Ultra-high Voltage Power Grid Research Articles

External Insulation Performance under DC Voltages of Polluted Post Insulators for Power Stations in Rainy Weather: A Brief Review and Recent Progress

The discharge and flashover phenomenon of post insulators in rainy weather has not been given sufficient consideration; however, with the construction of ultra-high voltage power grids, the performance of the external insulation and the ability to withstand special climate conditions need to be guaranteed. Therefore, it is meaningful to conduct studies on the discharge characteristics of contaminated post insulators under rainfall conditions. Moreover, the conventional perception tends to confuse the flashover of polluted insulators in the rain with the pollution flashover that occurs in the fog; however, in fact, the discharge of contaminated insulators that occurs during rainfall has characteristics that can be distinguished from the pollution flashover. In this study, firstly, the current status of research on the external insulation characteristics of post insulators was analyzed through an examination of the available literature. Secondly, the concept of a ‘pollution rain flashover’ of insulators was established and clarified, to distinguish it from the traditional meaning of ‘pollution flashover’ or ‘contamination flashover’. Thirdly, research results on the pollution rain flashover of post insulators used in power stations in recent years were summarized, which included the characteristics and mechanism of the discharge, parameters and factors influencing the flashover voltage, and their influence laws. Particularly, the gap discharge between insulator sheds triggered by raindrops, which is the most significant feature of the pollution rain flashover, and the profile optimization of sheds, which is an effective way to improve the performance, were emphasized in this work. Fourthly, the prevention methods were studied, which mainly include the application of rainproof sheds and the shed optimization for pollution rain flashover of post insulators. Finally, a brief prospect is given for future research.

Analysis of harmonic characteristics of UHV AC / DC power network considering the influence of geomagnetic storm

The resultant harmonic effect of geomagnetically induced current (GIC) caused by geomagnetic storm has an impact on the safe and reliable operation of ultra-high voltage (UHV) AC / DC power grid in China, which in severe cases may lead to power grid breakdown or even large-scale blackout. Firstly, the harmonic effect model of converter transformer under the action of GIC is established based on the GIC calculation results of China's UHV power grid during the super-geomagnetic storm in November 2004. The harmonic voltage of transformer equivalent model port is described in phasor form. Secondly, the characteristic harmonic model of the converter is established based on the switching function modulation theory. By analyzing the working principle of the equivalent circuit of 12-pulse rectifier, the harmonic coupling model between DC magnetic bias harmonic voltage of transformer and converter is established, and the harmonic coupling characteristics of AC / DC power network under the action of GIC are analyzed. Lastly, the simulation model of ±800 kV UHV AC / DC transmission system in China is built by using PSCAD/EMTDC software as the simulation platform. The non-characteristic harmonic current and voltage on the AC side and DC side of the AC / DC power grid are calculated. The results show that the harm caused by GIC invading converter transformer is more serious than that caused by GIC invading UHV transformer. When both of them are invaded by GIC, the non-characteristic harmonics generated by mutual superposition and coupling have a greater impact on the power grid. The research results of this paper can provide a theoretical basis for space disaster prevention of UHV AC / DC power grid in China.

Performance Analysis of Routable GOOSE Security Algorithm for Substation Communication through Public Internet Network

Traditional unidirectional power systems that produce large-scale electricity and supply it using an ultra-high voltage power grid are changing globally to increase efficiency. Current substations’ protection relays rely only on internal substation data, where they are located, to detect changes. However, to more accurately detect changes in the system, various data from several external substations, including micro-grids, are required. As such, communication technology regarding data acquisition has become an essential function for next-generation substations. Data aggregators that use the GOOSE protocol to collect data inside substations in real-time have been developed, but data acquisition from external substations is challenging in terms of cost and security, so only internal substation data are used. This paper proposes the acquisition of data from external substations by applying security to R-GOOSE, defined in the IEC 61850 standard, over a public internet network. This paper also develops a data aggregator based on R-GOOSE, showing data acquisition results.

