UHVDC Converter Station Research Articles

Design of Secondary Circuit Visualization System for UHVDC Converter Stations

For the problems of complicated work content and error-prone workload of secondary circuits, a three-dimensional visualization method is proposed for the visualization and management of the physical circuits of the control and protection system of the converter station based on digital twin technology. The system can be used to improve the work efficiency of operation and maintenance personnel by constructing a secondary circuit information data model, generating corresponding data through artificial intelligence image recognition and manual review of secondary circuit drawings and schematics, and performing accurate corresponding circuit data analysis and 3D visualization management of the secondary physical circuits of control and security equipment, which can visualize the circuit information of control and security equipment in the station from outside to inside at multiple levels and multiple dimensions.

Current and temperature-rise effect of contact condition for connection terminals in UHVDC converter stations

The heating phenomenon of connector terminals in converter stations has become increasingly common, it has become a serious safety hazared affecting the operation of UHV lines. This paper determined the overlapping model of Al plate-Al plate based on the heating phenomenon of connector terminals in converter stations, conducted the tests which included disassembly and assembly contact surface roughness impact test, pressing force impact test, operation impact test, electric composite grease impact test, anti-loosening measure impact test. Analyzed the main influencing factors of current and temperature-rise for connector terminals heating, and analyzed the influence rule of each factor for current and temperature-rise of connector terminals. Test shows that: bolt tightening torque and electric composite grease was the main influencing factors for current and temperature-rise of connector terminals, and bolt tightening moment was the first main factor, bolt looseness and the performance degradation of electric composite grease directly causes an increase in the contact resistance and temperature rise level of the connector terminals.

Analysis of an Abnormal Faults of UHV DC Low-end YD-A Phase Converter Oil Chromatography

The article introduces an abnormal malfunction of YD-A converter oil chromatogram at the low end of UHVDC converter station, through oil chromatography data, ultrasonic positioning, on-site feeding, returning to plant disassembly and simulation calculation, which confirmed that the breakage of the isopotential of the converter electrostatic plate is the cause of the abnormal oil chromatogram and put forward corresponding suggestions and measures.

Parameter setting method of coordinated control between synchronous condenser and DC system based on dynamic reactive power optimization

It is of great significance for improving the safety and stability of the system to realize the coordinated and optimal control between synchronous condenser and DC system in UHVDC converter station. However, the existing dynamic reactive power optimization methods emphasize that the two systems can be scheduled uniformly, which are independent in actual engineering. Therefore, an area-diagram strategy for synchronous condenser and a dividing-stage strategy of reactive power exchange for AC/DC system are proposed here. Then, the setting methods of control parameters for the two systems based on dynamic reactive power optimization are proposed. The work of this paper fully considers the abilities and requirements of the two systems. Taking an UHVDC converter station in Northeast China as an example, the effectiveness of the proposed method is analysed. The simulation results show that the proposed method can effectively reduce the operation times of reactive power compensation devices and improve the operation level of system voltage.

Research on Influencing Factors of Current-carrying Temperature Rise on Connector Terminal of Current Circuit in UHVDC Converter Station

Relying on the high current temperature rise test, starting from three aspects of different materials, different structural strengths, and different contact conditions, the research on the current-carrying-temperature rise characteristics of the joint terminals of ±800kV UHVDC converter stations under different conditions is carried out. The results show that, for joint terminals of the same structure type and contact area, the difference in resistivity of joint terminals of different materials has a significant impact on the temperature rise level. When the material is the same, the temperature rise level can be reduced to a certain extent after the silver (tin) layer is added to the contact surface of the terminal. When the contact resistance of the joint terminal and the current density are the same, after increasing the contact area, the temperature rise and decrease level of the aluminum alloy plate lap type joint terminal is significantly better than other types of joint terminals. The contact resistance and temperature rise of the joint terminal decrease with the increase of the bolt tightening torque, and become stable when it reaches more than 80%. When the bolt tightening torque reaches more than 90%, the surface finish of the contact surface has no obvious effect on the contact resistance of the joint terminal. By controlling the material properties, structural strength, contact conditions, significantly reduces the temperature rise of the level of the joint terminal, effectively ensuring the safety ±800kV UHVDC converter station stable operation.

