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IEEE Standard 519-1992
• Limit harmonic current injections from end users so that harmonic voltage distortion is tolerable.
• Limit harmonic voltage (responsibility of utility).
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utility system
PCC other customers
I
L customer under study utility system
PCC
I
L customer under study 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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Total harmonic distortion of voltage is normalized with the system nominal rms voltage :
T HD
V n
 h

 1
V n
V h
2
 100 %
Total demand distortion for current (as before) :
TDD  h

 1
I h
2
I
L
 100 %
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Bus Voltage at PCC, Vn
[kV,LL]
Vn < 69
Individual harmonic voltage distortion
3.00%
69<Vn<161 1.50%
161<Vn 1.00%
Total voltage distortion
THD_Vn
5.00%
2.50%
1.50%
Table 6.1 Harmonic voltage distortion limits in % of nominal fundamentalfrequency voltage
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Vn < 69 kV
Isc/IL
0-20 h<11 11<h<17 17<h<23 23<h<35 35<h
4.0% 2.0% 1.5% 0.6% 0.3%
TDD
5.0%
20-50
50-100
100-1000
>1000
7.0%
10.0%
12.0%
15.0%
3.5%
4.5%
5.5%
7.0%
2.5%
4.0%
5.0%
6.0%
1.0%
1.5%
2.0%
2.5%
0.5%
0.7%
1.0%
1.4%
8.0%
12.0%
15.0%
20.0%
69<Vn <161 kV
Isc/IL
0-20 *
20-50
50-100
100-1000
>1000
161 kV<Vn
Isc/IL
0-50
>50 h<11 11<h<17 17<h<23 23<h<35 35<h
2.0% 1.0% 0.75% 0.3% 0.15%
3.5%
5.0%
6.0%
1.75%
2.25%
2.75%
1.25%
2.0%
2.5%
0.5%
0.75%
1.00%
0.25%
0.35%
0.50%
7.5% 3.50% 3.0% 1.25% 0.70% h<11 11<h<17 17<h<23 23<h<35 35<h
2.0% 1.0% 0.75% 0.3% 0.15%
3.0% 1.50% 1.15% 0.5% 0.22%
TDD
2.5%
4.0%
6.0%
7.5%
10.0%
TDD
2.5%
3.8%
* line applies to all power generation equipment regardless of Isc/IL ratio
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• I h is rms magnitude of individual harmonic current
• I sc is the short-circuit current at PCC
• I
L 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 q / 6
2 .
For example, if q  12, then multiply by
I
L
 kWD kWD pf

 3  kV rated average billed demand in kW pf  average billed power factor kV rated
 nominal LL voltage in kV
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• 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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• 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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• 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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C
A
B
C
B A
N
Zig-zag transformer
N
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• Place the transformer to supply balanced triplen harmonics (and any other zerosequence 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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a b c
I
3 n
3I
3
Unloads the neutral conductor upstream
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• 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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• Shunt passive filters are
– notch filters, tuned to a specific harmonic frequency, or
– high-pass filters notch filter high-pass filter
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• 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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• 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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• In-line reactors (or chokes) for ASD
• Isolation transformers can help
• Isolation transformers can be reconnected with different phase shifts
X s
X t reactor 0-5% on ASD kVA
ASD
M
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Isolation transformers X~5%
480 V bus
ASD
M
M
ASD
Approximates a 12-pulse converter with 6pulse converters by putting half on Delta-
Delta transformers and the half on Delta-Y.
12-pulse has I h
= 0 for h = 5, 7
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• 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
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