Xu Shuang Ankerui Electric Co., Ltd.    Jiading 201801 1 Introduction With the development of science and technology, a large number of electronic products are used, and a large number of harmonics are generated in the power grid. As designers need to understand the causes and hazards of harmonics, in order to better defense and governance, and improve power quality. In recent years, the electrical product industry has actively used new technologies for energy-saving and production needs, and has used a large number of non-linear load devices such as controllable inverter devices and variable frequency speed controllers. The harmonic problems it generates have a direct impact on the power quality of the utility grid, which has attracted widespread attention. 2 Causes and Effects of Harmonic Generation 2.1 Causes of Harmonics Harmonics in the power grid mainly refer to the harmonics of integral multiples of the power frequency (fundamental frequency) and the interharmonics of non-integer components of the power frequency, which are all important causes of power quality pollution in the power grid. According to the results of a large number of field tests, it was confirmed that the power transformer is also an important harmonic source of harmonics in the power system. Exciting current of power transformer, core saturation and asymmetry of the three-phase circuit and magnetic circuit cause the third harmonic component in the line voltage and line current of the transformer delta winding, especially when the load is low, with the voltage of the grid. As the voltage rises, the saturation of the transformer core increases and the harmonic content increases. With the commissioning of a large number of capacitive devices in the power grid, it has been found through on-site harmonic measurement that harmonics are not only zero-sequence components that can be looped by the transformer's delta winding, but affect the entire network, and provide normal operation of the capacitor device and the power grid. Bring influence and threats. In civil buildings, UPS power supply, electronic speed control equipment, energy-saving lamps and household appliances, computers, microwave ovens and other power electronic equipment and electrical equipment applications increased, and hospitals and other special occasions, such as radiation X-ray machine, CT machine, etc. Large-scale medical equipment and the like have caused harmonics of various types of non-linear loads to be injected into the power grid to increase day by day, causing greater and greater impacts on the power quality of power grids. Harmonic pollution is already serious in areas where these devices are used in a concentrated way, such as hospitals, shopping malls, residential areas, office buildings, and hotel apartments. The influence of harmonic pollution makes the quality of power significantly reduced. Therefore, the suppression and control of the harmonic pollution of power quality are inescapable. 2.2 Analysis of Harmonic Sources 2.2.1 Power Electronic Equipment Power electronic equipment mainly includes rectifiers, frequency converters, switching power supplies, static converters, thyristor systems, and other SCR control systems. As industrial and civilian power equipment is commonly used in such power electronic equipment and circuits, such as rectifying and frequency conversion circuits, the load characteristics are generally divided into inductive and capacitive. Single-phase rectifier circuit of inductive load is a current containing odd harmonics. Harmonic source. The capacitive load single-phase rectifier circuit, because the capacitor voltage will be fed back to the power supply through the rectifier, is a voltage-type harmonic source, the harmonic content and capacitance value of the size, the greater the capacitance, the greater the harmonic content. Since the harmonic source of the frequency conversion circuit adopts phase control, its harmonic components not only contain harmonics of integer multiples, but also interharmonics with non-integer multiples. 2.2.2 Saturable equipment Saturable equipment mainly includes transformers, motors, generators, etc. Saturable devices are non-linear devices. Compared with power electronic devices and arc devices, the harmonics of saturable devices can often ignore the harmonics in the case of saturation. 2.2.3 Electric arc furnace equipment and gas electric light source equipment 1 The non-linear effects of electric arc furnaces in the smelting of metals will generate a large number of harmonics 2 Gas light sources include fluorescent, neon, and halogen lamps. According to the volt-ampere characteristics of this kind of gas discharge light source. Its non-linear characteristics are very serious and contain negative volt-ampere characteristics. The gas luminaire works in series with an inductive ballast, and its integrated volt-ampere characteristics are no longer negative to function properly. Because the ballast's nonlinearity is quite serious, and its third harmonic content is above 20%, its characteristic is a symmetric function and contains only odd harmonics. All gas electric light source devices belong to the current source harmonic source. 