UHVDC Lines Research Articles

Research on continuous current characteristics and operating load characteristics of EGLA in UHVDC lines

In order to ensure the safe and stable operation of UHVDC transmission system, line arresters with series gap (EGLA) are often installed on UHVDC lines in engineering. When the line is struck by strong lightning, the series gap of EGLA will be broken down and the lightning will flow through the SVU. After lightning flows, EGLA needs to cut off the continuous current in time and reliably to restore the high resistance state. Therefore, the research on the characteristics of continuous current and operating load of EGLA is related to the design and selection of EGLA parameters, which has important engineering significance. However, due to the lack of UHVDC experimental platform, the relevant research is less, resulting in the lack of basis for determining SVU parameters. Based on the ±800 kV UHVDC transmission line from northern Shanxi to Nanjing in Jiangsu Province, this paper uses the method of control variables to simulate and study the characteristics of EGLA under different lightning strike modes, line positions and transmission capacities, and draws the conclusion that compared with back flashover on the tower, the peak value of EGLA under lightning shielding failure is smaller but the absorbed energy is larger, and the influence of transmission capacity is more obvious. When the lightning shielding failure on the middle tower of the line, the absorbed energy of EGLA is the largest and the continuous current is smaller.

Implications of intercontinental renewable electricity trade for energy systems and emissions

A rapid global energy transition, including the ramping up of electricity generation from renewables, is needed to limit global warming to 2 °C or 1.5 °C. However, renewable resource endowments vary widely between regions, and renewable electricity is currently mainly used locally. Here we use a global integrated assessment model to explore the implications of renewable electricity trade via a set of planned direct-current-type ultra-high-voltage (UHVDC) transmission lines for global energy transition and climate change. We find that renewable electricity trade across large world regions via the underlying UHVDC interconnection can boost renewable electricity production and reduce 2020–2100 cumulative CO2 emissions from the power sector up to 9.8%. Financial investments in the UHVDC lines are offset in the long term by reduced investments in other electricity-generation options, including nuclear and storage. Finally, we find that renewable electricity trade can substantially reduce air pollutant emissions in importing regions. Projects are under way for direct-current ultra-high-voltage transmission lines that would allow trading of renewable electricity across world regions. Guo et al. use integrated assessment models to explore different scenarios for the operation of these projects and assess their potential for decarbonization.

Interaction Mechanism and Coordinated Control of Commutation Failure Prevention in Multi-Infeed Ultra-HVDC System

Commutation failure (CF) is an inherent drawback of line-commutated converter high-voltage DC (LCC-HVDC) system. And CF prevention (CFPREV) control is widely applied in UHVDC lines to mitigate the subsequent CF. However, the formation of a multi-infeed UHVDC system induces power exchange and voltage interaction between AC buses during the transient process, making the behaviors and mitigation of CFs more complex. Consequently, exploring the impact of CFPREV control on adjacent stations and optimizing the CFPREV control to adapt to the interaction characteristics in a multi-infeed system is necessary. Considering the interaction characteristics, the impact of CFPREV control on the commutation process of inverters in a multi-infeed system is analyzed through formula derivation and simulation verification. It is found that although CFPREV control can effectively mitigate the CFs of the inverter near the fault, it will further increase the risk of concurrent CF (CCF) of remote inverters due to the interaction on the AC side. To solve this problem, a coordinated control scheme of CFPREV controls in a multi-infeed UHVDC system is proposed. The output of the CFPREV control of the inverter near the fault can be adjusted adaptively according to the commutation margins of remote inverters. And the probability of CCF caused by CFPREV control is consequently decreased. Case studies are conducted based on Henan provincial multi-infeed UHVDC system in China to verify the analysis result and the effectiveness of the coordinated control scheme of CFPREV controls.

A Study of Protection Method for Hybrid Multiterminal UHVDC Lines Based on CEEMDAN–Teager Energy Operator

In the research, a protection scheme for hybrid multiterminal UHVDC lines based on the CEEMDAN and Teager energy operator is proposed. The fault direction criterion is proposed according to the polarity difference of the sudden variable of the mode component of the current line on both sides of the T-zone after the fault of the EHV multiterminal hybrid DC system. When the fault is located on the left or right side of the T-zone, CEEMDAN is used to decompose the mode component of the fault transient current and obtain the intrinsic mode function (IMF component) at different local characteristic time scales. Then, the Teager energy operator is used to calculate the instantaneous energy of the current high-frequency IMF1 component. Finally, the faults inside and outside the line are judged by comparing the maximum value of current high-frequency IMF1 instantaneous energy with the setting value. When the fault is located in the T-zone, it is determined as a fault outside the line zone. The protection scheme of hybrid multiterminal UHVDC lines is given. The simulation model of the Kunliulong hybrid multiterminal UHVDC line system is built in a PSCAD/EMTDC simulation platform, and the proposed protection method is verified. A large number of simulation results show that the protection scheme has certain anti-transition resistance ability and high reliability.

