AbstractIntroducing the hazards and types of harmonics, and analyzing the principles of active harmonic filters.
KeywordsHarmonics; Passive Filters; Active Filters
Introduction
Currently, many substation loads contain a significant amount of nonlinear loads, such as rectifiers, AC-DC variable frequency devices, steelmaking electric arc furnaces, electric locomotives, AC welders, and computer switching power supplies with electronic ballasts for fluorescent lights, which generate non-sinusoidal currents during operation. When harmonic currents flow through various impedance elements in the system, including generators, transmission lines, and transformers, they inevitably cause non-sinusoidal voltage drops, resulting in varying degrees of distortion in the voltage waveforms at different points within the AC system. The degree of voltage distortion depends on the relative ratio of load capacity to grid capacity and the impedance of the power supply system to harmonic frequencies. The distorted voltage then affects the current waveform drawn by the rectifiers from the system. Therefore, harmonic currents and harmonic voltages are produced and influenced by each other. Harmonics can have adverse effects on the normal operation of electrical equipment, so it is necessary to install active filters in the power supply lines to resolve harmonic issues.
Types of Adverse Effects Caused by Harmonics
1.1 Communication Interference
Due to harmonics generated by the non-linear load power supply system, static induction and electromagnetic induction occur in adjacent communication lines, resulting in adverse effects on the communication system.
Impact on Synchronous Generators 1.2
Synchronous generators in power systems, particularly those primarily driven by non-linear loads or supplying generation voltage directly to non-linear loads, are subject to significant adverse effects from higher harmonics. Harmonic currents cause additional losses and temperature rises, particularly in the stator and rotor sections, thereby reducing the rated output of the generator.
Impact of 1.3 Power Capacitors
Due to the inverse relationship between the reactance of capacitors and frequency, power capacitors are sensitive to harmonic voltages. Harmonic voltages accelerate the aging of the capacitor dielectric, increase the dielectric loss factor, and are prone to failure and reduced lifespan. Harmonic currents often cause capacitors to overload and experience unauthorized temperature rises. Capacitors may also experience dangerous resonances within the power system. In such cases, capacitors can become exponentially overloaded, resulting in abnormal fuse blowing and rendering the capacitors inoperable. Overvoltage is commonly observed during resonance in the resonant section.
Impact of Insulation on 1.4 Cable Lines
For cable lines, non-sinusoidal voltages accelerate insulation aging and increase leakage current; when parallel resonance overvoltage occurs, it may cause explosions and puncture the cable.
Impact on Transformers 1.5
Harmonic voltages increase the excitation current of transformers, degrade the frequency, and worsen their power factor. Harmonic amplification can cause abnormal sounds in the main transformer.
Impact on Measurement Instruments 1.6
High-order harmonics can cause errors in inductive active and reactive electricity meters, with the error increasing as the frequency rises, and all being negative errors. 1.7 Impact on relay protection automatic devices.
When harmonic voltage levels are excessively high, there is an increased error in the automatic voltage regulation of the power supply system. High-order harmonic currents in the negative sequence system have adverse effects on relay protection devices with negative sequence current filters. Harmonic currents can worsen and even disrupt the operation of motion devices using power lines as communication channels. High-order harmonics may cause pulse loss and damage to silicon-controlled rectifiers (SCRs) in pulse-width-phase control systems.
Due to these harmful effects of harmonics, it is necessary to adhere to national standards when designing and constructing substation for nonlinear loads.
Types of Harmonic Generation
Harmonic load current is generated by all nonlinear loads, which include the following types:
Switch-Mode Power Supply (SMPS)
(2) Electronic Fluorescent Ballasts
(3) Variable speed transmission device
Uninterruptible Power Supply (UPS)
(Magnetic Core Assembly)
Principles and Working Characteristics of Active Filters
3.1 Principle
The working principle of an active filter involves detecting harmonic currents from the compensation object, generating a compensating current of equal magnitude but opposite polarity by the compensation device to offset the harmonics produced by the original harmonic source, thereby ensuring that the grid current only contains the fundamental wave component. The core component is the harmonic current generator and the control system, which rely on digital signal processing (DSP) technology to control the fast insulated bipolar transistors (IGBTs).
3.2 System Composition
The Active Power Filter System is primarily composed of two major parts: the command current detection circuit and the compensation current generation circuit. The command current detection circuit's function is to isolate the harmonic current components and fundamental reactive current from the load current, then reverse their polarity to generate the command signal for the compensation current. The compensation current generation circuit calculates the triggering pulses for each switch device in the main circuit based on the generated compensation current, which are then applied to the main circuit via the drive circuit. This ensures that the source current only contains the fundamental active component, achieving the purpose of eliminating harmonics and performing reactive compensation. Based on the same principle, the power active filter can also compensate for the negative sequence current component in an unbalanced three-phase circuit.
