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Zs measurement on IT Systems

Geof I.

I have a project where the customer has IT power distribution system (AC) - Normally in the pre-commissioning procedure I would add a requirement to check the Zs for each piece of equipment based on the trip curve and type of MCB on the incomer to the equipment (TN-x systems) ; However when I was thinking about this ....

Is there any benefit / is it possible to perform Zs measurement on IT distribution? My gut says there is no requirement / benefit, but my brain is nagging I'm missing something.

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    how are you verifying the continuity from chassis of the system back to the origin - how is insulation monitoring for ADS performed?

    I'd expect  something akin to an R2 test at least.

    Mike

  • 0 in reply to mapj1

    The problem overall is we are supplying equipment to be ship mounted. The ship supply is IT based and we will verify chassis to 'Earth' (Hull/Sea) via milliohmmmeter. 

    The ADS is not our supply and part of the vessel hull supplier and we have no knowledge of this system. My package designers have placed Type B and C circuit breakers in our equipment cabinets, which in pre-commissioning i would normally request Zs calc / measurement  to ensure trip time is maintained. 

    Obviously? Zs for an IT based system is probably not relevant as the fault path is pretty much restricted to L-L faults (shorts) within the end equipment cabinet. 

    I'm thinking  line- Line (or 2xR1 assuming equal lines) calc/measurement should probably be used in place of Zs for this type of system to ensure trip timing. 

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  • 0 in reply to mapj1

    The problem overall is we are supplying equipment to be ship mounted. The ship supply is IT based and we will verify chassis to 'Earth' (Hull/Sea) via milliohmmmeter. 

    The ADS is not our supply and part of the vessel hull supplier and we have no knowledge of this system. My package designers have placed Type B and C circuit breakers in our equipment cabinets, which in pre-commissioning i would normally request Zs calc / measurement  to ensure trip time is maintained. 

    Obviously? Zs for an IT based system is probably not relevant as the fault path is pretty much restricted to L-L faults (shorts) within the end equipment cabinet. 

    I'm thinking  line- Line (or 2xR1 assuming equal lines) calc/measurement should probably be used in place of Zs for this type of system to ensure trip timing. 

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