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DIYPete

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Could you please assist an end-user with limited knowledge:-

The system we installed in our new-build is 7.83 Kw of PV with a 'Solax X3' 3 Phase inverter. A later addition was a Tesla Powerwall 2 with the later gateway. Following a series of short (2min) power cuts and lights flickering UKPN monitored incoming voltage for a week. Result was fluctuation between 202v and 257v - they are now checking sub-stations. Not sure if that is relevant but mention it in case.

Problem - UKPN engineer noted reverse current on our new 'Secure Sprint 211 Smets 1' 3-phase meter. I understand that this must relate to the PV array in some way. Electrician has identified an imbalance across the 3 phases, typical figs are - AC Power 1 =130w, 2 = 137w and 3 = 152w this morning and AC Power 1 = 1913w, 2 = 2065w and 3 = 2070w this afternoon. There are no error codes showing on the display or web portal.

It is now 2027hrs and the meter is still flashing on L1 indicating reverse current (as per installer's manual)

Two questions please - Is the imbalance a problem and, if this is the cause of the reverse current, why is it still flashing at night?

Any assistance you can give would be appreciated - Solax Tech Support is simply an answer phone shut in a cupboard with no response.

Thanks
Pete
 
Do you only have one Powerwall2?

Could you send me a photo of your installation so I can work out to which phase (ie L1, L2 or L3) the PW2 is connected?

Does your home use one, two or all the phases? Again some photos of your supply intake would be helpful. In the UK most homes only use one phase. Some pictures of the routes of the cables from the main supply cable through the meter to the consumer unit(s) would assist me.

Do you have an a electric or hybrid car which is charged from the mains? If you do please tell me the details of the charger.

And only 'cos I like to know where OPs I help live what is the first half of your postcode?

(please forgive the terseness of the questions - no discourtesy intended :) )
 
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Marconi

Thank you for your response. As it happens I also spoke to installer of (the single) battery and he called in. He did not find any faults but - isolated the PV panels........... imbalance/reverse current still there. Then isolated the inverter and that stopped the reverse current (cannot recall situation re imbalance). Battery was then rebooted for good measure.

Have been outside twice tonight and ....... brill.........there is no reverse current. Did not check imbalance as weather was terrible - no solar to speak of. Will try again tomorrow and give update in evening.

Yes, 7kW Rotec for the charger, all 3 phases in use. We have a Memshield 3 and it is a jungle in there, will try and locate cables tomorrow. TN21.

Regards
Pete
 
Marconi

Another evening and no reverse current recorded after dark. So, hopefully, that's one problem solved. Still have a differential of 15% - 25% between highest and lowest phases during the day. I am aware that such an imbalance on an electric motor may cause permanent damage but does the same apply to an inverter under these circumstances, is there an acceptable level?

Regards
Pete
Pete
 
Generally, the difference between the highest and the lowest phase voltages should not exceed 4% of the lowest voltage. So, your variation is way out and you should contact your distribution network operator (DNO) for them to investigate and fix. Your inverter 'will not like' this range of voltage differences.
 
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Hi - quoting from the original post -
Electrician has identified an imbalance across the 3 phases, typical figs are - AC Power 1 =130w, 2 = 137w and 3 = 152w this morning

Two questions please - Is the imbalance a problem
From my couch I don’t see this as a big issue. I’m not sure what is the cause, but it could be shading of the array. I note the 2nd set of data points showed that Ph1 had the lowest kW charging rate again, but Ph2 and Ph3 were charging at a similar rate. If I was there I’d probably idle away a few hours to find the cause :).

A difference in the charging rate shown on your generation meters does not immediately translate to a difference in Line voltages, that would need to be separately monitored. The supply V does vary throughout the day but hopefully the phases move together if your DNO has the local loads balanced.
 
Marconi and Wilko

Thanks for info. Have been waiting for a drop of sun so as to give varying readings from inverter. No joy, overcast for 2 days, minimal readings (Wilko - no shading on panels, due south with just a field beyond).

