UHV AC Transmission Lines Research Articles

Analysis of gap distance of ultra high voltage AC transmission lines in areas with altitude above 2000m

Abstract Research on long-wave front discharge characteristics of lines and long gaps of substation equipment in high-altitude areas needs to be conducted in a systematic manner immediately in order to guarantee the safety and economy of high-altitude UHV lines with respect to external insulation. However, at present, the gap discharge test of transmission lines is mainly carried out in areas below 2000m above sea level. The actual test is challenging to conduct in the high altitude region, and the test data is incomplete. To further confirm the validity of extrapolation of existing altitude test data to high altitude areas, this paper conducts theoretical analysis based on the real test data under standard meteorological conditions provided by GB/T 24842 standard. The altitude correction methods in IEC 60071-2: 2018 and IEC 60060-1: 2010, the m-coefficient method and g-parameter method, are used to correct the lightning impulse, power frequency, and standard switching impulse of AC transmission line gaps. The discharge voltage in areas below 5000m above 2000m is obtained, and several significant discharge characteristic parameters are obtained. Based on the 50% discharge voltage requirements of various voltage types of 1000kV transmission lines, combined with the discharge voltage curves at multiple altitudes, the minimum air gap distance of transmission lines at the altitude of 2000m-5000m is obtained. The comparative analysis of the correction results of the two methods provides a way of thinking for the next step to carry out the true test of UHV AC transmission line gap discharge in higher elevation regions.

Numerical model of lightning attachment on UHV-AC transmission lines and effects of operating voltage, phase angle, and terrain

Numerical model of lightning attachment on UHV-AC transmission lines and effects of operating voltage, phase angle, and terrain

Audible noise analysis of 750‐kV AC transmission line in high‐altitude area under different weather

AbstractIn order to build UHV AC transmission lines at high altitudes, it is necessary to analyze the audible noise (AN) characteristics of the existing EHV transmission lines at high‐altitude areas to guide the design. The typical test data of AN for 750‐kV single‐circuit transmission lines measured at the Guanting long‐term observation station, located at an altitude of 1854 m, were collected. Two methods of sorting the test data of AN and extracting valid data were given. Then the levels of AN under different weather conditions were analyzed, which showed that AN was raised with the increase of instantaneous rainfall and snowfall. Typical frequency spectrums of AN under different weather were also obtained, the pure tone at 100 Hz was more prominent under rainy and snowy weather, and the pure‐tone oscillation attenuated at different positions. The statistical results and the calculated difference of AN over 5.5 h with continuous rainfall were obtained. For the 750‐kV transmission line in the quiet plateau areas, the calculated difference between AN during rainy days and fair weather can be taken as 25 dB, and the calculated value of the altitude correction coefficient of 2.85 dB/1000 m is better consistent with the measured value.

Insulation Coordination of a UHV AC Transmission Line Considering the Switching Overvoltage Waveshape

This paper presents the determination of insulation coordination for phase-to-ground switching over voltages by a practical method in which the effect of the switching overvoltage waveshape, especially the impact of the time to crest on insulation strength is considered. This work is carried out on the world’s first 1200 kV transmission line by modelling it in PSCAD.

Three-phase adaptive reclosure technology for half-wavelength transmission lines using residual voltage frequency difference to identify fault existence

• The single-phase reclosing technique should not be used in half-wavelength transmission systems. • The residual voltage of half wavelength transmission system can be used to determine the existence of faults. • The frequency difference of residual voltage can be used to determine the existence of faults. • We propose a complete and feasible three-phase adaptive reclosure scheme for half wavelength transmission system. UHV AC transmission lines use adaptive reclosure technology not only to avoid reclosing in the permanent faults, but also effectively prevent the emergence of reclosing overvoltage, adaptive reclosure is of great significance, and its technical principle is based on the study and judgment of the existence of the fault. The reactive power of half-wavelength transmission lines along the line was self-balanced, no shunt reactor equipment, there is no "beat frequency" phenomenon, and very little information is available after the three-phase trip. In this paper, we analyze the fault traveling wave's frequency characteristics and identify the fault's characteristics based on the residual voltage frequency difference of the line after the three-phase trip. After the disappearance of the line fault, the stable frequency difference obtained by CVT reflects the entire length of the line, which is not affected by the system boundary conditions and can complete the reliable identification of the disappearance of the line fault. The two-terminal criterion is given for the short-line dead zone problem, and then a three-phase adaptive reclosure scheme for half-wavelength transmission lines based on the frequency difference to identify fault disappearance is proposed. Extensive RTDS digital-analog hybrid tests show that the method is correct and robust.

Eiffel Effect on Towers of UHV AC Transmission Lines

The principle of Eiffel Effect on transmission towers was analyzed, and the necessity of considering Eiffel Effect on transmission towers, especially multi-loop transmission towers, was proposed. A comparative analysis on calculation methods for Eiffel Effect on tower mast structures both at home and abroad was conducted and the applicability of various calculation methods to transmission towers and their advantages/disadvantages are proposed. On this basis, the analysis method for Eiffel Effect on transmission towers is proposed. The Eiffel Effect was calculated by taking four tower types of EHV/UHV AC multi-circuit transmission lines on the same tower as examples, during which the stress state of member bar of each tower type after considering the Eiffel Effect, the influence of the intersection angle between the main members of the tower on the Eiffel Effect, and the minimum bearing capacity requirement of diagonal members etc. were analyzed. The analysis shows that: It is simple, reasonable and convenient to consider the Eiffel Effect on the tower with the rigidity-reduction method for engineering application; both the diagonal member and the diaphragm member of the tower are influenced by Eiffel Effect, where its influence on the latter is higher; it may be unsafe if designing the minimum bearing capacity requirement for the diagonal member with the internal force not less than 5% of the main members to satisfy the Eiffel Effect on the tower for the UHV transmission towers, and especially for the transmission towers with EHV/UHV AC multi-circuit transmission lines on the same tower.

Prediction of Breakdown Voltage of Equipotential Live-Line Work Air Gaps in Transmission Lines: A Computational Discharge Model

Equipotential live-line work (EPLW) is an indispensable technology to ensure the power supply. Due to the huge risks of the strong electric field, the distance of the EPLW air gap should be greater than the minimum approach distance (MAD). MAD is determined by calculating the hazard probability according to the characteristics of the switching overvoltage and the 50% breakdown voltage of EPLW gaps. Currently, the 50% breakdown voltage is obtained by a great many actual-size discharge tests, which costs a large amount of time and workforce. In this article, a computational discharge model was presented to solve the problem. First, the discharge process of EPLW air gap was analyzed based on the test experience. Subsequently, according to each stage of the discharge process, a computational discharge model for predicting the 50% breakdown voltage of EPLW gaps was presented. Finally, the computational discharge model was applied to EPLW air gaps of ±800 kV UHVDC and 1000 kV UHVAC transmission lines. The calculated results agreed well with the test results, and the errors did not exceed 6%. This research can provide theoretical support for the transmission line design and lineman safety protection.

Design of electromagnetic induction calculation and auxiliary calculation software under UHV transmission line

With the development of 1000 kV UHV transmission technology and the shortage of line corridor resources, UHV will inevitably cross the building area. Although many scholars had studied the power frequency electromagnetic field under UHV AC transmission line, it is very difficult to accurately calculate the electric field strength and induced voltage, which cannot be applied in engineering. At present, there is no relevant literature to study the problem of induced electricity in buildings with a large number of steel frame structures under the line and the estimation method of induced electricity in buildings. By summarizing and analyzing the simulation data, the estimation method of induced voltage and induced current density of steel frame buildings under UHV lines was proposed. An auxiliary calculation system was developed. The calculated values of the software were compared with the measured values, which accuracy of voltage and current can reach 91.5% and 92.7%, and fully meet the engineering needs.

Novel Differential Protection Approach of UHV AC Transmission Lines Based on Tellegen's Quasi-Power Theorem

When current differential protection is applied to an AC transmission line, synchronous sampling at the two ends is required. The use of GPS synchronization increases the difficulty and cost of project implementation while the use of ‘ping-pong’ synchronization requires that the communication channel has equal transmission and reception delay. To overcome the impact of these issues, power differential protection has been proposed. However, power differential protection cannot fully identify the fault zone for solid single-line-to-ground fault. This paper proposes a novel differential protection approach based on the Tellegen's quasi-power theorem. The approach retains the advantages of current differential protection. Meanwhile, it is not affected by load condition and distributed capacitance. This paper also proposes a time synchronization method based on the Tellegen's quasi-power theorem to calculate and correct the time synchronization error. Therefore, the proposed pilot protection has a high synchronization accuracy and has no requirement on the communication delay. In this paper, different simulation models are established by using MATLAB/Simulink and PSCAD and extensive simulation studies verify the effectiveness of the proposed protection approach and time synchronization method.

Simulation Research on Distribution Characteristics of Electromagnetic Field of AC UHV Transmission Line

With the development of UHV and long-distance power transmission technology in my country's power grid, the electromagnetic environment of 100kV UHV transmission lines will be one of the key issues affecting the feasibility of UHV transmission. The impact of low-frequency noise from UHV AC transmission lines on the lives of residents along the corridor should not be ignored. In particular, pure AC sound attenuates slowly along the line and spreads far away, which often has more serious impacts on the lives of nearby residents. In order to study the distribution law and influence degree of pure sound, this article mainly conducts a more in-depth study on the wiring method of UHV transmission lines through theoretical calculation and computer simulation.

