Harmonic Mitigation
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Group 2: reduction of harmonic emission
Group 3 Reduction of the Coupling Between Sensitive Load and Harmonic Source
Group 4 Reduction of Load Sensitivity to Disturbances
Group 1: voltage distortion reduction
End user
Electricity supplier
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3 Solutions
How to reduce the load sensitivity
Mitigation Technique VS Installed Cost
How the load is being affected by any disturbances
Compensation of the line impedance
Advantageous solution
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The components of the electromagnetic environment that need to be concern
1) Create heat in the load
2) Reduce efficiency of theload
3) Malfunction of the equipment
1) Transformer Derating
2) Motor Derating
3) Cable Derating
Transformer derating
- Design transformer with higher K Rating
- Reduce eddy current losses
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interference source
receptor (load)
transmission path
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to ensure good quality of electric power
1)Reduction of harmonic emission from non-liner load by STRUCTURE MODIFICATION
need to limit the magnitude of generated harmonics.
Series capacitors of variable capacitance
Series capacitors of fixed capacitance
Conclusion
Sufficiently large short-circuit capacity at the
point of connection
Larger voltage distortion can be
accepted
continuously monitor the voltage distortion level
Motor derating
-l
- The higher the harmonic voltage factor, the lower the rating factor
Cable Derating
- Single-core cable : Install a double-sized neutral conductor, either as two separate conductors or as one single large conductor
- Multi-core cable : To apply appropriate corrective coefficients to the cable capacity by considering the current flowing in the neutral in calculation of cable capacity
prevent magnification of the voltage resonance.
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main connection between the source and the load
Supplying large non-linear loads directly from an HV line
non-linear load which is the source of harmonics
an external disturbance which may degrade its performance
technocal solution to reduce magnitude of the generated harmonic DEPENDING ON THE LOAD
1) Line Reactor : to reduce level of converter current distortion
Disadvantage
Advantages
Low cost
Moderate reduction
Provide increase protection for AFD
Insensitive to system changes
May require larger enclosure
Produce heat
Harmonic reduction might not be sufficient
Increase short-circuit capacity at the PCC
•Application of transformers of larger power and/or lower short circuit voltage
•Parallel operation of supply lines and transformers
•Elimination of series reactors
•Extension of the supply system
Multi-Pulse Converter :Reduce converter current distortion factor
Can be connected in series or parallel in order to provide appropriate phase shift between the voltage supplying the bridges of the converter
3)isolation and high harmonic reduction transformers
2)high harmonic filter
Active
Passive
Multipulse VFDs - 12 Pulse
Advantages
Disadvantages
Multipulse VFDs - 18 Pulse
Advantages
Relatively inexpensive
Used to:
Shunt the harmonic current off the line
to block their flow between parts of the system by tuning the element to create resonance at selected harmonic frequency
Single-tuned filter is commonly used due to it being sufficient for the application and inexpensive
to present low impedance to a specific harmomic current
Provide PF correction in addition to harmonic suppression
divert harmonic current from their normal flow path
Disadvantages of passive filter
Requires careful analysis of the frequency characteristic
Effectivenes strongly depend on the supply network impedance at the point of connection
Filters are subect to detuning due to variations in the supply frequency and changes in LC component values
Third order harmonic current circulate in the delta windings of transformer.
Isolation transformer is needed to take care of this extra losses by isolating the the harmonic component
Same benefit can be obtained using zigzag wound transformer
Zigzag trasnformer are star configuration autotransformers between the windings that are connected in shunt with the supply
Shifting the voltage to provide mutual cancellation of the 5th and 7th harmonics in the case of nonlinear loads.
Advantages
Moderate reduction in harmonics
Isolation from ground
Moderate cost
Disadvantages
Large footprint
Separate mounting
Harmonic reduction may not be sufficient
Protection problem
Cost varies
Substantial reduction
almost complete cancellation of 5th and 7th harmonics
Insensitive to changes
Cost varies
Increase weight
More complex
Doesnt guarantee with compliance of IEEE 519
Guarantee compliences with IEEE 519
Excellent for large drive
Substantial reduction in harmonic
Disadvantages
Higher cost
More complex
Increases size and weight