Xu Shuang Ankerui Electric Co., Ltd.    Jiading 201801 1 Introduction In the LED large screen, multi-power distributed switching power supply has been widely used, and the harmonic components generated by it have an increasingly serious impact on power grids and electrical equipment. How to suppress harmonic components has become a concern. Switching power supplies generally use high-power semiconductor devices as switching elements, control the switches according to certain rules, and adjust the duty cycle to adjust the output voltage. The switching power supply is generally composed of a rectifier and a filter capacitor, and the AC input voltage is converted into a DC output voltage after entering a filter, a rectifier, and a filter capacitor. Nowadays, switching power supplies are gradually being developed to high frequency, high reliability, low power consumption, low noise, anti-jamming and modularization. 2, LED display harmonics cause The LED needs low-voltage DC drive, so a large number of display projects use switching power supply to provide the drive for the display module. In order to reduce the loss of low-voltage direct current in various transmission links, the display panel distribution generally uses a large number of low-power switching power supply modules and is configured as a distributed local low-voltage DC power supply mode. This realization method solves the problem of low-voltage transmission loss, but it brings problems such as harmonic pollution and excessive midline current. The reasons are: The switching power supply is a typical harmonic source. Its harmonic content is very high and its waveform is an intermittent spike. Since the generally used switching power supply has a small capacity (a typical case is the power supply of a laptop), it does not attract sufficient attention. However, if a large number of switching power supplies operate at the same time, the harmonics generated by them will not be ignored. If they are not dealt with, they may cause pollution to the power supply network and cause unpredictable damage to other devices in the same network. For a conventional three-phase balanced load, the normal current of the neutral line is generally less than 30 % of the phase current . No matter how the load distribution is configured on the display screen system, instantaneous three-phase imbalance will eventually occur due to changes in the display screen. In addition to the effects of harmonic currents, the zero line current can reach 280 % of the phase current . 3, LED display harmonic harm Excessive harmonics cause excessive current in the neutral conductor. Excessive current in the neutral conductor is a serious fire hazard. There is no overcurrent protection device on the zero line, unlike the fuses on the phase line, which can be cut off when the current is too high. Current. When the current on the neutral line is too large, it can only allow its temperature to rise, accelerating the aging of the cable, and even cause a fire. Not only for harmonic current harmonics, and because the harmonic current impact on power supply voltage contain harmonics, voltage waveform odd change will make serious and may result in adverse effects on other sensitive electrical equipment, and even make it work properly with Related legal liability problems, such as the network server of a company in the same building, caused a sudden power outage and caused losses. 4. Application of ANAPF Low Voltage Active Filter in LED Display Place a large outdoor LED display, the display power supply system of distributed switching power supply 850 30OW parallel operation, the total power of a total of 250kw. Switching power supply is a typical harmonic source. It has the characteristics of high current harmonic distortion, large harmonic content, wide harmonic spectrum, capacitive load, and low power factor. When a large number of switching power supplies are used in a centralized manner, the neutral line current is too high, the power factor is low, and the current harmonic distortion rate is high, which affects the normal operation of the LED display. 4.1 Harmonic Control Scheme Based on the characteristics of the site, an ANAPF -type active power filter is installed in parallel . The equipment parameters are as follows: Wiring Three-phase three-wire or three-phase four-wire Access voltage 3×380V ±10% Access frequency 50Hz ±2% Dynamic compensation response time Dynamic response < 4ms , full response time < 20ms ; On-off level 10kHz Harmonic compensation times 2-21 times Type of protection DC over-voltage IGBT over-current device temperature protection Overload protection Automatic current limit in the set value, no overload occurs cooling method Smart air cooling noise < 65db ( in the cabinet and operating in the rated state ) Working temperature -10 °C to +45 °C Working environment humidity < 85% RH non-condensing Installation occasion Indoor installation Altitude ≤1000m (for derating at higher altitudes) Incoming and outgoing ways Down in and out Protection level IP21 Intelligent communication interface RS485/MODBUS-RTU Remote monitoring Optional Weight (kg) Three-phase four-wire Three-phase three-wire 30A , 50A 75A , 100A 30A , 50A 75A , 100A 280 360 240 290 4. 