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Line impedance query

me1899
Hi 


I am looking at a job where a supply to a replacement CT scanner has to be calculated.


The current scanner is fed by a cable with line impedance 0.06 at source end of the sub panel that feeds it.


The new scanner must have a line impedance no more than 0.06 so basically I can't use the way on the current panel.


The client engineer has said to run from the intake and provide a cable calc to prove the line impedance is OK for the new scanner feed (this is D and B).


I am using AMTECH and was wondering if there was a way to output line impedance or if I need to show a calculation another way?


The client engaged a firm to do line impedance tests, and their report shows values measured between L1-L2, L2-L3 and L1-L3, but looks like they did testing at the sub panel and not at the intake.


This is basically like PSCC right? So I can get PSCC from AMTECH, divide by root 3 and work out impedance from there?


Am I on the right track? Assistance would be much appreciated.


Regards


Anisur
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  • 0
    Somewhere around the few hundreds of metres it would become  cost-effective to move the HV and transformers nearer for any load that is that hostile - as an aside I have just calculated the following -

    You are asking for 150A per phase , and a droop of 9V at full load (150A* 0.06 ohms) - i.e. 3.8% voltage drop  (9/230 )

    A typical substation transformer droops 5% on full load, so you need a transformer rated for at least twice the load you are proposing to connect, to leave some voltage drop allowance for the cables.

    I am not familiar with modern designs, so there may well be subtelties I am not aware of, the last large X-ray rig I saw in pieces a good few years ago (15-20 years at least) used a klystron about the size and weight of my wife (but not the same form factor you will be pleased to realise) to switch the primary current into a pulse transformer that fired the actual Xray generator, and had more in common with a RADAR driver than any of the guys building it realised.

    I think as others said, you need the designers on-side.
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  • 0
    Somewhere around the few hundreds of metres it would become  cost-effective to move the HV and transformers nearer for any load that is that hostile - as an aside I have just calculated the following -

    You are asking for 150A per phase , and a droop of 9V at full load (150A* 0.06 ohms) - i.e. 3.8% voltage drop  (9/230 )

    A typical substation transformer droops 5% on full load, so you need a transformer rated for at least twice the load you are proposing to connect, to leave some voltage drop allowance for the cables.

    I am not familiar with modern designs, so there may well be subtelties I am not aware of, the last large X-ray rig I saw in pieces a good few years ago (15-20 years at least) used a klystron about the size and weight of my wife (but not the same form factor you will be pleased to realise) to switch the primary current into a pulse transformer that fired the actual Xray generator, and had more in common with a RADAR driver than any of the guys building it realised.

    I think as others said, you need the designers on-side.
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