Viktor Bolgov

Reactive power compensation for spot welding machine using thyristor switched capacitor

High-power industrial spot-welding machines make use of transformers that have very high reactive power consumption. Simple reactive power compensation schemes cannot be used however, because of the cyclic nature of the spot welding transformer operating. This paper describes the development of a simple reactive power compensator solution for the spot-welding machines. Focus is also put on the transformer saturation and current transients that can emerge from deployment of such reactive power compensation methods.

EMC education and related problems at Tallinn Technical University

Taking into account the importance of electromagnetic compatibility (EMC), modern electrical education requires more attention to give future electric and electronic engineers with good EMC knowledge. The purpose of this paper is to present the current situation with EMC educational and lab activities, as well as plans for the future at Tallinn University of Technology, Estonia. The paper describes the existing course and contents of creating courses in EMC given in the Department of Electric Machines and Fundamentals of Electrical Engineering. The aim and proposed effect of the courses are outlined.

Interlock delay time minimization and its impact on the high-voltage half-bridge DC/DC converter

In DC/DC power converters, as in many other applications with inverter circuits, the interlock delay time between IGBT switching on and off in the opposite inverter arms is used to avoid a short circuit in a DC link. It is suggested by several handbooks that 20% of the half period should be used. However, in some applications, e.g. power supplies with extended input voltage variations, much smaller interlock delay time must be used to ensure correct operation of the inverter. In this paper the interlock delay time minimization possibility is analyzed on an example of an existing experimental device based on 6.5 kV IGBTs. Moreover, the possible impact of interlock delay time minimization on the isolated DC/DC converter components, operability and efficiency is evaluated.

Current Stabilization for Improving Electromagnetic Compatibility of Highly Varying Loads by Use of Saturable Reactor

Power quality control in the case of powerful abruptly variable loads, e.g. electric arc furnaces, becomes an actual problem due to the deregulation of electricity markets. A way to mitigate distortions on a power supply network, especially the flicker, is load current stabilization. The saturable reactor is proposed as a solution.

New theoretical approach to input current shaping in ac-dc power converters

A new method for an input current waveform correction in typical power converters is described. It assumes an implementation of the so-called virtual transformer with a fast-changing voltage ratio. Theory and calculations are presented to confirm the method validity. Practical implementation is left out of the scope of the given paper due to size limitations.

Economical feasibility of off-grid hybrid power supply for estonian remote areas—part 1: Hybrid components sizing

The paper considers the implementation of an off-grid hybrid power supply as an alternative to the construction of a conventional power supply lines in sparsely populated remote areas in Estonia. In the first part of the paper, the economical study of off-grid hybrid systems was conducted at different typical geographical conditions including coastal and inland ones. The load demand and interest rate were the parameters for sensitivity analysis. The configuration of the studied systems could include photovoltaics, wind turbines, a diesel generator, and batteries. The components were sized through optimization procedures. The levelized costs of energy were calculated for the considered cases.

Suppression of Voltage Flicker by Saturable Reactor Operating under Forced Magnetization

Power quality control in the case of powerful abruptly variable loads, e.g. electric arc furnaces, becomes an actual problem due to the deregulation of electricity markets. A way to mitigate distortions on a power supply network, especially the flicker, is load current stabilization. The saturable reactor is proposed as a solution.

The methodology of risk evaluation for power equipment technical state assessment

The paper provides the methodology of power network equipment technical state assessment risk evaluation to ensure effective power network operation and optimization of maintenance and repair schedules. The analysis of existing approaches for risk assessment is carried out from the point of mathematical formulation and existing application practice. The case study illustrates the calculation of technical state assessment risks for 110 kV oil-filled power transformer, based on neuro-fuzzy inference approach.

Economical feasibility of off-grid hybrid power supply for estonian remote areas—part 2: Determination of breakeven grid extension distances

The paper considers the implementation of an off-grid hybrid power supply as an alternative to construction of a grid connection in sparsely populated remote areas in Estonia. In the previous part, the proper configurations of the off-grid hybrid system and component sizes were determined through optimization procedures at different typical meteorological conditions including coastal and inland ones. In this part, levelized costs of energy (LCOEs) were found for a newly built grid connection under the same load demands and interest rates. They were compared with the LCOEs for the off-grid systems in order to find breakeven grid extension distances. As a result, the recommendations on the expedience of off-grid hybrid power supply were obtained for different regions of Estonia.

Environmental considerations in lifecycle based optimization of electrical machines

This paper describes the environmental considerations that have to be taken into account in lifecycle based design and optimization of electrical machines. As the electrical machines and electric motor-drives are the most electrical energy consuming apparatuses, in depth optimization of them during the design process is essential to support energy efficient and environmentally friendly development in electrical engineering and industry processes. Lifecycle based optimization grants a possibility to evaluate a wider range of variables that affect the environment and energy requirements as well as consumption of the machines. An overview of gross energy requirement estimation possibilities and environmental risks through the lifecycle of the machines is presented in the paper.