Terminals Of Lines Research Articles

A fault location scheme based on composite traveling wave with transients in adjacent fault-free lines

As the speedy expansion of power gird, the traveling wave fault locator in substation may not always connect to newly added transmission lines in time, which reduces the effectiveness of fault locator. In this paper, an adjacent fault-free line based fault location scheme for newly additional line is proposed. Since the traveling wave from adjacent fault-free line results in severe difficulty for identification of traveling waves from faulty line, the time–frequency matrix is performed to screen traveling waves. Firstly, in order to remove the influence of waves from remote terminals of adjacent fault-free line, the current refraction coefficient is theoretically analyzed. Due to the negative refraction coefficient, traveling waves from remote terminals of adjacent fault-free line can be reduced by the proposed composite traveling wave. Secondly, the time–frequency matrices of composite traveling wave and original traveling wave is obtained by S-transform. Then, these matrices are applied to form ratio matrix which thoroughly eliminated waves from remote terminals of fault-free lines. Moreover, the robustness of the proposed fault location scheme is thoroughly validated by the simulation of PSCAD/EMTDC. Finally, the proposed fault location method has the great accuracy in simulation tests and field data test.

Liquid metal droplet shuttling in a microchannel toward a single line multiplexer with multiple sensors

Multiple sensors and actuators integrated in a small space, especially an elongated thin structure, require equivalent number of signal lines between microdevices, but there is limited space for signal wires. Thus, we propose a mechanism using a single microchannel where a liquid metal droplet moves and shuttles. A shuttling droplet switches multiple terminals of signal lines along a microchannel based on a traditional switching mechanism using a liquid metal droplet. Electrically conductive gallium alloy liquid metals (Galinstan) can flow in a microchannel due to their fluidity. The terminals consist of opposing electrode pairs in a microchannel. A change in a variable impedance connected to a terminal as a pseudo sensor can be read when a droplet flows in and connects electrode pairs. This paper presents switching and addressing objective terminals of chromium electrodes by a shuttling conductive droplet (500 µm in diameter and 10 mm long) in a microchannel (500 µm in diameter and 100 mm long). A demonstrated simple mechanism enables communication between multiple microdevices along a microchannel. We anticipate wide application of proposed mechanism toward a multiplexer, especially in microfluidic devices because of the advantages of utilizing microchannels as common microstructures for both microdevices and signal lines.

A Traveling Wave-Based Fault Location Method Employing VMD-TEO for Distribution Network

In this paper, a traveling wave based fault location method is proposed for distribution networks. Before fault occurs, an intrinsic distance difference matrix (IDDM) is established based on the characteristics of traveling wave propagation and the topology of distribution network. After the fault, the initial fault traveling wave signals are decomposed into several intrinsic mode function (IMF) signals by variational mode decomposition (VMD), and the first IMF signal is analyzed by teager energy operator (TEO) to determine the arriving time of initial fault traveling waves. According to the double-ended traveling wave method and the arrival time of traveling wave at all recorders, a fault distance difference matrix (FDDM) is built. By comparing the difference between IDDM and FDDM, a fault branch determination matrix (FBDM) and the lateral index Q are used to locate the fault. The effectiveness of the proposed method is verified via EMTP/ATP simulations. Results show that the proposed method has a high fault location accuracy, and does not need that all terminals of lines are installed traveling wave recorders.

Emergency Control Systems in the Uninterrupted Traction Power Supply of Subways

Traction dc power supply systems with a traditional feed voltage of 825 V are part of the basic transport infrastructure of metropolitan cities. The development of electrified railroads has resulted in the mainstream use of these systems. There are many works about their strengths and weaknesses; however, modern circumstances make it necessary to operate and upgrade these systems, maintain their usability, and improve their efficiency. New rolling stock with asynchronous engines is being launched for subway service with increased loads and travel speeds. In these conditions, one of the main features of maintaining the course of transportation is to guarantee uninterrupted power supply of electric rolling stock. This can be made possible through appropriate and timely responses by maintenance personnel, power dispatchers, automation and emergency control systems. The microprocessor systems used at the modern level of technological development have been embodied in intelligent terminals of feeder lines of electric traction networks used in subway service. Their algorithmic part must be improved and upgraded for compliance with the current realities of subway service by integrating emergency control equipment algorithms, full-scale analysis of analog processes in the electric traction network, discrete signals of automatic controls and telemechanics, and states and switches of cross-connect equipment, which must facilitate increased automation of the traction substation and make it completely unattended.

