Search

Substations, as critical components of the power system, are frequently exposed to various external risks during operation. Without timely monitoring and effective evaluation, the risks caused by anomalies can undermine the stability of the mining area’s power system, potentially leading to significant production interruptions and safety accidents. However, current research mainly focuses on the substation internal risks. Regrettably, there is currently a lack of implementable external risk assessment methods for substations. To detect substation external risk level effectively, an external risk assessment method for substations based on single and superimposed anomaly risks is proposed. First, the CAVF (Identification credibility C, anomaly area proportion A, anomaly development velocity V and correction factor F) external risk assessment model is constructed, based on the improved PES (Probability, Exposure, Sequel) operational risk assessment method. Next, the collaborative set pair analysis of uncertain AHP (Analytic Hierarchy Process) is used to assign weights to the importance of different anomalies, addressing the differences in the impact of each anomaly and the fuzziness of expert judgment. Then, the IDO (Identity Difference Opposition) contact measure method is adopted to determine the substation external risk level under multiple superimposed anomalies, with the importance weight vector of anomalies. Finally, the substation external risk level is evaluated, comprehensively considering the risks of single and multiple superimposed anomalies. A case in an actual scenario shows the effectiveness of the proposed method, highlighting its significant impact on optimizing maintenance configurations and ensuring the safe operation of substations.

In order to improve the ability to detect and identify topological errors and measurement errors, and further enhance the rapidity and reliability of substation state estimation, this paper proposes a three-phase linear state estimation method for substations based on zero impedance model. Firstly, for the shortcomings of the traditional regularized weighted residual method with many cycles and slow calculation speed, improvements are made to improve the rapidity of state estimation while suppressing the residual flooding phenomenon. Based on this, the zero-impedance model of the substation makes full use of the three-phase telemetry and telecommunication state data to establish the power measurement equation for zero-impedance initial power state estimation, and proposes a discrimination method to identify measurement errors and topological errors and to determine the state of the switching circuit breakers. Based on the secondary power state estimation, a voltage measurement equation is established based on the voltage measurement information to estimate the substation voltage state. The simulation results show that the method can accurately identify and locate the simultaneous measurement errors and topology errors, and can also identify individual measurement errors, thus improving the estimation accuracy of state estimation.

This paper introduces a physical scaled-down realistic substation laboratory model development for translational research and education in smart grids. The development of a substation panel with four 3- $\phi $ feeders of 415 V, 65 A rating is described in detail. The developed substation model can be configured to realize seven widely used substation bus bar arrangements. A programmable logic controller (PLC) is used to create interlock mechanisms for mimicking the actual substation operation practices. Provision is made to realize the gang and independent pole operation of circuit breakers, the manual and remote modes of operation, and different types of current transformer arrangements. The substation panel can host up to 10 commercial IEDs, and multiple substation panels can be cascaded to form a bigger station using the master-slave configuration of PLCs. All the potential transformer and current transformer measurements, circuit breaker, isolator, and earth switch status signals are made available for connecting field devices. The developed substation model can be used for advanced research on substation automation using IEC61850, validation of new protection strategies, implementation and testing of new algorithms (such as topology processing, state estimation) for energy management systems (EMS) like how they get implemented in the field.

This papers presents a numerical approach based on computational fluid dynamics (CFD) that was developed to ensure that gravity oil-water separators at Hydro-Québec electrical substations comply with the environmental legislation in place. More precisely, multiphase simulations are performed for two operating conditions of an in service separator, and an experimental setup is used to produce an oil spill and to measure the time-varying oil concentration at the separator outlet. The results show that, for the tested conditions, the oil droplet size at a separator inlet generally follows a log-normal distribution and that the droplet diameter varies between 100 and 1000 µm with a mean value of 475 µm. Furthermore, both the experimental and numerical results show that the time required for the oil droplets to reach the separator outlet is quite shorter than the theoretical mean residence time. Finally, this study demonstrates that the numerical model predicts the separator efficiency within 1% of the measured value, and that it can be a valuable tool to investigate existing separators or to design new ones. [ABSTRACT FROM AUTHOR]

