View
214
Download
0
Category
Preview:
Citation preview
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 1
1999 IEEE T&D ShowNew Orleans
Panel Session PN13
Non-periodic Currents:Causes, Effects and Identification
Interharmonics in Power Systems
Erich W. Gunther
Electrotek Concepts, Inc.
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 2
Interharmonics in Power Systems
Definition Standards Sources Impacts Solutions
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 3
Interharmonics - Definition
IEC-61000-2-1 defines Interharmonics as:
“Between the harmonics of the power frequency voltage and current, further frequencies can be
observed which are not an integer of the fundamental. They can appear as discrete frequencies or as a wide-band spectrum”
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 4
Standards and Working Groups
IEC 61000-4-7 - Measurements IEEE Task Force on Interharmonics IEEE 519 - under revision - adds interharmonics Cigre 36.05 - Voltage Quality Working Group
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 5
IEC Harmonic / InterharmonicMeasurement Standard: IEC 61000-4-7
Number of cycles to sample chosen to provide 5 Hz frequency bins 10 Cycles for 50 Hz Systems 12 Cycles for 60 Hz Systems
Grouping concept Harmonic factors calculated as the square root of the sum of
the squares of the harmonic bin and two adjacent bins. Interharmonic factors calculated as the square root of the
sum of the squares of the bins in between the harmonic bins (not including the bins directly adjacent to the harmonic bin).
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 6
Frequency Bin Grouping
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 7
Frequency Bin Grouping
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 8
Interharmonic Sources
Arc furnaces Cycloconverters Power line carrier communications PWM power electronic systems Interaction of controls and power system
components
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 9
Example Case Where dc Arc Furnace Caused Unacceptable
Flicker Levels
Converter control problems result in increased interharmonic generation
System resonance magnifies the interharmonic component (186 Hertz)
Result is 6 Hertz modulation that causes light flicker over a wide area
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 10
Example System One Line Diagram for Harmonic and Flicker
Evaluations
Customer
Customer
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 11
Frequency Response with Initial Filter Design
0 200 400 600 800 0
25
50
75
100
125
150
Frequency (Hz)
Dri
vin
g P
oin
t Im
ped
an
ce (
Oh
m) 186 hertz
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 12
Voltage at the 26 kV Bus
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 13
Current at the 26 kV Bus
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 14
Effect of the Rolling Mill
Modern rolling mills will typically use cycloconverters. They also generate significant interharmonic components.
Example waveform and spectrum used for design purposes:
CASE41>S35K3A-FEED3A(Type 9)
270 280 290 300-2000
-1000
0
1000
2000
Time (mS)
Cu
rren
t (A
)
Max:Min:Avg:Abs:
RMS:CF :FF :
1536.08 -1498.02 821.937 1536.08 940.961 1.63245 1.14481
DERIVED>S35K3A-FEED3A(Type 9)
0 6 12 18 24 0
10
20
30
40
Frequency (Hz pu)
Cu
rren
t (A
)
Freq :Fund :THD :TID :TD :
RMSh :RMSi :
RMSfh:RMS :
ASUM :TIF :IT :
1 966.448 6.40455 0 6.40455 61.8967 0 968.428 968.428 1349.88 146.679 142048
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 15
Impacts
Similar to impact of harmonic distortion Heating Altered/multiple zero crossing Telecommunications interference
Unique impacts Light flicker Torsional oscillation excitation
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 16
Light Flicker due to Interharmonics
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 17
Solutions
Fix control problems to reduce level of interharmonic generation.
Non-characteristic harmonics and interharmonics must be considered in the filter design for dc arc furnaces and other interharmonic producing loads.
Resonances created by the filters in parallel with the system inductance can magnify interharmonic components causing high distortion and flicker.
Damping should be included in filter designs to avoid interharmonic problems.
http://www.pqnet.electrotek.com/pqnet/main/tech/intharm/ Interharmonics - 18
Conclusions
Interharmonics have always been around, they are just becoming more important and visible.
Power electronic advances are resulting in increasing levels of interharmonic distortion.
Traditional filter designs can result in resonances that make interharmonic problems worse.
Light flicker is the most common impact. Measurement is difficult, but standards make them
possible and the results comparable.
Recommended