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Ze & Ipscc

Frankie 223
I am preparing an electrical model for a project and have asked ukpn to confirm the Ze, Ipscc and Z% of the transformer so I can input the data in the software.


I got the following figures back which I am not sure I understand:

Ze=0.15

Ipscc=32kA

Z for the 11kV/400V 1.5MVA Tx 5.5%


Based on the Tx Z and Ipscc I would expect a much lower Ze. Am I missing something or do you think that the above figures make sense?
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    Yes - for a TNC-s connection, the Zs will be more like Vo/PSSC and  with a 5% transformer the PSSC  for a single phase fault could be 20 times the FLC (maybe twice that for a phase-phase fault of the worst kind.

    (So in big hand fulls of no great precision

    FLC = load current per phase of 2 to  2.5kA,

    single phase PSSC of maybe 40kA  (20 times 2kA )

    and a  Zs of half a dozen milli-ohms  (240V / that 40kA )

    at the transformer, and resistance rising, current falling as you move away down the cable.)


    I suggest you do check the  design for your own figures as well as theirs ?, yours are more credible. If Ze is TNS  and the earth so thin, that resistance is that high you may need an earth fault relay or similar as part of the design.
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  • 0
    Yes - for a TNC-s connection, the Zs will be more like Vo/PSSC and  with a 5% transformer the PSSC  for a single phase fault could be 20 times the FLC (maybe twice that for a phase-phase fault of the worst kind.

    (So in big hand fulls of no great precision

    FLC = load current per phase of 2 to  2.5kA,

    single phase PSSC of maybe 40kA  (20 times 2kA )

    and a  Zs of half a dozen milli-ohms  (240V / that 40kA )

    at the transformer, and resistance rising, current falling as you move away down the cable.)


    I suggest you do check the  design for your own figures as well as theirs ?, yours are more credible. If Ze is TNS  and the earth so thin, that resistance is that high you may need an earth fault relay or similar as part of the design.
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