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Line impedance query

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 Former Community Member over 5 years ago

Computerized Tomography (CT) scans, combine a series of X-ray images taken from different angles around your body and uses computer processing to create cross-sectional images (slices) - so basically it's an x-ray set and line impedance is important.

The scanner is a severely disturbing load when operating and the voltages can end up all over the place based on both voltage depressions and the extent of harmonic distortion caused by the load - the load can also be quite impulsive.

The short order solution mandated by most CT suppliers is to limit load impedance - and to take Mike's comment above "a dedicated short, fat cable route" - if you are a long way from the transformers, then you need some pretty big cabling to limit the voltage bouncing around like tigger on acid

One point about the "life safety" issues - I accept that diagnostics isn't a life safety issue in itself - if you can walk in you can walk out kind of thinking. However, many procedures in CT may well involve catheterization which is conductive - so they should be Medical Location Group 2 and should have medical IPS for shock risk. It is also pretty usual for the main equipment room to have small UPS support to manage shut down. It's entirely possible the designers may not have appreciated that fact

Regards

OMS
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0 Former Community Member over 5 years ago

Computerized Tomography (CT) scans, combine a series of X-ray images taken from different angles around your body and uses computer processing to create cross-sectional images (slices) - so basically it's an x-ray set and line impedance is important.

The scanner is a severely disturbing load when operating and the voltages can end up all over the place based on both voltage depressions and the extent of harmonic distortion caused by the load - the load can also be quite impulsive.

The short order solution mandated by most CT suppliers is to limit load impedance - and to take Mike's comment above "a dedicated short, fat cable route" - if you are a long way from the transformers, then you need some pretty big cabling to limit the voltage bouncing around like tigger on acid

One point about the "life safety" issues - I accept that diagnostics isn't a life safety issue in itself - if you can walk in you can walk out kind of thinking. However, many procedures in CT may well involve catheterization which is conductive - so they should be Medical Location Group 2 and should have medical IPS for shock risk. It is also pretty usual for the main equipment room to have small UPS support to manage shut down. It's entirely possible the designers may not have appreciated that fact

Regards

OMS
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Line impedance query

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