Estimating the environmental impacts of HVDC and UHVDC lines for large-scale wind power transmission considering height-dependent wind and atmospheric stability

Due to the imbalance of China’s resources allocation, inter-provincial high voltage direct current (HVDC) transmission grid is considered to be the promising solution to solve to the large-scale wind power transmission, which could tackle the reverse regional distribution problem of energy resource and electricity load. In this contribution, a power law profile model of wind speed on embedded atmospheric stability is developed for calculating the height-dependent wind speed. The Monin-Obukhov length is introduced to determine the atmospheric stability. The ion flow environment model considering height-dependent wind speed is proposed to estimate the influence of height-dependent wind on ground-level electric field environment of DC transmission line and the iterative flux tracing method-finite difference is proposed to solve the model. It is observed that the stable, neutral and unstable atmospheric conditions have a large influence on transverse wind speed and then indirectly influence the electric field and ion current environment of DC lines. For the electromagnetic environment of the practical DC line used for the wind power transmission, the proposed model provides a reasonable agreement with measurements from a perspective of practical engineering application.

A new principle of UHVDC line pilot protection based on trigger angle control characteristics

Abstract A new principle of UHVDC Line pilot protection based on internal parameters of the trigger angle of converter is proposed, in order to improve the ability of the protection to withstand transition resistance. Through the analysis of UHVDC control system, it is found that, due to the regulation of control system, in terms of trigger delay angle of rectifier side and trigger leading angle of inverter side, the change tendency in internal fault and external fault is different. Thus, the protection criterion is constructed. Compared with the traditional protection principle using voltage and current to establish protection criteria, this principle uses internal parameters as protection quantity. The simulation based on PSCAD/EMTDC verifies the effectiveness of the protection principle.

Reliability Evaluation and Sensitivity Analysis to AC/UHVDC Systems Based on Sequential Monte Carlo Simulation

With the sequential Monte Carlo simulation (sMCs), the duration of the system state is obtained by the difference of the state sequences of related equipment. The state probability is not the explicit function of the reliability parameters. Therefore, it is difficult to derive the sensitivity directly. A new sensitivity model for the sMCs is proposed in this paper, which is based on the derivative of the state duration to the reliability parameters, and the sensitivity model is applied to the AC/UHVDC system. The states and durations of the related equipment from the beginning of the simulated years to the generated time of the system state are considered and differentiated to describe the derivative. To obtain the sequence of the UHVDC line, the possible reached state, mean duration, and probability for each state transition are considered. By combining the sensitivity model of the UHVDC line itself, the equivalent transition rates are applied to connect the system state duration and reliability parameters of the UHVDC components. The numerical results based on a provincial system in China are provided to validate the feasibility and accuracy of the proposed model.

Electric field calculation on residential houses near UHVDC lines using 3D reconstruction method

Prediction of electric field impact on residential houses is required in the design of UHVDC transmission lines. The calculation of electric field distribution on houses is a 3D problem, however, the effectiveness of some 2D calculation methods has been validated by specific reduced-scale experimental models. The 2D methods are simple in operation and quick in computation compared with the 3D methods. In this paper, the deviation ranges of 2D electric field calculation results on houses are discussed. Then, a 3D electric field reconstruction method is proposed to correct the 2D results according to the size and location of the houses. The 3D electric field distribution on the houses can be obtained based on efficient 2D calculations, and a direct 3D calculation is avoided. Finally, the validity of the calculation methods is verified by the measurement results of a full-scale experimental system.

Calculation and Analysis of Electromagnetic Environment Indexes and Influence Factors of ±1100 kV UHVDC Transmission Lines

In order to study the influence of electromagnetic environment of ±1100 kV Changji-Guquan the UHVDC lines, the ground total electric field and ion current density of the HVDC line is studied in this paper by using the charge simulation method and Deutsch’s hypothesis-based analytical method. And the correctness of the method is verified by the measured results. The EPRI formula and CISPR formula are applied to study the audible noise and radio interference. At last, the influence of UHVDC transmission line parameters on the electromagnetic environment is analyzed, and the influence factors that restrict the construction of the UHVDC transmission lines are also studied. The results show that the minimum height of the pole is limited by the total electric field strength, and the influence of the roughness coefficient should also be taken into account when calculating the minimum height of the wire, while the selection of the diameter of the wire is constrained by both the ground total electric field and the audible noise.

