Short-circuit Ratings Research Articles

Optimal reconfiguration for Extra high voltage transmission networks using an enhanced Brute-Force algorithm

Over the last decade, Extra high voltage (EHV) transmission networks are becoming excessively meshed to reliably accommodate different types of generation and meet the operational security constraints during steady state and transient conditions. However, excessive meshing, combined with the addition of new power plants, can result in short circuit levels that exceed the capability of switchgear components. As such, there is a growing need to limit, the degree of meshing to accommodate the short circuit capability of the existing network assets, thus avoid catastrophic implications that may lead to very expensive equipment damage and personal safety concerns during fault conditions. Under different network conditions, the operators may have to reconfigure the EHV transmission grid differently to avoid exceeding the short circuit rating of the network assets, while maintaining the grid reliability following the next contingency. This paper proposes a new deterministic optimization model for determining the best EHV transmission network reconfiguration for short circuit relief, while meeting the network steady state and transient security requirements. The optimization model is solved using an enhanced Brute force algorithm that limits the search space, hence improves the computation efficiency of the classical Brute Force technique. To test the accuracy and computation efficiency of the proposed optimization model and enhanced algorithm, the IEEE 39-bus model and a real-size practical EHV network model were used as testbeds. The results demonstrate that the algorithm managed to successfully identify optimum EHV grid reconfiguration that would limit the short circuit levels while satisfying the steady state and transient security requirements mandated by the network operators.

Application of Superconducting Fault Current Limiter in Power Grid - Survey

Introduction of Distributed Energy Sources (DES) is the highest change happening to the distribution network. This paper describes different types of current limiting methods which reduce the magnitude of the fault current. The interconnected distributed energy sources to the conventional grid improves the power generation capacity of the power system but also increases the magnitude of fault current which cannot tolerate by the short-circuit ratings of the circuit breaker, relays, isolator etc. This paper reviews on the innovative electric equipment i.e. Superconducting Fault Current Limiter (SFCL), which reduces fault current magnitude in first cycle of fault current. Keywords: Distributed Energy Sources, Fault current, Superconducting Fault Current Limiter (SFCL), Protection Equipment.

Application of Superconducting Fault Current Limiter in Power Grid - Survey

Introduction of Distributed Energy Sources (DES) is the highest change happening to the distribution network. This paper describes different types of current limiting methods which reduce the magnitude of the fault current. The interconnected distributed energy sources to the conventional grid improves the power generation capacity of the power system but also increases the magnitude of fault current which cannot tolerate by the short-circuit ratings of the circuit breaker, relays, isolator etc. This paper reviews on the innovative electric equipment i.e. Superconducting Fault Current Limiter (SFCL), which reduces fault current magnitude in first cycle of fault current. Keywords: Distributed Energy Sources, Fault current, Superconducting Fault Current Limiter (SFCL), Protection Equipment.

Influence of Temperature on the Pressure Distribution Within Press Pack IGBTs

Press pack (PP) packaging technology has been applied to insulated-gate bipolar transistors (IGBTs) for high-voltage and high power density applications in recent years. The pressure distribution within PP IGBTs is very important because it affects both the electrical and thermal contact resistances, thermal cycling capability, and short-circuit current rating. Too much pressure will mechanically damage the chip and too little pressure will increase the thermal contact resistance, which eventually leads to chip thermal damage. In this paper, a finite-element multiphysics model cocoupled with an electrical field, thermal field, and mechanical field is proposed to analyze the collector current distribution, pressure distribution, and junction temperature distribution within PP IGBTs. The most important coupling variables, such as electrical and thermal contact resistances, for this cocoupled multiphysics model are calculated or measured by experiment through a single IGBT/fast-recovery diode chip submodule. Based on this multiphysics model, the influence of the high temperature generated by the chip's power dissipation on the pressure distribution within PP IGBTs (in the heating phase) is discussed, and then, compared with the pressure distribution in the clamping phase. The results show that the pressure distribution within PP IGBTs in the heating phase is extremely uneven and different from the value in the clamping phase. Furthermore, the mechanical model and its boundary conditions are verified through the pressure distribution experimental results in the clamping phase, which is measured based on the Fuji prescale film and the clamping test bench. Based on the simulation and experimental results, an optimization of the collector electrode and pedestal is proposed to improve the pressure distribution within PP IGBTs in the heating phase.

