kV Line Research Articles

Influence of a lossy ground on the lightning performance of overhead transmission lines

• Accurate lossy ground representation impacts lightning overvoltages simulation. • Carson's classic formulation may lead to inaccuracies for high-resistivity soils. • Accurate lossy ground representation in simulations leads to higher TLs outage rate. • An increase up to 15% in TL outages was found when ground is accurately represented. This paper investigates the impact of incorporating both displacement currents and frequency-dependent soil parameters in the calculation of the ground-return impedance for the determination of the backflashover rate of 138 kV and 230 kV overhead transmission lines due to direct lightning strikes. This is done by considering the Sunde's formulation for calculating the ground-return impedance, which is incorporated in a time-domain simulator using an alternative implementation of Marti's transmission line model. The obtained results show that the peak of the lightning overvoltages computed considering Sunde's formula, along with frequency-dependent soil parameters, leads to higher amplitudes in comparison with those simulated using the classical Carson's formula, which neglects the frequency dependence of soil parameters and assumes conductive currents in the soil much larger than displacement currents. This effect is more pronounced in high-resistivity soils and leads to an increase in the line backflashover rate within 4-6%, 7-12% and 9-15% for 1000 Ωm, 5000 Ωm and 10000 Ωm soils, respectively, considering 138 kV and 230 kV lines, and assuming a typical median first stroke lightning current. Analyses performed with slow and fast first stroke currents confirm the trend of increase of the backflashover rate with the consideration of Sunde's formula.

Analysis of the technical condition and service life of 35-110 kV overhead power transmission lines in the Oryol Region

The assessment of the technical and operational characteristics of overhead transmission lines of voltage classes 35-110 kV in the Oryol Region has been carried out in accordance with the methodology presented in the order of the Ministry of Energy of the Russian Federation dated July 26, 2017 No. 676; their service life was determined according to STO 56947007-29.240.01.053-2010. The analysis of the length of overhead lines and the types of conductors used has taken place using support-by-support schemes. In the construction of 35 kV lines, steel-aluminum wire (sectional area - 70 mm) is mainly used, the length of which is 1,358,456 km, and 110 kV overhead lines are made using an AS-120 conductor (1,094 km). Overhead transmission lines are characterized by high indicators of technical condition, since 40 % of lines of voltage class 35 kV and 53 % of lines of voltage class 110 kV are in very good technical condition with a wear rate of no more than 15 %. The study has found that 71 % of overhead lines with a voltage of 35 kV and 85 % of lines with a voltage of 110 kV have been in operation for more than 35 years; at the same time, due to the implementation of a timely strategy for maintenance and repair, the lines are characterized by high indicators of technical condition.

Analysis of 330 kV B busbar tripping accident in a 330 kV substation

In this paper, the damage to the bus conductor and expansion joint caused by the tripping accident of bus B of a 330 kV line in Northwest China was taken as an example, and the reasons for the tripping accident were analyzed and improvement measures were proposed utilizing macro inspection and cross-cut test. The results showed that the main reason for this failure is that the manufacturer did not strictly implement the coating process, resulting in insufficient coating adhesion, and the coating gradually cracked and fell off during operation. The peeling coating caused air gap breakdown and ground flashover.

Novel Solution to Back Flashovers on High Voltage Transmission Lines: The Embedded Ground Conductor

It is well known that for high voltage transmission lines in the range of 245 kV–525 kV, particularly in regions of high ground resistivity, lightning back flashover problems could be a major concern. Line arresters have been used successfully to address the problem. Underbuilt ground wires have been proposed as a viable alternative. The present paper shows that the full potential of additional ground wires could be achieved by optimizing their position on the tower. Such optimization often results in a preferred position at the level, or higher than the attachment height of the lower phase conductors; therefore the designation Embedded Ground Conductor. An essential requirement is that such positioning does not infringe in any way on the dielectric integrity of the electrical clearances and, under the influence of induced charge, does not become a source of positive streamers that may lead to additional radio or audible noise. It is found that a streamer- inhibited conductor, when properly placed, fully satisfies the above requirements. It is determined that for 245 kV, 345 kV and 420 kV lines, a streamer-inhibited embedded conductor could improve the back flashover rate by a factor of 10 or more

