Subtransmission Lines Research Articles

Failure type and failure level detection of insulators according to monitored leakage current

Due to the ever-increasing growth of electric energy consumption, the production of high-quality, reliable and high-reliability electricity is very important. Therefore, it is essential to have distribution and sub-transmission networks with a good reliability factor. In power distribution and sub-transmission lines, it is necessary to somehow isolate the conductors under voltage from the towers, and insulators are used for this purpose. These insulators have two main tasks. One of the main tasks of insulators is to isolate (insulate) the line conductor from the body of the tower. The insulators must be able to isolate the high voltages of the lines from the body of the tower without having a leakage current, and on the other hand, the insulators must be able to withstand the mechanical forces resulting from the weight of the conductors and the applied forces caused by wind and ice. Also, leakage current is one of the important parameters for condition monitoring of insulators in power grid lines. Failure to inspect the insulation for contamination and health conditions will lead to insulator failure and will cause faults in the electrical system. Therefore, it is very important to monitor the condition of the insulator. Based on this, in this paper, according to the data related to leakage current and also according to the introduced wear out function, a procedure for measuring the condition of insulators has been obtained. Finally, the condition of each insulator will be determined according to the defined indicators. Also, the failure level of each monitored data will be obtained using sensitivity analysis.

Examination of Gas Active Arc Extinguishing and Lightning Protection for Transmission Lines

The study investigated the gas active arc extinguishing and lightning protection for transmission lines. Lightning is one of the most significant sources of over voltages in overhead transmission lines. The lightning over voltages could lead to failure of the devices connected to the transmission line. Fundamental constraint on the reliability of an electrical power transmission system is the effectiveness of its protective system. The role of the protective system is to safeguard transmission system components from the effects of electrical overstress. Shield wire and surge arresters are an important means of lightning protection in transmission and distribution systems. Therefore, it is necessary to analyze the influence of over voltages caused due to lighting. The requirements of system security for lightning protection technology reach the high standard that lightning strike tripping and wire breakage are not allowed. Both the power supply side and the demand side have very high requirements for lightning protection of transmission lines, but the lightning accident rate remains high. This situation poses a great threat to the reliability and safety of power network, it is urgent to solve this problem. The gas active interrupter principle is put forward. From two latitudes of lightning overvoltage and power frequency over current, the effective control of lightning accident rate caused by large probability and multiple lightning strike is realized. This paper is aimed at evaluation of protection level of transmission line by using gas active arc extinguishing, shield wire and line surge arresters against lightning overvoltage. When lightning strikes, the internal short gap of the main body and the air gap break down, and the lightning arc enters the arc-extinguishing body through the breakdown channel. Arc is compressed by force to form internal and external gradients temperature in order to produce jet airflow. Jet airflow acts on the subsequent power frequency follow current arc, a model coupling an arc and a compressed jet airflow in a multi-fracture compression airflow arc-extinguishing structure is established and simulated. The increase in voltage due to lightning are investigated by using the MATLAB software. Direct and induced, types of lightning strokes are considered. The model of a 33kV three-phase overhead power transmission line is developed considering the RL circuit. The simulations are performed based on time domain analysis. Also, numerical analysis is made for 133kV tower structure transmitting power over 220km from 132 KV Sub-transmission Lines in port Harcourt region. Based on the simulation study this research study gas active arc extinguishing and lightning protection for transmission lines, are very important in computer application like Electromagnetic Transient Propagation (EMTP) and Power System Computer Aided Design (PSCAD) which are used in future study. These soft wares provide an alternative way to bring the precise result in study of lightning protection level of high voltage transmission line.

