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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
    Hi all, just an update FYI. The main consultant came back after speaking himself with the manufacturer and said:

    "Yes I spoke to them and they confirmed that they require 0.06 of a ohm on each conductor. i.e no one conductor can have an impedance of greater than 0.06 of an ohm, from transformer to there unit.

    In relation to the generator they are more concerned about how quick it turns on as the capacitors have to discharge and re energise, I would ask XXX to formally advise you on what the time is from mains failure to generator taking up load and of course is the existing CT on the generator."


    From that I can work out line impedance for a conductor at the source by dividing L-N voltage by L-N fault current and then add on the submain conductor impedance.


    On Genny, a bit more digging required.
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  • 0
    Hi all, just an update FYI. The main consultant came back after speaking himself with the manufacturer and said:

    "Yes I spoke to them and they confirmed that they require 0.06 of a ohm on each conductor. i.e no one conductor can have an impedance of greater than 0.06 of an ohm, from transformer to there unit.

    In relation to the generator they are more concerned about how quick it turns on as the capacitors have to discharge and re energise, I would ask XXX to formally advise you on what the time is from mains failure to generator taking up load and of course is the existing CT on the generator."


    From that I can work out line impedance for a conductor at the source by dividing L-N voltage by L-N fault current and then add on the submain conductor impedance.


    On Genny, a bit more digging required.
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