2 harmonic current estimation of ANAPF active filter device Harmonics are generated by non-linear devices, and the actual operating conditions of each device are different. Therefore, the actual harmonic current needs to be measured with special equipment. Considering the technical and economical performance of the equipment, the harmonic compensation current designed for the harmonic control device should be slightly larger than the system harmonic current. Because the measurement and calculation of the harmonic current itself are more complicated, and it is often difficult to collect enough harmonic data in use of the electrical equipment during design, the harmonic current can be estimated according to the following formula. Among them, K1 is the load ratio: that is, the ratio of the load to the rated capacity of the transformer, usually 0.7-0.8; K2 is the harmonic coefficient, which varies according to the system situation; ST is the rated capacity of the transformer in kVA; US is the low voltage system voltage, which generally takes 0.4. Based on the estimated values, a 100A ANAPF active filter was selected for harmonic control. 4. 3 ANAPF active filter input before and after comparison 4. 3.1 ANAPF active filter when not mounted LED screen control switchgear line-side power quality data When the active filter is not installed , the LED screen controls the maximum total harmonic current content on the incoming side of the switchgear cabinet 98.4% , the total harmonic voltage distortion ratio 8.4% , and the total line harmonic distortion rate 1724.3% . Among them, the 3rd harmonic is the maximum harmonic current , A phase 41.8A , B phase 41.7A , C phase 38A , neutral line current 122.2A , including harmonic power factor 0.68 , the total harmonic voltage is seriously beyond the national standard 380V low voltage side harmonic THDu wave voltage distortion value of ≤5% requirement. 3 more severe over standard abroad harmonic voltage 380V low voltage side of the odd-order harmonic distortion THD≤4% requirement. 4. 3 .2  After the installation of active filter device , the LED screen controls the incoming line power quality data of the switchgear After the active filter was put into ANAPF LED screen control switchgear line-side maximum total current harmonic content is reduced to 51% total harmonic voltage distortion to 3.1% neutral 94.1% total harmonic distortion. The 3rd harmonic current A phase 1.4A , B phase 1.1A , C phase 1.8A , neutral current 9.8A , including harmonic power factor increased to 0.81 . THDu total harmonic voltage distortion value to 3.3%. 3rd harmonic voltage drop below the national standard 380V low voltage side of the odd-order harmonic distortion THD≤4% requirement. From the above figure, we can see that the ANAPF active filter protects the safety, stability, and economic operation of the LED power supply system, prevents misoperation of the over-current quick-break protection, and is conducive to the safe and stable operation of the power grid and the system. 5, ANAPF low voltage active filter quotes and major components list 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 6. Conclusion As the size of the display screen becomes larger, harmonic pollution caused by screen engineering on the grid has become a problem that cannot be ignored. Various hazards brought about by harmonics have already appeared, and the resulting grid operation accidents and legal responsibilities may occur at any time. This article analyzes the characteristics and hazards of harmonics in LED display screens, and analyzes the situation before and after the input of active power filters through actual application cases. It also shows that the harmonic filter treatment of active filters is an effective means to improve the quality of power supply. First, the generated harmonics can be controlled within the minimum range to achieve scientific and rational use of electricity, suppress grid pollution, improve power quality, and ensure the safe operation of equipment. References : [1] Wang Keliang, Qi Shizun, Chen Jian. Design of Switching Power Supply [ J ] . Electronic Components Applications, 2004, 6 (3): 17-19. [2] The application of three-phase four-wire active filter in the harmonic treatment of LED displays of the National Grid Museum of the Shanghai World Expo. [3] Ancorui Electric Co., Ltd. Product Manual. 2013.01. About the Author: Xu Shuang, 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. . Corrugated Roof Roll Forming Machine is one type the roofing sheet machine, it is another type which are widely used in house building area. For this Kind machine,we have several types like double layer roofing sheet machine, single layer roofing sheet machine and glazed tile Roofing Sheet Roll Forming Machine. 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