In this paper a new method to mitigate a cyclic voltage flicker using electronically switched tap changed transformer is investigated. The idea of this method is based on injection of a signal, with the same frequency rate as that of the flicker, into the feedback path of the controller. This method utilizing electronically controlled tap-changed transformer provides flicker free secondary voltage. Further in this paper a new switching technique implemented to control a single-phase tap changedtransformer in order to eliminate the internal flicker problem is investigated. The suggested method was subjected to both theoretical and experimental investigations.

Flicker, Electronic Tap-Changed Transformer.

Tap changer converter periodically connects and disconnect transformer tap hereby achieving continuous voltage regulation. Commutation cell with bi-directional switch and high frequency switching is a basic building element. Used technique requires additional inductances or use accurate current measurement and has potential hazards. Different solutions are suggested in the paper and verified by simulation and experimental study. For tap changer converter commutation it is important that the commutation is symmetrical. A symmetrical smart commutation technique without necessity to measure current is developed and presented. Experiments verify the simulation results. The application of such a commutation is demonstrated on 500kVA tap changed transformer. Voltage regulation with tap changer is demonstrated too. Introduction

Power Quality, Converter Circuits

In this paper it will be shown that the switching of the power electronic switches can be a cause (source) of flicker. A new switching technique implemented to control a single-phase tap changed-transformer in order to eliminate the internal flicker problem is investigated. The suggested method was subjected to both theoretical and experimental investigations. Further in this paper a method to mitigate a cyclic voltage flicker using an electronically switched tap changed transformer is investigated in Caspoc. The idea of this method is based on injection of a signal, with the same frequency rate as that of the flicker, into the feedback path of the controller. This method utilizing electronically controlled tap-changed transformer, provides a flicker free secondary voltage.

Smarttrafo, flicker

The switching of high-voltage capacitor banks for reactive-power or voltage support can produce significant transients. It is well understood that reactors, pre-insertion resistors, pre-insertion inductors, and synchronous switching can mitigate the transients. Circuit inductance can limit peak currents but resistance damps the oscillations most effectively. Computer simulations of transient inrush for single and back-to-back capacitor banks indicate that pre-insertion resistors can significantly reduce transients. The ability to incorporate another circuit parameter, the pre-insertion resistor, provides opportunities for improved high-voltage capacitor bank design. This paper presents an overview of capacitor switching options and the results of computer simulations for a “typical” application showing the expected transient currents in single-bank and back-to-back switching, as well as the effect of various reactor and pre-insertion resistor combinations. Results of the simulations are summarized in a table and provide the reader with a simple overview of the results of using pre-insertion resistors in capacitor switching applications.

In this paper, the issues of interconnecting large wind parks to the electrical power network are discussed and possible solutions to counter-act problems are presented. In order to proceed with these large-scale wind farm projects, an integrated approach using key wind farm technologies, AC and DC transmission technologies, as well as network load-flow and dynamic stability mitigation and storage technologies (FACTS) are required. Practical and realistic limits for classic wind power generation are discussed. The feasibility of a 6 GW offshore and 100 MW near-shore wind farm are discussed as case studies, using integrated storage and STATCOM options.

Commutation cell with a high frequency switching is a basic building element of a tap changer and also different topologies. In the paper. Existing technique requires accurate current measurement and has potential hazards. Different solutions are suggested in the paper and verified by simulation and experimental study. A novel commutation technique without necessity to measure current is developed and presented. Experiments verify the simulation results.