Study on Ecological Environmental Impact Assessment Index System of UHV AC Transmission and Transformation Engineering-A Case Study of 1000kv UHV Transmission and Transformation Engineering from Zhangbei to Xiongan

Ultra-high voltage (UHV) power grid is a new transmission and transformation technology, which has the advantages of large transmission capacity, long transmission distance, low line loss, saving land resources and obvious economic benefits. Taking the Zhangbei-xiongan 1000kv AC high voltage power transmission and transformation project as an example, this paper constructs the eco-environmental index system of the UHV transmission and transformation project by using the pressure-state-response model, and constructs a set of 18 indexes eco-environmental index system, it mainly includes three aspects: the eco-environmental pressure index caused by the construction behavior in different construction stages of power transmission and transformation projects, and the eco-environmental state index given by on-the-spot investigation and study of projects, based on the construction unit on the ecological environment impact management response measures given indicators. The index system provides a basis for comprehensive and systematic evaluation of the impact of power transmission and distribution projects on the ecological environment, and finally draws the corresponding project construction evaluation conclusions. In this paper, the eco-environmental impact assessment index system of power transmission and transformation engineering has certain universality, and it has certain reference and guiding significance for the ecological environment evaluation of power transmission and transformation engineering.

Research on influence factors of micro-bubbles generation mechanism in oil paper insulation of 1000 kV transformers

The 1000 kV transformer is one of the most important equipment in ultra high voltage (UHV) power grid, and its service life largely depends on the state of its oil paper insulation system. Especially when micro-bubbles appear in oil paper insulation, the insulation performance of oil paper insulation will be greatly reduced. In this paper, the oil paper insulation micro-bubbles generation platform has been built in the laboratory for 1000 kV transformers. Based on the platform, the influence of temperature rate on oil paper insulation micro-bubbles was studied firstly. By setting the heating power, the micro-bubbles generation experiment of oil paper insulation samples with 3.0% water content was carried out. It is found that with the increase of heating rate, the initial temperature of micro-bubbles generation will increase and the time interval of micro-bubbles escape will be shorten. Then, the oil paper insulation samples aged for 0 day, 20 days and 40 days were tested. It is found that the longer the thermal aging time, the higher the micro-bubbles begin temperature, which directly shows that thermal aging could inhibit the generation of micro-bubbles. In addition, it is found that different layers of insulation paper also have an effect on the generation of micro-bubbles. These results can provide theoretical data support for the operation load setting and fault diagnosis of 1000 kV transformers.

The propellant role of the mega-grid in regional economic growth: Evidence from China base on the panel smooth transition regression model

One of the secrets for China's economic growth miracle is continuous investment in infrastructure, and the role of power infrastructure is irreplaceable. However, previous studies mostly focused on generation-side indicators rather than grid-side indicators, ignoring the importance of the mega-grid established in China. As a result, this paper is committed to exploring the economic growth pulling effect of power grids with different voltage levels in the nonlinear framework. On the premise of determining the robustness of estimation parameters by instrumental variable method, the panel smooth transition regression (PSTR) model is used to capture panel heterogeneity. To be exact, the regional economic growth driven by extra-high voltage (EHV) and ultra-high voltage (UHV) power grids presents a regime transition accompanied by the growth of regional power generation and electricity consumption per capita. This means that the mega-grid is more conducive to the economic growth of energy bases and load centers. To further build and improve the state-leveled mega-grid into a nationwide basic platform for trans-regional renewable energy transmission and distribution is a key measure to enhance China's sustainable economic growth under the constraints of carbon peak and carbon neutrality targets.

An adaptive under-frequency optimal control strategy for power system combined pumped storage and under-frequency load shedding.

With the construction and development of ultra-high voltage (UHV) power grids, large-scale, long-distance power transmission has become common. A failure of the connecting line between the sending-end power grid and the receiving-end power grid will cause a large-scale power shortage and a frequency drop in the receiving-end power grid, which can result in the frequency collapse. Presently, under-frequency load shedding (UFLS) is adopted for solving the frequency control problem in emergency under-frequency conditions, which can easily cause large load losses. In this context, a frequency coordination optimal control strategy is proposed, which combines the mode transition of pumped storage units with UFLS to deal with emergency under-frequency problems. First, a mathematical model of the frequency dynamic response is established, which combines the mode transition of pumped storage units with UFLS based on a single-machine equivalent model. Then, an optimal model of the minimal area of the power system’s operation frequency trajectory is introduced, yielding the optimal frequency trajectory, and is used for obtaining the action frequency of the joint control strategy. A simulated annealing algorithm based on the perturbation analysis is proposed for solving the optimal model, and the optimal action frequency is obtained that satisfies the transient frequency offset safety constraint of the power system. Thus, the joint optimal control of the mode transition of the pumped storage units and UFLS is realized. Finally, the EPRI-36 bus system and China’s actual power grid are considered, for demonstrating the efficiency of the proposed strategy.

