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Harmonic Mitigation (Group 3 Reduction of the Coupling Between Sensitive…
Harmonic Mitigation
Group 3 Reduction of the Coupling Between Sensitive Load and Harmonic Source
Compensation of the line impedance
Series capacitors of variable capacitance
Series capacitors of fixed capacitance
Advantageous solution
Supplying large non-linear loads directly from an HV line
Conclusion
Sufficiently large short-circuit capacity at the
point of connection
Larger voltage distortion can be
accepted
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
Group 4 Reduction of Load Sensitivity to Disturbances
How to reduce the load sensitivity
1) Transformer Derating
2) Motor Derating
3) Cable Derating
Transformer derating
Design transformer with higher K Rating
Reduce eddy current losses
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
Mitigation Technique VS Installed Cost
How the load is being affected by any disturbances
1) Create heat in the load
2) Reduce efficiency of theload
3) Malfunction of the equipment
Group 1: voltage distortion reduction
End user
to ensure good quality of electric power
need to limit the magnitude of generated harmonics.
Electricity supplier
continuously monitor the voltage distortion level
prevent magnification of the voltage resonance.
The components of the electromagnetic environment that need to be concern
interference source
non-linear load which is the source of harmonics
receptor (load)
an external disturbance which may degrade its performance
transmission path
main connection between the source and the load
Group 2: reduction of harmonic emission
3 Solutions
1)Reduction of harmonic emission from non-liner load by STRUCTURE MODIFICATION
technocal solution to reduce magnitude of the generated harmonic DEPENDING ON THE LOAD
1)
Line Reactor
: to reduce level of converter current distortion
Disadvantage
May require larger enclosure
Produce heat
Harmonic reduction might not be sufficient
Advantages
Low cost
Moderate reduction
Provide increase protection for AFD
Insensitive to system changes
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
Multipulse VFDs - 12 Pulse
Advantages
Cost varies
Substantial reduction
almost complete cancellation of 5th and 7th harmonics
Insensitive to changes
Disadvantages
Cost varies
Increase weight
More complex
Doesnt guarantee with compliance of IEEE 519
Multipulse VFDs - 18 Pulse
Advantages
Guarantee compliences with IEEE 519
Excellent for large drive
Substantial reduction in harmonic
Disadvantages
Higher cost
More complex
Increases size and weight
3)isolation and high harmonic reduction transformers
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
2)high harmonic filter
Active
Passive
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
divert harmonic current from their normal flow path
Provide PF correction in addition to harmonic suppression
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