Electric field and discharge voltage characteristics of UHV AC transmission line–tower air gaps

In high voltage transmission projects, the discharge voltage prediction of practical air gaps is a troublesome and long-awaited objective. For transmission line–tower air gaps, full-scale discharge tests can be expensive and prolonging. For the gap geometries in practical engineering, we cannot completely simulate all of them. In this paper, test samples taken for simulation are two types of actual gap geometries used in UHV transmission systems. The discharge path needed for a 250/2500μs 1000 kV switching impulse was found. For this, the two-dimensional finite element models of a UHV cup-type transmission line and a UHV compact type transmission line were established for electric field calculation. Then some features were extracted from the hypothetic discharge channel between the bundled conductor and the tower. Thus, various electric field features of the geometries are obtained. These values are verified by comparing it with the values obtained from the extensive literature survey. Discharge voltage characteristics of both geometries are also calculated and compared for different gap distances.

Analysis of Electric Field Distribution on Composite Insulator of 500kV AC Typical Tower and Its Effect on Decay Fracture

A new type of composite insulator mechanical failure named decay-like fracture happens rather often in UHV AC transmission lines. However, the cause from the point view of electric field is not clear. To investigate the effect of electric field on the occurrence and development mechanism of decay-like fracture, the 3D tower-conductor-insulator models for ZB2-type and CZ34-type transmission tangent towers are established and analysed based on the finite element simulation. The conclusion can be drawn that the tower type has a significant effect on the electric field distribution along the axial direction of the insulator string, and the degradation is more likely to occur in high-voltage side of the B-phase string, which is consistent with the fracture failure investigation. Simulation results also show that the withstand electric field strength is 297kV/m. The distribution of surface potential and electric field under the actual operating voltage provide a new idea for the condition monitoring of the decay-like fracture of UHV AC composite insulators in transmission lines, as well as a reference for further research in the field of decay-like fracture failure.

Improving the outdoor insulation performance of Chinese EHV and UHV AC and DC overhead transmission lines

Power girds in different countries face different types of threats and in China the threats severely affecting grid reliability were in the past large power outage accidents caused by pollution flashovers. First records of pollution flashover accidents in China can be traced back to 1950s in industrial areas in Northeast and East China. Thereafter, such accidents occurred occasionally, but after 1970s they started to expand and were recorded in most of the country's provinces. The very first large area outage accident caused by pollution flashover happened in early 1974 in Northeast China around the local largest cities Shenyang and Fushun. Between 1971 and 1994, 3542 pollution-caused line trip-outs (several trip-outs on one overhead line (OHL) happening the same day is counted in China as a single event) were recorded on 35-500 kV OHLs and 1768 substation trip-outs. A total of 44 large area outage accidents caused by pollution flashovers took place during the 30 year period before 2007, as shown in Figure 1, while the outages recorded between 1981 and 2001 accounted for 43% of the total number. Among them, outages of super large character occurred every 5-6 years, e.g., in 1990 in North China and Northeast China, in 1996-1997 in East China and Central China, 2001 in North China and Northeast China [1-3]. Here we refer to the large area outage accidents as flashover events on several main transmission overhead lines and substations, appearing during one or several consequent severe meteorological events and continuing for several days. They affect several big cities within one province and stretch over an area of less than 100 thousand km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . For super large area outage accident, we refer to the accidents stretching across several provinces over the area of 200-300 thousand km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and resulting in hundreds of pollution flashover events.

Switching Surge Design of 1200kV UHVAC Transmission Line

With the increase in operating voltage of transmission system to transport large amounts of power to meet increased demand switching surges became governing factor in the insulation design of EHV and UHV systems. Insulation failure probability under switching surges that is switching surge flashover rate (SSFOR) is the main concern in the switching surge design of transmission lines. In this paper, SSFOR of 1200kV UHVAC transmission line under switching surges which are generated during energization of no-load transmission line is estimated.

Effects of power frequency electric field exposure on kidney.