Analysis of 132-33 KVA Grid Sub-Transmission Line along Gombe to Yola Power System of Nigeria

Abstract: In Nigeria, effective electric power transmission is a top priority. Power generating and the network of power distribution are connected via electric power transmission. A research project was conducted to determine the status of the networks in order to improve performance, which resulted in the performance evaluation of the 132KV Sub-transmission lines. Data from the Transmission Company of Nigeria (TCN) substations under investigation were utilized in the research work. The Gombe-Yola Sub-region's 132KV networks are divided into two 132KV active networks and 11 33KV active networks, with a total of 443.617MVA in active loads connected to the 33KV buses. The network was modeled and simulated using the Electrical Transient Analyzer Program (ETAP 12.6), and the bus voltages and network power losses were investigated using MATLAB and Simulink. It was discovered during simulation that the bulk of the network's equipment, including transformers, buses, and transmission lines, experience numerous disturbances that result in forced outages and a corresponding loss of load and productivity. All transformers were critically loaded based on the results of the base-case simulation, with several exceeding 100% loading. As bus voltage magnitudes went outside the +/- 5% nominal rated values, the percentage operational bus voltages were below threshold. Additionally, the systems had undesirable power factor levels. Threatening discoveries prompted an effort to strengthen the networks. In this study, three system enhancement algorithms—capacitor placement, transformer upgrade, and transformer load tap modifications—were applied. To get the best outcome, these algorithms were successively stacked. As a result of significant system improvements, both networks' performance in the final simulation result was within allowable bounds. System-wide apparent losses decreased to a 50% reduction enhancing the networks' efficiency in the process.

Acceleration of distance protection second zone: A non-pilot method based on the healthy phases data

Nowadays, power systems are operated closer to their stability margins and therefore, the need for faster protection algorithms is escalated. The second zone of distance protection is conventionally set to operate with some lengthy delay, which increases the fault clearing time for the end part of the protected line. Therefore, the acceleration of zone-2 for internal faults can remarkably increase the speed of line protection. This practice is traditionally performed by pilot protection systems, which rely on communication channels. This paper proposes a new non-pilot solution to this challenge using only local measurements. A phasor-based algorithm is proposed to detect the remote circuit breaker operation (RCBO) using the healthy phases data. The proposed method has been developed for both single- and three-pole circuit breaker (CB) mechanisms, which makes it practical for transmission and sub-transmission lines. Thanks to using the healthy phases data, the proposed method is immune to the current transformer saturation and capacitor voltage transformer transients. The performance of the proposed method is simulated and investigated in various critical situations besides some experimental tests. The obtained results approve the efficiency and robustness of the proposed method for different scenarios, e.g. noisy conditions, evolving faults, and parallel lines.

Optimal subtransmission switching using a reliability simulation-based multi-objective optimization model

The growth of subtransmission network aims at satisfying load growth, maintaining a contingency level, and providing a high quality and reliable electricity service. Utilities direct the investments to reinforce this system and thus a meshed network with multiple-point feeding to the transmission system arises. At this point, an efficient alternative to achieve these objectives is to carry out a diagnosis of the network architecture and, taking advantage of the switching capability, to plan the switching of the subtransmission lines. An optimal subtransmission switching approach is proposed based on constrained multi-objective optimization that deals with energy losses and reliability, in addition to using information on the characteristics of loads and generation. A simulation-based optimization framework is constructed using the non-dominated genetic classification algorithm NSGA-II in the optimization phase and reliability assessment during simulation phase. As a result, a set of non-dominated solutions approximating the Pareto front is obtained, which allows the planner to make decisions based on its priorities and needs. The performance of the proposal is assessed with a real subtransmission system of an Ecuadorian power utility. This approach to the operational planning of a meshed subtransmission network constitutes a powerful decision-making tool that could be adopted by distribution utilities.

Tripping Profile Analysis of the 33 kV Feeder of Ugbowo 2 x 15 MVA, 33/11 kV Injection Substation

