Current measurements from electromagnetic current transformers are essential for the construction of secondary circuit systems, including for protection systems. Magnetic core of these transformers are at risk of saturation, as a result of which maloperation of protection algorithms can possibly occur. The paper considers methods for recovering a current signal in the saturation mode of current transformers. The advantages and disadvantages of methods for detecting the occurrence of current transformers core saturation are described. A comparative analysis of mathematical methods for recovering a current signal is given, their approbation was carried out, and the most promising of them was revealed. The stability and sensitivity of recovery methods were tested by adding white noise to the measured signal and taking into account the initial flux density (remanent magnetization) in the current transformers core. Their comparison is given on the basis of angular, magnitude, and total errors at a given simulation interval.

It is a common practice to use 2 ^nd order polynomial load model for steady-state power flow calculation. The paper describes the technique for identifying coefficients of the load model based on remote metering system data. Also, an example of the implementation of the technique for the reactive power system is presented in the paper.

The aim of the research is to develop and test technique for obtaining load static characteristics of large industrial enterprise. The research is initiated because the available data about Russian power system load have become outdated due to the change of power system structure, load content and behavior. At the same time the existing methods do not properly solve the problem of ill-conditioned data which is essential for such stochastic system as electrical load. The solution of this problem can be provided only on the basis of multiple experiments accounting different operating conditions of power system. The results of the first stage of such experimental work scheduled for the next several years by Russian System Operator is presented in the paper. To collect the data required for developing and testing of new multistage technique for identification of static polynomial load model, an active experiment was conducted. The proposed technique combines the successive approximation method and least-square method for filtering ill-conditioned data and estimation of polynomial model parameters. The obtained results confirm the efficiency of the proposed technique.

This paper proposes a structured hierarchical-multilevel approach to calculating the power flows and losses of electricity in radial electrical networks with different nominal voltages at given loads and voltages of the power source. The researched electrical networks are characterized by high dimensionality, dynamism of development, but also insufficient completeness and reliability of state information. The approach is based on the representation of the initial network graph in the form of a hierarchical-multilevel structure, divided into two stages with rated voltages $U_{nom}\le 35$ kV and $U_{nom}\ge 35$ kV, and using the traditional (manual) engineering two-stage method, where the calculation is performed in a sequence from bottom to top (stage 1) and from top to bottom (stage 2), moving along the structure of the network. The application of the above approach makes it possible to obtain an algorithm for implementation on a computer, which is characterized by universality (for an arbitrary configuration and complexity of the network), high performance and low requirements for the computer memory.

In the last few years, a great number of methods for identifying the load model parameters have been proposed. This article discusses the use of statistical approach to estimate the substation equivalent load model parameters for supplying to oil-producing industrial region. The disadvantages of existing statistical approach are the low accuracy obtained for the parameter estimates, especially when using samples size is small. To eliminate this deficiency, the current measurement data archive from SCADA system of electrical parameters for 15 months was collected. For the purpose of verifying the obtained results of statistical processing of SCADA data, a full-scale experiment was carried out in relation to the studied substation. The article describes the statistical method used to process the current SCADA measurement data, the results of archived statistical processing and experimental SCADA data. The electrical load models’ parameters received from the experimental studies results are of practical importance.

The paper briefly describes existing methods for processing measuring data of voltage, active and reactive power with a view to identify the mathematical model of substation load for calculating steady-state power system conditions. The authors proposed a classification of methods, described its key features and made a bibliographic list of works for each group.