Investigation of line surge arresters application to the 150 kV system of Rhodes

• The application of line surge arresters to 150 kV overhead lines is investigated. • The required energy absorption capability of line surge arresters is determined. • Non-gapped line arresters and externally gapped line arresters are compared. • Surge arrester installation configurations are evaluated for critical lines. • Lightning performance improvement of a critical 150 kV overhead line is quantified. This paper investigates the application of Line Surge Arresters (LSAs) to 150 kV double-circuit overhead lines through ATP-EMTP simulations. The 150 kV lines under study are the backbone of the autonomous electrical system of Rhodes island in southeastern Aegean Sea, Greece. Hence, lightning-related insulation flashovers causing outages of these lines may lead to a blackout of this isolated system. In this work, both Non-Gapped Line Arresters (NGLAs) and Externally Gapped Line Arresters (EGLAs) are evaluated. Two installation configurations with 3 and 6 LSAs per tower are considered protecting one circuit and both circuits of the line, respectively. Simulations were performed for both lightning strikes to phase conductors and tower; these may cause shielding failure flashover and backflashover, respectively. The conducted current through the LSAs and the voltage at their terminals are computed, enabling the estimation of the energy stressing the LSAs. The effects of the lightning current time to half value, the phase angle of the operating voltage, and the power frequency ground resistance of towers are assessed. The required LSA energy absorption capability is determined. The lightning performance of a critical overhead line of the Rhodes 150 kV system is estimated and its improvement due to LSA installation is quantified.

Analysis of Influence of Distributed Photovoltaic on 10kV Line Relay Protection

Photovoltaic power generation is the most significant way to utilize solar energy in the world today. Facing the severe fossil energy crisis and environmental crisis facing the world today, photovoltaic power generation has obvious advantages from the perspective of resource sustainability and environmental friendliness. The access of distributed photovoltaic power sources will change the power flow distribution in the distribution network. If the grid-connected load of photovoltaic access is light, the photovoltaic capacity is large. After the photovoltaic is connected, the distribution network will become a multi-source network, and the photovoltaic output will be large. During this period, the line is prone to reverse current flow, which increases the line voltage and affects the power quality of the distribution network. Thence, it is essential to consider adopting strategies to control the voltage of the distribution network to ensure the safe and steady operation of the distribution network.

Construction Technology of Tower Erection with Mobile Crane Adopting the Relaying Auxiliary Device

The use of cranes to complete the tower assembly in the plain and hilly areas has been widely used in the construction of the tower assembly. But its construction safety hazards are obvious. Tower erection by using crane based on docking device is an advanced construction technology in the field of power grid construction at home and abroad. It has the advantages of high construction efficiency and good safety. This construction technology has certain requirements on construction technology, supporting docking auxiliary devices, and crane operator skills. In this paper, the design and feasibility of the docking device and construction technology are discussed in combination with the tower erection construction of Qinglong-Liangzhuang 220kV line project. Successful application through engineering shows: The docking device is safe and reliable, and the construction process is reasonable and feasible. This experience provided reference for the erection of other types of transmission towers using crane based on docking device in power grid construction.

Transformation of a three‐phase double‐circuit overhead transmission line into a six‐phase feeder to increase power transfer capability

The UK net-zero target requires the integration of significant renewable energy resources into the electrical grid. This, together with the projected growth in electricity demand imposes practical challenges on the power transfer capability of existing transmission feeders. For environmental and planning reasons, construction of new overhead lines is problematic, and where possible upgrading of existing substations and lines is preferred. This paper investigates the feasibility of transforming an existing three-phase (3Φ) double-circuit 400 kV line into a six-phase (6Φ) feeder for a simulated future GB scenario. Results indicate a 6Φ feeder, operating at a ‘phase-adjacent phase’ voltage of 400 kV can effectively solve the constraints of boundaries in transmission networks. When considering the various operating contingencies, associated with an important UK network boundary and its expected near-future winter-peak power transfer requirements, the thermal overload issues are mitigated by transforming a feeder from 3Φ to 6Φ. The paper demonstrates upgrading to 6Φ technology is a potential solution to certain future boundary constraints and in these cases avoids the need to build new underground or overhead AC/DC lines.

