Power quality Innovation in harmonic filtering by jennyyingdi


									                                   Power Quality
            Innovation in Harmonic Filtering

ABSTRACT:                                          the Basic concept of harmonics, their
                                                   generation, problems created by
          Power quality has become a               them         and          HARMONIC
great    concern          for   both   energy      FILTERATION as a solution for
suppliers     and          their   customers       this problem of Harmonics.
because     the      increasing        use    of
sensitive devices and the significant
consequences         of     a   poor    power      INTRODUCTION:
quality for the competitiveness of the
companies.                                                  “POWER        QUALITY”        is
        The increasing developments                defined as “the concept of powering
need increasing use of electricity.                and grounding electronic equipment in
While meeting this power demand,                   a manner that is suitable to the
there causes a pollution in electrical             operation of the equipment ina manner
system      called        Harmonics.         The   that is suitable to the operation of that
harmonics are integer multiples of                 equipment and compatible with the
fundamental                currents/voltages.      premise wiring system        and other
Substantial presence of harmonics                  connected equipment.
results in excessive overheating of
the equipments and other problems.                 power quality has become a strategic
Harmonics are created by non linear                issue for the following reasons:
loads that draw current in abrupt                        The economic necessity for
pulses rather than in a smooth.                           businesses to increase their
Different problems due to harmonics                       competitiveness.
have different solutions.              In this           The     widespread      use    of
paper we are going to present you                         equipment which is sensitive to
        voltage disturbances and /or             the voltage magnitude at a point in the
        generates disturbances itself.           electric
       The      deregulation         of   the   System and lasting from 0.5 cycles to
        electricity market.                      few        seconds.     Either   switching
        In this context, it is essential for     operations or any type of faults as well
the utility and the customers to prevent         as fault clearing process can cause a
and detect power quality problems and            voltage dip. Switching like those
to have solutions available to fix them.         associated       with      a     temporary
The power quality correction and                 disconnection of the supply or flow of
harmonic filtering system give solution          heavy currents associated with the
to solve the problems of harmonic                starting of large motor loads is the
disturbances and voltage fluctuations.           most common. These events maybe
                                                 originated at the utility side or at the
                                                 customer site.

MAIN          POWER               QUALITY        VOLTAGE               VARITIONS      AND
DISTRUBENCES:                                    FLUCTUATIUONS:-

