Executive SummaryWith the extensive use of electronic devices, an increasing number of nonlinear loads are present, making harmonic pollution in corporate power grids a critical issue that cannot be overlooked. The adverse effects of harmonics degrade power quality, increase additional losses, reduce grid reliability, affect the normal operation of supply and demand equipment, and even damage devices, causing electrical faults. The discussion covered the generation of harmonics, followed by an analysis of their hazards, and finally, the study of harmonic suppression and detection.
Keywords:Harmonics; Detection; Hazards; Management
Introduction
As pharmaceutical companies expand, there is a significant increase in the application of various power electronic devices within the industry. Among them, rectifier units account for a large proportion. The required DC power for inverters, DC choppers, and other devices primarily comes from rectifier circuits. Common thyristor phase-controlled rectifier circuits or diode rectifier circuits are severe harmonic sources. Although the individual capacity of electrical equipment is small, their numbers are immense, and most contain switch-mode power supplies. The usage of various switch-mode power supplies and inverters is on the rise, along with harmonics generated by fluorescent lights, making harmonic pollution of the power supply increasingly prominent. Harmonic voltages and currents cause severe distortion of the power supply waveform, affecting the quality of power supply to electrical users. Harmonic issues within the power system are also becoming increasingly severe. Grid harmonics distort the waveforms of voltage and current, leading to numerous abnormal phenomena and faults in the company's power system and electrical equipment, causing significant harm and impact. Effective suppression of harmonics has become an important aspect of ensuring the safe operation of the company's power system.
2 Causes of Harmonic Generation
An ideal clean power supply system provides users with a constant frequency sine wave voltage. In simple circuits that only contain linear components (resistors, inductors, and capacitors), the current flowing through the circuit is directly proportional to the applied voltage, and the current is also a sine wave. In actual power supply systems, due to the presence of electrical equipment with nonlinear impedance characteristics (i.e., nonlinear loads), non-sinusoidal currents are formed when the current flowing through the circuit is not linearly related to the applied voltage. Any periodic waveform can be decomposed into a fundamental frequency sine wave plus a series of components that are integer multiples of the fundamental frequency, collectively referred to as harmonics. The ratio of the harmonic frequency to the fundamental frequency (n=fn/f1) is called the harmonic order. For example: the fundamental frequency is 50Hz, the second harmonic is 100Hz, and the third harmonic is 150Hz. It should be noted that the harmonics referred to in the power system are steady-state waveforms that are integer multiples of the fundamental frequency, and transient changes in the power grid, such as inrush currents, various disturbances, or faults causing overvoltage or undervoltage, do not fall under the category of harmonics.
The Impact of 3rd Harmonics on Enterprise Power System Equipment
The impact of power grid harmonics on systems and equipment is mainly reflected in several aspects.
Harmonics in transformers and motors increase core eddy current losses, harmonics current leads to higher copper losses, rising temperatures, and accelerated aging of insulation. This reduces efficiency and utilization rates, as well as shortens service life.
Under the influence of harmonic voltages, capacitors will experience additional power loss, accelerating the aging of the insulation medium. More seriously, a large amount of harmonic current can likely trigger parallel or series resonance between capacitors and other system components, resulting in amplification of a specific harmonic current and an increase in harmonic voltage. This dangerous harmonic overvoltage and overcurrent not only causes capacitors to overheat and fail but also damages all lines and equipment in the distribution circuit connected to the capacitors due to voltage flicker, overvoltage, and overload. Statistics show that more than 70% of harmonic faults occur in capacitor installations.
(3) For power cables and distribution lines, the increased frequency of harmonic currents causes a significant skin effect, leading to increased conductor resistance, greater line losses, enhanced heat generation, premature aging of insulation, and a higher likelihood of ground fault occurrences, which can form potential fire hazards. Additionally, the third harmonic significantly increases the N-line current in the three-phase balanced load.
High harmonic current content in the distribution circuit can reduce the circuit breaker's interrupting capacity. This is because, when the distorted current passes through zero, the rate of change of the arc current over time is greater than that of the AC sine current, and the recovery of the arc voltage is much faster, making the arc more likely to reignite. It has been proven that air electromagnetic circuit breakers cannot interrupt fault currents with waveform distortion rates exceeding 50% within their interrupting capacity range, which can also lead to damage to the circuit breaker.
