Computation of corona effects in transmission lines using state-space techniques

We present calculations of the third-order intercepts for planar transmission lines that contain a distributed nonlinear inductance or capacitance. We model such a transmission line as a series of small nonlinear elements that interact only weakly. This approach allows us to use simple lumped-element models to describe nonlinear effects in transmission lines longer than the effective wavelength. We use this approach to calculate the third-order intercepts for a lossless transmission line, and also for a transmission line with finite attenuation. Calculations for the lossless case agree well with third-harmonic measurements of high temperature superconducting transmission lines as a function of line length. For transmission lines with loss, the calculations agree well with third-harmonic measurements of transmission lines of variable length incorporating ferroelectric thin films.

Distortion analysis of nonlinear circuits is very important for designing analog integrated circuits and communication systems. In this letter, we propose an efficient frequency-domain approach for calculating frequency response curves, which is based on HB (harmonic balance) method combining with ABMs (Analog Behavior Models) of Spice. Firstly, nonlinear devices such as bipolar transistors and MOSFETs are transformed into the HB device modules executing the Fourier transformations. Using these modules, the determining equation of the HB method is formed by the equivalent sine-cosine circuit in the schematic form or net-list. It consists of the coupled resistive circuits, so that it can be efficiently solved by the DC analysis of Spice. In our algorithm, we need not to derive any troublesome circuit equations, and any kinds of the transformations.

We review literature on high voltage transmission lines and their effect on wild reindeer (Rangifer tarandus) migration patterns and area use. We conclude that reliable knowledge is lacking on the effects of transmission lines on reindeer ecology. This condition relates to the lack of long-term monitoring of reindeer migration patterns in relation to existing lines. It is also related to the fact that nothing is known about hearing in reindeer (or any other deer species in Norway) in relation to transmission line noise, which is considered an obstacle for migrating reindeer.We then outline a research programme that includes a laboratory study to determine the audiogram in reindeer and two field studies to examine the proximate effects of transmission lines - independently as well as combined with ambient environmental variables - on reindeer behaviour. The audiogram in two yearling male reindeer has been determined; this part of the study will be completed this year with the determination of a corresponding audiogram in two female yearlings. The behaviour study of domestic reindeer under high voltage transmission lines was completed in September 1999. The behaviour study of wild reindeer in the area crossed by a 420 kV power line will continue this year and its completion is anticipated in 2001.

Animations of electromagnetic transients in power transmission lines by means of the two-dimensional numerical Laplace transform

A new finite element technique that allows nonlinear time domain analysis of power electronic circuits containing magnetic components is presented. The new technique is shown to compute the same voltage waveform in a nonlinear RLC circuit as previously published circuit techniques. The new technique is demonstrated for a circuit containing an inductor with a nonlinear B-H curve, finite conductivity and a given geometry including air gaps. >

Based on the wavelet transform results of the transient signals from all ends of the line, a unit protection for high voltage power transmission line is presented. The attenuation effects of high voltage transmission line and busbar capacitance to high-frequency current signals are analyzed. The Transient Current Content Ration(TCCR), Transient Voltage Content Ratio (TVCR) and Transient Voltage Singularity Ratio (TVSR) are deduced according to the analysis of the differences during high frequency voltage transients at each end of the transmission line when in-zone faulted and out-zone faulted. Protection criterion using TCCR and protection criterion using TVSR are proposed, and the principles of protection settings are given. The wavelet modulus maxima of transient signals are used to calculate TCCR and TVSR. Simulation experiments of different faults with EMTP are carried out to test and analyze the protection criteria. A 100kHz sampling rate is used in the simulation experiments. According to the simulation results, the protection criteria prove to be simple, reliable and good for whole line protection.

A simulation model in ATP-EMTP is proposed for calculating lightning transient responses of transmission lines. Both frequency dependent characteristic of transmission line and impulse corona effect are considered in this model. The frequency dependent characteristic is analyzed by Marti line model and a user defined corona model is applied to simulate the effect of impulse corona. The expression of geometric capacitance is derived by means of image theory and the dynamic capacitance for line with corona is computed. The simulation results show that the effect of corona plays a more important role than that of frequency dependent characteristic on lightning overvoltage, while it is more accurate to take both the effects of frequency dependent characteristic and impulse corona. The model presented in this paper can calculate the possible overvoltages on transmission line to provide reliable guidelines for insulation coordination and lightning protection design of transmission line.

CIRCEC is an interactive general puirpose simulation program performing AC, DC and transient analysis of non-linear electronic circuits. A library of user-defined FORTRAN models is available. CIRCEC is easy to use, economical and allows simulation of a large range of circuits.

Electrical power systems are different in their sizes because of their amount of generation power stations, substations, transmission lines and loads. Therefore, these factors may impact on short circuit levels values. Capacity of power stations and dummy transmission lines in Extra high voltage grid (400kV) of the Iraqi Electrical power grids cause high short circuit levels values such that exceed both rating of the peak and breaking capacity of switchgear equipment's. Reduction of short-circuit levels by using Fast-acting Flexible Alternating Current Transmission Systems (FACTS) types devices in power grids maintain the operation of power grids with acceptable value of short circuit levels for their electrical equipment's and preventing cascading event outages which may lead to blackouts. This paper mainly studies strategies on how to add Short Circuit Current Limiter (SCCL) device by determining its number, value and location of connection in power grids by programing with (PSS™E version 30.3 Package Program). IEEE 25-bus system is used for testing the adding series SCCL at power transmission lines method procedure. The results of adding series SCCL with power transmission lines give significant reducing short circuit levels for the stations have highest short circuit levels in order to prevent the blackouts of overall power grid.