Placement of Fault Current Limiters in a Power System Through a Two-Stage Optimization Approach

With the sustainable growth in the number of new power plants and scale of transmission systems, the probability of the current exceeding the short-circuit rating of circuit breakers increases. A fault current limiter (FCL), which can be used to reduce current surges, has attracted considerable attention from utilities. However, the appropriate placement of FCLs in a power system for obtaining the most effective cost-to-benefit solution is crucial. This paper proposes a two-stage placement approach, where Stage I combines the hierarchical fuzzy logic decision (HFLD) method and Hashing-integrated generic algorithm (HIGA). The HFLD method is used for sorting feasible solutions, and the HIGA determines an optimal FCL placement in the reduced search space. Particle swarm optimization is then employed in Stage II for optimizing the FCL parameters. To verify the effectiveness of the proposed approach in solving the optimal FCL placement problem, the method is verified using the IEEE 30-bus system and system of a manufacturing factory in Taiwan. The numerical results show that the proposed method achieves a favorable solution in a short time with fewer placements of FCLs.

Reliability assessment of HV substations equipped with fault current limiter considering changes of failure rate of components

Owing to the increasing electricity load demand on one hand and in order to have a reliable electric network on the other hand, constructions of new transmission lines and generation sources are extremely essential. Such expansions, however, raise the fault current level which can even exceed the maximum short-circuit level rating of the circuit breakers (CBs). High fault current, in addition to the adverse effect on the CB function, can damage other substation equipment suddenly or over the time. To this end, severity of the fault current is a key factor in the substation reliability assessment. In this context, fault current limiters (FCLs) which are employed to decline the fault current level need to be precisely modelled and their impact should be extensively studied. In this study, the effect of FCL on the failure rate of substation equipment is first investigated. A computational technique for assessing the substation reliability is accordingly devised. As the location of FCL installation in a given substation or in substations with different arrangements would not be the same, various credible configurations are incorporated here. The results show that from the perspective of reliability indices, double-bus double-breaker and one breaker and a half configurations are more suitable for FCL installation.

Placement of Fault Current Limiters in Power System through a Two-stage Optimization Approach

With the sustainable growth in the number of new power plants and scale of transmission systems, the probability of the current exceeding the short-circuit rating of circuit breakers increases. A fault current limiter (FCL), which can be used to reduce current surges, has attracted considerable attention from utilities. However, the appropriate placement of FCLs in a power system for obtaining the most effective cost-to-benefit solution is crucial. This paper proposes a two-stage placement approach, where Stage I combines the hierarchical fuzzy logic decision (HFLD) method and Hashing-integrated generic algorithm (HIGA). The HFLD method is used for sorting feasible solutions, and the HIGA determines an optimal FCL placement in the reduced search space. Particle swarm optimization is then employed in Stage II for optimizing the FCL parameters. To verify the effectiveness of the proposed approach in solving the optimal FCL placement problem, the method is verified using the IEEE 30-bus system and system of a manufacturing factory in Taiwan. The numerical results show that the proposed method achieves a favorable solution in a short time with fewer placements of FCLs.

Short-Circuit Current Ratings: Key Considerations for the Safety of Commercial and Industrial Electrical Systems

The interrupting rating (IR) and short-circuit current rating (SCCR) of equipment is a key consideration for the installation of equipment in electrical distribution systems. To emphasize this consideration, the 2005 National Electrical Code (NEC) added SCCR marking requirements for various types of equipment that previously was not required to be marked. The marked SCCR of equipment is determined by the product standards as part of the listing and labeling process of the equipment or an approved method, such as UL 508a, UL Standard for Safety for Industrial Control Panels. UL 508a supplement SB is an analytical (nontested) method of determining the SCCR of industrial control panels. This method basically determines the weak link of all power circuit components in the industrial control panel and the lowest-rated component then determines the assembly rating. Additional changes to the 2011 NEC have been made to ensure that equipment has sufficient SCCRs for the available short-circuit (fault) current where the equipment is installed.

Characteristics, Selection Guidelines, and Performance of Circuit Protection Devices for ASDs

The goal of all circuit protection devices is to mitigate and minimize collateral damage when a failure occurs to either the source (ac line) or the equipment. The circuit protection device is often given little attention, i.e., until erroneous trips hamper performance or unexpected damage occurs within the equipment. Then, the devices are often reviewed for performance characteristics and operating conditions. To meet this need, various devices have been designed for this purpose, and various standards have been written to provide guidance for the usage of those devices. The focus of this paper will be on the interplay between adjustable-speed drive (ASD) short-circuit current rating and protective device sizing, as well as the scaling of such systems, i.e., if a fuse sized for a 10-A circuit should have the same guidelines as that used for a 1000-A circuit. This paper will review the impact of Underwriters Laboratories 508A and 508C, and the National Electric Code on the ASD protection requirements. This paper evaluates a test setup scheme to measure the fuse performance. The peak current and I <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> t test results with both test schemes from three protection devices, a time-delay (TD) Class J fuse along with two non-TD Class J and T fuses, are presented and explained. A novel method of comparing the results is offered by viewing the collateral damage associated with a failure. This methodology has a minor impact at low power ratings, but it has major implications with high power ratings, where equipment is often field repairable.