USE OF PYTHON, MATLAB, AND R FOR DEVELOPING ARTIFICIAL NEURAL NETWORK FOR IDENTIFICATION TYPE IN OVERHEAD TRANSMISSION LINES OF FAULT

Due to the increased devouring of electricity by a consumer, generating stations must provide an uninterrupted supply of electricity to load. For that intend, many steps had been taken for the detection of fault locations in overhead lines. Whenever any fault takes place in the transmission line, Fault Passage Indicators quickly detect fault and help the crew for clearing of fault as soon as possible. This will help in maintaining the constant supply of electricity to enduser equipment and increase the reliability of the load. These can be installed at different points for better operation in line. But all these traditional methods for detection of faults are time-consuming, hence with developing trends in Machine Learning and Artificial Neuron networks their concept can be used for the detection of faults in transmission lines. This report deals with the development of Ann for detection and identification a fault type in the 220kv line. As of 2020, python with Keras and Tensor Flow API is considered the best method for developing Ann models, hence a neural network is developed with them for the classification and detection of a fault utilizing Fast Fourier Transform. A Radial Basics Neural Network is formulated in MATLAB utilizing wavelet transform. A network is trained utilizing voltage sag and swell phenomena with a Resilient back propagation network in R language. At last, this report assists in understanding the nature of fault, occurring in transmission lines.

The scoping study of Kazakhstan-China-Republic of Korea power interconnection

Electric interconnection is an essential trend for future large-scale development and utilization of renewable energy. China has proposed the concept of Global Energy Interconnection to realize the clean utilization of energy through the interconnection of power grids and optimize the allocation of global energy resources. This study proposes the Kazakhstan-China-Republic of Korea networking scheme, analyzing the characteristics of power supply and demand in these countries. Based on the regional economic analysis and power development, four interconnection schemes are proposed utilizing UHVDC technology. Accordingly, existing problems and favorable factors are fully considered. The investment analysis of ± 1100 kV and ± 800 kV lines, configuration scheme of the converter station, and investment estimation of four interconnection schemes are given.

Adopting Differential Lightning Protection Measures to Reduce Simultaneous Trip Probability of 220 kV Double-Circuit Transmission Line on the Same Tower

Double-circuit lines on the same tower are more widely used due to the increasing shortage of transmission corridors. If lightning strikes cause simultaneous tripping, it will cause severe economic losses and safety problems. Transmission lines with 220 kV voltage level are an essential part of the main grid. Reducing the simultaneous tripping rate of 220 kV lines is extremely important for the safe operation of the power grid. This paper analyses the advantages and disadvantages of several typical lightning protection methods for double-circuit lines on the same tower by simulation calculation. Combined with the characteristics of several typical double-circuit towers, lightning protection design for double-circuit lines is studied, and the differentiated lightning protection methods and basic protection processes for typical lines are proposed.

Analysis on process management of soil and water conservation design for transmission line projects in Qinghai Province

The first part is a brief introduction of soil and water conservation (SWC) and loss condition of transmission line projects and in Qinghai Province；In the second part, based on the Qinghai Yuqia-Toesu 750 kV line project, and combined the experience and methods concluded during the soil and water conservation (SWC) design work, the process management for SWC design in Qinghai’s transmission line projects is analyzed; The third part is the conclusion and the suggestion. Through the introduction and analysis of the three parts, the thinking pattern of SWC design of transmission lines in Qinghai Province are clearer, which can be a reference for Qinghai’ SWC designer.

Analysis on process management of soil and water conservation design for transmission line projects in Qinghai Province

The first part is a brief introduction of soil and water conservation (SWC) and loss condition of transmission line projects and in Qinghai Province；In the second part, based on the Qinghai Yuqia-Toesu 750 kV line project, and combined the experience and methods concluded during the soil and water conservation (SWC) design work, the process management for SWC design in Qinghai’s transmission line projects is analyzed; The third part is the conclusion and the suggestion. Through the introduction and analysis of the three parts, the thinking pattern of SWC design of transmission lines in Qinghai Province are clearer, which can be a reference for Qinghai’ SWC designer.

A Single-Circuit Extra-High Voltage Line of Increased Transmission Capacity

Conventional single-circuit EHV AC lines, widely used around the world, feature an essential drawback: in the case of most probable single-phase sustained failures, the line is fully disconnected. An advanced single-circuit EHV line is proposed, one phase of which is made as two semi-phases operating in parallel to each other. In emergency modes, one of these semi-phases is used as a backup phase, and two usual phases are equipped in the line middle part with series compensation devices for balancing the line operation mode. An algorithm for calculating normal operation modes has been developed. Taking the example of an advanced 500 kV line, the ratio between the transmission capacities of the proposed line and a conventional single-circuit line is shown. A scheme is proposed, with which it becomes possible, in the case of a sustained damage to one of the semi-phases or in case of damage to one of the phases, to switch over for operation in the post-emergency mode with the possibility of transmitting at least 50% of the power of the initial maximum operation mode. A technical and economic comparison of a conventional double-circuit and the advanced single-circuit lines was carried out.