Recently, the grounding system of substation has been seriously invaded by earth current generated by flourishing urban rail transit network. The invasion leads to abnormal vibration of transformer and even some electrical safety problems. This article presents a dc and harmonic current suppression system (DHSS) applied to the neutral point of transformer. The design and development of the DHSS are described in detail. The power circuit is designed as a segmented structure with dc current blocking and harmonic current suppression. The high-speed bypass protection circuit is implemented to ensure the reliable grounding of neutral point in any case. The matching control and protection system is developed. The proposed controller for suppressing harmonic current is applicable for the neutral point and meets the requirements of relay protection. The design details and difficulties are discussed. The development, commissioning, and experiment are completed in the laboratory. The developed prototype has been subjected to high current impulse tests. The performance and reliability are verified by the presented results. This prototype is running on-site in a 220 kV substation. [ABSTRACT FROM AUTHOR]

To evaluate the earthquake-resistance capability of an entire substation, which is a complex multi-input-multi-output system (MIMOS) composed of many various types of electrical equipment interconnected by conductors, a flow-based analysis model integrating the merit of the flow block diagram and state tree method was introduced. Two performance indicators of a substation were defined from different stakeholders, one is the expected total power transmission capacity and the other is the power accessibility to the targeted users from the substation. And directed graph logic system analysis models were developed on the Simulink platform based on the original internal logic relationship among distributed components and the power delivery path in the substation with different function types. Afterward, the defined reliability indicators associated with the overall system under a certain seismic intensity level can be obtained by combining the seismic vulnerability curve at the equipment level through the Monte Carlo simulation method. The feasibility and accuracy of the proposed system vulnerability analysis model were verified by comparison with the analytical solution through the illustrative simple MIMOS. Then A case study on a practical 220/110 kV substation was conducted, the analysis results can assist decision-makers in seismic optimization of different retrofitting measures and distribution plans for substations. [ABSTRACT FROM AUTHOR]

To balance the potential distribution on the surface of a substation, an equal spacing arrangement of the grounding grid conductors is not an economical solution. The implementable solution is an unequal placement of its constituent elements. The design methodologies of such a configuration are complex and require computer-assisted numerical analysis. This paper proposes and validates a very simple method, based on an arithmetic progression, of arranging the conductors of the grounding grid that guarantees the reduction of touch and step voltages, ensures the efficiency of the material used and has no limitations on its applicability for atypical substation surfaces (too large or too small), respectively for few or many parallel conductors. To certify the method, the proposed algorithm is analyzed, through the CYMGRD Substation Grounding Program, and compared to the technologies currently applied, for the substation grounding grid presented as an example in the IEEE Guide for Safety in AC Substation Grounding 80™- 2013 standard.

This paper presents the possibilities of reducing emergency situations and reducing the time of failure in the power grid. The paper contains a detailed description of the method (algorithm) of operation in emergency situations on the example of a Gas-Insulated Switchgear (GIS) located in one of the system-forming (node) stations in the power grid. The level of detail contained in this paper, which has not been previously encountered in previous publications, favors an in-depth understanding of the possible solutions that result from these emergencies. The above method (algorithm) of activities has been developed based on three levels of research: simulation, theoretical and practical. This means that the simulation analysis that was performed based on theoretical information was experimentally tested as part of an emergency situation in one of the system-forming (nodal) stations in the power system. In order to achieve the result described in this article, one of the most promising types of devices used in power systems was selected - the GIS. This has been confirmed by numerous analyzes of the effectiveness of these devices included in this article. The paper contains a detailed description of the individual steps in the field of corrective actions and aimed at minimizing downtime. In addition, this article provides guidance to monitor possible emergencies that are designed to increase the reliability of the power grid. [ABSTRACT FROM AUTHOR]