Useful to know max. variation on voltage of 4%. Hopefully have interpreted that correctly - Multimeter across the 3 phases in distro board from Neutral to L1,L2 and L3 = typical 245, 241 and 249V. An 8V difference I presume is therefore acceptable (4% of 241 = 9.64V). From that perhaps I can assume that the inverter is giving imbalance.

Will try same exercise with various inverter outputs when we get a bit of sun.

Regards
Pete
 
DIYPete: Wilko and I were discussing your opening post yesterday. Could you expand on what you think is the problem or anomaly please? eg: Is it the voltage or the power imbalance between phases? Is it an imbalance in the power meter readings between phases? Or something else?
 
This started with an attempt to identify the reason for the short power cuts. That is down to the fluctuating voltage which, hopefully, UKPN are now investigating with our sub-station or beyond.

That highlighted the reverse current which has been resolved, presumably, by rebooting the inverter and battery. Again, investigating one problem raised another issue, namely the imbalance across the phases.

The inverter web portal gives the output in volts and watts. In earlier discussions it was suggested that these should balance across the phases, my query therefore relates to this aspect.

Wilko says it is not a problem but worth investigating. This I would like to do but do not have the knowledge with 3 phase systems (have renovated and extended 4 times now involving complete rewiring but never 3 phase).

If you say all is well then I would be happy to accept that but if we can improve our system then I am all for that. Hope that helps.

Regards
Pete
 
I'll read up on the Solax X3 inverter first.

Apart from your EV charger everything else is single phase and fed by only one phase?

The PowerWall is single phase: is it on the same phase as your home's circuits?

Phases are identified as red, yellow and blue in old colours and brown, black and grey in today's. Sometimes they are all the same colour but marked as L1, L2 and L3

We love pictures to study........

:)
 
EV Charger is on an NCN132 C32 MCB.

The Powerwall does not have its own trip on the board, the incoming tails are inturrupted on L1, I understand and go to the 'Gateway Control'. Hefty cable from there to battery.

Photos attached as requested - the board is as left by the installing sparks other than 2 changes:-

1) 10mm cable running to garage and W/S where I put in a sub-board with RCD. I was getting nuisance tripping on my lathe and found by changing the 'W/S' RCBO on the main board for an MCB it solved the problem.

2) 3 x sensors added for battery.

Thanks for your persistance
Pete
 

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I’m thinking it’s Fire T(something) Control - maybe Threat, as the MVHR system may be equipped with fire activated dampers or some such.

But what first came to mind was Felix the Cat :)
 
DIYPete (and Wilko fi):

I have read the manual for the Solax X3 3 phase inverter - pretty standard stuff:

https://www.solaxpower.com/wp-content/uploads/2020/06/X3-MIC-User-Manual.pdf

It behoves me to remind you that on the PV side there are dc voltages up to 1000V and on the ac side voltages of 400V phase to phase. Even when shut down it takes the Solax a while to discharge all the electrical energy it stores inside it and no connections should be touched without first confirming they are dead. ELECTRICITY CAN DO HARM FROM SHOCKS AND BURNS AND OFTEN KILLS. So I help on the understanding that you employ a professional electrician to attend to any wiring. Taking the lid of the MEMSHIELD is as far as we will go. Agreed?

I have also read some material on the Tesla Powerwall 2. So that you and I can share a common understanding would you read this reference please on the TPW2.

https://www.spiritenergy.co.uk/tesla-battery-solar

And to end for today all your loads are single phase even the electric vehicle charger and spread over the 3 phases L1, L2 and L3. Only L1 is backed up (ie: maintained in the event of a power cut) by the Power Wall - but I need to confirm this is actually the case so don't treat that as gospel right now. What I need to establish is whether your 3 phase PV/Inverter will continue to generate - when it is sunny enough- in the event you have a power cut over one, or two or three phases. For a single phase supply and single phase inverter and PW2 on that phase it would but I suspect if L2 or L3 or both are de-energised the Solax X3 will shut down to prevent 'islanding' that is electricity being fed back into the mains which could shock or electrocute DNO workers.
 