This paper investigated the tripping profile of the 33 kV feeder of Ugbowo 2 x 15 MVA, 33/11 kV electric powerdistribution network. The annual data of daily tripping of the 33 kV feeder from September 2019 to August 2020were collated and collected from the Ugbowo injection substation. The daily outage of the 33 kV feeder was usedto compute the monthly and yearly tripping profile of the sub-transmission line (33 kV feeder) of the Ugbowoinjection substation. The monthly and yearly failure rate, MTTR, MTTF, MTBF, availability, unavailability, SAIFI,SAIDI, ASAI, ASUI, etc. for the period of twelve (12) months were analyzed using the Load Point Indices (LPI)and Microsoft Excel was used graphically to interpret the results of the tripping profile of the 33 kV feeder. Theresults obtained from the analyses of the 33 kV feeder of the network showed that yearly failure rate, MTTR,MTTF, MTBF, unavailability, availability, SAIFI, SAIDI, ASAI and ASUI were 4.32%, 6.520 h, 23.148 h, 29.668h, 21.98%, 78.02%, 0.0358 interruptions/customer/yr, 0.2336 h/customer/yr, 78.03%, and 21.97%, respectively.These results revealed that the performance indices of the 33 kV feeder with annual total outage frequency (SAIFI)and percentage availability (ASAI) were a far cry from the recommended values of the internationally acceptablestandard value (IASV) of 0.01 and 99.99% respectively. This poses a threat to the reliability and availability ofelectricity supply to consumers.

Analysis of wind farm penetration on power swing detection in distance relays

Distance protection plays an essential role in the protection of sub-transmission and transmission lines in power systems. However, power swings have occasionally led to the mal-operation of this type of protection. A significant number of large disturbances, such as blackouts, start with power swings. Thus, improving the circumstances leading to this disruptive phenomenon becomes a great priority. Nowadays, the wind power share of worldwide electricity generation and the use of wind farms have increased. As a result, to predict future events, it is necessary to assess the network in the presence of these renewable sources. In this paper, the effects of the wind resources penetration on power swing have been evaluated. Simulations and analyses have been performed in PSCAD/EMTDC and MATLAB environments, respectively. To provide a comprehensive analysis, maximum power passing through the transmission line and power swing frequency have been utilised as criteria. The results show that wind farms presented acceptable behaviour in the presence of power swing and instability. Therefore, in view point of a power swing, induction generator based wind power plants, compared to synchronous generators, led to better overall conditions. Finally, the effect of fixed and variable speed wind turbines on power swing is compared.

Optimal scheduling of resources for a price-maker distribution company in electricity markets considering network component failures

Electricity generation and storage resources, demand-side participation, along with modern communication infrastructure, have led distribution companies (DisCos) to increasingly play a strategic role in wholesale electricity markets. Although these resources have increased the security of power supply in modern distribution networks, this is still affected by random failures of distribution and sub-transmission network components. Therefore, the main issue that needs to be addressed is how the random failure of the components of the network has an impact on the performance of the strategic DisCos. In this paper, a new framework is proposed to assist a strategic DisCo to determine the strategy of purchasing electricity from the wholesale market and selling electricity to end-users, considering the failure of network components. The proposed model is designed as a stochastic bi-level optimization problem that, at the upper-level, aims at maximizing the expected profit of the DisCo, optimal decisions on the use of resources, and prices offered to the wholesale and retail markets are adopted. Distributed generation (DG) units, battery-based storage sysetm, demand response (DR) programs, and load curtailment (LC) are the resources of the DisCo. Random failures of components are modeled by a set of scenarios. The expected energy not supplied (EENS) is used as the reliability index. The lower-level problem involves the wholesale market clearing problem, with the aim of maximizing the social welfare in which the power allocated to DisCo as well as locational marginal prices (LMPs) are calculated. The model is recast to the MPEC model and then linearized to a MILP model by KKT optimality conditions and dual theorem. Simulations show that, due to the constraints in the distribution network, the failure of distribution and sub-transmission lines reduces the strategic role of the DisCo in the wholesale market. The proposed model can used for analyzing the behavior of strategic DisCos in electricity markets under uncertainty.

Lightning Performance Evaluation of Italian 150 kV Sub-Transmission Lines

A significant majority of overhead transmission lines’ (OHLs) outages is due to backflashovers caused by direct lightning strikes: the realistic assessment of the lightning performance is thus an important task. The paper presents the analysis of the lightning performance of an existing 150 kV Italian OHL, namely, its backflashover rate (BFOR), carried out by means of an ATP-EMTP-based Monte Carlo procedure. Among other features, the procedure makes use of a simplified pi-circuit for line towers’ grounding system, allowing a very accurate reproduction of transient behaviours at a very low computational cost. Tower grounding design modifications, aimed at improving the OHL lightning performance, are also proposed and discussed.

