Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Suggested Answer
  • Replies 36 replies
  • Helpful Answers 2 Helpful answers
  • Subscribers 39 subscribers
  • Views 1820 views
  • Users 0 members are here
Options
You may also be interested in

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 AJJewsbury

    Hi Andy. Was thinking along the lines of a combination of both a inverter’s safety features, its G99-certified anti-islanding protection (disconnection <0.5s via relay and active/passive methods) and an external contactor that together to try and meet the isolation requirements. While the inverter ensures rapid disconnection to prevent back-feeding, an external contactor compliant with BS 7671 Table 537.4 (per Regulation 537.2.2.1, referenced by 826.1.1.1) provides the necessary mechanical isolation for maintenance and grid worker safety under ESQCR Regulation 21. Do most inverters now comply with isolation requirements of 7671 when transferring to EPS ? Then no additional devices are required. 

  • 0 in reply to AJJewsbury
    AJJewsbury said:
    As I understand it, EPS mode is normally "automatic" - i.e. keeps the power on continuously to the critical loads

    That is UPS or CPS, not 'EPS'. If the loads are "critical" enough to be safety services, BS 7671 does state the standards to which the source for safety services should conform (BS EN 62040 series, or BS EN 50171 if it's a CPS).

    I'm sure that most solar/battery inverters are not to those standards ...

    'EPS' appears to be a marketing designation for an attempt at what should be called 'island mode' operation. Importantly, 'continuity' of power ("no break") is not guaranteed with island mode.

    AMK said:
    Do most inverters now comply with isolation requirements of 7671 when transferring to EPS ? Then no additional devices are required. 

    They should but I think 'buyer beware' is the current advice.

  • 0 in reply to gkenyon

    Maybe BS EN 62040 series, or BS EN 50171 need to be updated to specifically include or exclude

    UPS

    CPS

    EPS

    gkenyon said:
    solar/battery inverters are not to those standards

    Maybe those standard also need to be updated?

  • 0 in reply to AMK
    AMK said:
    isolating the inverter’s line and neutral in,  to prevent backfeed during EPS mode. 

    Designers will need to factor this into the the CU design as the isolation may affect the characteristics of trip times/ADS/PFC thus would the humble 30mA RCBO/MCB/AFDD perform the same under normal operating conditions as it would under Island mode?

  • 0 in reply to Sergio Fernandez
    Sergio Fernandez said:
    Maybe BS EN 62040 series, or BS EN 50171 need to be updated to specifically include or exclude

    I'm not so sure.

    The product standards have a defined scope.

    BS EN 62040 series is for UPS - Uninterruptible power systems.

    BS EN 50171 is for CPS - Central power systems for systems like emergency lighting

    EPS - new term coined for the purposes of what, and defined where?

    The term in IEC 60364 series is 'island mode', so 'island mode power' might be better than 'EPS'.

    Sergio Fernandez said:
    gkenyon said:
    solar/battery inverters are not to those standards

    Maybe those standard also need to be updated?

    Why ? The standard covers inverters ... it's rather specific.

    If we are talking about 'system' standards, this is perhaps supposed to be covered in IEC 62933 series, which covers electrical energy storage systems [of the kind we are looking at] but this set of standards is way behind schedule, and it's not being developed quickly enough.

    Hence, manufacturers have nowhere to go, other than IEC 60364-8-82, to pin functional and related safety requirements on.

    Given that, manufacturers would be perhaps advised to take care they are addressing all of the essential requirements of the relevant legislation, in addition to what standards are published.

  • 0 in reply to Sergio Fernandez
    Sergio Fernandez said:
    thus would the humble 30mA RCBO/MCB/AFDD perform the same under normal operating conditions as it would under Island mode?

    mcb ... yes.

    AFDD ... you'd have to check with the manufacturer

    RCD/RCBO ... might depend on the type.

Community Rules & Guidelines