Although natural disasters have recently imposed enormous damages to power system infrastructures, resilience enhancement through hardening measures is not usually compensated in conventional power system planning. In this article, a framework is proposed to enhance the resilience of distribution systems against earthquakes. In particular, it focuses on substations’ retrofit whose failure can affect the distribution system, imposing outages to the customers connected to it. A knapsack based heuristic method, which considers the bus configuration of substation is proposed to select the substation components for hardening. The potential failure of substation components that would lead to complete unavailability of substation is evaluated through minimal cut set-fault tree analysis. A criterion for resilience enhancement is proposed, including hardening cost, cost incurred by damaged components, cost of customers’ interruption in the distribution system level, and power generation cost of Distributed Energy Resources. A penalty mechanism taking into account the component repair time is used to estimate interruption costs. The impact of earthquakes on substation components is modeled using fragility curves. A case study with real earthquake characteristics is considered and Monte Carlo simulation is used to capture the stochastic failure of substation components. The results show that power transformers and circuit breakers at 20 kV are the most critical components in the retrofitting strategies. [ABSTRACT FROM AUTHOR]

Recent development and cost down of PV(Photovoltaic) technology drive change of power system structure. The participation of PV generation is increasing, and the size of each PV farm is getting larger. In order to integrate large PV farms into the main grid, substation for interconnection needs to be sized properly. Unlike substations for load and conventional generators, PV farm substation has an uneven utilization ratio due to characteristics of solar radiation. With proper sizing method for the capacity of the substation can reduce the building cost of facilities. A combination of an energy storage system can further reduce the capacity of the substation. Battery energy storage system (BESS) can shift the peak production of PV during the daytime to midnight. According to market circumstances, BESS can reduce further construction costs by producing profit based on time difference of electric cost. For proper sizing of substation capacity, several factors must be considered including environmental factors, market structure and BESS in the system. In this article, a series of assessment methodology is introduced to calculate the optimized capacity of substation and BESS for PV farm interconnection. The long-term solar radiation data is analyzed for a given site of the PV farm. Based on market structure, the operation of BESS is optimized to make maximum profit during operation. The iterative calculation of each step results in the calculation of the optimized capacity of BESS and substation for given PV farm size.

Many existing petrochemical facilities are replacing outmoded high voltage (HV) air insulated switchyards (AISs) with new gas insulated switchgear (GIS) substations. Modularization or prefabrication has strategic advantages over site-built substations. While medium voltage (MV) and low voltage (LV) substations have been modularized for many years, the HV GIS substation modularization has not caught up with the construction industry. The modularized HV GIS substations are significantly different compared to other electrical MV or LV substations. This article addresses the modern philosophy and approach to modularization and how the end-user can benefit, in terms of design flexibility, cost-effectiveness, reduced lead times, premium quality, and accelerated site execution in a new or an operating facility. It describes the technological developments, design concepts, quality assurance, and environmental impact in delivering complete solutions based on site conditions. [ABSTRACT FROM AUTHOR]

Substation bus ampacity calculations perform a steady-state heat transfer analysis on a unit length of bus. In this analysis, the convective heat transfer coefficients for rectangular, universal angle bus (UAB), and integral web bus conductor (IWBC) have historically been calculated by applying flat plane correlations to the individual bus surfaces. The research presented here will show that the Nusselt correlations developed for the specific bus, similar to what is currently used for round bus, increases accuracy in bus ampacity predictions. Additionally, the correlations are easier to use and less likely to result in calculation error. This paper presents natural and forced convection correlations for rectangular, universal angle bus, and integral web bus. [ABSTRACT FROM AUTHOR]

