The industrial revolution changed life with technology, notably electrical power globally distributed by utilities. Today, power quality is essential for constant equipment operation, demanding glitch-free, stable power for domestic and industrial users. Utilities mandate high-quality equipment to prevent system power issues.
Power electronics-based devices have significantly contributed to fuel and power savings but have also introduced harmonics, leading to polluted voltages. Both commercial and domestic users employ these devices, which draw harmonic currents. As a result, ensuring a clean power supply has become a mutual interest for both users and utilities.
Harmonics have long been a critical topic within the power quality domain. Various international organizations, including IEEE, IET, and IEC, have established design standards to maintain harmonically free power supplies.
Manage power systems require utilities to manage harmonics at their origin to prevent grid instability.A comprehensive approach to harmonics control involves three key stages:
1. Identification of harmonic sources
2. Measurement of harmonic levels
3. Implementation of purging techniques
Utilities' R&D departments are researching to keep harmonic levels within allowed limits. Key research areas include:
Regulatory bodies focus on designing and implementing standards for harmonics control. These methods include:
This chapter aims to explain the sources of harmonic generation, their identification, measurement, and purging/suppression techniques. It aims to provide value to all electrical engineers, particularly utility engineers.
In electrical power engineering, harmonics refer to sinusoidal waveforms that are multiples of the system frequency. The harmonics of a system can be description as below.
Harmonic divided into positive, negative, and zero sequences. Positive sequence harmonics vary with the fundamental frequency, while negative sequence ones oppose it. Zero sequence harmonics are unaffected by the fundamental frequency.
Phasor direction is critical, especially in motors. Positive sequence harmonics drive motors correctly, while negative ones reduce torque. Examples include 7th, 13th, and 19th for positive sequence, 5th, 11th, and 17th for negative, and 3rd, 9th, and 15th for zero sequence.
Utilities focus on harmonics up to the 11th order due to decreasing amplitude. Managing these is crucial for power quality and system reliability.
Harmonics in electrical networks are produced by various sources, including:
Voltage distortions from AC generators occur due to uneven magnetic fields.
In large power systems, maintaining a smooth output from the generator is vital. However, any deviations in the circuit can lead to harmonics in the current flow. Also, harmonics can originate from the iron cores in transformers, which have a non-linear magnetic behavior.
Managing these harmonic sources is essential for maintaining power quality, ensuring the efficiency and reliability of electrical systems, and preventing potential damage to equipment.
Harmonic frequencies in electrical systems can lead to several issues:
· Resonant Conditions: Harmonics can create resonant conditions when combined with power factor correction capacitors.
· Increased Losses: System elements, including transformers and generating plants, experience increased losses.
· Insulation Aging: Harmonics accelerate the aging of insulation materials.
· Communication Interference: Harmonics can interrupt communication systems.
· False Tripping: Circuit breakers may experience false tripping due to harmonics.
· Neutral Wire Currents: Large currents can flow in neutral wires, causing potential safety hazards.
Harmonic identification in AC power networks led to standards by IEEE, IEC, and IET for monitoring and evaluation. These standards help maintain power quality, with modern AI techniques aiding in improving and enforcing these regulations globally.
In a harmonically polluted environment, identifying the best measurement point is challenging. Modern electronics contribute to widespread harmonics, with load profiles varying throughout the day. Accurate harmonic identification requires power quality analyzers or digital oscilloscopes for Fast Fourier Transform (FFT). IEEE Standard 519-1992 outlines procedures for harmonic measurements, but utilities must maintain precise logs for accurate monitoring and mitigation.
• Power Quality Analyser
• Instrument transformers based transducers (CT and PT)
Active Power Filters (APFs) use power electronics to mitigate harmonic distortions from non-linear loads. They focus on developing control algorithms and load current analysis.
Active Power Filters (APFs) are crucial for improving low-voltage power quality, two type as below:
• series active filters
• shunt active filters
Shunt active filters, or parallel filters, counteract harmonic distortions in AC networks caused by non-linear loads. They act as a current source in parallel with the load, detecting harmonics with micro sensors and using IGBTs.
This chapter discusses basic power quality issues, covering sources of harmonics and their effects on electrical components. It discusses regulatory standards for harmonic control and effective measurement techniques. Highlighted are strategies for harmonics mitigation, including the innovative use of Active Harmonic Filters (APFs).
APFs are pivotal solutions for maintaining high-quality power, enhancing system reliability, and optimizing power efficiency.
Any interest of APF, welcome contact: sales@yt-electric.com
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