2.3 Harmonic effects on all aspects 2.3.1 Impact on the Power Grid 1 Causes increase of power loss of power grid, shortened service life of equipment, malfunction of grounding protection function, abnormality of remote control function, overheating of lines and equipment, and especially third harmonic generation of very large neutral current, making the neutral line of distribution transformer The current even exceeds the value of the phase current, causing unsafe operation of the equipment. The influence of harmonics on the safety, stability, and reliability of the power grid also manifests itself in the possibility of causing the grid to resonate, causing normal power supply interruptions, expanding accidents, and cracking the power grid. 2 Cause partial or parallel resonance of substations, causing damage of voltage transformers and other equipment; causing additional harmonic losses to equipment and components in substation systems, causing heating of power transformers, power cables, motors and other equipment, damaging capacitors, and speeding up Insulation material aging; causing the time for the arc extinguishing of the circuit breaker to prolong, affecting the breaking capacity of the circuit breaker; causing relay protection of electronic components or automatic devices to malfunction; affecting the normal operation of electronic instruments and communication systems and reducing the communication quality; Increase the interference of nearby magnetic fields. 2.3.2 Impact on Electricity Safety 1 Fire effects. Some building fires have been proven to be related to harmonics of the power. At present, the application of switching power supplies in energy-saving lamps, dimmers, and electrical equipment is common and the intention is to save energy. However, these terminal equipments, as harmonic sources, are very harmful to the power grid. According to the determination of relevant departments, the neutral line current is very large, and some even exceed the line current, causing overheating to become a factor in the use of hotels, commercial buildings, internet cafes, computer rooms, and residential quarters where there are a large number of electrical equipment. Major fire hazards. 2 device impact. The pollution of power quality may affect the normal operation and operation of relay protection, computer systems, and precision machinery and equipment of precision manufacturing, and reduce the normal service life of the equipment, even causing malfunction of relay protection and causing unnecessary accidents. , resulting in varying degrees of impact and damage. 3 Communication effects. Harmonics are an important factor in the grid's interference with communication, mainly through electrostatic induction (capacitive coupling, voltage action) and electromagnetic induction (current action), and produce audio interference on the communication line. When the harmonic frequency is high, noise may occur, causing audio interference on the communication line, and may also trigger the telephone ringing in severe cases. Shielded cable communication can eliminate the influence of electrostatic induction, but it can not eliminate the electromagnetic induction interference. At the same time, for a distribution network with multiple neutral grounds, when the three-phase load is asymmetric, the zero-line current will cause interference to the reference potential shift in the communication system that uses the earth as the reference potential. 2.3.3 Impact on Various Electrical Equipment 1 Effect on power capacitors. Capacitors account for the largest proportion of grid reactive power deployment capacity, where user capacitors account for about two-thirds of all capacitors. Most of the design of these capacitors only take into account the amount of reactive power compensation, and do not consider the actual pollution of the power quality of the installation point. Therefore, when the power quality index of the operating point is low, some accidents are often caused, such as the failure of the compensation device, the reduction of the service life of the capacitor, the fusing of the capacitor protection fuse, and even the series-parallel resonance, which leads to the over-voltage and over-current of the harmonic of the capacitor. Causes the capacitor to explode. In addition, the user's capacitor management is still based on the assessment of the average power factor, the capacitor is rarely switched according to the actual operation of the power grid, or even vote only, intangible in the grid voltage has lost the adjustment margin, so that the voltage deviation, etc. Power quality indicators are difficult to control. 2 The impact on the transformer. Harmonic currents increase the copper loss of the transformer, causing local overheating, vibration, noise, and additional heating of the windings. The harmonic current contained in the transformer excitation current causes the harmonic current in the closing inrush current to be too large. This kind of harmonic current will pose a threat to the safe operation of the transformer under the condition of resonance. 3 Effect on synchronous generators. The user's negative sequence current and harmonic current injected into the synchronous generator in the system will generate additional losses, causing local heating of the generator and reducing the dielectric strength. At the same time, due to the generation of additional harmonic components in the output voltage waveform, torsional vibration occurs in the synchronous generator rotor of the load, which reduces its operating life. 4 impact on the circuit breaker. Harmonics will make the magnetic blow coils of some circuit breakers not work properly, and the interrupting ability of the circuit breakers will decrease, and the fault currents whose waveform distortion rate exceeds a certain limit cannot be interrupted. Harmonic frequency surge voltages may occur when the medium voltage circuit breaker cuts off currents. Rekindling causes the breaker contacts to burn. 5 The impact on the automatic control device. With the large-scale use of digital control technology, many precision loads impose higher requirements on the power quality indicators of the received power. The harm of power quality pollution to this type of equipment mainly includes three aspects: the introduction of distortion in the monitoring module of the equipment, the analysis and calculation of the interference, and the resulting erroneous output. In addition, it will cause irreversible damage to the hardware of the equipment, such as precision motors and switching power supplies. Interference load protection circuit, causing malfunction and so on. 3 Harmonics governance methods and measures In summary, due to the many effects and harms of harmonics on the power system and users, effective measures must be taken to suppress the harmonics in the power system. At present, there are two main governance measures at home and abroad. 