For extended critical infrastructures such as the power grid, electromagnetic compatibility (EMC) testing of electronic components alone is not sufficient to assess the risk of electromagnetic (EM) attacks. This paper presents results on a methodology for high-power EM based risk assessment of large structures considering the example of smart grid substations. The evaluation involves control, protection, and communication equipment used in substations as part of supervisory control and data acquisition systems and ready for the smart grid. The methodology developed in this paper evaluates the threat, vulnerability, impact, and protective measures as indicators in various scenarios of both conducted and radiated intentional EM interference (IEMI) threats to these systems. In order to assess these indicators, fundamental data on available IEMI sources, generic substation layouts, and their mitigating effects, coupling paths, and IEMI susceptibilities has been gathered in several test campaigns and studies. Electrical field strengths generable by commercially available power sources inside substations have been estimated considering measured shielding characteristics of the buildings and attainable target distances. A comparison with measured susceptibilities of control equipment to IEMI reveals noticeable security issues. In particular, expected field strengths inside substation buildings can be much higher than the immunity levels for control systems as requested in EMC standards. [ABSTRACT FROM AUTHOR]

Substation annual maximum electricity demand events are extreme, as customers respond to infrequent and extreme weather. Despite the extreme nature of annual maximum demand, the statistical theory of extreme values has only rarely, if ever, been applied. To support long-term planning, utilities typically complete energy consumption and maximum demand forecasts, which are often conducted separately through two different process, leading to inconsistent trends and messages. To address these shortcomings, a point process approach from extreme value theory is proposed to model substation maximum demand as a function of trends in three common factors already required by utilities including customer count, average demand, and installed photovoltaic capacity. The point process model can be parameterized as a nonstationary generalized extreme value distribution with location and scale parameters dependent on the trends of these factors. As the generalized extreme value distribution governs the behaviors of block maxima (annual maximum demand) with forecast trends of three common factors, substation maximum demand can be estimated as per quantiles required by planning standards. Therefore, the proposed approach is not only realistic and flexible to forecast maximum demand but also ensures consistent outcomes and messaging between the two outputs from energy consumption and maximum demand forecasts. [ABSTRACT FROM AUTHOR]

Growing cybersecurity risks in the power grid require that utilities implement a variety of security mechanisms (SMs), including VPNs, firewalls, authentication, and access control mechanisms. While these mechanisms provide some level of defense, they also may contain software vulnerabilities which allow an attack to bypass their protection. Because the same SM type is often used to protect a large number of substations, a single vulnerability could enable a coordinated attack by simultaneously targeting many substations. To protect against such an attack, utilities can adopt a strategy to use a diverse set of SMs, such that the impact from a vulnerability in any SM is minimized. This paper introduces a game-theoretic graph coloring technique to determine the optimal allocation of SM diversity that minimizes the impact of security vulnerabilities to the grid. This paper demonstrates that the proposed approach provides a Nash equilibrium solution. Furthermore, the technique is demonstrated against cyber-physical models for both IEEE-14 and IEEE-118 bus systems, and compared with other non-strategic diversity allocation methods to demonstrate its effectiveness. [ABSTRACT FROM AUTHOR]

Built upon real-world supervisory control and data acquisition (SCADA) and other measurements of a featured utility-scale testbed, this paper addresses the participation of customer side battery energy storage in providing peak load shaving at a 12.47 kV distribution feeder. A stochastic optimization-based battery operation framework is developed that enables feeder load peak shaving under offline (day-ahead) as well as online (close-to-real-time) control settings. Both designs work through establishing a secured communications line to the utility’s feeder-level SCADA system. Multiple field experiments are conducted, including a full day test with complete control of a 1 MWh/200 kW battery system, as well as various numerical assessments based upon one year of real feeder data. [ABSTRACT FROM AUTHOR]

A thin-wire model of conductors with arbitrary cross sections for a finite-difference time-domain (FDTD) method is proposed for the study of lightning transients in electrical systems. The proposed thin-wire model considers both the frequency-dependent characteristics of the wires and the influences of the surrounding media. The model represents a wire using four FDTD cells with an equivalent side length and modified material parameters. A rational equivalent circuit is added at the center edge of the FDTD cells to represent the internal impedance of the wire. An analytical formula for determining the equivalent side length and the modified material parameters of the FDTD cells are also presented. The proposed formula gives a new prospect to build the thin-wire model in FDTD. In this model, the equivalent side length can be set arbitrarily and much larger than the original wire, which can greatly reduce the computation time. Meanwhile, the method can be extended to the thin-wire structure with arbitrary cross sections. The model is verified with various measurements. Finally, a practical grounding grid of a substation with external water supply is analyzed. [ABSTRACT FROM AUTHOR]