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DIYPete: I forgot to ask you in my earlier post which PW2 mode of operation is selected -
  • Self-powered. This mode is purely for solar self-consumption, with no charging from the grid. It will prioritise charging from the solar at all times and discharge whenever it can to maximise self-usage.
  • Advanced - Time-based control (Balanced). Balanced mode is the same as self-powered, except you can tell Powerwall the peak and off-peak times for your tariff and the battery will discharge at peak times in preference to off-peak times to maximise savings. There is still no charging from the grid in this mode.
  • Advanced - Time-based control (Cost-saving).

I have sketched out what I think is your installation. I'll draw it up on 3D Paint for your to confirm.
 
Whoops, sorry did not notice earlier posts. Responses:

Yes, well aware of need for caution (in a previous life attended related fatalities). Aware inverter will hold charge (capacitors?).
Investigation only by me, as per previous posting I have no practical knowledge of 3 phase systems. Previous amendment (RCBO to MCB) was following discussion with qualified friend.Hoping to glean sufficient inf. to recall sparks if indeed we have a problem (yes?).
Tesla - Yes we are using the Self-powered mode with a 10% reserve on L1. Works fine (we do get a number of cuts in this area). Was not aware that it is simply a single phase unit though.
Re check on phases in use following power cut - Presumably I can cut all power on a sunny day and put multimeter across L1,2 and 3 plus common neutral to check incoming from the inverter?
Think that covers quereies raised.

Much appreciated
Pete
 
My 'starter for ten' drawing of your installation. Only L1 is using self-powered mode of PW2 and backed-up as you only have one PW2 and it is connected to L1. Solax is actually three inverters (I1, I2 and I3) synchronised and timed to produce a three phase output. If Solax has a maximum power output of say 9kW then each inverter is 3kW. Also, only Inverter 1 can charge the PW2. So excess power(ie inverter generation - load for that phase) generated by Inverter 2 or Inverter 3 will be exported - not stored in PW2. You would need a second and third PW2 to store excess power from I2 and I3.

Happy to discuss further later. A bit rushed right now.
 

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Re #17: Re check on phases in use following power cut - Presumably I can cut all power on a sunny day and put multimeter across L1,2 and 3 plus common neutral to check incoming from the inverter?

Yes. I expect you will only have L1-N energised or none of the phase-N pairs energised. It depends on how the inverter's anti-islanding works.

If I had designed the '3 phases + N from one box' Solax then the loss of only one grid/supply phase would disconnect the Solax (ie all three inverters) from the grid. I will ask the inverter supplier I use for some advice on what happens.

One grid-tied inverter anti-islanding technique is to set up the frequency of the inverter to drift away from 50 (or 60Hz) or undulate around it . However, when the grid/supply is present the inverter frequency generator can detect and lock itself to the grid/supply rock -steady 50/60Hz waveform. While lock is maintained the grid supply is present; when the supply suffers an outage lock is lost, the frequency drifts and once it crosses a threshold (say 50 +/- 3 Hz) the inverter is shut down. Voltage is not a reliable indicator of loss of supply since the grid-tied inverter itself produces an emf and is connected to the supply. The Solax X3 uses the frequency drift scheme.
 
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Interesting - it had not occurred to me that generated power from 2 phases are grid-bound when usage is minimal. Would not justify 2nd battery though - average drawn from grid in last 8 weeks is 190kW per week with around 25kW 'returned' to grid. Awaiting Green Grant Voucher, will ensure proposed solar thermal and emersion diverter switch on L2 and L3.

Will turn off inverter tomorrow, sun expected.

Pete
 

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