Calculation of Lightning Induced Overvoltages on Overhead Lines: Model and Interface With MATLAB/Simulink

This paper presents a macro-model, which can be used to calculate the lightning-induced overvoltages (LIOVs) on overhead lines on MATLAB/Simulink platform. First, a macro-model according to Agrawal’s field-to-line coupling model is derived, in which the distributed equivalent voltage sources due to the horizontal components of the incident electric fields are lumped at the terminals of the transmission lines. In order to interface with MATLAB/Simulink, the propagation function of the transmission line is approximated by a delayed rational function and described by a state-space representation, and Brune’s synthesis is adopted to model the equivalent multiport equivalent circuit of the transmission line in order to overcome the passivity violation problem. Combining with the built-in components in MATLAB/Simulink, the proposed modeling approach is applied to evaluate LIOVs of an overhead lines system, and the influence of the arrester and ground wire on the LIOVs is discussed in this paper. Furthermore, considering that the peak values of LIOVs are mainly concerned in the insulation coordination, a simple model for the early time response is proposed, which can further simplify the procedure. The accuracy of the proposed modeling method is validated by some examples.

Modeling of VHF Current Conversion From Excited Antenna Mode to Differential Mode at Transmission Line Terminals

The current induced by an incident electric field can convert from the antenna mode to differential mode at unbalanced terminals of transmission lines (TLs), causing severe interference to a number of applications such as broadband power line communication, especially in the very high frequency (VHF) band. The previous work on modeling the current conversion is not applicable to VHF. We present a new model of the VHF current conversion which includes a general formula for the antenna mode characteristic impedance and two solutions to the formulated problem: 1) a numerical solution referred to as the antenna theory numerical (ATN) approach, which gives the exact value of the characteristic impedance; 2) an analytical solution referred to as the enhanced TL approximation (ETLA) approach, which gives the mean of the characteristic impedance. This is the first reported work to obtain the antenna mode characteristic impedance by the antenna theory. Furthermore, the ETLA approach outperforms the previous frequency-independent solution and requires a reduced complexity over the ATN approach. Our model is general as it converges to the previous model at lower frequencies. Simulation results also show the relationship between the antenna mode characteristic impedance and the power of the interference caused by the current conversion.

Spatial Power Network Expansion Planning Considering Generation Expansion

This paper introduces an efficient approach on static spatial power network expansion planning integrated with generation expansion, while considering complicated environments based on the raster map in geographic information systems (GIS). Candidate plants could be built on any cell in the map, which means that terminals of candidate lines connected to candidate plants are not fixed. This is a remarkable difference from the literature in which the terminals of candidate lines are fixed. The objective is to minimize the total system cost, subject to prevailing investment and operation constraints. The model is formulated as a mixed-integer linear programming (MILP) problem via integer algebra techniques. A two-step approach is proposed to address the computational complexity. The first step searches optimal electric line routes via dynamic programming, while the second step solves a simplified MILP problem for obtaining final optimal generation and transmission planning strategies based on optimal line routes derived from the first step. In most cases, the proposed two-step approach would derive the same global optimal solutions as those by solving the original formulation directly. Thus, the proposed two-step approach can significantly improve the computational efficiency while maintaining the solution optimality. Numerical examples demonstrate the effectiveness of the proposed approach.

Study on Very Fast Transient Overvoltage of Closing No-load China UHV Transmission Demonstration Project Jindongnan-Nanyang-Jingmen 1000 kV Transmission Lines

When the ultra high voltage (UHV) substation used the gas insulated switchgear (GIS) system to switch lines with capacitive current, the pre-breakdown and multiple reignition will occur between switching contacts. Because of discharge characteristics of SF6 and special structures of GIS system, the variations of the electromagnetic transient process and very fast transient overvoltage (VFTO) are very fast and extremely complex. The development process and characteristics of VFTO remain to be dealt with to seek effective suppression measures. The overvoltage of closing no-load long lines on GIS system is analyzed in detail. The simulation model of the very fast transient process of closing no-load long lines on UHV GIS system is established. The VFTO of closing no-load China UHV transmission demonstration project Jindongnan-Nanyang-Jingmen 1000 kV transmission lines is analyzed using electromagnetic transient simulation software ATP-EMTP. The VFTO of closing no-load long lines on UHV GIS system is simulated and calculated, when the system has no additional closing resistors and lightning arresters, additional single stage closing resistors, additional multistage closing resistors, lightning arresters in two terminals of lines, lightning arresters in two terminals and the middle of lines, and additional multistage closing resistors and lightning arresters in two terminals and the middle of lines. The simulation results show that the additional multistage closing resistors and lightning arresters in two terminals and the middle of lines can effectively restrain the VFTO of closing no-load long lines on UHV GIS system.