Electricity companies have been under a great pressure to improve their technical and financial performances in order to survive and thrive in the deregulated environment. Therefore, these companies are seeking for innovative approaches to take the most out of the restricted resources. These approaches inherently concentrate the available budgets to the most critical components. In this regard, prioritizing the system components and identifying the most critical ones play a vital role in the planning and operation of the system. This paper presents a novel approach to prioritize power transmission system components. In the proposed methodology, a criticality factor is defined and implemented to rank the components based on their impacts on the operation of the power system. Furthermore, a complete model of substations including misoperation of circuit breakers and protection systems is, for the first time, taken into account in the critical component identification process. The proposed approach is used to identify the vulnerable parts of the system and assist the decision makers to manage the limited resources. The proposed methodology is, then, applied to the IEEE 24-bus Reliability Test System, and components are prioritized accordingly. [ABSTRACT FROM AUTHOR]

This paper focuses on assessing the electric field exposure in the whole substation by the fault tree analysis. The component-level exposure situation along the path is studied by the reliability analysis, where the field distribution and the moving people are integrated. The system-level exposure situation is then analyzed by generating the exposure fault tree based on the component-level data. The exposure failure probability of the whole substation is ultimately evaluated by analyzing the fault tree's series-parallel system. The influences of the layers and the bounded parameters on the size of the fault tree are also studied in this paper. The results of the case study show that, with the help of the fault tree analysis, the complex exposure situation in a large substation can be clearly evaluated by a probability value. [ABSTRACT FROM PUBLISHER]

Optimizing the grounding grid configuration is an effective approach to improve the performance of grounding grid. On the other hand, configuration of grounding grid is necessary for some defect diagnosis method to detect the faults existing in grounding conductors. This paper employs the transient electromagnetic (TEM) method to draw the configuration of a substation grounding grid. The surface magnetic field is recorded by receiver coils above the grounding grid. Based on the regular distribution characteristics of a recorded magnetic field, the grounding conductor is accurately located from the curve of magnetic intensity. The complete process of configuration detection of the grounding grid is described in detail. After fast inversion calculation of the recorded magnetic field, the equivalent resistivity is obtained. The configuration of the grounding grid will be clearly and accurately shown in the contour map and three-dimensional (3-D) surface map of equivalent resistivity. Model study is performed, and a field test is also conducted. The results are in good agreement to demonstrate the effectiveness of TEM method for configuration detection of the substation grounding grid. [ABSTRACT FROM AUTHOR]

The operating voltages of low-voltage control circuits in power plants and substations have decreased with the installation of digital control equipment. This increases the susceptibility of control equipment to abnormal surges, which arise mainly from lightning. To protect control equipment from lightning, it is necessary to predict lightning surges invading power plants and substations and design effective lightning protection methodologies. Compared with conventional simulation techniques based on circuit theory, full-wave numerical approaches are advantageous in handling three-dimensional structures such as transmission line towers, grounding structures, nonhorizontal wires, such as incoming power lines to power plants and substations, and lightning-induced effects. In this study, to apply the finite-difference time-domain (FDTD) method to the lightning surge analysis of an air-insulated substation, we first propose techniques for simulating the nonlinear breakdown characteristics of short-air-gap arcing horns and transmission line surge arresters installed in 77 kV transmission lines for FDTD-based surge simulations, and compare the breakdown characteristics calculated using the proposed techniques with measured results for validation. Second, as an example of the application of the proposed techniques to practical surge analysis, it is confirmed that we can reproduce the measured results of lightning surges invading a 77 kV air-insulated substation in the case of a direct lightning strike to its nearby transmission line tower by taking into account lightning-induced voltages arising from the lightning current flowing through the lightning channel and transmission line tower, which are commonly ignored in conventional circuit-theory-based simulations, multiphase back-flashover phenomena, and the effect of applied AC voltages. [ABSTRACT FROM PUBLISHER]