Phasor measurement units (PMUs) and wide area monitoring systems (WAMS) are undoubtedly the important technologies in power systems [1]. One of their implementations is online parameter identification using current and voltage phasor vectors from sending and receiving ends [2]. Transmission line (TL) parameters online updating could help to solve different tasks, such as state estimation, power flow analysis, and Q/V optimization. The updated TL parameters could provide the data to identify the fault localization. Using FACTS devices gives a possibility to automatic control the operating voltage along the TL [3]. For the task of Q/V optimization not only active resistance updating is required but also renewing the corona losses (CL) value and the dependence between CL and operating voltage (OV). It is well known that instant CL value depends heavily on the weather conditions (wind velocity, air humidity, ambient temperature, precipitation, etc.) along the TL and on the voltage profile along the line. Due to the challenge in commercially installing weather stations along the TL, TL parameters identification based on PMU measurements is the most viable and effective solution. There are some papers considering CL and OV relation as a quadratic function due to a pi-circuit [2], [4]. These papers suggest defining CL from TL conductance. It has been established that real dependence between CL and OV constitutes the 4-8 order polynomial [5]. Given that, the better the weather is, the higher the order is observed.

The solutions of differential equations of transmission line are generally difficult to obtain due to the convolution integral present. Considering this, there are models proposed for the study of electromagnetic transients in transmission line. In this paper a single-phase transmission line is represented by two models. The first model represents the transmission line by its distributed parameters and its differential equations in the time domain are transformed into algebraic equations in the frequency domain. This model is named ULM. Once the solutions were obtained in the frequency domain, using the ILT implemented numerically, the solutions are obtained in the time domain. The second model uses lumped circuits parameters and it considers the transmission line represented by π-circuits connected in cascade. This model has the advantage of being developed directly in the time domain, but there is a need to apply numerical integration methods to solve the equations. A fact observed in the responses using this models is the spurious oscillations. In this paper are shown spurious oscillations presents in simulations and using FT to analyze the spectral content of this oscillations for a single-phase transmission line considering different conditions as its length, represented by different quantities of π-circuit and submitted to diverse conditions of energization.

A new simulation technique for analysis of power electronics circuits is presented. It is based on using the Chebyshev polynomial to derive an adaptive stepwise quadratic state-space model for each piecewise-linear circuit topology, where the state-space equation sets are integrated with modified nodal formulations (MNF). The key feature of this algorithm is to determine an optimum step size for the model to achieve desired accuracy. The switching instants are directly calculated by solving simple quadratic equations. No prior knowledge of the circuit operations is required. The theoretical predictions are verified with the results obtained in the available literature.

It is known that the occurrence and existence of ferroresonant oscillations at the subharmonic frequency (SHC) in power transmission lines (TL) and in power supply systems is extremely undesirable, since they cause ferroresonant overvoltages at different frequencies. At the same time, there is a wide class of nonlinear electrical circuits, in which the excitation of autoparametric oscillations (AIC) at the frequency of the SHC forms the basis of frequency converting devices serving as secondary power sources. It is shown that three-phase nonlinear systems are in one way or another equivalent circuits for power transmission lines, the main elements of which are: longitudinal compensation capacitors, transverse compensation reactors, and transformers with a nonlinear characteristic. To study the regularities of the excitation and maintenance of SHC at a frequency in three-phase electro-ferromagnetic circuits (EFMC), theoretical and experimental studies of an equivalent model of a three-phase circuit with nonlinear inductance were carried out. For the analysis of the steady-state mode of the SHC at the frequency, the method of a small parameter (averaging) was applied. A shortened differential equation of motion for a three-phase nonlinear circuit is obtained. By solving them, the regions of existence of the SHC and the critical parameters of the chain were determined. The obtained results of theoretical research are confirmed by experimental studies.

Along with the rapid economic development in recent years, people's demands for electricity have also been increasing very rapidly, which makes the power industry grow very fast, however, there have also been new challenges for the safety of the grid. Due to the complexity of China's topography, many power transmission lines under construction and planning are inevitable to pass through the high-altitude areas. Due to the high altitude and low air pressure, a number of external environmental factors are quite different from these of the low-altitude areas, and all these factors have a great impact on the power transmission lines, which will bring a lot of special problems to the design and operation of the power transmission lines. This paper describes the finite element method analysis which is used to calculate the relevant parameters of power transmission lines in high-altitude areas, as well as the status quo of the research on high-voltage AC power transmission lines in high-altitude areas. By analyzing the status quo of these studies and combined with the actual terrain situations of high-altitude areas, we can provide the construction of high-voltage AC power transmission line in high-altitude areas with some valuable references, thus to ensure the safe operation of such power transmission lines.

Trip faults are obviously increased by frequent lightning strikes, and increasing lightning trip-out seriously affects a system’s stability and power supply reliability. In this paper, the reasons for high lightning trip-out rates in electric power transmission lines are analyzed in detail from three perspectives, as follows: the substandard lightning resistance level, lightning complexity at a mid-point between towers, and the complexity of first and subsequent lightning stroke conditions. Experiments and simulations demonstrate that the solid-phase gas arc-extinguishing method has a strong ability to extinguish power–frequency continuous-current arcs and to protect against first and subsequent lightning strokes. Since the time taken by gas arc-extinguishing is much less than the response time of relay protection, trip accidents caused by lightning strikes can be avoided and the trip rates of lightning strikes can be reduced using this method. The case analysis and practical operation results show that the solid-phase gas arc-extinguishing lightning protection method can reduce the lightning trip-out rate by more than 90%, completely solve the problem of high lightning trip-out rates, and significantly improve the reliability of power supply.