3.3 Features
The active power filter, once operational, significantly suppresses harmonics in the power supply source, reducing the harmonic content to less than 5%. This results in a marked improvement in the waveform of harmonic currents flowing into the grid and the waveform of the grid voltage. The energy-saving effect is also notable, as no harmonic path needs to be established, and the device itself consumes very low energy.
The key feature of the active harmonic filter is its rapid dynamic tracking of varying harmonics, dynamically compensating for the harmonics of the load. It not only filters out higher-order harmonics but also compensates for the reactive power of the fundamental frequency, achieving consistency between the load's current waveform and the system's voltage waveform, thereby enabling a single device to perform multiple functions, making it an ideal device for harmonic control. Compared to passive harmonic filters, it boasts high controllability and rapid response characteristics, as well as the ability to track and compensate for various harmonics, automatically generating the required reactive power changes. Its characteristics are unaffected by the system and pose no threat of harmonic amplification, with a relatively small size and weight. As the active harmonic filter continues to be widely promoted and applied in China, it has brought about significant economic and social benefits.
4 Ankoray APF Active Power Filter Product Selection
DSP + FPGA control method, with short response time, full digital control algorithm, and stable operation.
(2) Multi-functional, capable of compensating both harmonic and reactive power, it can fully compensate for harmonics from the 2nd to the 51st order or selectively compensate for specific harmonic orders.
(3) Equipped with comprehensive bridge arm overcurrent protection, DC overvoltage protection, and device overtemperature protection functions.
(4) Modular design, compact size, easy installation, and convenient for expansion.
(5) Featuring a 7-inch color touch screen for parameter settings and control, it offers ease of use, user-friendly operation, and straightforward maintenance.
(6) Installed filter devices at the output end to reduce the impact of high-frequency ripple on the power system.
(7) Multi-machine parallel connection to achieve a higher level of current output.
4.2 Model Description
4.3 Size Specifications
4.4 Product实物展示
ANAPF Active Power Filter
5 Ankerai Smart Capacitor Product Selection
5.1 Product Overview
The AZC/AZCL series intelligent capacitors are the latest generation of reactive power compensation equipment designed for energy saving, reducing line losses, improving power factor, and enhancing power quality in 0.4kV, 50Hz low-voltage distribution systems. They consist of an intelligent measurement and control unit, a thyristor composite switch circuit, a line protection unit, and two common or one split common low-voltage power capacitors. They can replace conventional automatic reactive power compensation systems that are typically composed of fuses, composite switches, mechanical contactors, thermal relays, low-voltage power capacitors, indicator lights, and other components interconnected within a cabinet using wires. They feature a smaller size, lower power consumption, ease of maintenance, longer service life, and high reliability, meeting the higher demands of modern power grids for reactive power compensation.
The AZC/AZCL series intelligent capacitors feature a fixed LCD liquid crystal display that can display three-phase bus voltage, three-phase bus current, three-phase power factor, frequency, capacitor circuit count, switching status, active power, reactive power, total harmonic voltage distortion rate, and capacitor temperature. Equipped with an internal thyristor composite switch circuit, they automatically locate the optimal insertion (removal) points, achieving zero-crossing switching, and come with overvoltage protection, phase loss protection, over-harmonic protection, and over-temperature protection functions.
5.2 Model Description
AZC Series Smart Capacitor Selection
AZCL Series Intelligent Capacitor Selection
5.3 Product Physical Display
AZC Series Smart Capacitive Modules | AZCL Series Smart Capacitive Modules
Ankore Intelligent Capacitive Compensation Solution for Non-Active Power Compensation Device
6 Closing Remarks
Active filters, as one of the key technologies to enhance system economy, safety stability, and improve power supply quality, have seen rapid development worldwide. With China making certain advancements in both theoretical and experimental aspects of active filters, the large capacity rolling mills in the non-ferrous metal industry face significant harmonic parameter variations in each pass, making it difficult for passive filters to meet the working characteristics of these large-scale rolling mills. Therefore, the application of active filters in the non-ferrous metal industry's large-scale rolling mills holds unparalleled advantages, and as the technology matures and prices continually decrease, they will gradually gain widespread adoption.
Through the above analysis, the installation of active filters on the power bus of rolling mills in the non-ferrous metal industry will effectively address a series of issues caused by harmonics, enhance the quality of power supply to the system, and ensure the reliable and safe operation of equipment.
Reference:
Zhu Dandan. Application of Active Filters in the Color Industry[J]. Aluminum Processing, 2010(04): 46-47.
Ankorri Enterprise Microgrid Design and Application Manual, 2022.05 Edition.
