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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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  • Former Community Member
    0 Former Community Member
    Chris Pearson:

    I don't doubt for one minute the expertise of Mike, Dave, and OMS, but this all seems to be OTT. Just how are scanners put into a ship or a field hospital?

     


    Reasonably easily - the source impedance requirements aren't that difficult to achieve. Back in the day, even the sockets used for mobile x-ray had impedance limits - most of this stuff has been in HTM documentation for many decades.


    As the OP indicated, the CT will still work, just that you get ever increasing image degradation  - which is then exacerbated if you need to share those images over networks resulting in further degradation


    To get this into context, in a modern acute hospital of say 500 beds, it wouldn't be unreasonable to have a firm 4MVA supply capability (so essentially 8MVA depending on how the source transformers are configured for A+B primary and secondary supplies into the Healthcare estate)


    Most hospital electrical loads are disturbing to some extent, so sensible design is needed in terms of what you try and do. It's never that sensible to have your main diagnostic capability as far away from your supply as possible - usually you would design for the opposite. There are a few idiotic cases such as where a know nothing project manager decided that installing a new MRI scanner in a room directly above a set of transformers was perfectly reasonable - the magnetic field of the MRI sweeping through the transformers resulted in some interesting disturbance issues - ohh how we laughed.


    The above aside - 0.06 Ohm limit is only roughly 4% voltage drop in a cable - so it's hardly unreasonable assuming you have decent transformers in place, and noting this is a swap out rather than an additional scanner.


    Regards


    OMS


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  • Former Community Member
    0 Former Community Member
    Chris Pearson:

    I don't doubt for one minute the expertise of Mike, Dave, and OMS, but this all seems to be OTT. Just how are scanners put into a ship or a field hospital?

     


    Reasonably easily - the source impedance requirements aren't that difficult to achieve. Back in the day, even the sockets used for mobile x-ray had impedance limits - most of this stuff has been in HTM documentation for many decades.


    As the OP indicated, the CT will still work, just that you get ever increasing image degradation  - which is then exacerbated if you need to share those images over networks resulting in further degradation


    To get this into context, in a modern acute hospital of say 500 beds, it wouldn't be unreasonable to have a firm 4MVA supply capability (so essentially 8MVA depending on how the source transformers are configured for A+B primary and secondary supplies into the Healthcare estate)


    Most hospital electrical loads are disturbing to some extent, so sensible design is needed in terms of what you try and do. It's never that sensible to have your main diagnostic capability as far away from your supply as possible - usually you would design for the opposite. There are a few idiotic cases such as where a know nothing project manager decided that installing a new MRI scanner in a room directly above a set of transformers was perfectly reasonable - the magnetic field of the MRI sweeping through the transformers resulted in some interesting disturbance issues - ohh how we laughed.


    The above aside - 0.06 Ohm limit is only roughly 4% voltage drop in a cable - so it's hardly unreasonable assuming you have decent transformers in place, and noting this is a swap out rather than an additional scanner.


    Regards


    OMS


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