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  • Author: Marcin Szewczyk x
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M. Szewczyk


Very fast transient overvoltages (VFTO) originate from steep voltage breakdowns in SF6 gas that are inherent to operation of any switching device of the gas-insulated switchgear (GIS) type. For power stations with voltage ratings exceeding 500 kV, the ratio between equipment rated- and withstand-voltage levels becomes relatively low, which causes the VFTO peak values to reach the component’s insulation withstand-voltage levels, thus becoming a design factor for high- and ultra-high voltage GIS. While well-established approach to VFTO analyses involves only single VFTO events (the so-called single-spark approach), there is often the need to analyze the entire VFTO generation process, for which the multi-spark approach to VFTO modeling is to be employed. The multi-spark approach allows one to evaluate the VFTO impact on the GIS disconnector design along with the impact of the VFTO on selection and dimensioning of the VFTO damping solutions. As the multi-spark approach to VFTO modeling is now being increasingly used in UHV GIS developments as well as for the insulation co-ordination studies of power stations, the present paper is motivated by the need to report on the VFTO multi-spark modeling approach and to lay a common ground for development works that are supported extensively with VFTO simulations. The paper presents physical assumptions and modeling concepts that are in use in such modeling works. Development of the multi-spark GIS disconnector model for VFTO simulations is presented, followed by an overview of examples of the model application for the GIS development works and for insulation co-ordination studies.

Open access

Piotr Oramus, Tomasz Chmielewski, Tomasz Kuczek, Wojciech Piasecki and Marcin Szewczyk


Electric arc is a complex phenomenon occurring during the current interruption process in the power system. Therefore performing digital simulations is often necessary to analyse transient conditions in power system during switching operations. This paper deals with the electric arc modelling and its implementation in simulation software for transient analyses during switching conditions in power system. Cassie, Cassie-Mayr as well as Schwarz-Avdonin equations describing the behaviour of the electric arc during the current interruption process have been implemented in EMTP-ATP simulation software and presented in this paper. The models developed have been used for transient simulations to analyse impact of the particular model and its parameters on Transient Recovery Voltage in different switching scenarios: during shunt reactor switching-off as well as during capacitor bank current switching-off. The selected simulation cases represent typical practical scenarios for inductive and capacitive currents breaking, respectively.

Open access

Łukasz Dziki, Justyna Sobolewska, Martyna Szewczyk, Jakub Włodarczyk, Aleksandra Sobolewska and Marcin Włodarczyk


The sex and age of the physician performing the digital rectal examination (DRE) procedure is one of the parameters influencing patients’ comfort. It is postulated that the stress related to DRE during admission to the surgical ward may affect the compliance.

The aim of the study was to characterize patients’ preferences according to their sex, age, socioeconomic status and according to DRE-related variables.

Material and methods. Patients admitted to the Department of General and Colorectal Surgery at Medical University in Łódź between October 2014 and June 2015 were asked to complete a questionnaire regarding their sex, age, ethnic background, socioeconomic status and preference for a physician performing the DRE during admission to the surgical ward.

Results. The study enrolled 225 patients, 52% (n=117) women and 48% (n=108) men. Most patients 73.3% (n=244) expressed no preference for sex of the physician performing the DRE during admission, while 22.7% (n=51) preferred a same-sex physician. Analysis showed that the age, female sex, lower education status, small amount of comorbidities and number of hospitalizations, and no previous colonoscopy experience were all associated with preference for a same-sex physician.

Conclusions. In our study most patients expressed no preference for sex of the physician performing the DRE during admission to the surgical ward. However, over one-tenth of patients reported such preferences. Most of these patients preferred a same-sex physician. It is important to offer these patients the choice of physician performing the DRE. Addressing patients’ preferences may improve the atmosphere in the clinical environment, reduce stress, and facilitate better treatment.