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

  • State Not Answered
  • Replies 21 replies
  • Subscribers 31 subscribers
  • Views 2017 views
  • Users 0 members are here
Options
You may also be interested in

Disconnection times on a system if a stand by generator is used

Anthony Smith

On a fully designed power distribution system, clearly the fault levels, earth loop impedances and ultimately fuse disconnection times are determined by the system parameters Transformer %Z etc one or two in parallel for min and max fault levels levels. What needs to be considered when bringing on a stand-by generator, clearly all Fault levels, Earth loop impedances and consequently fuse disconnection times would change because of the Generator parameters. How would you design in these new parameters, bearing in mind that disconnection times on a large system may no longer be achievable 

Parents
  • 0

    I would agree totally, but on a large distribution system, with a stand-by generator used at source, this would be impossible and I believe you are right, but I have never seen this in practice, to maintain disconnection times for stand by, cables sizes would be so large as to make this impractical

Reply
  • 0

    I would agree totally, but on a large distribution system, with a stand-by generator used at source, this would be impossible and I believe you are right, but I have never seen this in practice, to maintain disconnection times for stand by, cables sizes would be so large as to make this impractical

Children
  • 0 in reply to Anthony Smith
    Anthony Smith said:
    on a large distribution system, with a stand-by generator used at source, this would be impossible

    RCDs may be used for ADS. .

    Anthony Smith said:
    but I have never seen this in practice, to maintain disconnection times for stand by,

    The design may require more RCDs, but ultimately, Andy is correct

    Further ...


    Regulation 551.4.3.1 requires ADS according to Chapter 41 to be provided for circuits supplied by the generating sets, and Regulation 551.4.1 requires fault protection to be provided for each source, or combinations of sources.

    So, if disconnection times not met (one way or another), then BS 7671 is not complied with.

    Therefore, if disconnection times are not met and the installation is supplied by a public supply network, this is potentially a breach of Regulation 21 of the ESQCR, which requires the installation to comply with BS 7671 where a switched alternative to the public supply is provided.

    Some people at this point may at this point discuss the operation of UPS (and application of BS 7671, in particular the two Regulations quoted above, and Regulation 551.4.3.2.1.

    However, I think it's very tenuous to determine that a UPS is not a "switched alternative" to the public supply, because, in bypass mode, the grid supplies the UPS loads, whereas in "inline" and "mains fail", the generator (UPS inverter) supplies the loads, powered by the DC 'charger' in 'inline' mode, or the battery in 'mains fail' mode. So, I think Regulation 21 of ESQCR ought to be applied to UPS (as well as relevant parts of Section 551 of BS 7671, including Regulation 551.4.3.2.1).

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines