EHV Lines Research Articles

The innovative EHV line and its main indicators

Single-circuit EHV lines widely used all over the world have a significant drawback, consisting in the fact that with the most probable single-phase stable failures, the line is completely taken out of operation. In this paper, a single-circuit EHV line is considered, one phase of which is made in the form of two parallel semi-phases, any of which is used as a backup phase in emergency modes. To symmetrize the conditions in the middle of the line, the Series Capasitor (SC) are included in the two usual phases. The article presents an algorithm for calculating normal modes, the main indicators of an innovative 500 kV line, consisting in its increased capacity, reliability and economic efficiency. The main provisions are illustrated by the example of a 500 kV line with a length of 500 km.

Increasing Transmitted Power With Cost Mitigation via Modified EHV Power Lines in Egyptian Grid

The main goal of this work is to mitigate the cost of modified EHV line of the Egyptian transmission network. The existing HVAC line is replaced by four configurations, the first one is double circuit operating with an AC potential and bipolar DC circuit of ±500 kV while the second one is a double circuit operating with 500 kV AC circuit and ±500 kV bipolar circuit with required conductor and/or tower modification. The third one is a double DC circuit working with two ±500 kV. The fourth configuration is working with three ±500 kV bipolar circuits. The study shows the increase in transmitted power percentage and the cost mitigation for each suggested configuration relative to the existing AC line. Starting from the break-even distance of each configuration to 500 km, each configuration result will be analysed. Configuration 1 has the shortest break-even distance at 148 km. The power percentage increased from 3% to 5% and the cost mitigated by 22.17%. Break-even distance of configuration 2 is 171 km. Configuration 2 has power percentage increase from 30% to 32% and the cost reduced by 22.45%. Above 212 km break-even distance, configuration 3 has the best cost mitigation percentage of 28.60% and the power percentage increased from 7% to 9%. Configuration 4 records the highest increase in the power percentage range of 60% to 64% and cost reduction of 27.72% after 221 km break-even distance.

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.

Influence of the Secondary Arc on the Operation of Single Phase Autoreclosure of the 400 kV interconnection between Hungary and Croatia


 
 Sažetak: Faults on EHV lines are generally single-phase-to-ground ones and not permanent in the majority of cases. Thus single phase auto reclosure (SPAR), at which the faulty phases are tripped for a short time, eliminates the predominant part of the faults [1,2]. The secondary arc, which follows the high power arc after tripping the faulty phases at both side of the line may endanger the successfulness of reclosing if the duration of the switched off interval (dead time) is not long enough to ensure the extinction of the arc. The secondary arcing times recorded on different EHV lines or measured in laboratory tests show significant spread, consequently, to select a dead time according to the longest experimental secondary arc extinction time is not feasible. During commissioning of the double circuit 420 kV interconnection between Hungary and Croatia several staged faults were initiated to analyze the arc extinction performance. Initially the line was in operation by connecting the two circuits in parallel along the 1/3rd of the full length. In this configuration the longest secondary arc extinction time was 4 seconds and the secondary arc has not extinguished in 27s in one of the tests, so the line had to be tripped out to clear the staged fault. Later on, the length of the Croatian section of the line has been significantly shortened after putting a new substation into service. The increased performance of SPAR of the new arrangement has been proved with field tests. A realistic representation of the secondary arcs is essential in determining the auto-reclosure performance of EHV transmission lines. As shown in the paper, the random variation of the arc parameters influences significantly the arc extinction time. The results of the field tests confirmed the importance of the distributed nature of the transmission line and the nonlinear characteristic of the arc resistance in the intermittent region of arcing, where temporary extinctions and sudden re-ignitions in the arc channel produce transient wave processes along the line.

Application of ANN and Genetic Algorithm for Evaluation the Optimum Location of Arresters on Power Networks due to the Switching Overvoltages

Switching surges are of primary importance in insulation co-ordination of EHV lines, as well as in designing insulation of apparatuses. The magnitude and shape of the switching overvoltages vary with the system parameters, network configuration and the point-on-wave where the switching operation takes place. This paper presents an artificial neural network (ANN) based approach to estimate the peak value of overvoltages and the global risk of failure generated by switching transients during line energizing or re-energizing in different nodes of a power network. Then a genetic algorithm (GA) based method is developed to find the best position of surge arresters on power networks so as to minimize the global risk of the network.