Research on differentiated quality control strategy of UHV converter transformer based on economic sensitivity analysis

±800kV converter transformer is the most difficult and valuable equipment in UHVDC converter station. The total price of converter transformer in a single project is up to RMB 4.9 billion. The converter transformer connects the AC power grid and the converter valve hall, which is the hub of DC transmission. It realizes the electrical isolation, power exchange, voltage matching and on load regulation of AC / DC system through electromagnetic induction. The cost and quality performance of UHV converter transformer also determine the economy and reliability of power system operation. The purpose of this paper is to ± Taking 800 kV converter transformer as the research object, through a large number of investigation and field investigation, the establishment of the ± Procurement cost estimation model of 800 kV converter transformer. In this study, through exploring the cost characteristics and quality characteristics of the main materials and components of the transformer, the concepts of cost sensitivity and quality sensitivity are proposed, and the four quadrant matrix analysis method is used to analyse the cost and quality control of the transformer, and then the differentiated quality control strategy is formulated. It can guide the quality grading control of converter transformer in engineering, and realize the collaborative improvement of power equipment economy and reliability.

Automatic Voltage Control of Large-scale Synchronous Condensers in UHV-DC Converter Station

Large-scale synchronous condenser can provide a powerful dynamic reactive power for the Ultra high-voltage (UHV) Direct Current (DC) transmission system. The dynamic characteristics of synchronous condenser ensure the reactive power support capability in the case of grid fault. In this paper, the control strategy and deployment of the synchronous condensers in East China Power Grid are presented. Taking converter station as an example, this paper introduces the main architecture of automatic voltage control (AVC) system, and the relationship between host computers and slave computers. In the substation, it describes the mechanism of several control modes, and designs the on-site test scheme of the control modes. After on-site testing, the correct operation of the large-scale synchronous condensers can be guaranteed.

The Electromagnetic Environment Analysis of Transmission Engineering in UHVDC Converter Station Based on Computer

UHVDC conveyance lines and unique advantages play a very special role in the construction of UHV power grid strategy. However, people gradually found that its related electromagnetism condition has become an important factor limiting its future development. At present, the problem of electromagnetic discharge in the living room and the electromagnetic discharge in the living room have aroused the attention of the experts[1]. First, this paper briefly describes the characteristics of UHVDC conveyance technique and the support of main equipment. Then, this paper describes the electromagnetic environment analysis of the UHV DC converter station transmission project based on the computer. Finally, the conclusion is drawn.

Computer Simulation Analysis and Control of Vibration and Noise in UHVDC Converter Station

In recent years, the progress speed of UHVDC converter station power grid is obvious. Although China’s power grid research started relatively late, we still made a lot of achievements. However, in the process of research, experts found that the noise in the living room of UHV DC converter station is very serious to people[1]. At present, the harm of audible noise has become an urgent problem. It is related to the maintenance of physical and mental health and the improvement of work efficiency of nearby residents and station staff. More seriously, it may affect the safety of the use of the grid. According to the research of scholars, the vibration of capacitor is the main reason of noise. In this paper, through the computer simulation analysis of UHV converter station vibration and noise, the final conclusion is obtained.

Research on new blast and fire stopping system of valve hall for UHVDC converter stations

In this paper, a new blast and fire stopping system of valve hall for UHVDC converter station is proposed. With the hydrocarbon temperature rise curve, the fire resistance test of a 1.4m×1.8m sample was carried out, a numerical model for blast resistant analysis of the firestop structure was established, and the blast resistant performances of the original firestop structure and the new structure were calculated. The results show that the new fire and blast stopping system proposed in this paper has a fire endurance time limit of more than 4 hours with the hydrocarbon heating curve. At the same time, compared with the original system, the blast resistant capability of the new firestop structure is greatly improved.

