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    Active Harmonic Filter Basics

    Uploaded by

    Aditya Pandey
    Active harmonic filters are ideal solutions for mitigating harmonics in industrial and commercial facilities. They work by injecting harmonic currents into the system that are equal in amplitude but opposite in phase to the harmonic currents from the load, cancelling them out. This allows them to reduce the total harmonic distortion to below recommended IEEE limits. The key advantages of active filters over passive filters are their ability to dynamically correct harmonic distortion in real-time and improve power factor and load balancing. Their use is especially suitable in applications with frequent load variations or high harmonic loads. The nominal current rating of an active filter is based on multiplying the initial harmonic current measurement by a safety factor, usually 20%.

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    Active Harmonic Filter Basics

    Uploaded by

    Aditya Pandey
    319 views4 pages
    Active harmonic filters are ideal solutions for mitigating harmonics in industrial and commercial facilities. They work by injecting harmonic currents into the system that are equal in amplitude but opposite in phase to the harmonic currents from the load, cancelling them out. This allows them to reduce the total harmonic distortion to below recommended IEEE limits. The key advantages of active filters over passive filters are their ability to dynamically correct harmonic distortion in real-time and improve power factor and load balancing. Their use is especially suitable in applications with frequent load variations or high harmonic loads. The nominal current rating of an active filter is based on multiplying the initial harmonic current measurement by a safety factor, usually 20%.

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    Active harmonic filter basics

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    Active harmonic filters are ideal solutions for mitigating harmonics in industrial and commercial facilities. They work by injecting harmonic currents into the system that are equal in amplitude but opposite in phase to the harmonic currents from the load, cancelling them out. This allows them to reduce the total harmonic distortion to below recommended IEEE limits. The key advantages of active filters over passive filters are their ability to dynamically correct harmonic distortion in real-time and improve power factor and load balancing. Their use is especially suitable in applications with frequent load variations or high harmonic loads. The nominal current rating of an active filter is based on multiplying the initial harmonic current measurement by a safety factor, usually 20%.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    319 views4 pages

    Active Harmonic Filter Basics

    Uploaded by

    Aditya Pandey
    Active harmonic filters are ideal solutions for mitigating harmonics in industrial and commercial facilities. They work by injecting harmonic currents into the system that are equal in amplitude but opposite in phase to the harmonic currents from the load, cancelling them out. This allows them to reduce the total harmonic distortion to below recommended IEEE limits. The key advantages of active filters over passive filters are their ability to dynamically correct harmonic distortion in real-time and improve power factor and load balancing. Their use is especially suitable in applications with frequent load variations or high harmonic loads. The nominal current rating of an active filter is based on multiplying the initial harmonic current measurement by a safety factor, usually 20%.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
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    of 4

    Issue 26

    –|VArWLFOH|–
    Basics of Active Harmonic Filter:

    Modern industries are defined by widespread use of non-linear loads such as DC drives, VFDs etc. which
    introduce large content of harmonics into the system and its subsequent effects. There arises the need for
    intelligent solutions for harmonic mitigation. Active harmonic filters have developed as the most ideal solution
    for harmonic filtering in both industrial and commercial facilities. Added advantage is that they also offer
    solutions for phase balancing and power factor improvement. This article briefs about its basic principle of
    operation, need for active compensation and sizing.

    Principle of Operation

    An active harmonic filter is based on the following principle:


      –
      O
    It detects the difference between the ideal current sine wave () and the actual current which has been
    deformed by harmonics (O). It, then, injects this difference (), which is the negative of the harmonic
    currents present in the load current, into the system on a real-time basis. This cancels out the high frequency
    harmonics and results in almost pure sine wave.

    Wave shapes of the currents - MAN, LOAD & FLTER Line Diagram of Active Harmonic Filter
    The active filter monitors the line Harmonic Supply
    current in real time and converts the Generating System
    data to digital signals. The Load
    compensating current, as already Current
    Coupling
    explained, is generated by an IGBT Sensing
    Reactors
    bridge using Pulse Width Modulation
    (PWM) technology. Source of IGBT IGBT
    Bridge is a DC link capacitor which is Bridge

    charged simultaneously with DSP /


    generation of compensating current Controller
    to the network. The generated DC Link
    output is injected into the network Capacitor
    via a reactor or filter circuit.
    Simplified Layout of Active Harmonic
    Filter
    dvantages over etuned & uned ilters

    Active Harmonic Filters provide many advantages over the various solutions for harmonic mitigation as under:

    Harmonic
    Filters

    Passive Active Hybrid

    ctive: IGBT-based power converter


    Detuned Tuned that reduces harmonic distortion

    Hybrid: Combination of passive and


    Mitigates harmonics by acting as a active filters
    7% 14% sink
    erits:
    Series LC combination helps in erits:  Reduces THD till 5% to 8%
    avoiding harmonic resonance  Reduces %THD  Dynamic correction of THD is
    and amplification possible
    emerits:  Improves Distortion PF
    erits:  Tuning efficiency is susceptible  Load balancing and Displacement
     Simple and economical to system frequency & load PF improvement possible
    variations leading to  Modular – Can be expanded along
    emerits: with the load
    overheating & failure of filter
     Marginal reduction of  Extensive harmonic audit is
    %THD mandatory before installation
     High VTHD will affect the
     Cannot handle wide harmonic
    performance
    spectrum
    eed for ctive Compensation:

    Unlike detuned passive filters, active filters provide actual reduction in THD as recommended by IEEE. The
    IEEE 519-1992 guidelines on limits for current and voltage harmonics at Point of Common Coupling (PCC) are
    as under:

    aximum Harmonic Current istortion in % 


    ndividual Harmonic Order (Odd Harmonics)
    sc /  <11 11 ≤ h <17 17 ≤ h <23 23 ≤ h < 35 35 ≤ h 
    <20 4.0% 2.0% 1.5% 0.6% 0.3% 5.0%
    20 - 50 7.0% 3.5% 2.5% 1.0% 0.5% 8.0%
    50 - 100 10.0% 4.5% 4.0% 1.5% 0.7% 12.0%
    100 - 1000 12.0 % 5.5% 5.0% 2.0% 1.0% 15.0 %
    >1000 15.0% 7.0% 6.0% 2.5% 1.4% 20.0%
    where
    Isc = maximum short-circuit current at PCC [Can be calculated as MVA/(%Z x V)]
    IL = maximum demand load current (fundamental frequency component) at PCC

    Voltage istortion imits


    Bus Voltage at PCC ndividual Voltage istortion VH
    ≤ 69 kV 3.0% 5.0%
    69 kV < V ≤ 160 kV 1.5% 2.5%
    > 160 kV 1.0% 1.5%

    The use of active harmonic filters helps in reducing harmonics as can been seen under:

    Before H fter H


    100 100

    80 80
    mplitude (%)
    mplitude (%)

    60 60

    40 40

    20 20
    0 0
    1 3 5 7 9 11 13 15 17 19 21 1 3 5 7 9 11 13 15 17 19 21
    Harmonics order Harmonics order

    Frequency spectrum of current before and after active harmonic filtering


    Some of the areas where active harmonic filters can be used are:

    • In areas with critical loads like automobile industry, precision equipment manufacturing etc., the
    harmonic load may vary frequently. This may have immediate adverse impacts like poor quality of
    manufactured products and equipment failures leading to huge monetary losses. Active filters prove to
    be suitable as they provide real-time reduction of THD.
    • Certain segments like textile industry, having huge VFD loads suffer from high harmonics. Due to this,
    the use of detuned filters may not be adequate, resulting in frequent capacitor failures and overheating
    or saturation of reactors. Only active harmonic filters provide necessary solutions in such cases.
    • Active harmonic filters have an added advantage of providing unsymmetrical reactive power
    compensation and also, provide load balancing.
    • Even usage of 14% reactor may not be sufficient to reduce neutral overloading due to triple-N
    harmonics. However, 3 phase, 4 wire active filter helps in achieving the same more effectively.

    Selection / Sizing of ominal Current of ctive Harmonic ilter

    Active harmonic filter is rated in Amperes. The current rating is decided on the basis of harmonic content (THD)
    in the system which can be obtained from harmonic study. The required nominal current can be obtained by
    multiplying the initial current of harmonics measured in the load by a safety factor (Sh) of 20%. In other words,

    filter (AHF) = 1.2 x load x %THD()


    Where,
    Ifilter (AHF) : Nominal Current of Active Filter (A)
    Iload : Maximum Load Current (A)
    % THD(I) : Load Current Harmonic Distortion (%)

    Majority of the energy saving devices are non-linear in nature. Consequently, the problem of harmonics has
    become inevitable. Advanced devices like active harmonic filter provide an ideal solution to this problem. These
    filters help in maintaining a stable and healthy power system thereby increasing productivity and efficiency.

    Product Management
    Reactive Power and Harmonics Management

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