A Fault Location Method for HVDC Transmission Lines

A fault location method for HVDC (High Voltage Direct Current) transmission lines is proposed in this paper, using voltages and currents measured at two terminals of dc lines in time domain. Fault traveling waves propagate from the fault point to both terminals along the faulted line. The position that the traveling wave head arrives at some moment after the fault can be used to calculate the fault location. To determine the arrival positions of traveling wave head at each time indirectly, propagation characteristic curves of traveling wave heads at local and the remote terminals are calculated with distribution currents using the stationary wavelet transform. The accuracy of fault location will not be affected by transition resistance and fault position. Simulation results show that the presented fault location method can achieve quick and accurate fault location on the whole line under probable operation modes of a bipolar HVDC transmission system.

Recent Developments in Power System Diagnostics and Protection: Synchronized Sampling and Phasor Measurement

The advent of GPS system and advances in computer technology have made it possible for the utility companies to implement synchronized sampling at all terminals of the protected lines. To achieve this, the phasor information of voltages and currents at different locations has to be acquired and evaluated to provide easy disturbance analysis and protection for the utility companies. This paper reviews and compares some recent patents regarding synchronous phasor measuring patents. Their possible applications are also discussed. Keywords: GPS system, time synchronization, sampling, synchronized phasor measurement, power system

A New Two-Terminal Numerical Algorithm for Fault Location, Distance Protection, and Arcing Fault Recognition

This letter presents a new numerical algorithm for fault location calculation and arcing faults recognition. The proposed algorithm is based on the synchronized phasors measured from the phasor measurement units (PMUs) installed at both terminals of the transmission lines. From the calculated arc voltage amplitude, a decision can be made whether the fault is permanent or transient. The proposed algorithm is tested through computer simulations to show its effectiveness

A NEW NUMERICAL ALGORITHM FOR FAULT LOCATION ESTIMATION USING TWO-TERMINAL SYNCHRONIZED VOLTAGE AND CURRENT PHASORS

This paper presents a new numerical algorithm for fault location estimation which uses data from both end of the transmission line. The proposed algorithm is based on the synchronized phasors measured from the PMUs (Phasor Measurement Units) installed at both terminals of the transmission lines. Based on the length of the transmission line, the proposed algorithms are divided into the short line (without shunt capacitance) and long line algorithm (with shunt capacitance). For the purpose of the unknown fault distance the phasor calculation method is used. The proposed algorithm is tested through computer simulations to show its effectiveness.

A New Fault Locator for Three-Terminal Transmission Lines Using Two Terminal Synchronized Voltage and Current Phasors

With the advent of the high synchronization accuracy of modern phasor measurement units (PMUs), a new approach for accurately locating faults on three-terminal lines is proposed. Using the data measured from two terminals of three-terminal lines, the proposed technique can provide an extremely accurate fault location. The EMTP/ATP simulator is used to demonstrate the performance of the proposed fault locator. The simulation results show that the accuracy of fault location is very high under various fault resistance, fault locations, prefault loading conditions, source impedance, and fault types.

Synthesis of time-domain models for interconnects having 3-D structure based on FDTD method

This work describes an efficient method to simulate transient responses of multilayer and multiconductor interconnects having three-dimensional structure. First, the impulse responses between any pair of terminals of lines are obtained by the finite-difference time-domain (FDTD) method, Next, the frequency responses are obtained by the Fourier transform of these transient waveforms. The time-domain models are synthesized from the frequency responses by using the least-square approximation and the complex frequency-hopping technique. Finally, with this model, the transient responses are rapidly simulated by the conventional circuit simulators. In conclusion, the validity of this method is verified by comparison with the time-consuming FDTD simulation.

Limit of safety against flame transmission for sintered metal flame arrester elements in the case of flashback in fuel gas/oxygen mixtures

In autogenous welding, cutting and allied processes, so-called dry safety devices are used to protect the outlet terminals of gas distribution lines. To prevent flame transmission, these units are fitted with sintered metal flame arrester elements. At the Federal Institute for Materials Research and Testing (BAM), extensive investigations have been carried out with an experimental flame arrester to determine the limits of safety against flame transmission for sintered metal flame arrester elements in the case of flashback in fuel gas/oxygen mixtures. On the basis of the results of these investigations, it is possible to estimate the pore sizes up to which a sintered metal element can prevent any flame transmission with a given fuel gas.