MATLAB/Simulink Analysis and Implementation of Fault Identification of EHV Lines Using Wavelet Transform based FLC

MATLAB/Simulink Analysis and Implementation of Fault Identification of EHV Lines Using Wavelet Transform based FLC

Exposure level control of power frequency electric field near angle tower of 500kV transmission lines

The distortion of power frequency electric field in the roof space near the angle tower of EHV line is serious, which is an important factor to be considered in transmission line planning and design. This paper establishes a three-dimensional electric field simulation model near the angle tower of 500 kV transmission line and verifies the validity of the simulation by field measurement. Based on this, the factors affecting the spatial electric field level on the roof of the house near the angle tower are analysed. Finally the control distance of the house near the angle tower is calculated according to the electric field exposure limitation in Chinese standards. The results show that the electric field near the transmission line is distorted and elevated by the house, and the electric field level of the roof decreases with the increase of the distance between the house and the line, and decreases with the decrease of the height of the house and the angle of the line.

A Simplified Approach for Assessment of Exposure of EHV and UHV Lines to Direct Lightning Strikes

Modeling of lightning attachment to multi conductor transmission lines is made more complex by the effects of mutual conductor proximity, ground field due to cloud charges prior to negative leader descent, and operating voltage of the line. In this paper, it is found that the lateral attractive distance <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds</sub> of any conductor can be expressed by a product of the corresponding value <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds0</sub> of a single free conductor and three dimensionless variable functions <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pr</sub> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eg</sub> , and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ov</sub> characterizing proximity, ground field, and operating voltage effects, respectively. The method is applied to 345-, 420-, 525-, 765-, and 1150-kV transmission lines and satisfactory agreement is obtained with the results of detailed modeling.

Design and Implementation of an Algorithm for Diagnosis of Load Encroachment in EHV Lines

Zone-3 mal-operation of distance relays was one of the important cause for many of blackouts in worldwide. The one of the root cause for the mal-operation is encroachment of load into the Zone-3 characteristics. Such zone-3 mal-operations can be prevented by improvising the zone-3 characteristics which eventually avoids cascaded line tripping. This paper proposes and validates a new algorithm based on the total DC component and Phase angle of the positive sequence impedance to prevent its operation during the load encroachment conditions. Based on the proposed algorithm, improvement in the operation of Zone-3 element can be achieved. The relay can differentiate between actual system faults and load encroachment and thus ensure the security of the system. The proposed algorithm supplements the Zone-3 operation by introducing the ability to identify a load encroachment condition, and thus can avert the possibility of blackouts.

Evaluating flashover performance of insulators under fire fighting conditions

EHV and UHV high voltage transmission lines frequently pass through high vegetation areas as well as national forests where there is a significant risk of wildfire by natural or manmade causes. Firefighters use aerial vehicles to douse fires by dumping large amount of fire retardant liquid that is conductive, thus increasing the risk of insulator flashover and power interruptions. In this paper, an ammonium polyphosphate based fire retardant liquid was evaluated to understand its effect on insulator flashover properties. Composite and ceramic insulators, suitable for 115 kV transmission lines, were studied by the solid layer test method. Tests were conducted with and without external wetting by fog. Results indicate that there is a high probability of flashover if the entire insulator is coated with the fire retardant liquid. Statistical methods were applied to extend the validity of testing results to predict flashover voltages at higher voltage levels of 230, 345 and 500 kV. It is shown that standard insulator dimensions used for EHV and UHV lines in fire prone areas could be deficient and additional insulation required to improve the flashover performance to acceptable levels in such locations has been determined.

Theoretical Analysis and Countermeasures on Iced Galloping of Overhead Transmission Line

Taking severe galloping accident in some lines in January, 2015 as an example, the conditions and processes of galloping’s occurrence and development belong to EHV and UHV lines was analyzed. And aiming at improving the theoretical cognitive level of galloping, and proposing to improve the power grid's ability against icing galloping, some suggestions were given on reasonable arrangement of anti-galloping fittings.

Cost Optimal Design of a Power Inductor for VAR Compensation in EHV Line

The paper presents the procedure for finding out inductive compensation required for an EHV transmission line at its terminals. It also presents the design methodology for the power inductor. The 3-phase power inductor is similar in construction to a 3-phase core-type transformer with the exception that it has only one winding per phase and each limb is provided with an air-gap, the length of which is decided upon by the inductance required.

Modeling and Fault Analysis of Doubly Fed Induction Generators for Gansu Wind Farm Application

Wind power is developing rapidly as a means of handling the world's energy shortage and associated environmental problems. The Gansu provincial wind energy resources have around 237-GW wind power potential in China. In this paper, a study on key technologies of Hexi 750-kV power transmission line protections has been carried out. The project includes some characteristics, such as large-scale wind power, long-distance EHV lines, and so on. We used 49.5-MW doubly fed induction generator (DFIG) wind turbines in this project and different situations when a fault occurs in the presence of DFIG are studied and investigated. By the aid of stator-flux-oriented vector strategy, the system is modeled in PSCAD/EMTDC software on the basis of the real information from the wind farm site. The fault analysis is studied while the fault location is changed and the crowbar protection is ON/OFF. The data and information have been obtained by field experience of the wind farm in Gansu province. Also, the matrix pencil algorithm has been applied as a novel method in this project. This analysis can ease the protection issues and push the schedule to the next steps. With these results, we are able to adapt our system with smart grids and provide some novel methods to stabilize and control the wind farm.

