Applied Harmonics Control of Harmonics

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Applied HarmonicsControl of Harmonics
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IEEE Standard 519-1992
Harmonic Distortion Evaluations

• Limit harmonic current injections from end users
  so that harmonic voltage distortion is tolerable.
• Limit harmonic voltage (responsibility of
  utility).

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customer under study
utility system
PCC
IL
other customers
customer under study
utility system
PCC
IL
other customers
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• End users are limited at PCC in terms of
• individual harmonic components and
• total demand distortion
• Utility is mainly responsible for limiting
  voltage distortion at PCC
• Evaluations
• Measurement of currents injected by load (over
  one week period)
• Calculation of frequency response of system
  impedances (using harmonic calculation software)

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Table 6.1 Harmonic voltage distortion limits in
of nominal fundamental- frequency voltage
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Table 6.2 Harmonic current limits
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• Ih is rms magnitude of individual harmonic
  current
• Isc is the short-circuit current at PCC
• IL is the fundamental component of the maximum
  demand current (average max demand over 12
  months)
• Individual limits apply to odd-order harmonics,
  even order limits are at 25 of indicated value

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• For power converters with more than 6 pulses,
  where q pulse number, multiply limits in table
  6.2 by

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Controlling harmonics

• Control only when harmonics create a problem.
  Types of problems
• load harmonic currents are too large
• path for harmonic currents is too long
  electrically (too much impedance) producing
  voltage distortion or communication-line
  interference
• response of system magnifies one or more harmonics

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Options for control

• Reduce magnitude of harmonic currents from load
• Add filters to do one or more of these
• short out (siphon off) the harmonic
• block harmonic currents from entering part of the
  system
• supply the harmonics locally
• Modify the frequency response of the system by
  filters or other means

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Reducing load harmonic current

• Sometimes transformer connections can be changed,
  for example
• phase shift on some transformers supplying
  6-pulse converters
• delta windings block triplen currents
• zig-zag transformers can supply triplens

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Zig-zag transformer
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Zig zag transformer

• Place the transformer to supply balanced triplen
  harmonics (and any other zero-sequence currents)
  to load
• This will unload zero sequence currents on
  circuits upstream of the ZZ transformer, with
  little or no effect downstream
• Fault study results may be affected

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Placement of ZZ transformer
a
b
c
I3
n
3I3
Unloads the neutral conductor upstream
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Filtering

• Shunt passive filter short-circuit harmonic
  currents close to their source
• Series passive filter block harmonic currents
  from power delivery system (may cause large load
  voltage distortion)
• Active shunt filter electronically supply
  low-order harmonics to a nonlinear load (used
  with simple passive filters for higher frequency
  components).

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Passive Filters

• Shunt passive filters are
• notch filters, tuned to a specific harmonic
  frequency, or
• high-pass filters

high-pass filter
notch filter
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Modifying system frequency response

• Add a shunt filter to the system
• Add a reactor (e.g., in series with a pf
  correction capacitor) to de-tune system
• Change pf correction capacitor size or placement,
  or remove capacitor bank entirely

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Where to control harmonics

• On utility system or end-user facility
• utility system is more difficult to filter unless
  we can move or change the size of or reconnect a
  capacitor
• end-user system may be easier to filter if we can
  access the feeder(s) where the harmonic currents
  are being produced

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Filters

• In-line reactors (or chokes) for ASD
• Isolation transformers can help
• Isolation transformers can be reconnected with
  different phase shifts

ASD
M
Xs
Xt
reactor 0-5 on ASD kVA
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Isolation transformers X5
480 V bus
M
ASD
M
ASD
Approximates a 12-pulse converter with 6-pulse
converters by putting half on Delta-Delta
transformers and the half on Delta-Y. 12-pulse
has Ih 0 for h 5, 7
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Harmonic studies

• Perform harmonic studies when
• a problem occurs, to find a solution
• planning large capacitor bank installation on
  either utility or industrial system
• planning installation of large nonlinear load
  such as adjustable speed motor drives (ASD)
• designing a harmonic filter or converting a
  capacitor to a harmonic filter