I. I. Nikulov

Bio: I. I. Nikulov is an academic researcher. The author has contributed to research in topics: Electromagnetic coil & Voltage. The author has an hindex of 3, co-authored 9 publications receiving 17 citations.

Resonance Overvoltages in Primary Winding of a Station Service Voltage Transformer

Abstract: The design of new types of transformer equipment, in particular, station service voltage transformers (SSVTs), requires a detailed consideration of all technical aspects and conditions of their application and their design features. One problem is to provide their resistance to effects associated with their interaction with the grid. During transient events in the network caused by the operation of switching equipment or short circuits, the transformers are affected by the oscillating voltage, which, under certain conditions, can cause resonance overvoltages inside their windings. The design of SSVTs differs from that of common power transformers, mostly because different types of windings are used, which determines the essential difference in the natural oscillation frequencies and the theoretical possibility of the development of resonance overvoltages under changed combinations of network parameters and switching conditions. In this paper, the problems of estimating the natural and dominating oscillation frequencies in SSVT windings and the voltages on the longitudinal insulation of SSVT windings under the resonance conditions are considered. The proposed approach is applicable not only to SSVTs, but also to other types of transformer equipment.

Studying the Impulse Overloads in the Windings of a Station Service Voltage Transformer

Abstract: One of the key factors determining the performance of a 110–500-kV station service voltage transformer (SSVT) is a compact insulation design that provides minimum winding sizes. Since SSVTs are new equipment that combine the operational features of a power transformer and the design features of a measuring voltage transformer, it is necessary to study the characteristic transient processes occurring under the impact of lightning-impulse test voltages and lightning and switching overloads in operation in order to ensure proper insulation design. The article presents the results of an experimental investigation of impulse transients in the windings of a full-scale mockup model of an active part of a 20-kV A SSVT with a rated voltage of 110 kV. The influence of grounding the low-voltage winding terminals on the maximum values and duration of impulse stresses on the longitudinal insulation of the high-voltage winding is revealed. It is shown that, unlike in the case of power transformers with disc windings, more significant effects on the insulation are produced when no load is applied on the low-voltage windings.

Using Dual Circuits to Simulate Electromagnetic Processes in Cascade Station Service Voltage Transformers

Abstract: —The scientific and methodological principles of development of the design models of a new device—station service voltage transformers intended for use in design study—are considered. The proposed models relate to the “white box” model class, which provide the maximum accuracy when solving such problems. The models are based on equivalent circuits of active parts, which are obtained using the principle of duality of magnetic and electric circuits. It is revealed that the determination of parameters and verification of models are possible only at the manufacturing plant of transformers. Special attention is paid to reproduction in the models of magnetizing process of transformer. The experimental oscillograms are given of magnetizing currents of magnetic conductors of the active parts and of the transformers as an assembly, which show the capacitances of high-voltage winding have a great effect on the open-circuit current. The algorithm for determination of the parameters of transformer model for calculation of steady state conditions is presented, which provides a good coincidence with experimental values for integral parameters, such as the power loss and the root-mean-square value of magnetizing current.

On Determination of Leakage Inductances of Transformer Windings

Abstract: —When designing a transformer structure and numerical simulation, it is needed to calculate the parameters of an equivalent circuit. One of the most important parameters is the leakage inductance of two windings or of their parts, the calculation of which can be relatively easily performed solely for simple cases of equal high windings. For more complex configurations, it is necessary to apply special methods, which are developed mainly for calculating the leakage inductances of high-power network transformers. Among these methods, one can distinguish the method of average geometric distances, methods based on the analytical solution of Maxwell’s equations in a two-dimensional axisymmetric statement, and the numerical finite elements method. In this work, these methods are used to calculate the leakage inductances of small-sized transformers with winding configurations typical for voltage transformers of inductive type and station service voltage transformers. The accuracy of methods is estimated by comparing the calculation results with experiment. The description of the experimental setup is presented, the general characteristics of calculation methods are given, and the results of comparison of calculated and experimental values of leakage inductances are analyzed.

