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Domestic EESS, island mode and island mode isolator

Downdraft

Hello,
I need some help please Slight smile

I am trying to understand if an 'Island mode' isolator is required for this particular inverter design.

The Solar PV Hybrid inverter has an 'EPS' (emergency power supply) output that we would like to use.
The inverter has an internal N-PE Bond relay.
In connected mode this takes its power direct from the grid.
In island mode the Hybrid inverter will have disconnected from the grid as per G98/99, and then the EPS is supplied from PV and/or battery.

So if the inverter is designed to disconnect from the grid during grid loss/outside protection limits is either an Automatic or manual changeover switch required?

  • 0 in reply to gkenyon

    I agree that it is very likely that relays are being used inside of the hybrid inverters that do not comply with chapter 53. I will ask the manufacturer and I will share the information.

    What may be tripping me up is that without battery storage my understanding is that these internal relays meet the requirements of G98/99 for anti islanding. So if we are using the EPS for dedicated circuits only why can we not rely on this relay?


  • 0 in reply to AMK
    AMK said:
     Is this the best way to ensure compliance to check the inverter model on the ENA Type Test Register (via the Energy Networks Association website) for G98/G99 certification.

    G98 certification doesn't cover island mode operation.

    G99 might have been gained on "connected mode" operation only? Even if it does cover both, it might not necessarily cover the requirements of BS 7671 in this regard.

    AMK said:
    perhaps, contact the manufacturer, ask Does their  inverter provide Chapter 53-compliant isolation per 7671 Reg 826.1.1.1 & ESQCR Regulation 21.  

    That might be the way to go. But ... I would add that there are ways you can, for example, build Product A into Product B, and "defeat" some of the provisions of the safety standard for Product A. If the safety standard for Product B doesn't have a way of verifying the provisions of Product A have not been defeated, that could be an issue.

    Downdraft said:
    What may be tripping me up is that without battery storage my understanding is that these internal relays meet the requirements of G98/99 for anti islanding. So if we are using the EPS for dedicated circuits only why can we not rely on this relay?

    Anti-islanding is the ability of the inverter to stop squirting power into the grid, when it stops converting.

    If it starts converting again, for island mode, is there any way power can "leak" (AC or DC) from one side of the converter to the other when you re-earth the "IPS" side ? This depends on a number of factors, and the particular topology ... but in some cases, there may well be a problem.

    There are also some considerations for multipole vs single-pole switching devices that might need to be considered.

  • 0 in reply to gkenyon

    Presumably all these (potential) issues are common with a typical UPS setup...? (which is what the inverter is behaving as in EPS mode)

       - Andy.

  • 0 in reply to AJJewsbury
    AJJewsbury said:
    Presumably all these (potential) issues are common with a typical UPS setup...? (which is what the inverter is behaving as in EPS mode)

    Not at all. In a UPS, the arrangement is selected, and the product fully conforms to, relevant parts of BS EN [IEC] 62040 series.

    A UPS never exports to the grid, and there is no possibility of "back-feed" to the grid. Bypass switching may be provided for faults downstream of the UPS, or to take it (or part of it) off line for maintenance.

    In this case, the inverter (often completely transformerless) operates in parallel with the grid, and when grid power fails, can provide a backup supply for use in island mode ... this is a Prosumer's Installation arrangement according to Chapter 82 of BS 7671 and Regulations 21 and 22 of ESQCR [Regulations 22 and 23 of ESQCR(NI)]

  • 0 in reply to gkenyon

    Is it a case of confirming the inverters relays are multipole (switching both phase and neutral), tested for low leakage currents (<5mA)  

    External to the inverter, lockable isolator installed on the EPS output side before the dedicated consumer unit.

  • 0

    Hello,
    The manufacturer has confirmed that they use relays and they shared this schematic:

  • 0 in reply to Downdraft
    AMK said:
    Is it a case of confirming the inverters relays are multipole (switching both phase and neutral), tested for low leakage currents (<5mA)  

    Contact gap also is important ... we are reliant on product standards for this ... relays don't appear in Table 537.4, and certainly in the past relay standards don't cover 'isolation' requirements. I'm not sure whether any relay standards have been, or are being, developed to address this.

  • 0 in reply to gkenyon

    So for a configured system where the inverter’s EPS setup powering a dedicated consumer unit, are we also required to install an external to the inverter, automatic, Line & N  island mode isolator on the inverter’s incoming side to ensure, auto disconnection of all live conductors during island mode, to comply with 826.1.1.1  and ESQCR Regulation 21? I can’t quite make out the image above, are both relays part on the inverter?

  • 0 in reply to AMK
    AMK said:
    So for a configured system where the inverter’s EPS setup powering a dedicated consumer unit, are we also required to install an external to the inverter, automatic, Line & N  island mode isolator on the inverter’s incoming side to ensure, auto disconnection of all live conductors during island mode, to comply with 826.1.1.1

    Only where the inverter, or kit of parts provided, doesn't include such a device. It's up to the manufacturer how they approach the issue.

    Other countries don't have ESQCR, and systems and legislation varies around the world ... even in Europe.

    In a global market, manufacturers may not be aware of UK legislation, although I agree they should investigate fully prior to coming to market (or, for importers, before importing to the UK ... or any other country for that matter).

    "Buyer beware".

  • 0 in reply to gkenyon

    So, purchasing a MCS registered inverter would likely meet UK-standards - 7671 & ESQCR for safe disconnection of live conductors (including neutral) no external device required for EPS mode

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