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Neutral and Earth voltage with battery storage

vantech

Hi,

I have a battery storage system which is grid tied. This has been G98 registered. The battery has a grid tie and a UPS backup circuit.

The system works as expected, however when in UPS backup mode, I have noticed something that I need to clarify.

When in normal grid tied mode, the following voltages are recorded on the UPS output: 

L-N = 230V 

L-E = 230V 

N-E = 0V 

When in UPS mode, the following: 

L-N = 230V

L-E = 130V

N-E = 130V 

The manufacturer confirmed that when in UPS mode, a N-E link is made automatically and disconnected automatically. I have contacted them but being in China, they are slow to respond.

What I noticed, is that if you switch off loads on the UPS output, the voltage between L&E slowly increases to around 200V. I haven’t as yet tested to see if the same is apparent with N&E. 

Any ideas? This is an inverter so I am unsure if this sort of reading/phenomenon is normal? 

Thanks. 

Parents
  • 0

    "Backup" mode (term used in BS HD 60364-8-2 is "island mode") is not "UPS" unless the product is certified to BS EN 62040 series.

    A comprehensive switching arrangement is required for the system to operate in island mode. BS 7671 Regulation 551.4.3.2.1 states that in this mode, the distributor's means of earthing cannot be used, so all lines and neutral of the supply must be physically isolated, and a new neutral to earth connection switched in.

    It sounds to me, that the island mode power arrangement may not have the required switching, and simply to add a neutral to earth reference may contravene the ESQCR as well as BS 7671.

    The IET Code of Practice for Electrical Energy Storage Systems covers the topic of "floating" (unearthed) backup power outlets in Appendix F (page 157 in the 2nd Edition), and states:


    It is not recommended that such a socket-outlet is provided with a means of connection to an electrical
    installation or a permanently installed item of equipment.

    The Code of Practice then goes on to provide reasons for this.

  • 0 in reply to gkenyon

    Hi, 

    Here is a data sheet for the inverter/battery which is certified to IEC 62040-1 and IEC 62477-1 (and the relevant G98 certification).

    zerohomebills.com/.../Data-Sheet-Alpha-SMILE-B3-EN-Solar-Battery.pdf

    It appears the output is a true UPS. 

    A customer owned earth rod has been attached to the MET, to remove the reliance on the DNO supplied earth.

    The manufacturer today confirmed the following: 

    A “N-E” bond is created on the UPS backup output when in backup mode. 

    Voltages of 130V between N-E and L-E are normal, due to capacitances in the UPS output.

    So they have clarified the findings are normal? It sort of makes sense, as this L-E voltage increases as loads are switched off. I am yet to test to see if the N-E voltages decrease when loads are removed. 

    Thanks. 

Reply
  • 0 in reply to gkenyon

    Hi, 

    Here is a data sheet for the inverter/battery which is certified to IEC 62040-1 and IEC 62477-1 (and the relevant G98 certification).

    zerohomebills.com/.../Data-Sheet-Alpha-SMILE-B3-EN-Solar-Battery.pdf

    It appears the output is a true UPS. 

    A customer owned earth rod has been attached to the MET, to remove the reliance on the DNO supplied earth.

    The manufacturer today confirmed the following: 

    A “N-E” bond is created on the UPS backup output when in backup mode. 

    Voltages of 130V between N-E and L-E are normal, due to capacitances in the UPS output.

    So they have clarified the findings are normal? It sort of makes sense, as this L-E voltage increases as loads are switched off. I am yet to test to see if the N-E voltages decrease when loads are removed. 

    Thanks. 

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