Determining the efficiency of the compensation of single-phase capacitive earth currents using arc-suppression coils of different designs implemented in an experimental workbench

Abstract: Results of the experimental comparison of the compensation of single-phase capacitive earth currents using arc-suppression coils of two cardinally different designs, i.e., plunger-type coils and coils controlled by magnetic bias, are presented. It was previously shown using the simple formula and the calculation grid model that the response time of the reactors determined through the time required to compensate the power component of the earth current depended on the phase angle of the voltage at the moment of earth fault [1]. If the earth fault occurs not at the moment of the maximum voltage, an aperiodic component appears in the coil current, which makes it impossible to compensate instantaneously the capacitive earth current. An experimental workbench with a voltage of 6 kV used to carry out the measurements is described. The measurement results show that the coils of both designs have similar response times, which are on average of the order of a few hundreds of milliseconds; these values substantially exceed the implied values of the response time of the coils. It is shown that the response time of the coils cannot be the criterion for their efficient operation. Therefore, to compensate for an intermittent arc capacitive earth fault, a comparative criterion for assessing the efficiency of the operation of the coil is proposed, which is based on the average value of the energy dissipated the site of fault.

Resonance Overvoltages in Primary Winding of a Station Service Voltage Transformer

Abstract: The design of new types of transformer equipment, in particular, station service voltage transformers (SSVTs), requires a detailed consideration of all technical aspects and conditions of their application and their design features. One problem is to provide their resistance to effects associated with their interaction with the grid. During transient events in the network caused by the operation of switching equipment or short circuits, the transformers are affected by the oscillating voltage, which, under certain conditions, can cause resonance overvoltages inside their windings. The design of SSVTs differs from that of common power transformers, mostly because different types of windings are used, which determines the essential difference in the natural oscillation frequencies and the theoretical possibility of the development of resonance overvoltages under changed combinations of network parameters and switching conditions. In this paper, the problems of estimating the natural and dominating oscillation frequencies in SSVT windings and the voltages on the longitudinal insulation of SSVT windings under the resonance conditions are considered. The proposed approach is applicable not only to SSVTs, but also to other types of transformer equipment.

Research On Ferromagnetic Resonance Overvoltage Based On Station Service Voltage Transformers

Abstract: Station Service Voltage Transformers (SSVT) combines the operating characteristics of power transformers and the design characteristics of measuring voltage transformers. Due to its lower initial cost and higher power supply reliability, its applications have been extended beyond that of auxiliary power. During transient events in the network caused by the operation of switching equipment or short circuits, the transformers are affected by the oscillating voltage, which, under certain conditions, can cause resonance overvoltage inside their windings. Based on the ATP-EMTP platform, the ferromagnetic resonance of SSVT is simulated and its simulation model, simulation algorithm, and waveform are analyzed. Based on the simulation analysis results, this paper puts forward the preventive measures of transformer ferromagnetic resonance from the perspective of voltage harmonics and insulation coordination.

Using Dual Circuits to Simulate Electromagnetic Processes in Cascade Station Service Voltage Transformers

Abstract: —The scientific and methodological principles of development of the design models of a new device—station service voltage transformers intended for use in design study—are considered. The proposed models relate to the “white box” model class, which provide the maximum accuracy when solving such problems. The models are based on equivalent circuits of active parts, which are obtained using the principle of duality of magnetic and electric circuits. It is revealed that the determination of parameters and verification of models are possible only at the manufacturing plant of transformers. Special attention is paid to reproduction in the models of magnetizing process of transformer. The experimental oscillograms are given of magnetizing currents of magnetic conductors of the active parts and of the transformers as an assembly, which show the capacitances of high-voltage winding have a great effect on the open-circuit current. The algorithm for determination of the parameters of transformer model for calculation of steady state conditions is presented, which provides a good coincidence with experimental values for integral parameters, such as the power loss and the root-mean-square value of magnetizing current.

Overview of Voltage Transformers Suitable for High Voltage Levels

Abstract: With the development of the power grid, high voltage transmission lines and smart substations are put into use This requires higher-performance voltage transformers Potential transformer(PT) can no longer meet the measurement needs Analysis of the voltage measurement requirements in the power grid, pointing out the limitations of traditional PT such as poor insulation performance and ferromagnetic resonance The principles, characteristics and application of three new voltage transformers, that is, resistance voltage transformer, capacitor voltage transformer(CVT), and optical voltage transducer(OVT) are described, and the practical problems of new voltage transformers are summarized and put forward