Wideband Corona Current Sensors for Ultra High Voltage DC Transmission Lines Fill the Domestic Blank
In order to meet the growth of China's electricity load, improve the power grid structure, and implement the strategy of "West East Power Transmission, North South Mutual Supply, and National Networking", it is imperative to develop ultra-high voltage power grids. Due to its advantages such as low cost and low power loss, ultra-high voltage direct current transmission has unparalleled advantages in long-distance, large-capacity power transmission, and asynchronous interconnection of regional power grids, and has been vigorously developed in recent years.
The electromagnetic environment (such as audible noise, radio interference, and synthetic electric field) caused by the corona of ultra-high voltage DC lines not only restricts the selection of conductors and structural parameter design of transmission lines, but also often brings environmental protection issues. With the increasing requirements for environmental protection and energy conservation and consumption reduction of transmission lines, relying solely on the measurement and analysis of corona effects such as audible noise, radio interference, and corona loss to study the electromagnetic environment of transmission lines is far from meeting engineering needs. It is necessary to continue to start from the source of line corona discharge - broadband corona current and its correlation with corona effects, and conduct in-depth research on the problem of line corona discharge.
The traditional corona current measurement system has a low measurement bandwidth (usually below 2MHz), and its measurement performance is far from meeting the research needs of audible noise, radio interference, and corona loss in ultra-high voltage DC transmission lines with gradually increasing voltage levels. Therefore, it is necessary to conduct broadband measurement of corona current in ultra-high voltage DC transmission lines and study the broadband characteristics of corona current, Thus providing technical support for the precise control of the electromagnetic environment of ultra-high voltage DC lines in China.
The engineering design of ultra-high voltage DC lines and the study of the mechanism of wire corona characteristics both require testing and research on the high-frequency characteristics of the line corona current. However, the development of a wide frequency domain corona current sampling sensor has become a bottleneck in the research related to corona current. To measure the high-frequency characteristics of corona current during corona discharge on ultra-high voltage DC lines, the invention proposes a broadband corona current sampling resistance sensor. Through a series of technical improvement measures, a corona current sampling sensor with a measurement bandwidth of up to 30MHz is achieved in ultra-high voltage environments. Its core invention points mainly include:
The structure of evenly arranging the split resistance beam on the outer side of the insulation tube effectively reduces the electric field intensity on the surface of the sampling resistor, ensuring that it is free from corona discharge in an ultra-high voltage environment.
The sampling sensor used in this invention includes more than one set of low inductance split resistance beams, which are composed of several evenly distributed split resistors in parallel on the outer side of the insulating tube. Due to the use of a split resistance beam in the present invention and the installation of voltage equalizing rings at both ends, the field strength on the surface of the sampling sensor is greatly reduced, ensuring that the sensor will not experience corona on its surface after being connected in series to an ultra-high voltage line.
By reasonably configuring the electrical parameters of the split resistance beam and shielding ring, the ratio of resistance to capacitance at high frequencies is reduced, greatly increasing the measurement bandwidth. To reduce the surface electric field intensity at the end of the sensor and avoid corona discharge, it is necessary to install metal shielding rings at both ends of the split resistance beam, which is connected to the shielding rings at both ends. However, after installing the shielding ring, the distributed capacitance of the sensor is increased, which may cause the frequency response of the sensor to deteriorate. Therefore, it is necessary to reasonably configure the electrical parameters of the split resistor and shielding ring to reduce the ratio of resistance to capacitance at high frequencies and improve the measurement bandwidth of the signal.
Connecting multiple sets of split resistance beams in series makes range switching flexible and measurement more accurate.
According to the different corona states of the wires, the variation of corona current on the wires is significant. When studying the corona characteristics of wires, it is usually necessary to test corona currents ranging from microamperes to tens of milliamperes. Due to the use of multiple sets of split resistance beams connected in series, the invention can have multiple measurement ranges and can be flexibly switched through programs at the control end to measure corona currents in different amplitude ranges, thereby making the measurement results more accurate.
The reason why this invention can increase the measurement bandwidth of the corona current sensor from 2MHz to 30MHz in an ultra-high voltage environment lies in the adoption of a split resistance beam structure and its combination with metal shielding rings on both sides. This not only greatly improves the measurement bandwidth of the invented sensor, but also enables the sensing element to have no corona discharge in an ultra-high voltage environment. This invention can be widely applied in ultra-high voltage direct current environments at ± 1200kV, achieving accurate measurement of corona current in a wide frequency range in ultra-high voltage transmission lines.
This technology has been updated by the Information and Communication Branch of State Grid Corporation of China and evaluated by the Chinese Society of Electrical Engineering. Experts unanimously believe that the project has reached an international leading level in the broadband corona current sensing of ultra-high voltage DC lines.
We have implemented a corona current sampling sensor with a measurement bandwidth of up to 30MHz, filling the gap in broadband corona current measurement for ultra-high voltage DC lines at home and abroad, expanding the research scope of frequency in corona discharge and its effects, promoting in-depth research in this field, and enhancing China's voice in the international arena.
The research results on electromagnetic environment have been applied to the optimization design of pole spacing for ± 800kV DC lines in Xizhe and Hazheng, reducing the pole spacing by 2m. This has saved a lot of corridor resources and reduced a large number of house demolition, which is of great significance for environmental protection and social harmony. The research results on corona losses conducted provide important technical support for the selection of conductors for Hazheng ± 800kV DC lines. The 6 × 900mm2 wire changed to 6 × The 1000mm2 conductor reduces the average corona loss by nearly 1kW/km, saving nearly 10 million yuan annually, which is of great significance for energy conservation and emission reduction.
The project is mainly completed by China Electric Power Research Institute and Beijing University of Aeronautics and Astronautics. The team has been researching broadband corona current measurement technology for ultra-high voltage direct current transmission lines since 2009. Over the past three years, the sensor has been successfully developed and equipped on experimental sections and corona cages in the National Engineering Laboratory of ultra-high voltage technology. At present, we have obtained nearly 20 authorized patents and published more than 20 papers in this research field. We have successively won the China Electrical Engineering Invention Award, the State Grid Corporation of China Science and Technology Progress Award, and the Beijing Science and Technology Progress Award.
