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Hybrid inverters with emergency back up circuits island mode. Inverter backup PFC

justinneedham

Domestic PEI and islanding mode PFC

Hybrid inverters having DC PV inputs, DC battery inputs, and a limited output to feed "emergency" loads in islanding mode appear to be getting very commonly available. I am receiving enquiries from my domestic customers, but am struggling with a seeming lack of significant info. 

Pulling up data sheets for numerous hybrid inverter models, I can't find any data for any of them relating to inverter PFC during "islanding mode" when the emergency loads are supplied directly, during network power failures, or presumably during planned periods. 

Reference 826.1.2.1. "Overload and short circuit currents shall be determined at every point..." And  I am getting no response from manufacturers I have emailed in this regard. 

I appreciate the PEFC might well be related to the local earth rod (assuming a situation of an otherwise connected external TN earth failure), and the short circuit PFC might be related to the chosen battery internal impedance characteristic in some way..

The inverter data sheets typically state only the power output capability/current (steady and peak values) for the emergency/backup load supply. How is one supposed to take these to and plan appropriate protection? The lack of info seems to be quiet universal with these devices. 

 

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    Let's suggest we aim to run a lighting system on it using B6 breaker. At 40A this would break in ~ 20 seconds, and by Adiabatic, require in excess of 1.5mm conductors. - Fair enough.

    The adiabatic starts to get silly much beyond 5s (as the heat loss from the cable starts to become significant) - a simpler approach is just to select a device that provides overload protection (e.g. In ≤ Iz) and has sufficient breaking capacity for it's position in the installation (hardly a challenge for small generators) - that's then deemed to provide fault protection in most circumstances (435.1). For MCBs fault protection (between live conductors) is provided by the thermal rather than magnetic element, and the time to disconnect isn't particularly well defined (and doesn't have to be). For L-PE faults (for ADS), RCDs disconnects plenty quick enough to protect the conductors, given the low fault currents.

       - Andy.

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  • 0

    Let's suggest we aim to run a lighting system on it using B6 breaker. At 40A this would break in ~ 20 seconds, and by Adiabatic, require in excess of 1.5mm conductors. - Fair enough.

    The adiabatic starts to get silly much beyond 5s (as the heat loss from the cable starts to become significant) - a simpler approach is just to select a device that provides overload protection (e.g. In ≤ Iz) and has sufficient breaking capacity for it's position in the installation (hardly a challenge for small generators) - that's then deemed to provide fault protection in most circumstances (435.1). For MCBs fault protection (between live conductors) is provided by the thermal rather than magnetic element, and the time to disconnect isn't particularly well defined (and doesn't have to be). For L-PE faults (for ADS), RCDs disconnects plenty quick enough to protect the conductors, given the low fault currents.

       - Andy.

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