Switchgear in Unusual Environments: Application Guidelines for Assuring System Reliability

With an increased emphasis on reducing the size of installations, switchgear designers are faced with the diametrically opposed requirements of increasing shortcircuit withstand and continuous current ratings while reducing space for the air that provides both primary insulation and cooling for the energized parts. Using modern material science, compact integrated dielectric systems can be developed without compromising the essential features for achieving higher short-circuit withstand and continuous current ratings. IEEE standards define the usual service conditions for proper equipment installation and also offer application guidelines for these conditions. This article will discuss these guidelines and define the owners' and manufacturers' responsibilities to assure system reliability by examining a specific installation and issues experienced.

345[kV] 전력용 변압기 %임피던스 변화에 따른 계통영향 분석

This paper deals with the impact analysis of the impedance change of 345/154[kV] power transformers on the KEPCO system's overall performance. Through the steady-state and dynamic analysis of power system, the maximum available impedance of power transformers were determined. Checking violation of short-circuit current ratings and transformer overload, parallel operation of power transformers, calculation of voltage variation ratio according to the impedance changes of power transformers are included in the steady-state analysis. In addition, transient and voltage stability analysis are also performed in the study. Available magnitudes to be able to change the impedance of the transformers in KEPCO system are finally determined in the paper.

TRV Rating Concepts and Generation of TRVEnvelopes for Synthetic Testing of Extra HighVoltage Circuit Breakers

Development in electrical power transmission system requires the use of circuit breakers with increasing breaking capacity. At present circuit breakers are to be installed on 245 kV to 1200 kV power system with short circuit ratings up to 120kA. To test high voltage CBs, direct testing using the power system or short circuit alternators are not feasible. The testing of high voltage CBs of larger capacity requires very large capacity of testing station. To increase testing plant power is neither an economical nor a very practical solution. Synthetic testing is an alternative equivalent method for testing of high voltage circuit breakers and is accepted by the standards. This paper presents a TRV rating concepts , IEC standards TRV envelopes and types of synthetic test circuits and their comparison. Analysis and mathematical modeling of 4-parameters TRV synthetic test circuit is done. A 4- parameters TRV synthetic test circuit based on parallel current injection method is designed and simulated for testing 420kV and 800 kV rating circuit-breakers as per new TRV requirements given in IEC 62271-100(2008).

Impact of Available Fault Current Variations on Arc-Flash Calculations

Prior to the arrival of the arc-flash hazard analysis and the incident energy calculations, it was common practice to perform short-circuit studies assuming an infinite source on the primary of the service transformer. With the main goal of a short-circuit study being to compare the maximum calculated short-circuit current to the short-circuit rating of protective devices, using an infinite source resulted in the most conservative short-circuit current. However, since the amount of energy available in an arc-flash incident is not only dependent on the available short-circuit current but also on the clearing time of the protective device, the assumption of an infinite source on the transformer primary will not guarantee the most conservative results for the incident energy calculations downstream of the transformer. This paper examines the effect of the utility available fault current on the incident energy calculations and proposes a new method to calculate the conservative arc-flash results in the event that the actual utility fault information is not available.

Short-circuit ratings and application guidelines for molded-case circuit breakers

A working group representing the Petroleum and Chemical Industry Committee (PCIC) and the Low-Voltage Protection Subcommittee of the IEEE Industry Applications Society, including both users and electrical equipment manufacturers, is preparing a guide to give users information for the correct selection and application of molded-case circuit breakers (MCCBs) under short-circuit conditions. This paper is intended to be a tutorial presentation that attempts to resolve issues that have been raised in a number of IEEE papers. This is phase one of a series of papers and tutorials relating to the selection and application of MCCBs.