(Harmonics cause interference and damage to relay protection and metering instrument signals in the power system.)
4. Utility System Analysis of Some Company
Our company's power system is divided into 6kV Phase I and 6kV Phase II. The main loads under each busbar are asynchronous motors and power transformers, with some synchronous motors as well. It is understood that synchronous motors are not used simultaneously with asynchronous motors; they are primarily for backup purposes when asynchronous motors are not in use. The parameters, quantities, and loads of the motors are shown in the system diagram.
Harmonic Test of Company 5's Product Conducted
The testing tool is the FULKE43B Power Quality Analyzer.
Test subjects were on the 6KVI busbar side. Field measured technical data is as follows:
The test subject is on the 6KVII busbar side. Field measured technical data is as follows:
The data in Tables 1 and 2 indicate that harmonic current exceeds the national standard by more than 3 times.
Company X's Governance Plan
Compensating capacitors are highly sensitive to harmonic voltages, which accelerate capacitor aging and reduce their lifespan. Harmonic currents can lead to overloading of capacitors, excessive temperature rise, and, worst of all, a rapid increase in current when the capacitor bank resonates with the system in parallel, causing circuit breakers to trip, fuses to melt, and capacitors to fail. To prevent parallel resonance, a series reactor is connected to the capacitors. The reactance rate is selected based on the harmonic frequency background. When the grid's background harmonics are 5th order or higher, a 4.5% to 6% reactance rate is recommended; for harmonics of 3rd order or higher, a 12% reactance rate is advisable.
6.1 Determination of Reactance Value K
(1) Harmonics are minimal in the system; selection is made only for limiting inrush current during closing.
K ranges from 0.5% to 1% to meet the requirements. It severely amplifies the 5th harmonic current and slightly amplifies the 3rd harmonic.
(2) When harmonic contents in the system cannot be ignored, investigate the background harmonic content of the power supply system and reasonably determine the K value. The configuration of reactance rate should make the harmonic impedance at the capacitor connection point inductive. When the grid background harmonics are 5th order or higher, a K value of 4.5% to 6% should be configured. Typically, the 5th harmonic is the largest, followed by the 7th, and the 3rd is smaller. Both domestically and internationally, K values of 4.5% to 6% are commonly used. Configuring a reactor with a K value of 6% effectively suppresses the 5th harmonic, but it also significantly amplifies the 3rd harmonic and resonance points at 204Hz, which is a significant margin from the 5th harmonic's frequency of 250Hz. Configuring a reactor with a K value of 4.5% slightly amplifies the 3rd harmonic, making it suitable for suppressing harmonics 5th order and higher while also minimizing the amplification of the 3rd harmonic. Its resonance point at 235Hz is relatively close to the 5th harmonic. When the grid background harmonics are 3rd order or higher, a series reactor with a K value of 12% should be configured. In the reactor-capacitor series circuit, the inductive reactance XLN of the reactor is proportional to the harmonic order; the capacitive reactance XCN of the capacitor is inversely proportional to the harmonic order. To suppress harmonics 5th order and higher, the resonance order of the series circuit for harmonics 5th order and higher should be less than 5. This way, for harmonics 5th order and higher, the reactor-capacitor series circuit is inductive, eliminating the conditions for parallel resonance; for the fundamental frequency, the reactor-capacitor series circuit is capacitive, maintaining the reactive power compensation effect.
6.2 Reactor Installation Location
Series reactors are identical in their function, whether installed on the power side or the neutral side, in terms of limiting inrush current and suppressing harmonics. When installed on the power side, the operating conditions are stringent due to the reactor's exposure to the impact of short-circuit currents and higher ground voltage (compared to the neutral point), necessitating higher dynamic and thermal stability. There is also a concern about core saturation in iron-core reactors. When installed on the neutral side, the requirements for the reactor are relatively lower, as it generally does not face the impact of short-circuit currents, and there are no special requirements for dynamic and thermal stability. The ground voltage it withstands is lower. It is evident that it lacks the ability to resist short-circuit current impacts compared to installation on the power side.
7. Efficiency Analysis
(1) Enhance Power Quality. Our company's grid purification device comprehensively improves the quality of electrical power, filtering out grid harmonics, compensating for reactive power, preventing grid series-parallel resonance, and safeguarding against voltage fluctuations and flickers. This increases the reliability of equipment operation, reduces the accident rate, and minimizes the costs and time for electrical equipment maintenance.
