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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
    Ok but I still think you need to speak to the manufacturers. Let us say you can get a supply with a 0.03 Ohm source, then you still need a cable giving let's say 0.02 Ohms for a 130m run corresponding to 0.15mV/A which gives a 300mm 4 core SWA. This is a 4-5x overdesign, of the 150A supply, but the supply may be around 80 kW during a scan, depending on the manufacturer. Where you can get a 0.03 Ohm supply is even more of a question which you need to work out. However this requirement seems very severe for a modern scanner with electronic power supplies, so back to my first point. You also need to check what the supply will be if from emergency generator power (which would be normal) as this is going to have to be a very large generator to get such a good supply. Fitting this cable in a building is a serious challenge due to its stiffness and minimum bend radius. Check my figures with Amtech. Good luck.
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  • 0
    Ok but I still think you need to speak to the manufacturers. Let us say you can get a supply with a 0.03 Ohm source, then you still need a cable giving let's say 0.02 Ohms for a 130m run corresponding to 0.15mV/A which gives a 300mm 4 core SWA. This is a 4-5x overdesign, of the 150A supply, but the supply may be around 80 kW during a scan, depending on the manufacturer. Where you can get a 0.03 Ohm supply is even more of a question which you need to work out. However this requirement seems very severe for a modern scanner with electronic power supplies, so back to my first point. You also need to check what the supply will be if from emergency generator power (which would be normal) as this is going to have to be a very large generator to get such a good supply. Fitting this cable in a building is a serious challenge due to its stiffness and minimum bend radius. Check my figures with Amtech. Good luck.
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