3.1 Traditional Harmonic Suppression Methods - Passive Filters Power passive filter is composed of series reactors on the capacitor. Its advantages are simple structure, reliable operation, convenient maintenance, and in addition to filtering, it also has the function of reactive power compensation. The capacity can be designed to be very large, with active filters. Compared to the lower cost, it is widely used. However, the passive filter also has its disadvantages. On the one hand, it is unable to filter the dynamically changing harmonics; on the other hand, the filtering effect is generally only 50%-60%. 3.2 New Harmonic Suppression Method - Active Filter Active power filter is a new type of harmonic suppression and reactive power compensation device. It is different from the traditional passive filter (which only absorbs fixed-frequency harmonics). It is essentially a high-power waveform generator. Harmonic waves emitted by the harmonic source are sampled and phase-shifted by 180°, and then completely copied out and sent to the incoming point of the harmonic source. The harmonic amplitude generated by the copied harmonics and the harmonic source is equal and direction Instead, it follows the change in harmonics. In this way, the harmonics generated by the harmonic source are completely canceled. Active power filters can be divided into two categories according to the way they are connected to the power grid, namely series active filters and shunt active filters. In order to take advantage of active filters in recent years, serial hybrid and parallel hybrid active filters have been designed. Although the active filter has its outstanding characteristics in harmonic control, but because of the high power electronic devices that should be shipped, its high active loss, the overall cost is much higher than the passive filter, so in a large-capacity filter device It has not been widely adopted yet. With the development of microelectronic controllers and power semiconductor devices, the cost-effectiveness of active power filters will increase, and the price of capacitors and reactances for LC passive filters will increase, so active power The filter will be the main development direction of the harmonic suppression device in the future. 4 ANAPF Low Voltage Active Filter Application at Port Terminal The vigorous development of the port industry has led to the development of other industries, while the demand for electrical energy has also gradually increased. A large number of gas discharge electric light sources in the port , such as fluorescent lamps, high-pressure mercury lamps, high-pressure sodium lamps, and metal halide lamps , are very nonlinear in such light sources and have negative volt-ampere characteristics. With the development of power electronics technology, thyristor-powered DC systems or AC - AC variable frequency speed control systems are widely used in domestic ports in recent years , and the number has increased year by year. These power conversion devices and their electrical equipment are non-linear loads and are typical sources of harmonics. When they work, they not only absorb a large amount of impact reactive power to the power system, affect the stability of the voltage of the power grid, but also inject a large number of harmonic waves into the power grid, which seriously affects the power quality of the power grid. 4.1 Project Background  Since the commencement of operation of Baoshan Luokai Wharf, the loading and crane cranes at the port have been damaged for no apparent reason, the frequency converter has often been burned, and the belt scale measurement does not seem accurate, which has seriously affected the normal operation of the port and brought serious negative economic benefits. . The survey found that a large number of inverters are installed in the port distribution system. These inverters drive the drives so that the loading cranes move back and forth. The frequency converter is a typical harmonic source, generating a large number of harmonics, and the load capacity of such projects is usually relatively large. There is a very serious harmonic pollution on the AC side, and it is harmonics that cause problems in Luojing Terminal. . Because the terminal is equipped with a large number of loading cranes, the load fluctuation is relatively large, and the magnitude of harmonics is closely related to the load rate. When the load rate changes within a certain range, the harmonic current may be extremely high. In this case, the voltage of the system will be greatly distorted. This will seriously affect the normal operation of the motor, while also greatly shortening the life of the transformer. In addition, there are belt weighers and other loads in the power distribution system. The belt weighers are sensitive devices. The harmonics generated by the inverter will cause harmonic pollution to the belt weigher Control System through conduction, induction, etc., which in turn will cause the work of the belt weigher to fluctuate. The accuracy of metering, at the same time, has an adverse effect on the longevity and safe operation of the equipment, and also has an impact on the economic efficiency of the port. The schematic diagram of the frequency conversion power supply system of Baoshan Luojing Terminal is shown in Figure 1. Figure 1: Schematic diagram of variable frequency power supply system The power supply system at Baoshan Luojing Terminal contains a large number of inverters. The frequency converter is one of the more widely used devices in the industrial adjustment drive field. The main circuit of the frequency converter is generally composed of AC-DC-AC. The externally