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Bi-directional power supplies

Daniel Strange

There are an increasing number of bi-directional benchtop power supplies commercially available for general applications such as battery testing and energizing magnets etc. All the manufacturers seem vague or do not mention regulations around grid connection. Are there any harmonized standards for these small scale installations where energy recovery is sporadic and not continuous at at fairly low levels eg Typically less that 1.5KW but definitely <10KW. In my application I would like to be able to ship to all the major areas of the world but navigating hundreds of separate regulations could be prohibitive.

  • Yes, there are ... same as solar PV.

    There are legal limitations on connecting parallel generation, see Regulation 22 of ESQCR in Great Britain, Regulation 23 of ESQCR(NI) in Northern Ireland.

    In addition, there are cases where it might damage residual current devices in the installation - see video and details regarding Amendment 3:2024 here: https://electrical.theiet.org/bs-7671/updates-to-18th-edition/

    Finally, it's possible to overload final circuits in to which these devices connect. General socket-outlet final circuits are not suitable. The circuit needs to be specially designed, or you need to use a dedicated circuit (Regulation 551.7.2 of BS 7671), and also check the consumer unit won't be overloaded (same Regulation).

  • in reply to gkenyon

    Thanks, So in theory if the device is type tested to G98 and registered with the ENA then installation would just require registering with the DNO in the UK? But for every European member state there could be different rules and regulations to follow?

  • But for every European member state there could be different rules and regulations to follow?

    Almost certainly - my PV (older G83) inverter has a "country" setting, as the rules for when to disconnect from the grid (variation in voltage, variation in frequency, rate of change of various metrics and so on) all seem to vary by territory (not to mention over time as grid authorities build up their knowledge - such as that incident a a few years back were one power station dropped off the grid, which triggered a wind farm to disconnect, which had a cascading effect that blacked some parts of the country).

    G98 I think restricts you to 16A/phase - so max 3.68kW if it's single phase (you could manage 10kW if 3-phase was available).

    It does beg the question of what you do with all this energy if the grid happens not to be available at the appropriate moment - do you have some other means of dissipating it?

       - Andy.

  • in reply to AJJewsbury

    The energy is only dumped when you want to change the magnetic the stored energy in the inductor, something you wouldnt be able to do if the mains supply failed. If the process has already started, a crowbar short allows the stored energy to decay over a long time constant through the current leads connecting the power supply until power is restored. In most cases it would be single phase and far less than 1Kw

  • in reply to Daniel Strange
    Daniel Strange said:
    would just require registering with the DNO in the UK?

    In theory ... but it can't be simply plugged into a socket-outlet.

    It must be installed in accordance with BS 7671, which will mean a dedicated circuit and a means of connecting other than a plug.

  • All the unit's I've ever encountered have dumped energy to a resistor bank - which has it's own problems if you're doing testing in a badly ventilated test room in the middle of summer.

    If you're telling me someone has a unit that exports then a very hot and sweaty former me is jealous.

  • in reply to gkenyon
    gkenyon said:
    In addition, there are cases where it might damage residual current devices in the installation - see video and details regarding Amendment 3:2024 here: https://electrical.theiet.org/bs-7671/updates-to-18th-edition/

    These kinds of power supplies would almost certainly have large DC potential that don't have simple seperation to the supply side and so any RCD protection would need to be type B.

    In a power electronics lab you ideally want to avoid RCD protection on the EUT and ATE supply. Interlocked guarding, IT supply with earth leakage monitoring, non-conducting location etc are all typically more appropriate methods of protection. You certainly don't want type A's.

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