The Research on Development of EHV Line Longitudinal Protection Debugging Device in Intelligent Substation

In smart substation, transmission line longitudinal protection debugging cannot take place, before the line communication channels construction, that cause it often occur that not fully debug, choose a suitable time for debugging in advance. In this paper, based on the analysis of the longitudinal protection debugging process, combining with the computer technology, and 3G/4G communication technology, design a set of intelligent substation EHV-line longitudinal protection device of temporary channels. Ensure, in intelligent substation, carry out advanced debugging, select the appropriate time debugging, debugging completely, before the longitudinal channel built, and establish a reliable foundation for the normal operation of the longitudinal protection equipment.

Reactor Failure due to Resonance in Zahedan-Iranshahr Parallel EHV Lines, Analysis and Practical Solutions

A reactor winding has been damaged due to induction of resonance voltages on the de-energized circuit of two parallel 230 kV shunt compensated lines between Zahedan and Iranshahr. The phenomenon is modeled in PSCAD and the safe range of shunt compensation is derived. In this study the effect of various faults on the lines, the reactor saturation and corona dissipation are considered and the results are compared to the electrostatic no-loss method results. Various ways are examined for damping the resonance condition and the best solution is chosen.

Fast Distance Protection for Proximal Fault of EHV Transmission Line

As the full length is considered in the traditional EHV line protection, proximal circuit fault can’t be moved in an ideal short time. A fast distance protection algorithm for proximal fault of EHV transmission line is proposed in the paper. Based on differential equation model and power frequency variation principle, the method has fast response speed and small workload. And the protection for proximal fault of long distance EHV transmission lines can be correctly implemented in a very short time. The method is realized with a low pass prefilter and without digital filter. Finally, through the RTDS simulation platform, a variety of fault modes of 500kV transmission lines is realized, and the accuracy and rapidity of the algorithm is verified by the simulation result. DOI: http://dx.doi.org/10.11591/telkomnika.v11i2.1984

Modeling and Simulation of power system using SMIB with GA based TCSC controller

Power system is always affected by transients that create oscillations & voltage instability. Several techniques are invented to overcome instability problems & improve power system performance. The most common used technique is power system stabilizer called PSS. The PSS has limit to damp the oscillations due to power grid network. So another device/stabilizer is required for system stability & reliability. These requirements generate the vacancy for FACTS & FACTS devices like SSC, IPFC, UPFC, SVC & STATCOM. In this paper we used TCSC as controller for stability of power system & tuning of TCSC is done by the genetic algorithms. The effect of TCSC controller is demonstrated by using SMIB. General Terms: In recent years, significant development has been come out in power system stability improvement, particularly FACTS transmissions & FACTS devices. The power systems are connected as large system through EHV lines. The methods of grid management & operation is also upgraded with advancement in the socioeconomics. Power system strongly demands security, reliability & stability, efficient & flexible operations. So it attract new researchers to developing new regulation techniques with enhance controller.

Optimum Compensation To Improve EHV Line performance

Series compensation and shunt compensation are being used in EHV lines to improve their performance. While planning the compensation, it is necessary to select properly the degree of series and shunt compensation, the appropriate location or locations of the compensating equipment. The optimum selection of series and shunt compensation ha to be such that the total MVAR requirement is lower, the line voltage profile is well within the limits, the transmission efficiency is high and the system stability is improve. In this thesis a systematic method is developed to select the optimum series and shunt compensation to be employed in EHV lines for a given loading condition .Case studies are presented and a comparison of different compensation scheme is made.

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.

An improved leader progression model for the analysis of the shielding performance of 1000 kV UHVAC transmission lines

AbstractThis paper presents an improved leader progression model (LPM). The model uses the proposed leader inception criterion for the analysis of lightning shielding performance of UHVAC transmission lines. It focuses on the discussion of the leader inception voltage of bundle conductors. The improved LPM is validated on 500 kV EHV transmission lines. The shielding performance of a UHVAC transmission line to be constructed in a Chinese Test Line Project is then evaluated. The results indicate that the power frequency operating voltage and the bundle conductor configuration have a greater influence on the shielding failure flashover rate (SFFOR) of 1000 kV UHV lines than that of 500 kV EHV lines. It is found that the UHVAC line to be built will not cause trip accidents due to shielding failure in flat terrain. In broken terrain, the SFFOR is only 0.0012 times/100 km·year, which is less than the design limit. Copyright © 2008 John Wiley &amp; Sons, Ltd.