Application areas:
Power system voltage harmonics, interharmonics, high frequency harmonics, etc.
solved problem:
With the development of new energy sources and the application of a large number of new technologies and new products in power systems, harmonic pollution in power systems is facing increasingly severe forms. Although photovoltaic power generation brings prospects for new energy development, harmonics generated by its grid-connected inverters cannot be ignored. The limited switching frequency of the frequency converter in wind power causes the wind turbine output current to be distorted and also has harmonic effects on the system. The application of a large number of new technologies, such as non-linear load electric vehicle charging stations, can cause a large amount of harmonics when the system is distorted after being connected to the system. In addition, the current high-speed development of electrified railways, although the AC-DC-AC locomotive has a good improvement in low-frequency harmonics, but more than 50 times higher than the higher frequency harmonics than other types of locomotives The resulting high-frequency harmonics not only have a serious impact on the power system, but also pose a hazard to the locomotive itself.
Accurate measurement of harmonic content and scientific analysis of harmonic effects not only provide a basis for further harmonic control, but also provide a guarantee for the harmonious development of power systems.
solution:
The harmonic detection method uses a conventional FFT to obtain the amplitude and frequency of each harmonic signal, and uses a windowing function to reduce the spectral leakage, and eliminates the error caused by the fence effect by interpolation. Overcoming the disadvantages of spectrum leakage and fence phenomenon in non-integer harmonic detection. In this paper, the Blackman window function is used to establish the harmonic analysis function in Matlab. The harmonics, interharmonics and high-frequency harmonics generated by the FLUKE6100A harmonic source are used as data acquisition tools by the ADLINK PCI-9846 high-speed digitizer. Experimental analysis of harmonics, interharmonics and high frequency harmonics, verifying the harmonic function and the feasibility and correctness of using PCI-9846 as an analytical acquisition tool. The PCI-9846's signal processing capability of up to 20MHz wide dynamic range input is fully utilized in processing high frequency harmonics in power systems.
Application of ADLINK PCI-9846 High Speed ​​Digitizer in Harmonic Detection
1, application background
1.1 Power system harmonics and division
Harmonic interference is typically generated by equipment with non-linear voltage or current characteristics. Harmonic problems in power systems caught the attention of the 1920s and 1930s, when voltage and current waveforms were distorted in Germany due to the use of static mercury arc converters. At present, the harmonic voltage source and current source of the power system can be divided into the following three types of equipment: 1 magnetic core equipment, such as transformers, electric motors, generators, etc.; 2 electric arc furnace, arc welding machine, high voltage discharge tube, etc.; 3 electronic equipment And power electronics.
In an actual grid system, due to the presence of a non-linear load, a non-sinusoidal current is formed when current flows through a load that is not linearly related to the applied voltage. This non-sinusoidal periodic waveform can be decomposed into a fundamental frequency sine wave plus a sine wave of many harmonic frequencies, and the harmonic frequency is an integral multiple of the fundamental frequency. Interharmonics, subharmonics, and high frequency harmonics are sometimes present in the power grid. Harmonics are actually an amount of interference that causes the grid to be "contaminated."
The low frequency range (0 to 9 kHz) is defined in Electromagnetic Compatibility EMC (Electro Magne TIc CompaTIbility). The harmonics, interharmonics, subharmonics, and high frequency harmonics are divided into the following tables.
Table 1 Harmonics and frequency range
1.2 Harmonic hazards
The hazards of harmonics are comprehensive and deep, such as:
1) The harm of harmonics to transformers, capacitor banks, circuits and rotating electrical machines in the power grid is mainly caused by equipment failure, additional loss, heat generation and the service life of the equipment.
2) Harmonics can cause malfunctions in the protection system and control circuit. The resonance caused by harmonics in the power grid will cause the harmonic voltage to rise and the harmonic current to increase, causing equipment damage and causing relay protection and misoperation of the control circuit. For example, the interference generated by harmonics on the basis of the negative sequence (fundamental wave) will affect various protection and automatic device systems with negative sequence filter as the starting component.
3) Harmonics can cause inaccuracies in the measurement and control instrument, which not only affects the accuracy of the measurement, but also causes serious interference to the control system.
4) The harmonics exceed a certain level, which not only affects the normal operation of the electronic equipment, but also causes damage to it. For example, harmonics can shorten the life of incandescent lamps and cause fluorescent lamp failure.
1.3 Harmonic detection method
The accuracy and dynamic response speed of harmonic detection are closely related to the detection method. The development direction of harmonic detection method is high precision, high speed and high real-time. The current common harmonic detection methods can be divided into:
1) Fourier transform-based harmonic detection methods, most of which use DFT or FFT to obtain the amplitude, frequency and phase of each harmonic signal. When the measurement time is an integer multiple of the signal period and satisfies the sampling theorem, the DFT and FFT detection accuracy is high, the implementation is simple, and the use is convenient. However, due to the large amount of calculation, the real-time performance is limited, and the detection of non-integer harmonics exists. In order to reduce spectrum leakage, a common method is to add a window function before the harmonic analysis operation.
2) Using artificial neural network detection methods, a variety of harmonic detection methods using artificial neural networks have been proposed. At present, many researches on artificial neural networks are simulation studies, and the research on hardware implementation is still a relatively weak link, and its practical value needs further development.
3) Wavelet analysis based harmonic detection method, wavelet analysis as an important tool for time domain analysis, overcomes the shortcomings of Fourier analysis in the frequency domain completely localized and completely non-localized in the time domain, in the frequency domain and time domain At the same time, it has locality, can calculate the frequency distribution at a certain time and decompose the spectral signals composed of different frequencies into signal blocks of different frequencies.
4) Harmonic detection method based on instantaneous reactive power is widely used in active power filter schemes, and its real-time performance is good, and the delay is small. For example, when detecting harmonic current, harmonics in the current of the detected object The composition and the difference in the filter will have different delays, but the delay will not exceed one power cycle. For the typical three-phase rectifier bridge harmonic source in the power grid, the detection delay is about 1/6 cycle, which has good real-time performance.
5) Adaptive harmonic detection method, good adaptive ability, good tracking and detection, high precision, but slow dynamic response. At present, the research on adaptive harmonic detection method is not only in software simulation, but also in hardware circuit. Going deeper and deeper.
6) The analog filter method, as an early method of harmonic current detection, is rarely used because of its difficulty in design, large error, sensitivity to grid frequency fluctuations and circuit component parameters. Commonly used analog filter methods include removing the fundamental component by a filter, obtaining a harmonic component or using a bandpass filter to obtain a fundamental component, and then subtracting the detected current to obtain a harmonic current component.
Hanukah candle /Chanukah Candle/Jewish candles for holiday use .small Spiral Candle and taper candles color popular in America and Isreal market .
there are 6 color in box , yellow red white green blue orannge color as your require ,
3.8gram/pc multi-color candle 44pcs/box 50box/ctn
7gram/pc multi-color candle 45pcs/pvc box 25box/ctn
shipment is very quickly ,in the 30days after get the depsoit .welcome to visit my factory
pls be free to contact with me .
Chanukah Candle
Chanukah Candle,Hand-Dipped Chanukah Candle,Colorful Chanukah Candles,Chanukah Candle Kits
Shijiazhuang Zhongya Candle Co,. Ltd. , https://www.zycandlefactory.com