At the Edge of Voltage Collapse in Slovenian Power System After Outage of NPP Krško and 400 kV Node Tumbri

A major disturbance that resulted in the tripping of the 400 kV line Tumbri (HR) – Hévíz (H) and the entire 400 kV node Tumbri in the Croatian system occurred on 27 August 2003 and almost led to a voltage collapse in that area. The disturbance was initiated by an accidental outage of a generator at NPP Krško (SLO) due to a human error during regular maintenance work. Its further development was the consequence of a hidden fault of the numeric protection at the 400 kV switchyard Tumbri. In the specific system operating conditions (network configuration and generator scheduling) at that moment, the systems of Slovenia and Austria in the central part of the UCTE system were brought near voltage collapse. At the same time the operational security level of the power systems of Croatia and BiH, then at the perimeter of the UCTE system, was also decreased. The sequence of events is described and discussed in the paper. Recordings of frequency and active power in representative transmission lines, taken at NDC Zagreb, are also given. A simulation analysis was performed first for the real disturbance scenario and then for the hypothetical scenario in which there was no failure of the protection at Tumbri substation and consequently the 400 kV node Tumbri would have remained in operation. The simulations showed that the loss of a NPP Krško generator would have only a local impact and would be barely noticeable at the UCTE level had the 400 kV node Tumbri remained in operation. Simulation results are in accordance with information obtained from the Slovenian power system where severely depressed voltages were recorded, particularly in the area around NPP Krško. It was also observed that the Slovenian system was acting as a reactive power sink while active power was flowing in the opposite direction, i.e. towards Croatia. Assessment of Croatian system security during the disturbance with respect to voltage stability, frequency and angle stability and congestion criteria was done on the basis of measurements and simulation results. The conclusion was that Croatian system security with respect to all the above mentioned criteria was preserved but it must be stressed that the initial system operating conditions were rather favorable from the stability point of view.

Lightning Performance Improvement Of 123 kV Line Ston – Komolac By Use Of Line Surge Arresters

This paper presents HEP - Transmission System Operator Ltd. Line surge arrester (LSA) application pilot project on the Ston – Komolac 123 kV line. This 44 km long single circuit shielded transmission line operates in the region with a high lightning activity (keraunic level about 70 thunder days). In addition, it was very difficult to obtain good footing resistance. For these reasons, considered line used to have very bad lightning performance. It was decided to install Line surge arresters for line lightning performance improvement. In order to optimize arrester installation configuration sigma slp software simulations were performed. LSA are installed according to the results of the software simulations. LSA are installed in summer 2007 (110 gapless, IEC-class II Line arresters). Sixty one LSA are equipped with Excount - II monitoring sensors (monitoring arrester leakage current and peak of the impulse current). Based on the 8-month experience, LSA installation has improved line lightning performance. New line performance is close to the targeted once (improvement by 50 to 60 %). Surge arrester monitors collect very interesting information. Collected info will be compared with the software simulations.

Mitigation of common mode failures at multi-circuit line configurations by application of line arresters against back-flashovers

Due to the limited number of corridors multi circuit line configurations are often applied. These overhead lines frequently consist of high towers that are subject to lightning strokes. In case of higher current amplitudes and higher footing resistances due to bad earthing conditions back-flashovers are caused leading to common mode failures and to severe outages. The paper describes investigations performed by means of computer simulations to identify the towers of a multi-circuit line consisting of voltage levels 380 kV, 220 kV and 110 kV that are endangered by back-flashovers of the 110-kV double-circuit lines. The footing resistance of towers of the targeted line section has been measured by an instrument at high-frequency. Influence of various factors on the back-flashover over 110 kV insulator strings has been studied by means of EMTP-ATP simulations. Different current waveforms of the lightning stroke have been used to represent the first stroke and subsequent strokes. The towers are represented by the models described in [3], [8]. Available flashover analysis methods [7], [8], [12], [13] like leader development method by Pigini et al and by Motoyama, and voltage-time integration method by Kind have been applied. The towers at which back-flashover is more likely to occur than at other towers are identified by the time integral of voltage according to Kind. Various factors like tower footing impedance, tower surge impedance and tower height are considered. Application of line a surge arrester is shown to be a successful mitigation technique to reduce the back-flashover rate of those 110 kV lines. The lightning overvoltage performance of surge arresters has been analyzed by means of digital simulations. Based on the results of investigations line arresters were installed on the towers in question. Since the installation no further common mode failure has been observed.