With the rapid development of ultra high voltage alternating current (UHV AC) transmission, the intensity of environmental power frequency electric field (PFEF) near UHV AC transmission lines increased continuously, which has attracted considerable public attention on the potential health effects of PFEF. In this study, the effect of PFEF exposure on the kidney was explored. Institute of Cancer Research (ICR) mice were exposed to 35kV/m PFEF (50 Hz). Two indicators relating to renal function (urea nitrogen and creatinine) were tested after the exposure of 7d, 14d, 21d, 35d and 49d. The pathological morphology and cellular ultrastructure of kidney were observed respectively by light microscopy and electron microscopy after the exposure of 25d and 52d. Results showed that compared with that of the control group, the concentration of urea nitrogen of 35kV/m PFEF exposure group significantly increased on the 21st and 35th days, and the concentration of creatinine significantly increased on the 14th, 21st and 35th days. However, the concentrations of creatinine and urea nitrogen both returned to normal levels on the 49th day. Furthermore, an enlarged Bowman's space, the vacuolation of renal tubular epithelial cells and the foot process effacement of podocyte were found after 25d exposure, but no abnormality was observed after 52d exposure. Obviously, a short-term (35d) exposure of 35kV/m PFEF could cause kidney injury, which could be recovered after a longer-term (52d) exposure. Based on this study and relevant literatures, one explanation for this two-way effect is as follows. Kidney injury was caused by the disequilibrium of mitochondrial dynamics under 35kV/m PFEF exposure. PFEF could also activate Wnt/β-catenin signal to promote the recovery of renal tubular epithelial cells and glomerular podocytes, so kidney injury could be repaired.

Study on electromagnetic environment of ±800 kV UHV DC and 1000 kV UHV AC parallel transmission lines

Aiming at the typical AC/DC parallel transmission lines which have been put into operation in China, the electromagnetic environment of parallel transmission lines is monitored and the interaction between AC and DC electromagnetic environment is analyzed. Monitoring results show that: The electromagnetic environment of UHV AC/DC parallel transmission lines meets the corresponding national standard limits. UHV DC transmission line has little influence on power frequency electromagnetic field, which is mainly affected by distance and wire height to ground. UHV AC transmission line may have a certain impact on DC composite field strength, and wind speed will have a greater impact on DC composite field strength.

Estimation of switching surge flashover rate of 1200-kV UHVAC transmission line considering switching overvoltage waveshape

The insulation of the power transmission system experiences stresses due to power–frequency voltage under normal operating conditions, temporary overvoltages at or near power–frequency and transient overvoltages arising either from switching operations and faults or from lightning discharges. However, in the insulation design of extra-high-voltage and ultra-high-voltage systems, transient overvoltages arising from switching operations and faults become the controlling factor. Insulation failure probability under switching overvoltages is the main impressive concern in the estimation of switching surge flashover rate. In this paper, a practical method is used to estimate the switching surge flashover rate of insulation under switching overvoltages generated during energization, re-energization, fault initiation and fault clearing of an unloaded transmission line, which considers the variable characteristics of the insulation strength of the transmission line according to the switching overvoltage waveshape. The results focus on the comparison between traditional and practical methods which considers the effect of the front time on the first 1200-kV UHVAC transmission line in India.

Electric field and discharge voltage characteristics of UHV AC transmission line–tower air gaps

Electric field and discharge voltage characteristics of UHV AC transmission line–tower air gaps

Optimal Design of 1200 kV UHV AC Transmission Lines in India using Newly Developed Standalone MATLAB GUI

Owing to tremendous growth in requirement of electrical power in the country, technological advancement in transmission systems is essential for transmission of bulk amount of power over long distances. Deciding value of corridor width for transmission lines are greatly influenced by magnitudes of electric and magnetic fields along its length. The precise evaluation of the electromagnetic fields and effects of corona like Radio Interference and Audible Noise generated by overhead transmission lines are thus of greater interest. This paper presents implementation of a novel GUI based technique to compute the fields generated by power transmission lines using three dimensional techniques. Actual case of Ultra High Voltage AC (UHVAC) line is considered for study. Transmission lines are analyzed by using newly developed software that facilitates computation and plotting of electromagnetic fields and corona effects in 3D coordinates. MATLAB is used as platform for development of GUI based software to analyze the fields along the entire length of transmission lines under study. It uses concept of charge simulation method (CSM) along with most fundamental Maxwell’s potential coefficient theory and 3D integration techniques.

Research on Electromagnetic Radiation Model of Corona Discharge with UHV AC Transmission Lines

The corona discharge pulse current has double exponential distribution characteristics. On this basis, the electromagnetic radiation model of corona discharge is established by using the theory of electric dipole. The corona discharge characteristics are analysed and compared with the measured results of 1000kV UHV ac transmission line. The results show that the electromagnetic field strength increases first and then decreases with time, and at the same time, the electromagnetic field strength decreases exponentially with distance. The simulated and predicted corona discharge radiation characteristics have the same variation law as the measured data, which verifies the correctness of the model.