Iraida Kolcunová

Measuring of the shielding effectiveness of electromagnetic field of brick wall in the frequency range from 1 GHz to 9 GHz

This paper deals with measuring of shielding effectiveness of electromagnetic field. The measurements were focused on measuring of shielding effectiveness in the range of high frequencies from 1 GHz to 9 GHz in the step 0,2 GHz. The measured object was a brick wall with a thickness 25 cm. Size of brick wall were 2×2 m. Measurement was preformed according IEEE Standard, Method for Measuring the Effectiveness of Electromagnetic Shielding Enclosures. Measurement was performed in the non-reflection chamber because exterior influence. Brick wall consisted of bricks porotherm 25×25 cm. The laying of bricks were the same as in the construction of buildings.

Research of electrophysical properties of oil-paper insulation

The transformer plays an important role in providing a reliable and efficient electricity supply and is one of the most critical equipment in electric power transmission and distribution systems. The mineral oil paper insulation system is successfully used in transformers for many years. Today great emphasis is accentuated on the use of materials environmentally friendly. Natural ester is considered to be a substitute of mineral oil. This paper is focused on electrophysical properties of rapeseed oil - paper and mineral oil - paper insulation system. Dissipation factor and breakdown voltage of paper impregnated by mineral oil and natural ester were measured. Properties of mineral oil paper insulation and rapeseed oil paper insulation are compared.

Measuring the shielding effectiveness and reflection of electromagnetic field of building material

Exposure to electromagnetic radiation is omnipresent. And we can expect the volume of electromagnetic radiation as well as the number of sources to continue to increase. This paper deal with the measuring of shielding effectiveness and reflection of electromagnetic field. The aim is to measure the shielding effectiveness and reflection in the range of high frequencies from 1 GHz to 9 GHz by step of 0.2 GHz. In this paper, the object of investigation is a brick wall with a thickness of 0.25 m and the surface area of 2×2 m. Measurements were performed according to the IEEE Standard, Method for Measuring the Effectiveness of Electromagnetic Shielding Enclosures. Measurements were performed in the non-reflection chamber in order to avoid the exterior influence. The brick wall was made of bricks type “Horizontally Perforated Clay” of the size 0.25ç0.25 m.

The influence of accelerated ageing on the oil impregnated paper

One of the most important parts of electric power equipment is the insulation system. Insulation system must be in a good condition for reliable and safe operation of electrical devices. During the lifetime of the electrical equipment, insulation system is exposed to various factors which could have negative influence on the properties of the insulation system. High temperature is one of the factors known to cause a degradation of the insulation system. Insulation system of transformers consists of two parts - liquid and solid. Liquid portion is represented by insulation oil and the solid one is represented by insulation paper. This paper focus on the investigation of how an accelerated ageing influences the properties of oil impregnated paper. Vegetable oil with its high flash point, high degradation rate and the reproducibility represents a potential new type of insulation oil which is expected to replace currently used mineral oils. Research of the vegetable oil properties is therefore a crucial step towards its future use. Properties such as relative permittivity, dissipation factor and the breakdown voltage will be described and analyzed.