SUPERCONDUCTING CABLES – ANALYSIS OF THEIR OPERATION AND APPLICATIONS IN ELECTRIC GRIDS

In this paper the use of high temperature superconducting cables for transporting electrical energy is analysed. The construction of a short model of a superconducting cable is explained, global progress in this field is examined and related electromagnetic phenomena are discussed, particularly those concerning pinning potential barrier formation. The paper analyses the results of investigations into the current-voltage characteristics of superconducting cable model working in the temperature of liquid nitrogen, allowing to reach the value of critical current equal to 45 A.

POLYANILINE DOPED WITH ACIDS. METHODS OF SYNTHESIS AND MODIFICATION

The research was aimed at the development of the composition and technology of semiconducting materials based on polyaniline. Such materials, which have simple methods of production, are lightweight and have high thermal resistance, may be used in electrotechnical, electronic, and automotive devices, such as power generators and cooling or heat recovery elements. The technology for the production of semiconductive materials based on polyaniline-modified hydrochloric or camphorsulfonic acid is presented. The influence of the acid type on the electrical conductivity of the polymer was determined. Thermal analysis was performed for the obtained materials.

SWITCHING AND LIGHTNING OVERVOLTAGES AND THE REQUIRED WITHSTAND VOLTAGE BETWEEEN THE OPEN CONTACTS OF 245 KV CIRCUIT BREAKERS

This paper deals with the surges generated in the network during switching operations and lightning surges. The level of both kinds of surge was compared with the required dielectric strength between the open contacts of 245 kV circuit breakers. Overvoltages greater than the electrical withstand voltage of the circuit breaker can cause arc ignition between the circuit breaker’s open contacts and power engineering service s have reported such cases. The results of such failures can be very serious. This is a problem especially for single-break circuit breakers, in which the stresses on the electrical insulation between the open contacts of the breaker are very high. A method for selecting lightning arresters to lower the overvoltages is proposed. The switching of short-circuit currents by a circuit breaker may cause a weakening of the circuit breaker chamber’s insulation and reduce its electrical withstand and durability.

INDIRECT TEST CIRCUIT FOR TESTING HIGH VOLTAGE FUSES IN OVERLOAD CONDITIONS

During direct tests of high voltage fuses in overload conditions, the tested fuse has to carry the rated overload current at the rated voltage for a long enough time to interrupt the overcurrent. These types of tests cannot be done in short circuit laboratories. A short circuit generator cannot be excited for the length of time needed to complete the test. Therefore the indirect test method is often applied. It uses separate current and voltage circuits in sequence: first the fuse is supplied from a low voltage current circuit to conduct a current of the recommended intensity and, at the moment of the current interruption, the fuse is disconnected from the low voltage circuit and switched to a high voltage circuit. To ensure the equivalence of the direct and indirect tests the switching time from the current to the voltage circuit should be as short as possible. This paper describes a fast operating switch for use in such tests.

ISSUES INVOLVED IN USING THE DIRECT METHOD FOR MAGNETIC FIELD STRENGTH MEASUREMENT OF ELECTRICAL STEEL SHEETS – REVIEW

The paper presents, based on a review of relevant literature, the existing problems of magnetic field strength measurements of electrical steel sheets by means of the indirect and direct methods. It also describes some attempts to solve these problems. The magnetic field strength sensors most widely used for testing electrical steel sheets are also discussed.

A NEW IMAGING ALGORITHM FOR ELECTRIC CAPACITANCE TOMOGRAPHY

A new imaging algorithm of permittivity for Electrical Capacitance Tomography (ECT) was proposed in this paper. Some aspects of sensitivity analysis and the application of adjoint variables were discussed. In the final section of this paper some advantages and disadvantages were shown.

EXTENDED CLARKE TRANSFORMATION FOR n-PHASE SYSTEMS

The article describes how to convert space vectors written in a stationary multiphase system, consisting of a number of phases where n > 3, to the stationary alfa beta orthogonal coordinate system. The transformation of vectors from a stationary n-phase system to the stationary alfa beta orthogonal coordinate system is defined The inverse transformation of a vector written in the orthogonal coordinate system to a stationary n-phase system is also defined. The application of the extended Clarke transformation allows control calculations to be performed in both stationary alfa beta or rotating dq orthogonal coordinate systems. This gives the possibility of performing different control strategies. It has a practical application for drive systems with five-phase, six-phase or dual three-phase motors.