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Thread: Transformer K- Factor For hospital project

  1. #1
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    Transformer K- Factor For hospital project

    Dear Forum Members,

    What is the recommended K-Factor of the transformer used for hospital project where there are a lot of harmonic generating medical equipments are used?
    Our specification is not specifying any rating of K-factor for transformer and the manufacturer is specifying in the fabrication drawings K-factor=1 which i think is not suitable for hospital project.
    I have to comments on the fabrication drawings to specify the correct K- Factor tramsformer.

    Valueable feedbacks are awaited.

    Thanks

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  2. #2
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    1. How do you know the equipment will result in harmonic distortion?
    2. Have you checked with the equipment suppliers as most new equipment has or can be order with built in harmonic mitigation?
    3. What percentage of load do you expect the K1 transformers to carry in normal operation?

    In the hospitals I have worked in K1 off the shelf transformers are the norm, with a higher K-rated transformer for specific equipment.
    Brian John
    Leesburg, VA

  3. #3
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    Do you plan to increase neutral sizes also?

  4. #4
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    Quote Originally Posted by publicgood View Post
    Do you plan to increase neutral sizes also?
    No Neutral size will not be increased.
    If you don't know, ask those who knows

  5. #5
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    Quote Originally Posted by brian john View Post
    1. How do you know the equipment will result in harmonic distortion?
    2. Have you checked with the equipment suppliers as most new equipment has or can be order with built in harmonic mitigation?
    3. What percentage of load do you expect the K1 transformers to carry in normal operation?

    In the hospitals I have worked in K1 off the shelf transformers are the norm, with a higher K-rated transformer for specific equipment.
    1) The medical consultant told that most of the medical equipments are with harmonic mitigation filters while there are still some equipment which are without filters.
    2) same as 1
    3) Our substations are double ended substation and loaded 50% only in normal case. It will run on full capacity when the bus tie is closed at the time of one transformer failure.

    One more thing is that we have capacitor banks with harmonic filter in each substations. Will it substitute the requirement of K-factor=1 rated transformers for harmonic mitigation?
    If you don't know, ask those who knows

  6. #6
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    You should consider the cap banks with harmonic filters.

    With that:

    K4 up to 65% nonlinear load
    K13 50-95% non-linear
    K20/30 95%+ (not commonly used)
    Harmonic mitigating when primarily nonlinear and very sensitive equipment above 65% non-linear

  7. #7
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    Also, it is most common: if you decide transformers need K rating, size the neutral 200% on the secondary of the xfrm at least up to the first disconnect.

  8. #8
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    Quote Originally Posted by brian john View Post
    In the hospitals I have worked in K1 off the shelf transformers are the norm, with a higher K-rated transformer for specific equipment.
    Same here. Specialized equipment such as radiology typically have there own isolation transformers engineered for their own problems.

    Roger
    Moderator

  9. #9
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    Quote Originally Posted by publicgood View Post
    Also, it is most common: if you decide transformers need K rating, size the neutral 200% on the secondary of the xfrm at least up to the first disconnect.
    I have found this not to be common anymore. K rated implies the expectation of harmonics. neutrals beyond 100% imply triplin harmonics part the capacity of the neutral.

    Oversized neutrals in my experience over the last bunch of years seemed to have gone the way of the isolated ground receptacles.

    15 years ago, that was a different story.
    Ron

  10. #10
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    From the discussion above i concludes that transformer with k-factor=1 will b workable fine for hospital when other harmonic mitigating filters are there in the system.

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