Is there a grid-connected effect of grid infrastructure on renewable energy generation? Evidence from China's upgrading transmission lines

China has built the world's largest power infrastructure. Those upgrading power grid facilities not only contribute to providing enough end-used energy for the world's factories, but also offering a basic guarantee for the clean strategy of Building a Beautiful China proposed by the Chinese government. The national grid system supported by extra-high voltage and ultra-high voltage grids as the backbone makes it possible for a non-dispatchable renewable energy source to be connected to the national grid and transmitted to terminal consumers in load centers. The aim of this paper is to test whether China's advanced power grids have played a positive role in promoting power generation of intermittent renewable energy source. A novel nonlinear estimation named panel smoothing transition regression is introduced to capture heterogeneous effects of grid-connecting renewable energy source across regions. The empirical results show that whereas power grid infrastructure generally enhances power generation of renewable energy source and consumption in energy bases and load centers, the effects change across different voltage levels of power grids. The extra-high voltage power grids show strong support for grid-connecting renewable energy source, while the effect of ultra-high voltage power grids is unexpectedly insignificant. The extra-high voltage power grids have not yet become the backbone of the national grid, which is the main reason for the inadequate grid-connected renewable energy source to the ultra-high voltage power grids, indicating the importance of upgrading the power grid infrastructure.

Modeling the 10,000-Year Geomagnetic Disturbance Scenarios Based on Extreme Value Analysis

Modeling the extreme geomagnetic disturbance (GMD) scenarios is of great significance for risk assessment of the power system. In this letter, we model the 10,000-year GMD scenarios using the extreme value analysis to complement the classical 100-year and 200-year events. The 10,000-year GMD event is required for safety-critical nodes such as the ultra-high voltage (UHV)/extra-high voltage (EHV) substations and nuclear power plants, etc. The return level of geomagnetic variation is estimated using the geomagnetic observations based on extreme value theory, which is then combined with the theoretical upper limit of the disturbance storm time (Dst) index to establish the 10,000-year GMD scenarios. Finally, we present an application example of 10,000-year geomagnetically induced currents (GICs) in the Sanhua UHV power grid.

Equipotential shielding voltage sensor for contact measurement of transient voltage in EHV/UHV power grids

In this study, an equipotential shielding voltage sensor is proposed to achieve contact measurement of transient voltage in extra-high voltage (EHV)/ultra-high voltage (UHV) power grids. Two design versions of the voltage sensor for engineering application are described. One version of the sensor is designed as a miniaturized sensor for non-disturbing measurement of potential distribution along power electronic equipment under transient voltage. The other version is designed for online measurement and monitoring in alternating current EHV/UHV power grids. Based on the design parameters, the performance of the sensor is evaluated, including stability of measurement, shielding effect against the interference from adjacent objects and frequency bandwidth. In order to verify the performance of this sensor, an experimental comparison between this sensor and a standard capacitive voltage divider used in high voltage laboratory was carried out and the results of comparison are presented. The results show that the difference of measured peak voltage between the two devices is no more than ±5%, and the difference of measured time parameters between the two devices is no more than ±15%.

Evaluation of optimal UPFC allocation for improving transmission capacity

A unified power flow controller (UPFC) combines the advantages of various flexible alternating current transmission system (FACTS) devices into a powerful format. Using a 500 kV power grid, this study evaluates the selection and use of a UPFC to improve transmission capacity. The “UPFC unit capacity control proportionality coefficient” is introduced to quantify the control effect of the UPFC, and an optimal calculation method for the UPFC capacity is presented. Following the proposal of a UPFC site selection process, the data of an existing power grid is used to conduct simulations. The simulation results show that the UPFC has a strong ability to improve transmission capacity, and its use is greatly advantageous. Additionally, by applying the proposed selection method, the control effect and economic benefits of the UPFC can be comprehensively considered during project site selection. These findings have a guiding significance for UPFC site selection in ultra-high voltage power grids.

Nonlinear ultrasonic nondestructive detection and modelling of kissing defects in high voltage composite insulators

This paper investigates a feasible nondestructive method for micron-sized kissing defects in the composite insulators, which are commonly utilized in ultra-high voltage (UHV) power grid. In this paper, cylindrical adhesive contact model was established to describe the obvious distortion of ultrasound propagation caused by kissing defects on the polymeric interface of composite insulators. The ultrasonic nonlinearity parameter was measured for each of the kissing defective and intact specimens. Moreover, the theoretical analysis has been proved by the test results on the kissing defective samples, which indicates that the 0.7 μm kissing defects existed in the composite insulators could be successfully recognized by the nonlinear ultrasonic methods and the nonlinearity is reduced by interface roughness.

