Ivars Zalitis

Usage of inrush current surge for early detection of inter-winding faults

This paper presents the development of micro-processor based device for improving the sensitivity of differential protection of power transformers. Power transformers failure may lead to high scale systems operations disruption and heavy economic losses, thats why the lever of requirements for power transformer protections is so high. Differential protection is usually used as a main protection against internal faults such as inter-windings faults, inter-coil faults or coil-core faults. For safe protection against incomplete winding faults protection device must be capable to detect differential current from such a very low value from nominal. The idea for a new device is to use information extracted from inrush current thru Fourier transformation to perform an early detection of faults usually hardly detectable due to very low impact on transformers primary current in steady condition. In case of fault device may operate with much higher sensitivity thus sensing fault on its early stage.

Numerical calculation method for symmetrical component analysis of multiple simultaneous asymmetrical faults

This paper present a numerical method for calculation of current and voltage symmetrical components in case of multiple simultaneous asymmetrical stationary power system faults. The proposed method first decomposes the complex fault into different sets of sequence networks. Each set represents one fault with interconnections of sequence networks and other faults with controlled current or electromotive force sources. Then the node voltages of sets are estimated by iterative technique while changing between these sets. This approach allows the current or electromotive force sources of following sets inherit values from previous sets. The proposed method provides an opportunity to solve complex faults problems with high speed and affordable computation cost. The obtained algorithm can be used as calculation core for larger tasks, fault location for example, when multiple asymmetrical faults are expected.

A power transmission line fault locator based on the estimation of system model parameters

This paper presents a method for fault location in transmission lines, which uses measurements from one substation during pre-fault and fault regimes to estimate unknown parameters of a wider power system model with an optimization algorithm. The optimization algorithm diminishes the difference between measurements and a power system numerical model output. This method incorporates random search within given limits of unknown parameters with a following search space reduction. An additional estimation of pre-fault regime model parameters reduces the number of free dimensions in the fault regime model thus increasing the feasibility of the fault parameter estimation. The utilization of a topological fault model with interconnected sequence networks allows accounting for fault resistance and presence of the zero sequence mutual coupling of parallel lines. Testing of the proposed method showed that it can provide results with a good tolerance despite using a system model with various simplifications.

A distance protection based on the estimation of system model parameters

Most of the distance relays base their operation on the measured apparent fault impedance. These relays are bound to have an error inflicted by the unknown remote end parameters and fault resistance. This paper presents a method, which diminishes such errors using optimization techniques. The proposed method executes a system model unknown parameter estimation by adjusting model output to measurements from the same substation with the Monte Carlo method in sequence to pre-fault and fault regimes. This allows the elimination of uncertainty, caused by incomplete scope of information, available to classic relays. The proposed method was tested on a three machine system with a fault in one of parallel lines bounded by a mutual inductance and was proved to obtain fault parameters with an acceptable tolerance. The proposed method can be applied in a standalone application or it can provide reliable fault parameter data and improve the distance protection sensitivity.

The modified Seidel method as a tool for the evaluation of the stability of a power system

Changes in a power systems network structure, technological advance and high loading conditions as a result of the energy market demand are reasons for further power system stability analysis. Research on new types of system stability as well as better methods for an evaluation of classic problems are ever more relevant. Providing the dispatcher with a tool for a quick evaluation of system stability would prove useful in these conditions. The target here is not only the current regime but also possible minor regimes derived from normal regime in case of element outage that is of significance for the system. This paper researches possibilities of using regime calculations, more precisely the convergence process of the modified Seidel method, to evaluate the static stability of the system. The proposed method has been tested on WSCC 9-bus system with MATLAB and ETAP software.