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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
    What CPDs are there in the scanner power supply? This number probably comes from these and a disconnection time in case of a fault, and this may not be the same as the GB numbers in BS7671, particularly if this is a US scanner. I suggest you contact the manufacturer and find out why this number is specified, as doing anything about it would be difficult and very expensive if you need a new cable from the supply TX just to meet the exact specification. You need to be aware that measured numbers which you have may not be very accurate, they could well be +- 20% with the average meter or even worse, at low values like this. How different are the measured values, one would expect very little difference between them, and again this measurement can be difficult depending on other loads connected to the supply? Refer to manufacturer (not a dealer or other intermediate as they will probably tell you anything) and get a written signed reply with a name in case of future problems with service contracts.
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  • 0
    What CPDs are there in the scanner power supply? This number probably comes from these and a disconnection time in case of a fault, and this may not be the same as the GB numbers in BS7671, particularly if this is a US scanner. I suggest you contact the manufacturer and find out why this number is specified, as doing anything about it would be difficult and very expensive if you need a new cable from the supply TX just to meet the exact specification. You need to be aware that measured numbers which you have may not be very accurate, they could well be +- 20% with the average meter or even worse, at low values like this. How different are the measured values, one would expect very little difference between them, and again this measurement can be difficult depending on other loads connected to the supply? Refer to manufacturer (not a dealer or other intermediate as they will probably tell you anything) and get a written signed reply with a name in case of future problems with service contracts.
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