Laboratory measurement and evaluation of energizing- and frequency-dependent surface impedances of cable sheaths, solid and stranded conductors

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Dr. Ladányi József
Department of Electric Power Engineering

The topic of my thesis is the examination of surface impedances of various conductors (solid and stranded conductors, cable sheaths). Surface impedances of conductors may most reasonably be determined by laboratory measurements for which purpose a coaxial reconducting tube is at disposal at the Department of Electric Power Systems.

My thesis consists of three main parts. In the first part the interpretation, theoretical basics of surface impedances of solid and stranded conductors, cable sheaths are discussed. The second part covers the elaborated measurement method, measuring instruments and measuring arrangement.

The basis of the measurements is to drive currents of various magnitudes and frequencies through the conductor to be measured and measure the voltage caused by the current along a section of fixed length of the conductor. My measurements can be divided into three groups: direct-current measurements, frequency-dependent measurements and excitation-dependent measurements. Before the measurements it was necessary to have the laboratory measurement setup arranged, to put together the aluminium reconducting tube and to prepare the conductors to be examined. To provide the measuring current I used a programmable power supply unit or a measuring transformer. Current and voltage were measured using digital multi-meters when performing direct current measurements and a collector of measurement data Type TRANSANAL-16 when performing alternative-current measurements. On the basis of the results obtained it was possible to determine the surface impedance of the conductors of unit length. In the course of the measurement I have fixed the phase angle of the voltage and the current so the components of the impedance could also be calculated. In the knowledge of further geometric data the values of specific resistance, relative permeability and penetration depth can be determined as well by calculation in dependence of excitation and frequency. The data of ferro-magnetic and non-ferro-magnetic conductors examined may serve as references for the measurement of cables.

Measurement of cables is rather complex, as in their case surface impedances of four types may be interpreted. It is nevertheless important for practical purposes to know these characteristics for determining various operational parameters.

The examinations shown here are valid for the definite piece of conductor only, as these parameters may be influenced by many factors, including even the quality of the material used for manufacturing. So the sphere of the conductors examined, shown in the thesis was restricted by the time at disposal only. At the same time a possibility appears for continuing the measurements later on.

Finally, in the third part of the thesis the measured results and their interpretation of the various conductors are displayed.


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