There are a large number of nonlinear, fluctuating and impulsive loads in the actual electric energy system, such as electric locomotives, semiconductor rectifiers, inverters, frequency converters, electrified railways, induction heating furnaces, electric arc furnaces, electric arc steelmaking furnaces, rolling mills, etc. These loads in industrial and domestic equipment cause waveform distortion (harmonic), three-phase imbalance, flicker, voltage fluctuation and asymmetry in the power grid, which seriously reduce the electric energy quality of the power grid. At the same time, the acceleration of wind farm construction in recent years also has some impact on electric energy quality. Precision electronic instruments controlled by computers and microprocessors are widely used in national economic enterprises, and are more and more sensitive to quality of electric energy supply. Therefore, higher requirements are put forward for electric energy quality, which makes problems of electric energy quality and their solutions gradually become the focus of research. At present, with the rapid development of the national economy, the scale of wind farm construction in northwest China is increasing, and the requirements of users for electric energy quality are also increasing day by day, which provides practical significance for the research of electric energy quality.
Through accurate monitoring and analysis of electric energy quality, we can measure the electric energy quality level in the power grid, analyze and judge the causes of various problems relating to electric energy quality to provide the basis for the improvement of electric energy quality and finally realize the improvement of electric energy quality in the power grid. The realization of electric energy monitoring
meets the requirements of electric energy users for electric energy monitoring and analysis, and realizes the functions of real-time data acquisition and online monitoring.
There are roughly three monitoring methods of electric energy quality in China: special measurement, regular or irregular monitoring and real-time online monitoring. Each monitoring method has its own advantages and disadvantages. According to the actual situation on site, economic bearing capacity and quality requirements of power grid and electric energy, appropriate monitoring methods should be selected.
Special measurement measures the influence of various interference loads or compensation equipment, such as electric arc furnace, rectifier equipment, capacitor bank, filter, etc. on various indexes of electric energy quality in the power grid before and after they are connected to the power grid, and determines whether they can be put into operation through comparison with relevant national standards. However, this kind of monitoring needs a clear target, a monitoring site and necessary conditions.
Regular or irregular monitoring aims at common electric energy interference sources, regular or irregular monitoring methods will be taken according to the size of the interference, harm degree and demand. Regular monitoring is mostly used for regular general survey of electric energy quality in the power grid. The main purpose is to understand the electric energy quality level of the whole network and the characteristics of interference sources. Irregular monitoring is to monitor and analyze the special problems of electric energy quality from electric energy users.
Online monitoring is also called continuous monitoring, whole process monitoring or daily monitoring. For large interference sources, such as steel mills and electrified railways, the voltage deviation, frequency deviation, harmonics, voltage fluctuation and flicker, three-phase imbalance and other indicators must be continuously tracked and monitored according to the electric energy quality standards. Due to the increasing number of grid users and higher requirements, online monitoring will be the future development direction. However, the monitoring requirements are getting higher and higher, and the cost of online monitoring is also gradually increasing. With the rapid progress of network communication technology and information technology, electric energy quality monitoring technology is developing in the direction of informatization and standardization in order to meet the needs of contemporary electric energy system operation.