Dynamic Reactive Power Coordination Control Method for UHVDC Converter Station

In recent years, UHVDC transmission has developed rapidly. However, large-capacity DC converters generally use semi-controlled devices. The receiving converter station consumes a large amount of reactive power, which is easy to change when the AC bus voltage drops. The commutation failure happened, and more reactive power is absorbed from the AC system, which threatens the stability of the bus voltage. In order to study the dynamic reactive power coordination control strategy of UHVDC converter station, this paper compares the commonly used reactive power compensation equipment, and points out that synchronous condenser (SC) has significant advantages in reactive power regulation. This paper proposes a DC control system and SC coordination control scheme, and simulates the strategy through the electromagnetic transient simulation software PSCAD. The simulation shows that the synchronous condenser can provide continuously adjustable dynamic reactive power support during the change of the system switching filter, avoiding the risk of grid voltage drop exceeding the limit and improving the stability of the AC bus voltage.

Research on Key Technical Parameters of 1100kV Live Tank Circuit Breaker for UHVDC Converter Station

Many of UHVDC transmission projects planned and under construction are hierarchical connected to 500kV and 1000kV AC grid in China. Live tank circuit breakers are selected for switching 1000kV filters. During the development of 1100kV live tank circuit breakers, the closing inrush current and transient recovery voltage are key factors for structure of extinguishing chamber of circuit breakers. In this paper, the above factors are analyzed by simulation, and key technical parameters of 1100kV live tank circuit breakers for UHVDC converter station are proposed.

Improved Control Strategy for AC-Filters Switching in UHVDC Converter Station

The AC-filter configuration, reactive power consumption, reactive power control function, switching and replacement strategy in SHANSHAN UHVDC converter station are introduced in detail. The various types of AC filters in the converter station are evenly configured in the large groups of filters based on their quantity. And the related types of filters within a large group are usually switched preferentially. The problem of this switching strategy that may cause large impact on the AC system and long reactive power recovery time during the large group of AC filter bus lines fault are analyzed. Then an improved strategy that the needed filters with same type are equally switched on the large AC-filter group is proposed. The proposed strategy can effectively reduce the influences of AC-filter bus fault to the AC system which will give some references for the design and operation of subsequent UHVDC projects.

Flashover performance of silicon rubber under combined AC-DC voltage and its improving method

Composite insulators in valve tower of UHVDC converter station withstand combined ac-dc voltage. The flashover performance of silicone rubber under combined voltage is investigated in this paper. The voltages on the post insulator of valve tower under different operating conditions are simulated in PSCAD/EMTDC, and the harmonic components of the voltages are analyzed. The simulation results indicate that the ac frequencies of the voltage on the post insulator are mainly 50 Hz, 3n and 6n±1 times harmonics. The flashover voltages of silicone rubber under different combinations of ac and dc voltages are tested, including different single frequency ac voltages superimposed on different dc voltages, and different combined harmonic voltages superimposed on different dc voltages. The test results indicate that different ratios of dc voltage to ac voltage and different percentages of harmonics have various influences on the flashover voltage of silicone rubber. Moreover, argon atmosphere pressure plasma jet (Ar APPJ) is applied to modify the surface of the silicone rubber under different modification times and voltages. The flashover voltages and the surface morphologies of the silicone rubber before and after surface modification are compared. Surface modification by Ar APPJ can improve the surface resistivity of the silicone rubber significantly, and the flashover voltage also increases.

The broadband frequency characteristics of major equipment in the ±800 kV converter station and their influences to the short-circuit fault transient

Due to the wide application of high-order resonant and nonlinear electric equipment in the UHVDC converter station, the electromagnetic transient process is a complex issue during the short-circuit fault transient of the system caused by lightning strike or other reasons. In this study, firstly, an operating ±800kV DC line is artificially short-circuited to simulate the flashover fault process. The instantaneous voltages and currents and the electrical fields are measured by advanced sensors and high sampling rate recording devices at different points in the converter station, in order to comprehensively study the high-frequency characteristics of the UHVDC system. Then, the portal impedances of the major UHVDC equipment as well as the stray parameters are systematically measured in an actual ±800kV station. Based on the data measured, the accurate high-frequency characteristics of the ±800kV converter station are analyzed. The results of the study can be used to guide the EMC and relay protection designs of the UHVDC converter station, so that the stability of the system can be improved.

