FEATURES OF BEHAVIOR OF FILLED POLYMERS FOR RESISTORS UNDER A CYCLIC LOADING MODE

Abstract

The relevance of the work is caused by the fact that ensuring uninterrupted power supply to enterprises in resource-extracting industries is an indispensable condition for their effective functioning. The latter, in its turn, is determined by the quality of protection of power-consuming equipment (primarily electric motors) from short-circuit currents and overvoltages in the supply network. Their limitation is provided by a set of measures; the most important of them is the use of high voltage bulk resistors capable of dissipating enormous power. In recent years, filled polymers have attracted the attention of specialists as materials for the manufacture of such resistors. Along with such their advantages as: the availability and low cost of starting materials, well-mastered technology for production of such compositions, they have a significant drawback – strong dependence of the specific volumetric resistance on temperature and, consequently, on the modes of their operation. Due to the variety of processes in filled polymers, stimulated by elevated temperatures, it is necessary to study their behavior depending on heating conditions. One of the most common modes of operation of polymer composite materials is repeated short-term exposure to current load, in which multiple changes in temperature occur, negatively affecting the stability of the resistor parameters. This makes it relevant to study the dynamics of volumetric electrical resistance, as the most important parameter of a resistor, in complex current load modes. The purpose of the work is to assess the possibility of operating rubbers filled with carbon black in the «heating–cooling» mode: studying the spread of the current value depending on the current load, operating time and pause during heating with alternating current. Due to the multicomponent structure, the stability of the electro physical characteristics is largely determined by the mode of their operation. Methods: instrumental measurements of electro physical characteristics of resistive polymer composite materials, statistical processing of measurement results, assessment of time series of changes in random parameters. Results. The authors have revealed the dependences of the magnitude of the alternating current flowing in carbon black butadiene-nitrile rubbers on duration of operation and duration of pauses in intermittent operation. The authors established as well the possibility of an ambiguous effect of the pause duration on current value stability. The possibility of using the Hurst exponent for assessing the tendencies of the time series by the change in the current load (volumetric electrical resistance) in intermittent operation was confirmed. The dependence of the value of the Hurst exponent itself on the duration of the analyzed time interval is shown. On the basis of the studies carried out, the authors developed the recommendations for operation of rubbers filled with carbon black under repeated short-term exposure to current load.

Keywords

• power supply of resource-extracting industries
• resource saving
• filled polymers
• resistors
• volumetric electrical resistance
• operating modes
• instability of characteristics
• elevated temperature
• hurst exponent