In recent years, Software Defined Networking (SDN) has experienced rapid growth. The unexpected deployment of SDN has impacted all kind of scenarios from data centers to campus and corporate networks. The wide adoption of SDN is due to its advantages in the field of network management and the flexibility in the implementation of solutions that lead to operational and capital costs reduction. Recently, SDN developments have also emerged around communication networks in power substations with the purpose of improving the management inside this type of networks, which demand high levels of availability and reliability, as the substation is a key element in the chain of energy generation and distribution. To provide a better degree of understanding about the challenges that arise in this area, and in order to generate new research interests in this field, this article presents a detailed review of the recent efforts to develop solutions through the appropriation of SDN concepts, around the demanding requirements of operation identified in communication networks in power substations. [ABSTRACT FROM PUBLISHER]

Excessive exposure to high levels of electromagnetic fields can induce adverse health effects. Numerical calculation is often used in the exposure assessments. However, in the traditional methods, the relative variables are all assumed to have fixed values without considering the effect of staff activity. To improve the deficiencies caused by this assumption, a new method for the exposure assessments based on the reliability theory was proposed in this investigation. As an example, the electric-field exposure in the booster station of a power plant with several paths was studied by the new method. The exposure reliability index and the failure probability of each path were first determined. Then, based on the determined reliability indices, the influence of the bus framework on the exposure was discussed by the sensitivity study, and a series system was set up to evaluate the electromagnetic exposure of the entire booster station. The proposed approach could be employed to assess the electric field in the substations by taking into account the staff activity, in order to improve the management of the occupational exposure in the power transmission and distribution projects. [ABSTRACT FROM PUBLISHER]

The electric field in and around a 2.6-m-long substation arrester, on which a 1 MV lightning impulse is imposed, has been analyzed using the finite-difference time-domain (FDTD) method. The arrester is represented as a combination of 10 mm × 10 mm × 10 mm cubic cells, each of which has a nonlinear resistivity (or conductivity) in each of the x-, y-, and z-directions, dependent on the electric field in each direction. This simple representation requires no iterative procedure, and is suitable and useful for the FDTD simulation of an overvoltage-imposed arrester. The transient electric field in and around the overvoltage-imposed arrester, and the spatial distributions of vertical and radial electric fields along the surface of the arrester are shown. The influence of a shield ring is also shown. [ABSTRACT FROM PUBLISHER]

Secondary or low-voltage (LV) networks are applied in many large cities throughout the U.S., and in some other countries. Various grounding schemes have been employed for the primary systems supplying these secondary networks. In this paper, characteristics of the different grounding schemes for the substation and primary feeders that supply the LV networks are reviewed. The impacts of primary system grounding on the ground fault currents, the unfaulted line-to-ground voltages, as well as the voltage sags in the LV network have been considered for the single line-to-ground fault on the primary. The differences between systems with network transformers having the delta- or grounded-wye-connected primary windings are discussed. The relationships between grounding characteristics and protection settings, including actual examples, have been documented. [ABSTRACT FROM AUTHOR]

This work proposes an integrated computational tool to support the designer engineer during the elaboration of projects of industrial distribution networks during the conceptual and basic design, presenting the methodology for a technical and economic analysis of electrical systems applied to oil refineries. [ABSTRACT FROM PUBLISHER]