A Mitigation Method Based on the Principle of GIC-Even Distribution in Whole Power Grids

The geomagnetically induced currents (GIC) caused by geomagnetic storms can inflict the anomalous operation of power systems, damaging electrical equipment, or even resulting in a large-area blackout of power systems. Therefore, to reduce the impact of GIC and avoid severe disasters has been a major challenge for the development of large-scale power grids. Considering the fact that geoelectric field may have random orientation in mid-low-latitude areas, this paper employs GIC-Benchmark model, to calculate the GIC of East-China 1000kV ultra-high voltage (UHV) and 500kV extra-high voltage (EHV) power grids under a uniform geoelectric-field of 1V/km. We further analyze the characteristics and the pattern of GIC in UHV power grid and identify high-risk nodes which can be vulnerable to GIC encroachment. Then we propose installing additional resistors in the transformer neutral points of high-risk nodes to even the GIC distribution in whole networks, and make the theoretical calculation of GIC in East-China 1000kV power grid after installation. The results show that the principle of GIC-even distribution can reduce edge effect remarkably, which works well in mid-to-low- latitude areas at least, thus we expect to avoid space weather disaster in power grids with power operation scheduling and other mitigation methods.

GIC Influence on UHV Power Grids Based on Kalman Filter and WAMS Data

Geomagnetically induced currents (GICs) flowing through transformers affect their normal operation and can lead to accidents in power grids. The reactive power loss caused by GICs is called GIC-Q. At present, geomagnetic data are usually used to calculate GICs in research. These methods do not have real-time characteristics and cannot be used for real-time research on GICs. Response mechanisms for GICs in 1000 kV ultra-high voltage (UHV) transformers and for the effect of GIC-Q on large power grids are urgently required to prevent damage. Based on the principle of Kalman filter, this paper presents a model and method of calculating and analyzing GIC disturbance using the reactive power measured by wide area measurement systems (WAMS). The proposed method exhibits superior characteristics for real-time analysis and solves the problem of real-time shortage in GIC research. The model provides a theoretical calculation of GIC-Q disturbance in a 1000 kV autotransformer. Further, this method was verified according to the measured reactive power in three 1000 kV substations in Shandong Province and the measured geoelectric field at the Anqiu geomagnetic observatory station on September 8, 2017. The calculation results show that the reactive power measured by phasor measurement units (PMUs) can be effectively used to calculate and analyze GIC-Q in the transformers, which is significant to prevent disasters in the power grid caused by magnetic storms through dispatch and operation.

Parameter optimization design method for a fast-switch-based fault current limiter and circuit breaker

With the continuous expansion of ultrahigh-voltage power grids, the short-circuit current level is drastically rising, and the hidden dangers of an insufficient circuit breaker (CB) interrupting capacity can seriously threaten the safety and stability of power systems. Fast-switch-based fault current limiters (FSFCLs) can play a vital role here. However, FSFCLs also affect the transient recovery voltage (TRV) of a CB. Hence, for reliable CB interruption, it is necessary to solve the matching problem between the FSFCL and the CB. In this paper, considering different fault conditions, a mathematical model of a CB connected to an FSFCL is established for a CB interruption characteristic analysis. On this basis, using the TRV indicators, the FSFCL withstand voltage and the short-circuit current level as the objective function, a parameter optimization design model for the FSFCL and CB is established. Furthermore, in combination with a genetic algorithm (GA), a parameter optimization design method for the FSFCL and CB is proposed. The practicability and accuracy of the proposed method are validated using Simulink.

Uncertainty Quantification of Geo-Magnetically Induced Currents in UHV Power Grid

Geo-magnetically induced currents (GICs) have attracted more attention since many Ultra-High Voltage (UHV) transmission lines have been built, or are going to be built in the world. However, when calculating GICs based on the classical model, some input parameters, such as the earth conductivity and dc resistances of the grid, are uncertain or very hard to be determined in advance. Taking this into account, the uncertainty quantification (UQ) model of the geo-electric fields and GICs is proposed in this paper. The UQ of the maximums of the geo-electric fields and GICs during storms is carried out based on the polynomial chaos (PC) method. The results of the UHV grid, 1000 kV Sanhua Grid, were presented and compared to the Monte Carlo method. The total Sobol indices are calculated by using the PC expansion coefficients. The sensitivities of geo-electric fields and GICs to the input variables are analyzed based on the total Sobol indices. Results show that the GICs and geo-electric fields can be effectively simulated by the proposed model, which may offer a better understanding of the sensitivities to input uncertain variables and further give a reasonable evaluation of the geomagnetic threat to the grid.

