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Diesel Generator Fault Levels

MG
Hello all,


I am looking to specify a temporary mobile diesel generator and as such looking into the disconnection times and the maximum fault current provided by the genset.

I have contacted a provider and got the specification of the alternator in their genset, images below of the fault current graph and the alternator per unit values.


I am looking into understanding what values to use. Am I correct in getting the sustained fault level and for an earth fault to apply the multiplication factor of 2.5 for sustained? I will make sure my disconnection times are less than the sustained maximum duration in order to not trip the generator breaker and loose all of the supply.


Alternator is 50Hz 415V

fc5681c638e7bada3947e466b96400fd-huge-newage-hci534e_1.jpg

3106a5e7994134e881a5487cbbe73194-huge-newage-hci534e.jpg


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  • Former Community Member
    0 Former Community Member
    On a 600kVA set, isn't your steady state around 800A - and as a first approximation of dividing by X"d of 0.09, would give you a fault current of around 8.8kA for a short duration (ie within the clearance time of the CPD)


    Which isn't that far away from Mike "multiply by 10" values (as you'd imagine) - for earth fault you really need to consider the use of symmetrical components and you'll require the zero sequence reactance of the machine.

    https://www.fecime.org/referencias/npag/ - try chapters 3, 4 and 5


    Regards


    OMS


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  • Former Community Member
    0 Former Community Member
    On a 600kVA set, isn't your steady state around 800A - and as a first approximation of dividing by X"d of 0.09, would give you a fault current of around 8.8kA for a short duration (ie within the clearance time of the CPD)


    Which isn't that far away from Mike "multiply by 10" values (as you'd imagine) - for earth fault you really need to consider the use of symmetrical components and you'll require the zero sequence reactance of the machine.

    https://www.fecime.org/referencias/npag/ - try chapters 3, 4 and 5


    Regards


    OMS


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