The management of transformers’ capacity is a vital task for planners and asset managers due to their high cost. This paper proposes an optimization model for capacity management of transformers in a substation over long-run. The model considers the present worth costs of investment, losses, maintenance, reliability, and the salvage value of transformers for providing the optimal selection and scheduling of multistage transformer installations and their refurbishments. In the optimization model, growing failure rate of transformers along with their age is incorporated and the cumulative loss-of-life (LOL) of transformers is also used in determining their salvage value. The developed model is applied for planning and management of transformer capacities for a residential load dominant two-transformer primary distribution substation over a period of 40 years. The simulations are performed for various case studies representing the situations encountered by utilities. An extensive sensitivity analysis is also conducted for several conditions of the system parameters. The numerical results indicate the worth of inclusion of variable failure rate and LOL of transformers in their capacity management. [ABSTRACT FROM AUTHOR]

Critical systems require zero recovery time when a failure occurs in a communications network. The soon to be implemented standard IEC 62439-3 defines the only two protocols, parallel redundancy protocol and high-availability seamless redundancy, which fulfill this requirement and ensure no frame loss in the presence of an error. These protocols also provide a hot-plugging capability, which allows elements to be added to or removed from the network without interrupting communications and the operation of the plant. The electricity sector has adopted these for power utility automation in the recently published IEC 61850-90-4. The challenge is to obtain an efficient approach for use in electronic devices, capable of managing the characteristic duplicates, and circulating frames of these protocols, coupled with agile architectures capable of dealing with real-time processing requirements, fast switching times, high throughput, and deterministic behavior. The main contribution of this paper is the in-depth analysis it makes of network parameters imposed by the application of the protocols to power utility automation, and the proposition of a frame management system based on a segmented memory system that improves frame detecting time and uses the smallest memory required in order to resolve all the issues dealt with. [ABSTRACT FROM PUBLISHER]

The accuracy of lightning overvoltage evaluation of electrical equipment has been improved based on circuit analysis such as the Electro-magnetic Transients Program, but analyzing phenomena whose plane wave propagation (TEM) mode cannot be assumed remains unsolved. Since numerical analysis of electromagnetic fields such as the finitedifference time-domain (FDTD) method directly solves Maxwell?s equations, it is an appropriate means for solving this issue. In this paper, the lightning surge waveform due to the back-flashover is analyzed using the FDTD method; bearing detailed modeling of transmission towers and incoming substation lines in mind. An open end of a circuit breaker of a 500 kV air-insulated substation was selected as the subject of analysis, and ac operation voltage was considered as an analysis condition. Following FDTD analysis, a 150 kA lightning stroke to the first tower, which is the standard lightning stroke of the lightning protection design, does not cause back-flashover, but a 200 kA lightning stroke to the first tower and a 150 kA lightning stroke to the second did do so. The flashover occurred in the later timing than the result of conventional circuit analysis, and the rise of the lightning surge was also slower. The voltage waveform of the open end of the circuit breaker reached its peak after repeating reflections, and the overvoltage value became lower than the circuit analysis. According to the FDTD analysis, the required withstand voltage value after the waveform evaluation with a 200 kA lightning stroke is 1,337 kV, which is lower than the present lightning impulse withstand voltage (LIWV) 1,550 kV. The lightning stroke current 200 kA is the value adopted in the lightning protection design of the UHV system. Therefore, the existing air-insulated substation equipment is considered highly capable of withstanding overvoltage at the time of a back-flashover. [ABSTRACT FROM AUTHOR]

The fault-free performance of outdoor insulators is a matter of great importance for power utilities as a single insulator fault may lead to an extended outage. Several factors related to operation conditions affect the performance of outdoor insulators, with pollution being probably the most significant one [1]?[3]. Coastal areas are considered heavily polluted due to the deposition of sea salt on the insulators. When the deposited salt is diluted in water through humidity, drizzle, fog, or light rain, a conductive solution is created and leakage current flows on the surface. The activity may advance, under favorable conditions, to flashover. Therefore, the local weather and climate is an important factor for the determination of pollution severity as strong winds carry more salt and frequent rains may provide natural cleaning. [ABSTRACT FROM PUBLISHER]