Sharif Digital Repository

Network equivalents can be used to represent parts of a power system to reduce the complexity and the computation time during the simulation of electromagnetic transients. The goal is to simplify the representation while preserving the accuracy of transients in the remainder. In this work a method is developed for construction of single and multi-port Frequency Dependent Network Equivalent (FNDE). In this equivalent model the input admittance matrix is approximated by a rational function in the frequency domain. This method is developed for both single and multi phase systems. Several examples showing the accuracy and efficiency of the developed FDNE is presented  

In this paper, a new method for the calculation of electromagnetic fields around a transmission line subjected to a lightning strike is described and discussed. The electric fields and magnetic fields are presented graphically as a function of spatial coordinate, as a function of time and as a function of both. It is believed that this exact solution have not been published before. First, a double exponential lightning surge current is injected into a transmission line. Once The temporal variations of current is known, then electric and magnetic fields can be calculated by using the field expressions for electric dipoles over infinitely conducting ground. As the calculation was done for each... 

The size and complexity of modern power systems necessitate the use of Frequency Dependent Network Equivalents (FDNE) for part of the system. In order to give realistic simulation the frequency response of the equivalent must mach that of the system it represents. In this paper a method for developing FDNE is presented and demonstrated by approximation its admittance matrix Y by rational function in the frequency domain based on vector fitting method. The developed FDNE is accurate and efficient. An example showing the accuracy and efficiency of the developed FDNE when used to reduce a radial network is presented. ©2006 IEEE  

Application of the network equivalent concept for external system representation in electromagnetic transient studies is well known. However, the challenge in application of an equivalent model, approximated by rational functions, is to guarantee passivity of the corresponding model. Therefore, there is a need to enforce passivity of the equivalent model. In this paper, the passivity enforcement problem is first formulated as a quadratic programming (QP) problem, and then solved based on an efficient implementation, using an infeasible-interior-point primal-dual method. An application of this method for passivity enforcement of a six-port admittance model (with large passivity violations)... 

Developing an accurate network equivalent to reduce the computational time of an electromagnetic transient study has been the major task of many researches in the past two decades. However, still no accurate wide band equivalent for an asymmetrical network is addressed in the literature. This paper presents a Hybrid equivalent for the external system, assuming that it contains an asymmetrical transmission system at the terminal of this external system. The proposed method is based on the introduction of an asymmetrical transmission system in the model through application of a real constant transformation matrix in the subsystem and dealing with its asymmetrical effects in the external... 

This paper proposes a novel FPGA-based matrix-inversion technique that is specifically tailored and optimized for real-time electromagnetic transients simulation of power electronic converters with high switching frequency. This is the first reported solution that is capable of solving the real-time equations related to using ideal switch model and the associated circuitry in very small time-steps (e.g., an average of 36 ns in a three-phase back-to-back converter case study), without requiring large amount of memory, being limited to small number of switches, adding parasitic elements, or depending on a priori knowledge of the circuit operation or switching strategy. The accuracy of the... 

This paper presents a novel approach for fault location of overhead transmission lines by voltage and current measurements in a remote substation. The method is applicable when not all of the transmission lines in an area are equipped with fault-locators, although there may be a critical substation (CS) in the area equipped with a digital fault recorder (DFR). In the proposed method, the circuit equations of the network are used to find the transfer function between the fault location and each voltage and current measurement in the CS. Next, two auxiliary variables are defined to transform the nonlinear fault location estimation problem into a linear least squares problem. A closed-form... 

This study presents a novel method for fault location of transmission lines by multiple fault current measurements. In contrast to conventional methods, it is proposed to utilise several current measurements, which may be far from the faulted line. The circuit equations of the network are used to express each fault current as a function of fault location. Fault location is then estimated using a least-squares estimation technique. To achieve a robust estimation of fault location, statistical hypotheses-testing is employed for identifying erroneous measurements. The method is applicable to both synchronised and unsynchronised measurements. Moreover, fault location can be estimated regardless... 

Smart transmission grids are intended to utilize various measurements for enhanced operation. In particular, synchronized phasor measurements have found many applications in this context. This paper presents a linear weighted least-squares (WLS) method for fault location estimation of transmission lines by synchronized voltage measurements. The measurements may be taken from the faulted line terminals or buses far from the faulted line. The circuit equations of the network are used to find the transfer function between the fault location and each voltage measurement. Next, two auxiliary variables are defined to transform the nonlinear fault location estimation problem into a linear WLS... 

In order to restrain ferroresonance in coupling capacitor voltage transformers (CCVT), two kinds of ferroresonance suppression circuits (FSCs) , are proposed in this paper: the resonant type, the fastsaturation reactor type which are connected to secondary side of CCVTs. Frequency domain analyses, for voltage ratio magnitude, are carried out for CCVTs to obtain preferable FSC. Furthermore, using surge suppressors such as metal oxide varistors (MOV) to improve the performance of the FSCs is investigated. Time domain simulations demonstrate that ferroresonance can be cleared in few cycles in presence of FSCs. The Electromagnetic Transients Program (EMTP) is used for modeling and fine-tuning... 

Rational function-based models have proved to be very efficient for accurate frequency-dependent modeling of power system components. These models are able to characterize the components terminal behaviours (analysing the admittance matrix) for nodal analysis. This provides a fast convergence and inherent stability to the solution routine of the model. This work presents a general framework for interfacing the dynamic phasor method to the rational models. That would be promising for the electromagnetic transient analysis (under harmonic distortion), in the frequency domain. Therefore, Y-element rational pole-residue models (employing the vector fitting method) are developed. Moreover, the... 

This paper presents a high performance real-time simulator for power electronic systems applications and primarily intended for controller hardware-in-the-loop (CHIL) testing. The novelty of the proposed simulator resides in the massively parallel hardware architecture that efficiently exploits fine-grained parallelism without imposing severe communication overhead time that can limit the performance. The simulator enables the use of a nanosecond range simulation timestep to simulate power electronic systems. Through the use of this nanosecond range simulation timestep, the simulator minimizes the error arising from the intersimulation timestep switching phenomenon associated with CHIL. The...