(2) Reduce power loss. By compensating for harmonic and reactive currents, the current in transformers and transmission lines is reduced, resulting in lower losses for both and energy savings.
(3) Enhanced power supply capacity. After harmonic compensation, the power factor increased from 0.8 to 0.94, resulting in significantly reduced harmonic currents, nearly zero, thus improving the transformer's power supply capacity. The wastewater undergoes direct and indirect electrochemical processes within the reactor, achieving the oxidation and decomposition of organic pollutants. The bottom of the electrocatalytic reactor is exposed to a small amount of ozone, which effectively enhances the reaction efficiency.
The γ-Al2O3 particles are filled in the ozone catalytic oxidation reactor tower, serving as carriers with various transition metal oxides such as Mn, Cu, and V catalysts attached to their surfaces. Ozone enters the reactor tower along with wastewater from the bottom of the reactor, forming a multiphase catalytic oxidation system. The catalysts in the system are non-leachable, and ozone can be converted into ·OH under the action of the catalysts. Through the oxidation of ·OH and the direct oxidation of O3, organic matter is efficiently decomposed.
The process combination boasts strong oxidative capacity and excellent synergistic effects, providing an effective method for the pretreatment of pharmaceutical wastewater. Ozone is generated through high-voltage discharge, so the second-stage process equipment consumes only electrical power, eliminating the need for additional chemical reagents in the treatment process and preventing secondary pollution. The equipment is highly controllable and easy to operate, particularly suitable for the pretreatment of intermittent discharge, high salinity, low pH, refractory, and high-concentration pharmaceutical wastewater, making it an environmentally friendly technology.
8Ankore APF Active Power Filter Product Selection
DSP+FPGA control method, short response time, all-digital control algorithm, stable operation.
(2) Multi-functional, capable of compensating harmonics and reactive power simultaneously; it can provide full compensation for harmonics from the 2nd to the 51st order or target specific harmonic orders for compensation.
(3) Features 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) Equipped with a 7-inch color touch screen for parameter settings and control, offering ease of use, simple operation, and maintenance.
(6) Added filtering devices at the output end to reduce the impact of high-frequency ripple on the power system.
(7) Parallel multi-machine configuration to achieve a higher level of current output.
(8) Features proprietary patented technology.
8.2 Model Description
8.3 Size Description
8.4 Product Showcase
ANAPF Active Noise Attenuation Filter
9 Ankeray Smart Capacitor Product Selection
9.1 Product Overview
The AZC/AZCL series intelligent capacitors are the latest generation of reactive power compensation equipment designed for 0.4kV, 50Hz low-voltage distribution systems to save energy, reduce line losses, improve power factor, and enhance power quality. They consist of an intelligent measurement and control unit, a thyristor composite switch circuit, a line protection unit, and two common compensation or one separate compensation 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. These capacitors feature a smaller size, lower power consumption, easy maintenance, longer lifespan, and high reliability, meeting the higher requirements of modern power grids for reactive power compensation.
The AZC/AZCL series intelligent capacitors feature a fixed-type LCD liquid crystal display that can show 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. Through an internal thyristor composite switch circuit, they automatically find the optimal insertion (removal) point, achieving zero-crossing switching, and are equipped with overvoltage protection, phase-loss protection, over-harmonic protection, and over-temperature protection.
9.2 Model Description
AZC Series Intelligent Capacitor Selection
AZCL Series Smart Capacitor Selection
9.3 Product Showcase
AZC Series Intelligent Capacitive Modules | AZCL Series Intelligent Capacitive Modules
Ankore's Intelligent Capacitor Solution for Reactive Power Compensation Device
Reference:
Weng Chaoming. Detection and Management of Harmonics in the Power Grid of Pharmaceutical Enterprises[J]. Medical Engineering Design, 2011, 32(02): 58-60.
Ankorri Enterprise Microgrid Design and Application Manual, 2022.05 Edition
Author Bio
Li Xuewei, female, currently employed at Ankelei Electrical Co., Ltd. Mobile: 178-2173-3155 (WeChat same number), QQ: 2881346390, Email: 2881346390@qq.com