input power frequency power supply is converted into a DC power supply through the rectifier circuit, and then the capacitor filter and high-power transistor switching element are converted into variable-frequency AC power. In the rectifying circuit, the waveform of the input current is an irregular rectangular wave, and the waveform is decomposed into the fundamental wave and each harmonic wave according to the Fourier series. The number of harmonics is usually 6n±1th harmonic. Figure 2 shows the voltage and current waveforms of the frequency conversion power system of Luoshan Wharf in Baoshan. The voltage wave peak distortion is quite serious. Figure 5 shows that the three-phase voltage distortion rate exceeds 7%, which is greater than the 5% requirement specified in the national standard GB T14549-1993 "Power Quality Harmonics in Public Power Networks". Severe voltage distortion not only affects the life of equipment, but also may It caused an accident. The current waveform in FIG. 2 has basically not seen a sine wave but rather a typical M wave. Combined current harmonic content data in Figure 4 can be calculated A phase, B phase, C phase current value is 270A, 261.6A, 283.6A, harmonic current harmonics of three-phase current are more than 50%, consult the national standard GB T14549 -1993 "Power Quality Harmonics in Public Power Networks" The harmonic currents of this system have exceeded the harmonic current limits allowed by the reference short-circuit capacity. Comprehensive voltage and current data, the power quality of the system is very poor. 4.2 Governance Measures and Effects According to the specific conditions of the terminal, it aims to control harmonic pollution. Through targeted harmonic pollution control, it will reduce or even eliminate its adverse effects on the distribution system, ensure the normal operation of motors, transformers, cables, and other equipment, increase power factor, reduce reactive power loss, and prolong service life of equipment. Reliable power supply. According to the load distribution of Baoshan Luokai Wharf's variable frequency power system, the centralized compensation method is adopted for harmonic control. That is , a 100A ANAPF active filter is installed on the secondary side of the two transformers, that is, at the A and B busbars. . After the treatment, the harmonics were significantly improved, and the voltage harmonic distortion rate dropped from 7% to 2 % . The voltage waveform is shown in Figure 6. The waveform is almost a perfect sine wave. The current waveform after the control is shown in Fig. 7, the current harmonic distortion rate is reduced from 50% to 5%, and the harmonic distortion rate is greatly reduced. The quality of voltage and current harmonics has been in line with the provisions of GB T14549-1993 “Power Quality Harmonics in Public Power Gridsâ€. After the treatment, the disturbance of the sensitive devices such as the metering and sensors in the belt scale is reduced, and the problem of the jitter and the measurement inaccuracy of the belt scale is effectively solved. According to feedback, its own source filter put into operation so far, loading crane operation failure rate was significantly lower, the inverter failure rate down to 3-4 times per month on average once every six months; failure by the belt scale once a month No more failures. Greatly improve the stability and efficiency of loading crane operation. 4.3 ANAPF Active Filter Quotation and List of Major Components Model Number: ANAPF100-400/B Reference price: 120,000 yuan/set The main product details: No. Name Model number Quantity 1 APF electrical cabinet 800X600X2200 1 2 Converter APFCOV-CVT100 1 3 Controller APFMC-C100 1 4 Reactor APF-RE.(S)DG-100 1 5 Active current transformer LT208-S7 3 6 filter DL-1TH1 2 7 breaker CVS160FTM160D4P3D 1 8 Contactor LC1D150M7C 1 9 MCB NDM1-63C32 1 10 Intermediate relay MY4NAC 2 11 R type transformer R320-0.38/0.22 1 12 Harmonic Detector ACR350EGH 1 13 wire 16mm 2 Some 14 wire 4mm 2 Some 5 Conclusion To sum up, with the changes of the times, new things and new products have been continuously introduced, and the constant application of high and new technologies has led to more and more complicated electrical environments. This article only briefly described the harmonic pollution. It can be seen that although the harmonic control requires a certain amount of capital investment, in the long run, the economic benefits brought by the protection of the equipment are very obvious. The social benefits brought about by improvements in electricity safety are also significant. ã€references】 [1] Shanghai Ankerui Electric Co., Ltd. Product Manual. 2013.01. [2] Cha Huiqin 《The Necessity of Harmonic Control and Case Analysis》  About the Author: Xu Haiyan, female, undergraduate, Ankerui Electric Co., Ltd., the main research direction for the smart grid power distribution, Email: Mobile QQ "AAPF Active Power Filter Device Design and Application Atlas" (atlas number: ACR13CDX701) is edited by Ankerui Electric Co., Ltd. This atlas combines the characteristics of ANAPF active power filter device products, based on electrical design specifications, research Eliminating the problem of high-order harmonics in the power supply and distribution system to achieve the goal of improving the quality of power supply and ensuring the safe operation of the power system. The Atlas is applicable to the design and modification of harmonic suppression and comprehensive management of electrical equipment in industrial, civil, and public buildings in new construction, reconstruction, expansion, and technological transformation projects. If you need atlas, please provide your organization's name, department, address, zip code, contact person, contact telephone number, email address, fax 021-69155331, mail or QQ to Ankeru Xu cream engineer, Ankerui Electric will give you a free gift. . 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