Subsynchronous Oscillation Problem Research in the UHVDC System of a Regional Power Grid in China

Along with the grid structure being more and more complex and the rapid development of the HVDC system, studying the subsynchronous oscillation (SSO) problem on HVDC system has more engineering practice significance. The paper studies subsynchronous oscillations problem of generators near the ±800kV UHVDC converter station, and analyzes the subsynchronous oscillation possibilities through PSCAD/EMTDC simulation. At last, though the researched UHVDC thermal plants have none SSO risk but it needs other measures to make the relevant generators return on normal operation.

Pollution flashover performance of full-scale ±800 kV converter station post insulators at high altitude area

On the background of the peculiar technology problems with the external insulation of UHV dc equipment in China, caused by high altitude and heavy pollution, this paper presents the pollution flashover performance of full-scale ±800 kV converter station post insulators at actual high altitude area. The tests were carried out according to the solid layer method, and the 50% withstand voltage (U50%) was determined by the up-and-down method. The artificial contamination test results indicated that the shed configuration and the rod diameter had a significant influence on the flashover voltages. Shed parameters of one big and one small alternating shed composite post insulator which had superior dc pollution flashover performance had been recommended. The relationship between U50% and insulation height was approximately linear at actual high altitude area for post insulators. It was found that partial discharges occurred at the top section firstly and partial arcs easily appeared at the parts nearby the connecting fittings during the flashover process. And arc floating phenomenon was significantly serious in actual high altitude area. Furthermore, comparison was made between the U50% values of composite post insulators in fog and in rain. The U50% values in fog of composite post insulators were generally higher than that in rain. Thus, the outdoor insulation design of composite post insulators should primarily consider the U50% value in fog. This work thus provides useful reference for the design, operation and maintenance of UHV dc converter stations outdoor insulators in China.

Influence of Modeling Methods on the Calculated Lightning Surge Overvoltages at a UHVDC Converter Station Due to Backflashover

The insulation coordination of the converter station is very important for the security and economy of the UHVDC power transmission system, and lightning surge overvoltages at the converter station should be calculated accurately. This paper mainly analyzes the influence of modeling methods on the lightning surge overvoltages caused by the backflashover of the incoming dc transmission lines by using the PSCAD program, such as the selection of lightning stroke current waveform, tower model, flashover criterion of the insulator, and so on. The simulation results show that modeling methods have a great influence on the backflashover lightning withstand level of the incoming dc transmission lines, but their influences on the lightning surge overvoltages of the equipment in the converter station are not so obvious.

The Noise Prediction and Control for UHVDC Converter Stations

The noise problem of UHVDC coverter stations which is more severe than that of HV ones, gets more and more attention. UHVDC converter stations noises mainly caused by converter transformer, smoothing reactor and capacitors and reactors of AC filter sets. Noise control measures must be taken by proper site selection, optimum general layout, sound source reduction, fully enclosed box of converter transformers, using low noise AC filter reactor and installing light sound insulation and sound barrier on walls surrounding the AC filter, etc. The noise of a UHVDC Converter Station is predicted by using the software of SoundPlan. The results show that the noise level of all the test points meets the standards after taking above measures. Both environmental benefits and economic benefits are realized.

Simulation Analysis on Conducted EMD Caused by Valves in $\pm$800 kV UHVDC Converter Station

Wideband frequency electromagnetic (EM) noise generated during the turn-on and turn-off processes of thyristor valves in converter stations is conducted along the primary circuitry, and may interfere with secondary systems. The EM interference (EMI) problem in a plusmn800 kV ultra-HVDC converter station is an important issue that should be studied carefully in the design stage. A method to analyze the conducted EM disturbance (EMD) based on time-domain wideband circuit simulation is proposed here, which is verified through the field test results of a plusmn500 kV converter station. Models of major equipment are described. The EMD levels of a plusmn800 kV converter station, which is currently being planned and built in China, are calculated, and compared with those of a plusmn500 kV converter station.