                                                 Voltage variations are variations in the
                                                 rms value or the peak value with
Power     quality       usually       involves
                                                 amplitude of less than 10% of the
characterising       low           frequency
                                                 nominal voltage. Voltage variations are
conducted                  electromagnetic
                                                 a series of voltage changes which are
disturbances which can be ranked in
                                                 characterised by the frequency of
different categories.
                                                 variation and the magnitude.
                                                 Voltage variations are caused by a
                                                 slow variation of loads
        Voltage     sag    is     a    sudden
reduction (between 10% and 90%) of
                                          current wave shapes, which in turn
                                          cause harmonic currents to flow, back
                                          into other parts of the power system.
                                          Consumers Generating Harmonics:
                                                    Harmonics are not generated by
connected to the network and mainly       power generators but are produced by
due to rapidly varying industrial loads   Non-linear loads as under:
such as welding machines.                 Loads that make use of semi conductor
HARMONICS:-                                  like transistor, thyristor i.e., static
Harmonics are currents or voltages           rectifiers.        (AC/DC conversion
with frequencies that are integer            using      SCRs),      static   frequency
multiples of the                             converters, static inverters like:
                                             -      Static Power converters (AC –
                                                    DC conversion using SCRs)
                                             -      Static rectifiers
                                             -      Static frequency converter
                                             -      Static     uninterrupted      power
fundamental power frequency. The                    supplies
fundamental frequency itself is called       -      Static induction regulators.
as the first Harmonic.      The second       i)         Variable impedance loads,
Harmonic as frequency twice that of                     using    electric    arcs,     are
the fundamental, the third Harmonic                     furnaces,       welding      units,
has frequency thrice that of the                        Fluorescent               tubes,
fundamental and so on. For example –                    discharge        lamps,      light
if the fundamental frequency is 50Hz                    control, brightness etc.,
then the second Harmonic is 100 Hz,          ii)        Loads        using        strong
the third Harmonic is 150Hz etc.                        magnetizing            currents,
                                                        saturated        Transformers,
Generation of Harmonics:-                               inductance,            furnaces,
Harmonics are created by non-linear                     reactors etc.,
loads that draw currents abrupt pulses
rather than in a smooth sinusoidal
manner. These pulses cause distorted
Office    automation        equipment        like   AC Filters: These are shunt connected
computers, UPS, printers and fax                    AC     harmonic       filters.    They     are
machine etc.,                                       connected between AC busbars and
PROBLEMS            DUE           TO     LOW        earth. They offer low impedance to
POWER QUALITY:                                      harmonic       frequencies        and    high
        Damaging           of         computer     impedance to power frequency. Thus,
         hardware and memory.                       harmonic frequencies are passed to
        Motors fail to start due to low            earth and are eliminated from the AC
         voltages                                   network.
        Setting    and          resetting    of
         electronic equipments will be
         out of control .
        Industrial and domestic loads
         will get damaged.
Solution to Harmonic Distortion:
Harmonic Filtration:
Harmonics in AC & DC waveforms
are minimized by following means:
                                                    AC shunt filters serve dual purpose
   1. Use of DC smoothing reactor.
                                                    on AC side:
   2. Use of DC harmonic filters.
                                                         1. They divert harmonics to earth
   3. Use of AC harmonic filters.
                                                            and     reduce      the    harmonic
DC Smoothing Reactor: This is oil
                                                            contents in main AC network.
cooled, oil insulated reactor having
                                                         2. They          provide            shunt
high inductance (0.35H to 1H).It is
                                                            compensation required on AC
connected in series on the DC side of
                                                            side for satisfactory converter
the converter. It smoothen the ripple in
the DC current. The DC reactor also
helps in reducing the rate of rise of
                                                    CLASSIFICATIONS                   OF      AC
current surges appearing on the DC
                                                    SHUNT FILTERS: -
side of the converter due to sudden
                                                    Tuned AC shunt filters are used for
changes in DC power flow due to
                                                    suppressing lower order characteristic
faults or load change.
                                                    harmonics eg. Separate tuned branches
                                                    for 5th, 7th, 11th, 13th harmonics. These
branches may be either single tuned for                        of a double tuned AC shunt
each    of        the    above      characteristic             filter consists of a RLC series
frequency or each branch double tuned                          circuit in series with another
                                   th   th        th
for two frequencies eg. 5 /7 , 11                  /13th,      L2, C2, & R3, L3 parallel circuit.
23rd/25th, 3rd/36th etc.,                                      The values are selected such
Tuned AC shunt filters are classified                          that the total filter has two
into two types.                                                resonant     frequencies           (One
    a) A Single frequency tuned                                given by CLL2C2 & other by
        Shunt filters is a single RLC                          CR3 L3).
        series           circuit         connected
        between a phase and earth.
        The filter is tuned to one
        particular                  characteristic
        harmonic frequency. Separate
        branches are necessary for each
        lower characteristic harmonic
        frequency. The filter is tuned
        to        the    resonates       frequency
        equal to the corresponding
        characteristic harmonic order.
                                                            1) High pass filter branches are
                                                               arranged        to          suppress
                                                               harmonics of higher order say
                                                               24th & above. With High pass
                                                               AC     shunt    harmonic           filter
                                                               connected near AC Bus bars,
                                                               all the higher harmonics are
                                                               diverted to earth and are not
                                                               allowed to proceed to the AC
                                                               Network.             At     resonant
    b) A Double frequency tuned                                frequencies, the circuit of the
        shunt filters has two resonant                         double       tuned        filter      is
                                   th        th        th
        frequencies eg. 5 / 7 , 11 /                           equivalent     to    two     parallel
             th     rd    th
        13 , 3 /36 . A typical circuit                         single tuned branches.                A
          double frequency tuned filter                  Harmonic currents & voltage
          has lowest impedance at two           distortion are becoming the most
          resonant frequencies.        These    severe     and     complex     electrical
          filters   are   also   called   as    challenge for the electrical industry.
          Damped Filters.                       So by designing and giving complete
                                                solutions in the form of detuned and
DC Harmonic Filters                             tuned harmonic filter systems, Active
          DC filters are designed to            filters and other protection systems for
reduce DC harmonics to minimize the             industrial installation that can ensure
telephone       interference     in    voice    the trouble free operation of electrical
frequency range (100Hz to 5 KHz). In            installation for industries.
addition to the telephone interference          By defining and implementing these
criterion, the DC filter is designed with       solutions users will be provided with
interior of avoiding the resonance              the right quality of power supply for
between DC filters & DC line at lower           their requirements .
order harmonics.

          Power quality has become a
strategic issue for consumers. In this
present      economic       context,      the
consequences of electrical disturbances
become more and more serious.

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