have a 2-phase supply to your home?


#3

grannos,

In the US, three phase power would be extremely rare for a residential system. What is typical is a single split phase system. The local utility will provide a single phase 240 V feed with a center tapped ground (neutral). Most residential devices will use a line to neutral connection at 120 V while larger appliances such as HVAC, ovens, etc, will use the full L-L voltage at 240 V. If you were to look at the L-N voltages for each “phase” on a scope, their waveforms would be 180° apart.


#4

Hi pjschaffer,

Thanks for the information. Three phase domestic supply isn’t uncommon here ( West Aus ). I had three phase connected when the house was built as I was anticipating installing a domestic garden bore ( 3 phase submersible pump ) in order to water the garden over the summer months - It’s 30m to the water-table where I live. I never actually installed a bore so I don’t have any three phase devices apart from the inverter.

If I recall correctly it was only a few hundred dollars extra at the time to get 3 phase over single phase.


#5

i have 3 phase supply in SA. apparently the whole development area was meant to have it but i know a few blokes down the road that still only have single phase.
it was actually cheaper for me to go 3 phase due to the length from the house to pole.
i have a single phase run to my bore pump controller with the pump controller turning it back into 3 phase for the motor…

some older house have 2 phase supply but dont see it too much.


#6

Sorry I didn’t make the power scheme clear. Here is the wiki for Single Split-phase power distribution commen in America.


It is a means of getting 120V and 240V power on a single phase power scheme.


#7

Hi,

Thanks for the explanation. It’s a different way of doing things. I assume here, where I live, that they run three phase down the street ( our cabling is underground ) and either hook a house up to all three phases ( if requested ) or some sort of round-robin for single phase to even out the load.

I’ve been battling planned and unplanned power outages over the last week. Makes a battery look like a good option.

G.


#8

Backup on 3-phase with batteries is tricky. Many solutions (e.g. Powerwall) can only provide backup on one phase.

Batteries still way too expensive anyway.

We get a lot of grid outages and so I went with a backup generator with a cutover switch wired into the main circuit board. Even though we are 3-phase, a regular generator can still be wired to supply power to all the phases in the home. Just bypass/exclude key circuits from the cutover switch, e.g. anything that requires a 3-phase supply such as big aircon units, and the inverter of course. I also bypassed the electric oven and induction stove.

Works a treat for us and during grid outages it means we have power supply to all the home’s power outlets and lights plus two outbuildings. Obviously we take care to not over draw the generator’s capacity. At 3kW it’s more than enough to keep us going, plus no real limit on how long the backup can run for. And it’s way cheaper than a battery.


#9

Just out of curiosity, where about in the world are you and what are your 3-phase Line to Line and Line to Neutral voltages supplied to your home?


#10

We achieved the same ‘whole house’ backup the other way - connected the single-phase battery to one of the three phases, and then had the distribution board re-wired so that all house lights and power circuits were connected to that same one phase. Phases 2 & 3 are only connected to the three-phase devices that need it - the aircon and induction cooktop. In a blackout, we have whole-house backup from the battery, except of course the main aircon and cooktop won’t work - but we’re comfortable with that. (The main aircon draws 6kW when operating, so we couldn’t run that off a battery, or a 3kW genset either, even if we wanted to!)


#11

Load balancing requirements means that’s not feasible for us. We have 3 buildings and a current limit of 32A per phase.


#12

Australia. The line to neutral AC voltage standard in Australia is 230V +10% / -6%. It dropped from 240V some years back although many areas still experience the older 240V standard as infrastructure is slow to be updated. The line to line voltage would be √3 x 230V or ~400V.

Our particular line voltages typically run at the upper end of the range and are quite variable, for various reasons not least of which I live in a rural area and at the end of a long line.


#13

Thanks @wattmatters. In the US, residential split phase systems are 240V L-L and 120V L-N. Most appliances and the standard elecrtical outlet operate at 120V while large appliances (HVAC, Electric Dryer, Ovens) operate at 240V. Commercial service to office buildings and the like are typically 3-phase 208/120V while industrial services are often 480/277V or higher.

The history of how these differences between countries occurred is interesting. Not much we can do now to standardize.


#14

…which you keep running using a 3KVA genset. That must be a bit of a balancing act in itself.


#15

Not really.

The circuits for the electric oven, induction stove and ducted aircon all bypass the backup power source.

Without those items it’s actually pretty hard to suck 3kW. Boiling a kettle is 2kW, which lasts a couple of minutes perhaps. Benefit of energy efficient devices. I only ask that a few other high power devices be avoided during that time. So far when on backup the generator copes very well.

The load balancing is necessary because when we are on the grid (which is 99.5% of the time) we need to ensure high power devices are spread across all phases.

Yet when we are on backup, I can still supply power to all phases (so all GPOs and light circuits are available), which you cannot do with a Powerwall.


#16

Hi @pjschaffer and thanks @wattmatters

Sorry. I’ve been away and have had very limited access to the Internet over the last week and a half.

We still see 240VAC here on the west coast of Australia and we’re NOT on the ‘National’ grid, so I guess that strict conformance with the voltage standards is less of a problem here. They used to sell incandescent globes here rated to 260VAC because the voltage used to be 250VAC and fluctuate quite a bit…

G


#17

Yeah, in reality though there’s not much difference.

The standard in WA is 240V (-6%/+6%), i.e. a range of 224.6V - 254.4V.
The NEM standard is 230V (-6%/+10%), i.e. a range of 216.2V - 253.0V

In reality large chunk of the NEM still sees voltage quite a bit higher than 230V. I guess it takes a long time for all the supply equipment to adhere to new standards, which is also why the upper end of the range was set to +10%, which kind of means we may as well have stayed with the old 240V standard.

I have a sample of grid line voltage on each phase every 5-minutes over the past 18 months.

Average 244.2V
Std Dev   3.6V
Minimum 221.3V
Maximum 258.7V

My inverter (Fronius Symo) has never triggered off due to over voltage but does need to manage outputs at times to deal with high voltage periods, especially on one particular phase.


#18

Voltage is highly variable - here in east coast (Sydney suburbs), just today, the grid voltage varied from 229V (lowest) to 238V (highest) and back again in just a few hours.


#19

That’s quite a gentle change. Try being on a rural network…

I’ll get a 10V swing in line voltage within seconds when the controlled load turns on and off. Every single day.

I have seen a 30+V variance in grid voltages in a day.

Just looking at yesterday, on line 2 my minimum was 232.4V and the max was 254.8V, a 22.4V swing. And it’s up and down like a yoyo all day and night. This is a typical line voltage variation we get every day.


#20

Thanks for the insights - I did appreciate that rural users have larger and frequent swings, being on the end of long thin metal strings, but great to have some real data war-stories for context.