HOW CAN HARMONICS IN A SYSTEM BE MITIGATED?

Harmonics in a system can be neutralized to a significant degree with proper understanding and analysis of harmonic contents at various frequencies. Analysis involves breaking down the harmonic distortion into its component frequencies and amplitudes at each frequency. Any irregular periodic waveform can be broken down inro a combination of series of regular sinusoidal waveforms using Fourier Series. This is done up to a frequency where the contribution of harmonics tends to become insignificant.

Measurement and analysis Techniques

Harmonic analyzers / power quality analyzers can break down any waveform into its fundamental and harmonic constituents in short time and typically detect up to about 40^th harmonic. Combination of these amplitudes and frequencies along with fundamental gives nearest waveform to that (original) being analyzed. Following methods are available:

1. Power Quality Analyzers: These devices are essential for measuring harmonics, capturing data on both current and voltage harmonics. They provide detailed harmonic spectra, total harmonic distortion (THD), and other disturbances like voltage swells and dips.
2. Clamp Meters: Specialized clamp meters can measure THD directly, providing a quick assessment of harmonic levels in current or voltage.
3. Digital Analyzers with FFT: Modern digital analyzers utilize Fast Fourier Transform (FFT) algorithms to convert time-domain signals into frequency-domain representations. This allows accurate measurement of harmonic amplitudes and phases up to the 40th or 50th order.

Power quality analyzers play a crucial role in harmonic mitigation by providing detailed measurements and analysis of voltage and current waveforms. They help identify the presence and magnitude of harmonics, which are distortions caused by nonlinear loads. This information is essential for diagnosing power quality issues and selecting appropriate mitigation strategies, such as installing filters or adjusting system configurations.  By analyzing harmonic distortion, these analyzers enable engineers to optimize system performance, reduce energy losses, and prevent equipment damage.

• Total Harmonic Distortion (THD): THD is a critical metric that quantifies the level of harmonic distortion in a system. It is calculated as the ratio of the RMS value of all harmonic components taken together, to the RMS value of fundamental frequency, expressed as a percentage. For voltage, THD values should ideally be below 5-8% to maintain power quality.
• Harmonic Spectrum: This is a graphical representation showing the amplitude of each harmonic component (e.g., 2nd, 3rd, up to 50th harmonics) relative to the fundamental frequency. It helps identify which harmonics are most prevalent and their potential impact on the system.

Harmonic Analysis Procedures

Site Surveys: Harmonic measurements can be conducted as part of preventive maintenance or troubleshooting. Measurements may be taken over a short period for immediate issues or continuously over weeks for comprehensive analysis.

Harmonic Mapping: This involves creating a profile of harmonic levels across different points in the distribution network to identify sources and assess compliance with power quality standards.

Frequency Scans: This method involves injecting a known current into a bus over a range of frequencies to observe the resultant voltage, helping identify resonance conditions and system impedance characteristics.

Digital Computer Simulations: These are used to model harmonic sources, simulate their impacts on system voltages and currents, and design harmonic filters. Simulations can help analyze harmonic penetration and compliance with standards.

Hand Calculations: While tedious and error-prone, manual calculations can be used for small networks to estimate harmonics based on known load characteristics.

Harmonic Indices Calculation: Analysts calculate various harmonic indices such as THD and compare them against standard limits to assess power quality compliance.

These methods provide a comprehensive approach to understanding and managing harmonics in power systems, ensuring that equipment operates efficiently and within regulatory standards.

Harmonic Mitigation

Best practices for designing and implementing harmonic mitigation systems involve a comprehensive approach that includes system analysis, component selection, and ongoing monitoring. Here are key strategies:

• System Analysis: Conduct a thorough analysis to identify sources of harmonics, types of loads, and levels of distortion. Use power quality analyzers to measure total harmonic distortion (THD) and determine the most effective mitigation solution23.
• Use of Filters: Use passive, active, or hybrid filters based on system requirements. Passive filters are cost-effective for specific harmonics, while active filters offer adaptability for dynamic conditions.

• Design Optimization: Optimize circuit layouts to minimize harmonic generation. Ensure balanced system design to prevent exacerbating harmonic distortion.
• Resonance Prevention: Detuned reactors form a series resonant circuit with capacitors, but their resonant frequency is intentionally set below the dominant harmonic frequencies (e.g., below the 5th harmonic).

This prevents resonance from occurring at these frequencies, which can amplify harmonic currents and cause equipment damage. By preventing resonance and harmonic amplification, detuned reactors protect capacitors, transformers, and other equipment from overheating, vibrations, and excessive wear, leading to longer equipment life and reduced maintenance costs.

 Best practices for designing and implementing harmonic mitigation systems involve a comprehensive approach that includes system analysis, component selection, and ongoing monitoring.