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Thread: Harmonics in Green Buildings

  1. #11
    T.M.Haja Sahib Guest
    Quote Originally Posted by Besoeker View Post
    Any harmonic mitigating measure is probably going to do that and add costs. Think about active front end variable frequency inverter drives. The front end bridge changes from a plain rectifier to an IGBT bridge of about the same rating as the output bridge. More complex, more losses, and more expensive.
    I think there are SMPS with input filter less design that may serve the purpose here.

    Quote Originally Posted by Besoeker View Post
    It what you put in the first thread. Your post doesn't make that clear.
    But 10% of what load?
    Installed kVA?
    kW?
    Current?

    For example if you had had 100kW of fixed speed motors installed, could you then have only 10kW worth of variable speed drives?
    Of course the ratio of the currents between the VSDs and the fixed motors is most probably going to be rather lower than 10%.
    And it the non-sinusoidal current that causes voltage distortion.

    All I'm asking is that you clarify what the 10% refers to.
    Let us take the name plate ratings and in that case, installed KVA, KW and current are all equivalent.

  2. #12
    T.M.Haja Sahib Guest
    Quote Originally Posted by robbietan View Post
    the IEEE standard for Harmonic total demand distortion ITDD at 5% should be more than enough to satisfy any "green building" requirement.

    this is the limit that utilities use in measuring harmonic emissions from customers.
    I think the 5% refers to voltage harmonic. Current harmonic limit may be much higher.

  3. #13
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    Quote Originally Posted by T.M.Haja Sahib View Post
    Let us take the name plate ratings and in that case, installed KVA, KW and current are all equivalent.
    As an example take a 55kW 400V 3-phase motor.
    Driven directly from the supply it will take about 107A FLC
    Use an active front end and that will take about 89A.

    Both 55kW rating.
    The supply loading for one is 74 kVA, the other 62 kVA.
    The supply power is 59kW for one and 62kW for the other.

    Would you perhaps like to reconsider your comment that installed KVA, KW and current are all equivalent?

  4. #14
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    Quote Originally Posted by T.M.Haja Sahib View Post
    I think the 5% refers to voltage harmonic. Current harmonic limit may be much higher.
    So, same question as before. Does your 10% refer to current or voltage?
    Or something else?

  5. #15
    T.M.Haja Sahib Guest
    Quote Originally Posted by Besoeker View Post
    As an example take a 55kW 400V 3-phase motor.
    Driven directly from the supply it will take about 107A FLC
    Use an active front end and that will take about 89A.

    Both 55kW rating.
    The supply loading for one is 74 kVA, the other 62 kVA.
    The supply power is 59kW for one and 62kW for the other.

    Would you perhaps like to reconsider your comment that installed KVA, KW and current are all equivalent?
    Does not the name plate rating distinguish between the two?

  6. #16
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    Quote Originally Posted by T.M.Haja Sahib View Post
    Does not the name plate rating distinguish between the two?
    Two?
    kW, kVA, and Amps are three quantities.

  7. #17
    T.M.Haja Sahib Guest
    You mentioned about two motors: one with active front end while the other one without it. If the one with the active front one is so provided in the field, such modification in its rating need be clearly displayed.

  8. #18
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    Quote Originally Posted by T.M.Haja Sahib View Post
    You mentioned about two motors: one with active front end while the other one without it. If the one with the active front one is so provided in the field, such modification in its rating need be clearly displayed.
    Active front end VFD.

  9. #19
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    Quote Originally Posted by T.M.Haja Sahib View Post
    I think the 5% refers to voltage harmonic. Current harmonic limit may be much higher.
    It is 5% VTHD and 5% ITDD for utilities here
    NEC 1968 and 1948

  10. #20
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    Quote Originally Posted by Besoeker View Post
    As an example take a 55kW 400V 3-phase motor.
    Driven directly from the supply it will take about 107A FLC
    Use an active front end and that will take about 89A.

    Both 55kW rating.
    The supply loading for one is 74 kVA, the other 62 kVA.
    The supply power is 59kW for one and 62kW for the other.

    Would you perhaps like to reconsider your comment that installed KVA, KW and current are all equivalent?
    I am trying to learn from these posts sir; can you post how you arrived at each value above please? thank you.

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