Jevgenijs Kozadajevs

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.

Phase plane usage for convergence analysis of Seidel method applied for network analysis

This paper presents the convergence analysis of Seidel method for solving power systems automatic tasks. In a condition of use of Programmable logical controllers with low capacity as a hardware, algorithm solution based on Seidel method have some advantages, such as memory saving. However, there are some limits for Seidel method convergence. If the electrical network condition is close to resonance there will be no assurance that Seidel method will converge. As a result of made experiments we can conclude that usage of relaxation method in conjunction with convergence control on the phase plane allows to solve network analysis problem with nonexpansible hardware.

Implementing energy efficiency and demand-side management in glasswork company

This paper provides in-depth analysis of the potential impact of demand-side management and energy efficiency improvements by evaluating energy consumption and efficiency according to the LVS EN ISO 50001:2012 standard at a glass-work company in Latvia. The electricity consumption monitoring system provides detailed data on energy consumption by the different types of production processes. In-depth analysis of production process energy consumption shows that glass tempering is included in almost all glass production processes and is the most energy-intensive process. By increasing the energy efficiency of the glass tempering process, the total energy consumption may diminish considerably, as may the share of electricity in the ultimate cost of the products, which is to result in diminished prime cost of the products. However, the process of refurbishing the glass tempering process is rather expensive and requires analysis as to the repayment of investment, considering the new law on the mandatory procurement component (MPC).

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.

Criteria for inter-winding fault detection within power transformers

Power transformers are highly valued power systems elements, transformers failure may lead to high scale systems operations disruption and heavy economic losses. This is the main reason for power transformer protection requirements to be so high. Sensitivity level is a key element in inter-winding faults detection. Incomplete winding faults that occur in the multi-wire transformer windings, when multiple parallel wires form a coil, are very hard to detect, this is why it is the most challenging issue for the differential protection. This paper presents the development of a criteria for inter-winding fault detection.

Current transformer error correction

This paper presents the development of micro-processor based device with ability to decrease protection-type current transformer measurement error in the area of small currents. Measurement transformers are available with a high precision class of 0.2 and 0.5 and maximal measurable current up to double rated value. Transformers, produced for relay protection purposes, are with error classes of 3, 5 and 10 meaning error rates of 3, 5 and 10 % respectively. Our idea consists in a new way for joining the characteristic curves of relay-type and measurement-type current transformers. The micro-processor based device may “teach” itself by forming some error correction table in its memory on the basis of core outputs compare during normal operation. In case of fault device may operate with much higher sensitivity thus sensing fault on its early stage.

Signal extraction from inrush current for inter-winding fault protection of power transformers

In case of transformer failure there is a high risk of losing part of power system, which can result in disruption for consumer power supply. This is the main reason for power transformer protection requirements to be so high. Power transformer is a complicated object considering its protection. Sensitivity level is a key element in inter-winding faults detection. Incomplete winding faults that occur in the multi-wire transformer windings, when multiple parallel wires form a coil, are very hard to detect, this is why it is the most challenging issue for the differential protection. Our idea is in creating a microprocessor based device that will use an inrush current surge as an information source for inter-winding fault detection within transformers.