Harmonics, Its Mitigation and Implementation......

Harmonics 




A harmonic is defined as a component of a periodic wave (or a signal) whose frequency is an integral multiple of the fundamental frequency. The typical 5th harmonic distortion is given below.?:
        

Voltage harmonics 

The harmonic current drawn by non-linear loads act in Ohm’s law relationship with the source Impedance of the power supply. The interaction of harmonic current with the source impedance will create Harmonic Voltages in the network (Harmonic Voltage = Harmonic current x Source impedance at harmonic frequency). The source impedance includes the Impedance of the power source (Transformer, Generator, and Grid, etc.Impedance of the Bus bars, Cables, Switchgears and other loads in the network.
        

Outcome of harmonics 


1. Blinking of Incandescent Lights - Transformer Saturation

2. Capacitor Failure - Harmonic Resonance

3. Circuit Breakers Tripping - Inductive Heating and Overload

4. Computer Malfunction or Lockup - Voltage Distortion

5. Conductor Failure - Inductive Heating

6. Electronic Equipment Shutting down - Voltage Distortion

7. Flickering Fluorescent Lights - Transformer Saturation.
        

Harmonics Distortion Limits: – IEEE – 519, 201


IEEE recommended practices and requirements for harmonic control in electrical power system: It represents a standard level of acceptable harmonic distortion in a power system.

Isc Short Circuit current at the point of common coupling (PCC), corresponding to system MVA level

IL Fundamental full load current in Amps

H Harmonic number

11<h<17 Limits of individual current at PCC

THD Total harmonic distortions.        

Solutions for Harmonic Mitigation : Harmonic mitigation provides several benefits that could be translated into financial savings for the investor and for the user


There are several harmonic mitigation techniques are available like?
        

1. Passive Harmonic Mitigation Technique

Series Line Reactors

Tuned Harmonic Filters

Series Induction Filters

DC-DC Converter Current Shaping

Parallel-Connected Resonant Filter

?Series-Connected Resonant Filter

Neutral Current Filter

Zigzag Grounding Filter

Higher Pulse Converters

12-Pulse Rectification, 18 - Pulse Rectification & 24 - Pulse Rectification
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2. Active Harmonic Mitigation Techniques

Parallel Active Filters

Series Active Filters
        

?3.Hybrid Harmonic Mitigation Technique

The combination of shunt AHF and shunts PHF.

The combination of AHF series with the supply and a shunt PHF.

AHF in series with a shunt PHF

p-q Method

d-q Method

Direct Testing and Calculating Method (DTC)

Synchronous Reference Fame Method (SRF)

Current Hysteresis Control

Triangle-Comparison PWM Control

Space Vector Modulation (SVM)s        

Currently, the research trends of the AHF control strategies are mainly towards the optimizing and practical application of the control strategies. At the end, the comparative criteria for PHF, AHF, and HHF could be summarized based on the following




Cost of the equipment and installation.

Harmonic indices?(ex. Ih,THDi ,?THDv , TDD, and PWHD.

Life time and failure rate.

Maintenance and engineering.
        

Our Implementaions : 200A AHF atone site and another 300A AHF other site .        

Conclusion : Passive Harmonic Filter is traditionally used to absorb harmonic currents because of low cost and simple robust structure. However, they provide fixed compensation and create system resonance. Active Harmonic Filter provides multiple functions such as harmonic reduction, isolation, damping and termination, load balancing, PF correction, and voltage regulation. The Hybrid Harmonic Filter is more attractive in harmonic filtering than the pure filters from both viability and economical points of view, particularly for high-power application

When attempting to meet IEEE 519-2014 standards for voltage and current distortion, Selection of the best-suited technique for a particular application is not always an easy or straightforward process. There are multiple harmonic mitigation options available, and each has its merits. With higher mitigation comes higher cost, and a cost-benefit analysis is critical to determining the best solution for your system.?