Limitations of fault-current limiters for expansion of electrical distribution systems

The application of fault current limiters (FCLs) has been recommended in the existing literature to retain underrated medium-voltage circuit breakers of lower short-circuit ratings in service, when the distribution systems are expanded and their short-circuit currents increase. However, the existing published literature does not describe the limitations of FCLs from system separation and loss of protective device coordination conditions, nor does it provide an analysis of short-circuit duties of medium-voltage circuit breakers used with FCLs. This paper shows how these evaluations can be carried out. Considerations of the high cost of replacements and the far greater loss of production, due to lack of coordination and availability of a proven alternate solution, should be included in an informed decision to use FCLs.

Wire and Cable Update-1985

Power distribution within a large modern petrochemical complex involves many thousands of feet of instrument and power cables that must be applied and installed with optimum life, reliability, and cost. Current practice and trends in evaluating, sizing, specifying, and installing the more commonly used cables and cable systems in petrochemical plants are reviewed. Current trends in industrial cable design and construction are considered. This includes low-and medium-voltage power cable, control cable, and instrument cable. The relative merits of various materials used in cable constructions are reviewed with particular emphasis on insulations, shields, jackets, and overall sheaths. Protection of cable from harsh environmental conditions is included. Methods are presented for selecting the proper cable construction for differing applications. Installation methods, including conduit, tray, and direct burial systems, are reviewed with emphasis on the additional ampacity tables for the 0-2000-V cables proposed for the 1987 National Electrical Code (NEC). These tables, as well as the existing NEC tables for the 2001-35 000-V cables, were generated using the Neher-McGrath method which permits the calculation of any conductor ampacity for a specific installation. Proper conductor sizing is presented based on short circuit rating, voltage drop, temperature rating, and actual cable installation method.

Safety against Lightning for Linemen Working on de-Energized Power Lines

Where the risk of accidental power-frequency energization is concerned, the safety ground has a short-circuit discharge duty determined by the configuration and parameters of the power system. Safety is thus assured by selecting a safety ground having a short-circuit safety rating which matches the duty imposed by the power system. Up to now, a similar matching for lightning currents has not been possible. This paper addresses this problem by: 1. Determining the lightning current rating of typical safety grounds. 2. Calculating the lightning current discharge duty of safety grounds in terms of the insulation level of the line and the distance from the location of the thunderstorm. The analysis shows that special precautions are needed when working on power lines of voltage classes above 360 kV.

Busway Short Circuit Testing Procedures

Every electrical system component must have recognizable predictable characteristics in order to be usable in today's modern electrical distribution system. The use of busways for power distribution in commercial and industrial buildings has become very popular in recent years due, in part, to the fact that it offers the requisite proven predictable electrical and mechanical characteristics. This allows the distribution system designer to use busway with confidence that it will perform as he intends. Of the many electrical and mechanical characteristics which must be evaluated, the busway short circuit rating has become one of the most important. This increased importance is the result of larger electrical services and lower loss supply equipment creating significant increases in available short circuit current levels. In addition, the present cost of equipment failure is at an all-time high. It is certainly better to spend a little extra (whether time or money) in the design and construction stages to provide maximum system performance under all conditions including possible short circuits.

Relationship of X/R, IP, and IRMS' to Asymmetry in Resistance/Reactance Circuits

The short-circuit current interrupting and/or withstand ratings of electric power distribution equipment are determined by the transient asymmetrical current available during the equipment testing procedure. The degree of asymmetry is a function of the X/R ratio and the point on the voltage wave at which the short-circuit is initiated. Power distribution equipment short-circuit current ratings, with rare exceptions, are given in symmetrical amperes. It is important to know what effect the stresses imposed by the transient asymmetrical current, which cannot be measured by standard ammeters, will have on the equipment during the first few cycles of current flow. Presented is an accurate evaluation of instantaneous asymmetrical current and equivalent asymmetrical rms current characteristics, during the transient period, by direct calculation. The data thus obtained should prove valuable to power distribution equipment designers and test engineers as well as equipment application engineers.

Scaling Criteria for Interruption Performance in Gas-Blast Circuit-Breakers

The high cost and complexity of short-circuit interruption testing of gas-blast power circuit-breakers make it essential to use most efficiently results of reduced power development tests in interrupter design. Due to the limited capacity of direct testing stations many EHV-breakers must be evaluated by indirect methods such as synthetic-testing of single interrupter units. The interpretation of synthetic-test data and the effective utilization of reduced power test data in circuit-breaker design can be enhanced by the development of accurate scaling criteria. The present paper demonstrates to what extend scaling of enthalpy-flow, current density, pressure, interruption capability, nozzle area ratio, contact spacing, and shape factors can extend the results of reduced power experimental tests to predict performance at full short-circuit ratings.