Detection of dominant points on an object boundary: a discontinuity approach

In a typical partial shape recognition scheme, each scene or model object is decomposed into a concise representation formed by a sequence of contiguous primitive features terminated by pairs of dominant points. A scene object is classified as a model object if its representations are similar. The main problem of this approach is caused by the inconsistency of the dominant point distributions as images of the same object are taken under different levels of noise interference and spatial variations. In this paper a robust dominant point detection algorithm is presented. The technique employs optimal discontinuity detectors for locating the structural nodes of an object boundary with high noise rejection and accurate localization capabilities. Members of a structural node include corners and the terminals of lines and arc segments which are unaffected by spatial variations. The algorithm has been tested with images of a set of hand tools grabbed under different scaling, camera orientations and noise interference. For the majority of cases, a similar set of dominant points is obtained for different images of the same object. The encouraging results demonstrate the feasibility of the approach and its potential as a reliable basis for object recognition.

Genetic Variability in Oviposition Preference among and Within Populations of the Cotton Bollworm (Lepidoptera: Noctuidae)

We investigated genetic variability in oviposition preference between and within colonies of the cotton bollworm, Helicoverpa zea (Boddie), originating from southern Texas, central North Carolina, and the Mississippi Delta. We established preference hierarchies using choice tests in which terminals of pubescent and glabrous lines of cotton and soybean were offered. Preferences of populations were compared using MANOVA techniques. The quantitative genetic technique of half-sibling analysis was used to estimate within-colony heritabilities of oviposition preference and genetic correlations between preference and pupal weight, developmental time, longevity, and fecundity. The Mississippi colony showed a significantly stronger preference for cotton than the other colonies, which did not differ significantly from one another. This difference is probably genetically based and could be related to the relative abundance of cotton coupled with the lack of host-crop heterogeneity in the Mississippi Delta region relative to the colonies originating from Texas and North Carolina. Half-sibling analyses detected significant levels of heritable genetic variability in oviposition preference in the Mississippi colony. In addition, a positive genetic correlation was found between proportion of eggs laid on hairy cotton and fecundity. These results suggest the potential for evolutionary change in oviposition preference by the population of H. zea in the Mississippi Delta. However, caution should be used in extrapolating results of this small-scale laboratory study to the field.

Prevention of transient voltage instabilities due to induction motor loads by static VAr compensators

The application of static VAr compensators (SVC) to prevent transient voltage instability due to the presence of large induction loads at the terminals of long transmission lines is discussed. Eigenvalue analysis is used to identify the conditions for voltage instability. The analysis is supported by transient time simulations for the complete power system following large disturbances. It is found that SVC can obviate transient voltage instabilities and maintain the load voltage near its rated value. It is shown that replacing the SVC with mechanically switched capacitors may not provide stabilization owing to the time delays associated with voltage drop detection and breaker operation. >

Nonconventional Transmission Zeros in Distributed Rectangular Structures

A lossless distributed rectangular structure, composed of a dielectric layer interposed between two perfectly conductive metallic layers, is considered. This structure is endowed with two ports, whose positions and widths are variable and is connected to the environment through uniform transmission lines. A procedure is exposed to obtain the impedance matrix at the terminals of the transmission lines. The existence of transmission zeros and of filtering properties is demonstrated.

Automatic switches to protect transformers

AN AUTOMATIC grounding switch in combination with an automatic air-break switch can be used in place of a circuit breaker in the 110-kv supply to a transformer. Since internal faults in transformers do not occur frequently, these high-voltage circuit breakers can be put to better use at terminals of transmission lines where faults are caused by lightning. The substitute for a circuit breaker on the high-voltage side of a transformer must provide for interrupting load, magnetizing, and fault currents. The low-voltage circuit breakers are necessary in all except very small single-bank stations for all three interrupting duties. An air-break switch on the high-voltage side of a transformer should be able to interrupt the magnetizing current or to break parallel in a station having two or three banks of transformers. The remaining duty is to interrupt current flowing from the 110-kv network into a faulted transformer. This can be done indirectly by putting a fault on the 110-kv bus which will operate circuit breakers at distant ends of the 110-kv transmission line. This is a drastic method of avoiding interruption of 110-kv fault current at the station flowing to transformer with an internal fault; but as this kind of fault occurs very seldom, such a general interruption can be endured occasionally. When two or more transmission lines are terminated at such stations, high-voltage circuit breakers are required at terminals of lines only, because the automatic air-break switch can be used to disconnect a faulted transformer after all sources of fault current have been removed.