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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 

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    Earth loop impedances and consequently fuse disconnection times would change because of the Generator parameters.

    Correct. So your design needs to cope with the characteristics of the supply when the supply is the generator alone (where that's one permitted combination). The requirements for disconnection times for ADS are the same regardless of the kind of supply. In some cases that'll mean you can't rely totally on overcurrent protective devices to provide ADS - so some kind of residual current operated devices may be necessary - RCCBs, RCBOs or earth trips on larger devices.

    With very small generators it may be permissible to adopt some other measure than ADS to provide shock protection - e.g. a separated system - but often that's only practical for very small systems - e.g. a portable generator feeding a single Class I tool.

          - Andy.

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  • 0

    Earth loop impedances and consequently fuse disconnection times would change because of the Generator parameters.

    Correct. So your design needs to cope with the characteristics of the supply when the supply is the generator alone (where that's one permitted combination). The requirements for disconnection times for ADS are the same regardless of the kind of supply. In some cases that'll mean you can't rely totally on overcurrent protective devices to provide ADS - so some kind of residual current operated devices may be necessary - RCCBs, RCBOs or earth trips on larger devices.

    With very small generators it may be permissible to adopt some other measure than ADS to provide shock protection - e.g. a separated system - but often that's only practical for very small systems - e.g. a portable generator feeding a single Class I tool.

          - Andy.

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