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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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  • 0

    A similar problem arises with small generators -there is not enough 'oomph' to operate over-current ADS at anything more than a small fraction of the full load output.

    As already noted, the trick is to use RCD or RCBO to do the safety of life type ADS with LE amd NE faults, and accept that dead short LN fault is not really going to be detected and  may not trip anything except the inverter internals may collapse after some un-specfied time.

    Mike

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  • 0

    A similar problem arises with small generators -there is not enough 'oomph' to operate over-current ADS at anything more than a small fraction of the full load output.

    As already noted, the trick is to use RCD or RCBO to do the safety of life type ADS with LE amd NE faults, and accept that dead short LN fault is not really going to be detected and  may not trip anything except the inverter internals may collapse after some un-specfied time.

    Mike

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  • 0 in reply to mapj1

    Thank you mapj1, that was really my point.. I have always wondered this for small generators generally, something till now I have not needed to dirty my hands with. "The inverter internals may collapse after some unspecified time" .. Yes it must do at some point.   

    "In all cases, compliance with Chapter 43 SHALL be fulfilled.." so we're good to go, shame there's no data. - Sign it off!

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