Study on the difference of chemical composition of insulator contamination on UHV‐AC and ‐DC transmission lines

For the ultra high voltage (UHV)-DC and UHV-AC transmission lines, their contamination characteristics are different. Thus, researching the contamination polluted degree of UHV-AC and UHV-DC lines by geoaccumulation index and enrichment factor method is an ingenious method. This study analyses and compares the chemical composition of contamination on parallel energised UHV-DC (800 kV) and UHV-AC (1000 kV) overhead transmission lines. The results indicate that the major cations of insulator contamination are Ca2+ , and NH4 +, and the major anions of insulator contamination are SO4 2− and NO3 − both on UHV-DC and UHV-AC lines. For the UHV-DC line, the concentrations of the same cations on the insulator bottom surface are higher than that of on the top surface. However, on the UHV-AC line, the same cation concentrations on the bottom surface close to the one on the top surface. The metallic elements of Ca2+ and Zn2+ are in seriously polluted degree. Also, the polluted degree of contamination on UHV-DC insulator is more serious than UHV-AC insulator. This study considers that field charging plays an important role in accumulating contamination.

A Novel Traveling-Wave-Based Main Protection Scheme for $\pm $800 kV UHVDC Bipolar Transmission Lines

The UHVDC transmission system has been increasingly used because of the advantages in long distance and large capacity transmission. However, the existing traveling-wave-based protection for UHVDC transmission lines is not sensitive enough to properly detect the internal fault with high fault resistance. A novel traveling-wave-based protection scheme for bipolar UHVDC lines is proposed in this paper. The discriminative characteristic between the internal and external fault, embodied in the backward traveling wave, is extracted to formulate the main protection criterion. The faulty line is identified by the polarity of the voltage fault component. In addition, only the single-pole voltage and current of rectifier side are required for the proposed protection scheme. The simulation and field data tests show that the proposed protection scheme can make a correct identification of the fault section and selection of the faulty line in the $\pm $ 800 kV UHVDC system and $\pm $ 500 kV HVDC system. Besides, the proposed protection can correctly detect the grounding fault with fault resistance up to 500 $\Omega $ .

Simulation Study on Transient Response of UHVDC Transmission Line Fault

The extraction and analysis of fault information is key to making the transmission line protection configuration scheme. This paper analyzes the mechanism of DC line faults, like lightning, mental and non-mental grounding fault, short to AC line. By referring to actual parameters of Yunnan-Guangdong ±800kV UHVDC transmission system, simulation model is established by PSCAD/EMTDC. According to simulation tests of dc transmission line faults: lightning, grounding fault, high resistance grounding fault and short to DC line, the transient responses of UHVDC line faults are summed up.

Fractal model of lightning channel for simulating lightning strikes to transmission lines

How to accurately evaluate the direct-strike lightning protection is one of the key issues in the design of transmission lines. In this paper, three important issues in applying the fractal simulation to the lightning protection of transmission lines were discussed, including the criteria and implementation of upward leader inception, the connection with the magnitude of lightning current, and the calculation and control of fractal dimensions. Then we conducted the simulation iterately, leading to statistical results, which indicate that even if the transmission line satisfies the perfect shielding condition, shielding failure fault remains possible. Furthermore, we calculated the shielding failure fault rates of an EHV line with different ground obliquities and distribution of strike points over the interval between two neighboring towers along a UHV-DC line to find out the weak point of transmission-line lightning protection. This work provides a promising approach for improving the lightning protection property of transmission lines by optimizing the configuration of shielding wires and phase or pole conductors.

A hotstick instrument for estimation of the potential of an HVDC conductor

In 1989-1990, New England Power Service Company (NEPS) and Bonneville Power Administration (BPA) jointly sponsored the UHVDC Live-Line Voltage-Estimator Project with three principal goals: to develop a technology which would permit moderately accurate estimates of the DC potential of a UHVDC line without requiring an electrical connection to ground or any other reference point; to develop an instrument embodying this technology which could be applied by a lineman in the field and to demonstrate that the system functioned as expected; and to develop and incorporate in the instrument a technique for estimating the induced AC component of the potential. As demonstrated at the BPA outdoor test facility on August 15, 1990, the first goal has been fully met. The authors report a demonstration that a properly located field mill can determine the DC potential to better than 10% of full scale over a range from 0 to +or-500 kV, even in the presence of wind and corona. Solutions to the remaining pair of goals have been defined, and an effort is underway to develop a field-hardy engineering prototype of a production instrument. >