Research and Design of Power Frequency Electric Field Measurement System

Electric field measurement is widely used in electric power, aerospace, medical and other industries. In recent years, with the gradual expansion of the coverage of ultra-high voltage power grids nationwide, the debate about electromagnetic environment brought about by high-voltage power equipment is increasing. The electromagnetic environment pollution problem of UHV transmission and transformation lines has aroused widespread public concern. The research on the electromagnetic environment of high-voltage transmission systems is rapidly emerging in China.

Characteristics of very fast transient currents in ultra high-voltage power system with Hybrid reactive power compensation

Hybrid reactive power compensation (HRPC) consists of a stepped controlled shunt reactor (SCSR) and a series compensation (SC), which will find applications in future ultra high-voltage (UHV) power grids to resolve the problems due to the frequent change of reactive power and bulk power transmission. However, very fast transient currents (VFTCs) are inevitably generated during switching, which would lead to insulation breakdown. In the present work, we first develop the equivalent model for HRPC, following which we deduce the expression of VFTCs in the time domain by using an inverse Laplace transform. The analysis indicates that the amplitude and frequency of VFTCs are both affected by the capacitance of the SCSR and of the SC, as well as the line length, stray capacitance, etc. The oscillating frequency, peak, and amplitude of the main frequency of the VFTCs in the substation can be modified by adjusting the silicon-controlled rectifiers in the SCSR when the disconnecting switch in gas-insulated switchgear is switched on. When the disconnecting switch in the SC is switched on, the VFTC oscillation frequency in SCSR decreases with increasing stray capacitance of SC, but the frequency and peak of the VFTC remains quite large. Increasing the line length between the SC and the SCSR suppresses the VFTC in UHV power systems. These results lay the foundation for developing HRPC methods to suppress VFTCs in UHV substations.

Space Plasma Distribution Effect of Short-Circuit Arc on Generation of Secondary Arc

Secondary arc is more severe in the ultra-high voltage (UHV) power grid. However, the mechanism for the generation process of secondary arc at the extinction moment of a short-circuit arc is not yet clear. It is of great theoretical significance and technological application value to study the generation mechanism and dynamic physical characteristics of secondary arc, and further to develop effective suppression technology. In this article, an arc numerical simulation model based on the coefficient partial differential equations combining with classical drift-diffusion model was established, and the implementation method based on the finite element software COMSOL (COMSOL Multiphysics 5.2a, COMSOL Inc., Stockholm, Sweden) was given. Then, the transient analysis method was applied to simulate the generation, diffusion and dissipation phenomena of the short-circuit arc strike, and further to explore the electric field, microscopic particle spatial distribution and reaction process during the arc discharge process. The simulation results show that the development of short-circuit arc mainly includes two processes: corona discharge and arc discharge, of which the former has a very short duration and the latter is caused by short-circuit. During the discharge process, the electron density first increases and then decreases, which is different from the general characteristics of streamer discharge. Although the concentration distribution curve of the positive ions and negative ions has the same trend, there are subtle differences. The diffusion effect of space ions in the initial discharge stage is almost zero, while radial diffusion direction in the peak discharge stage and axial direction in the late discharge stage. The electric field intensity in space has an S-shaped upward trend during discharge. The time relationship of the ion source generated by the neutralization reaction and by the short-circuit arc discharge are basically the same, and the rate of neutralization reaction is lowest near the electrode. When the ionic reaction is approaching the end of the simulation, the ionic concentration is higher than the initial level, which proves that the space ionic concentration is increased due to the short-circuit discharge, and providing the necessary environmental conditions for the subsequent generation of the secondary arc.

Does grid-connected clean power promote regional energy efficiency? An empirical analysis based on the upgrading grid infrastructure across China

Abstract On the basis of the fact that China is setting up world's largest electricity network with the extra high voltage (EHV) and ultra high voltage (UHV) as their backbones, creating the foundation for large-scale accession of clean power which may deeply affect regional energy efficiency across the country, this paper attempts to empirically study the joint effects of clean power accessing to power grids on regional total-factor energy efficiency. To complete this job, we first measured the total-factor energy efficiencies of 29 provinces in China over the period 1991–2013, based on one of the data envelopment analysis methods, then, the static panel model considering panel fixed effect with instrument variable (FE-IV), dynamic panel model of system generalized method of moments (SYS-GMM) and panel smooth transition regression (PSTR) were employed, respectively, to investigate separate and joint effect of clean power and its grid-connection with EHV and UHV electricity network. The results show that the joint effect of clean power accessing to EHV and UHV power grid is either not significant or even negative although clean power itself separately promote regional energy efficiency. Thus, while the investment in grid infrastructure continues to increase, the grid-connection mechanism of clean power needs to be optimized therewith.