Centralized protection scheme for smart grid integrated with multiple renewable resources using Internet of Energy

Transmission and subtransmission lines in smart grid systems are designed as multitapped lines to supply loads or integrate wind or solar farms as medium-sized generation technologies. Transmission lines with multiple taps are an economical solution to prevent building new substations. However, these types of tapped lines create operational and protection challenges. When renewable resources are added to feeders, they act as transmission lines where energy flows in either direction in protection relays. Then, fault current flows in different directions and the coordination protection for this configuration fails. Modern protection schemes based on standalone decisions are not suitable in such cases, and new system protection methods should be devised. A key factor for future energy supply is information and communication technology based on the Internet of Energy (IoE), which is utilized to exchange information among all measurements on transmission and subtransmission systems in an environmental domain for accurate unit protection and the optimization of the coordination process. This information is collected by employing integrated electronic devices (IEDs). In such cases, the data measured by IEDs and exchanged in the environmental domain using IoE can achieve accurate unit protection for optimizing the coordination process. This system is a new development in the protection field using informatics; it is named i-protection. i-protection provides a novel method of accurately detecting faults using IEDs and IoE through wide-area wireless networks such as the IEEE 802.16 WiMAX technology. This is the first study to apply i-protection for protecting complex configurations with multiple taps at two different levels, i.e., transmission and subtransmission. The protection method considers the studied power system as one zone rather than multiple separate protection zones, which are used by conventional protection. The results show that the proposed protection method can successfully detect all types of faults in complex multitapped transmission lines with renewable resources. Moreover, the initial results indicate that the IEEE 802.16 network can meet the latency requirement of the proposed protection scheme.

Flashover and Back-Flashover Analysis with Lightning Strokes of 69 kV and 24 kV Lines in Thailand Using ATP/EMTP

Lightning is the principal source of disturbance in power system leading towards outages and damage of expensive equipment in the electrical power network. Induction of disastrous voltages across string insulators from the lightning that causes flashovers and back flashovers have been the major study in recent researches. Efficient parameterization of lightning and it is associated with behavior provides a significant knowledge towards successful operation of the electrical network. Therefore, this work studies the effects of flashover and back flashover affected by negative lightning (single and double) strokes in the operation of 69 kV sub-transmission line and 24kV distribution line of Metropolitan Electricity Authority, Thailand. Seven poles spanning 24 km were considered in this study. Lightning was initiated at the vertex of the fourth pole and mid-span of the third and fourth pole, and investigations were carried out by lightning magnitude and multiplicity when it hits an overhead ground wire (OHGW) and phase A of the 69 kV line by using ATPDraw. Results showed that negative lightning stroke of -34 kA and above could induce disastrous voltages across string insulators that leads to back flashover and flashover when hits at the top and mid-span of OHGW and phase conductor respectively. Power failure in 69 kV may cause double failure to the network since it is the main power source of 24 kV line. Consequently, a double failure may direct towards reduced reliability and extra maintenance cost of catastrophically damaged line insulators. Therefore, the concept of flashover and back-flashover can help to improve the lightning performance of MEA power lines.

Optimal control of novel fuel cell-based DVR using ANFISC-MOSSA to increase FRT capability of DFIG-wind turbine

Although Doubly fed induction generator (DFIG)-based wind turbine has several significant advantages, any voltage fluctuation can severely disturb its normal and safe operation, i.e., it is characteristically very sensitive. Hence, fault ride-through is determined as a prominent benchmark for DFIG which must be enhanced by a voltage compensator. Dynamic voltage restorer (DVR), a voltage fluctuation mitigator, is connected in-series with distribution and sub-transmission lines so that DFIG can appropriately operate during any type of disturbance. In this paper, a new two switches boost converter (TSBC) coupled with quinary multilevel inverter (QMLI) is proposed which is fed by fuel cell to produce staircase sinusoidal voltage for DVR. The proposed step-up DC/DC presents two important advantages: low current ripple and low switch stress, while QMLI can create high-step staircase sinusoidal voltage without considering a number of switches. TSBC-QMLI-based DVR has been controlled by neuro fuzzy inference system controller (ANFISC). As the control problem is multi-objective and complex, Multi-Objective Salp Swarm Algorithm (MOSSA) has been applied to optimally tune the ANFISC’s parameters, and then compared with Non-dominated Sorting Genetic Algorithm II (NSGA-II). To verify and validate the compensation capability of proposed DVR, it has been thoroughly evaluated under different voltage disturbances. Eventually, the simulation results have validated the compensation capability of the suggested TSBC-QMLI-based DVR which is accurately controlled by MOSSA-based ANFISC to mitigate the balanced and unbalanced voltage sag and swell along with the flicker and harmonic voltage.

Evaluation of regulatory impacts on investments of distributed generation and upstream network under uncertainty: a new stochastic bi-level model

A new framework is proposed to study impacts of regulatory incentive policies on distributed generation (DG) investment, as well as upgrading of upstream transmission substations and sub-transmission lines. Investment incentives are fuel cost, firm contracts, capacity payments and investment subsidy. Conventional and wind generation technologies are considered as expansion candidates for investor which participate in wholesale and contractual markets. High Temperature Low Sag (HTLS) conductors are used as expansion candidates for lines. The problem is modelled as a stochastic bi-level optimization problem, where the upper-level consists of investor’s decisions maximizing its own profit, while both market clearing and decision on upgrading of substations and lines aimed at minimizing the total cost are considered in the lower-level. Due to non-convexity of lower level problem, an algorithm based on enumeration and mathematical optimization is used where for each expansion strategies of substations and lines, the bi-level problem is converted to a stochastic mathematical programming with equilibrium constraints and then converted to a mixed-integer linear program. The effectiveness of the proposed model is tested through on an actual 22-bus [The west of MAZANDARAN Regional Electric Company (MREC) sub-transmission network as an area of Iran interconnected power system.] network.

WSN-based monitoring and fault detection over a medium-voltage power line using two-end synchronized method

Traditional fault detection and location methods depend upon the values of system parameters calculated by potential and current transformers. During the faulty period, the secondary current is not the exact replica of primary current. Fault locators are being used since many years for fault location in two-end synchronized measurement system. These fault locators pose problems when faults occur at the zero crossing of sub-transmission line voltage or current. It eventually disturbs the economy too. This issue is more momentous in high-impedance lines as compared to low impedance. To remove such issue, this research presents the concept of using wireless sensors with sensor node gateways as a tool for fault location. The wireless sensors measure the magnitude of fault quality momentarily in discrete times. The concept is based on placing the wireless sensor network (WSN) at the sending and the receiving ends of sub-transmission line and analyzing the response on both sides. Peer concept of WSN for identifying and localizing the power system faults such as phase to phase and single phase to earth faults are considered in this research work.

Support at Decision in Electrical Systems of subtransmission through selection of Topologies by a Paraconsistent Simulator

In this work, we present a Simulator Program that identifies the topologies and supports operation staff in decision-making about loads reassignments and changes in electric network, offering a selection of the best settings. Facing a contingency situation or action of relocation of electrical system of subtransmission lines, the Simulator considers the current state and uses special algorithms that detect the current network topology, interprets results and presents for operation the possible different maneuvers with their respective degrees of reliability. For these actions the software Simulator elaborates the states investigation of circuit breakers and electric keys, analysis of load flow, makes risk prediction and the mathematical analysis of remote sensing values. The software Simulator uses in some of his actions, special algorithms that are based on Paraconsistent Annotated Logic (PAL), which is a non-classical logic whose main property is to accept contradiction in their fundamentals. These algorithms based on PAL offer greater speed of processing and allows the Paraconsistent Simulator of topologies (ParaSimTop) to be implemented in real time.