Line Arrester Application on a 110 kV High Alpine Overhead Line to reduce Lightning-Caused Outages

This contribution discusses a project, which aims to increase the reliability in an existing 110 kV overhead transmission network by taking measures addressing lightning and grounding issues. Due to the fault statistic in the past, a single overhead line was identified as a main reason for the lightning-caused outages in the area. In this work a number of possibilities for the reduction of lightning-caused outages are discussed and the measures taken in the network are described. All considerations took the special geographical situation of 2300 meter above sea level, the grounding resistance of up to 1200 Ohm and the local lightning activity of more than 6 lightning strikes per km² and year into account (4 to 5 times higher than in other Austrian regions). An analytical process was carried out to evaluate relevant parameters and to develop a concept of practical measures. Within these evaluations, the footing resistance, the effectiveness of the shielding angle of the shielding wires and the line arrester locations were analyzed. A multiplicity of numerical calculations were performed to assess the application of surge arresters regarding the insulation coordination for the system. To improve the line performance and to decrease the line outage rate, a number of practical measures were applied to the 110 kV line. In the past, the double three phase systems of the 110 kV overhead line was constructional converted into one active single three phase system with two additional earth wires. According to the numerical results, 18 surge arresters have been installed in a line section of 9 towers, located in a high alpine part and in an area of high lightning activity. Three years of field experiences have shown that the theoretical investigations and the practical measures led to a significant decrease of lightning caused outages. In the year 2007 a new project was started to evaluate a reconstruction of the line into the original double three phase system. New numerical calculation routines were made to apply line arresters at this important 110 kV system in an Austrian extreme mountain region. Based on this results, a new application of line arresters and the constructional change of the system is planned.

EVALUATION OF ENERGY STRESS ON LINE ARRESTERS

Line Surge Arresters (LSAs) are efficient means for the improvement of the lightning performance of transmission lines. Determination of optimal LSA number, location and rating is important for the improvement of the reliability and availability of a transmission system. In selection of the LSA special attention should be paid to their energy stress which depends on complex interactions between the arrester locations, grounding, shielding and the local lightning environment. LSAs experience higher energy stress compared to station arresters, because the incoming surge to a station is limited by insulator flashover on the transmission line and impulse corona. In this paper calculations of energy stresses were carried out for a double-circuit 220 kV line with a single shielding wire. Parametric studies were conducted in which arrester discharge energy was a function of: time to half value of stroke current, number of towers with arresters, footing resistance, span length and angle of power frequency voltage. Arrester energy stress is analyzed in case of stroke to tower and shielding failure. From conducted analysis it can be concluded that energy stress on LSAs is lower for shorter span lengths. Tower footing resistance has only minor effect on the discharge energy. Arrester discharge energy strongly depends on time to half of the stroke current, number of towers with installed arresters and angle of power frequency voltage.

Reduction of the double-circuit flashovers on a 400 kV overhead line

Double circuit flashovers may cause very severe system disturbances when taking place on some critical double-circuit lines of an electrical network. Line arresters offer an efficient solution to protect these specific lines against double circuit outages due to lightning. This paper will study, on a double-circuit 400-kV line, the protection provided by line arresters against double circuit outages due to lightning. The efficiency of several configurations of line arresters will be compared. For that purpose, the double-circuit lightning flashover rates of the line with and without line arresters will be calculated using a newly developed software which includes a three-dimensional electro-geometric model and is able to take into account the random nature of lightning. This software automatically launches EMTP-RV (restructured version of EMTP) for analyzing fast front overvoltages impressed on line insulation. The energy stressing the line arresters will also be calculated in order to evaluate the risk of failure of the line arresters due to excess energy absorption. Furthermore, the effects of several other parameters such as the tower footing resistances, the lightning withstand voltages of insulator strings as well as the protective levels of line arresters will also be investigated.