Tower Grounding Improvement Versus Line Surge Arresters: Comparison of Remedial Measures for High-BFOR Subtransmission Lines

This paper presents a technical/economic comparison between remedial measures aimed at improving the lightning performance of an existing Italian three-phase 150-kV overhead line. The line is characterized by a very high back-flashover rate (BFOR), due to large grounding resistance values. Two countermeasures are proposed: grounding system improvement with additional vertical rods and line metal oxide surge arrester (MOSA) installation on one or all phases. A Monte Carlo ATP-EMTP procedure developed by the authors, which takes into account both the tower grounding nonlinear transient response due to soil ionization and MOSA nonlinear response, has been applied to evaluate and compare the effectiveness of the proposed countermeasures. The installation of MOSA on all phases is technically the best option, but it is relatively expensive. Tower grounding improvement and MOSA installation on the lower phase yield very similar BFORs: the economic comparison strongly depends on tower's accessibility and soil nature.

Grounding Design Improvement to Reduce Back Flashover Rate of 69 kV Subtransmission Line in Power’s Distribution System

This paper presents the grounding design improvement to reduce back flashover rate from the lightning of distribution system. The Purpose to reduce effects of lightning overvoltage from back flashover. And study analysis of the condition effects of lightning performance of 69 kV on Metropolitan Electricity Authority (MEA)’s distribution system of Thailand. The technique objective function is an attachment the external ground wire connected between the overhead ground wires and a ground rod for reduce back flashover. Back flashover is one of the major causes of sustained interruption data. Occurs when the amplitude of lightning overvoltage is more than the limit of insulator strings specification. Then generated flashover on insulator skin and induces the voltage line. This paper simulation with Alternative Transient Program-Electromagnetic Transient Program (ATP-EMTP) and analysis of lightning performance in terms evaluated pole top voltage and back flashover rate (BFOR). Result after installing the external grounding design system can reduce the effects of lightning and can improve the reliability in distribution system. And the grounding systems designed is can use for guide line to the features typically at locations subject to lightning damage.

Evaluation of Inter Regional Power Flows in Planning Studies

Power System Transmission Planning involves huge investment in the Power Sector. The network condition, the available load and generation are the factors to be considered for proposing the power transfer between regions. However if the envisaged power flow could not be achieved due to constraints after commissioning of the Transmission Lines or Sub-Transmission Lines it could lead to huge financial loss to the Utilities. Hence a case study of 14 bus known network with different contingencies is brought out in this paper to visualize the limitations in inter regional power transfer in spite of available generation to be exchanged within the regions.

Improving The Lightning Performance of Overhead Distribution and Sub-transmission Lines Applying Additional Underbuilt Shield Wire

This paper analyzes the lightning performance of 22 kV single and double circuit overhead distribution lines and 115 kV sub-transmission line with 22 kV circuit underbuilt by means of installation the additional underbuilt shield wire. The three different shield wire sizes of 25, 35 and 50 mm2 and the placement locations from ground which is taken into account the clearances from the phase conductors and ground have been considered. Evaluating were performed using ATPDraw and calculations by applying the equations from IEEE std. 1243-1997 and 1410-2010 to determine the best placement location and size. For the systems being studied, both for overhead distribution and sub-transmission lines, the additional underbuilt shield wire can be used to gain better lightning performance besides the overhead shield wire.

Electrical and Economic Study of Applying the ACSS Conductor in TREC Subtransmission Network

Increased energy consumption in industrial and commercial subtransmission networks has considerably increased the loading of transmission lines. In order to satisfy consumer demand, this capacity should be increased. Three main ways of increasing capacity are using high-temperature low-sag (HTLS) conductors, increasing the number of bundles, and building new subtransmission lines. This paper is a report on an attempt to increase the power transfer capacity of Tehran Regional Electric Company (TREC) subtransmission network through the above-said methods. For the purpose of re-conductoring, the existing LYNX conductors (ACSR) in the network under study were replaced with equivalent HTLS conductors (ACSS). Calculations were performed for sag tension, current carrying capacity, and electrical parameters. The methods were simulated using DigSilent software for the peak load in the year 2014. The three methods were compared in order to determine which one produces the best results. The comparison took account of the costs associated with power loss and considered technical and economic issues. Keywords: Increasing current capacity, HTLS conductor, Subtransmission lines, Economic Studies, Tehran Regional Electrical Company