Известия Томского политехнического университета: Инжиниринг георесурсов (Mar 2018)
Method of indirect overheating protection for electric drives of mining installations
Abstract
The relevance of the research is caused by the necessity of reliable thermal protection for noncontrolled induction motor drives of mining machinery and installations, especially for underground mining and enrichment processes. The key feature of this task is operating of mining electrical equipment at obviously arduous conditions with two factors. The first is the high content of dust and gas in the air that raises up the explosion hazard due to overheating of external surfaces caused by fault inception and its progression. The second is the electric drives intermittent duty with frequent starting and shutdown of mining installations in heavy loading conditions involving a wide range of load variation, frequent overloads including long-term operation, motor shutdown and starting with maximum load. The application of direct temperature measurement methods for solving this problem is impossible because the most part of induction motors under consideration is not equipped with built-in thermal sensors. In-situ methods of induction motors overheating protection based on the time-current protection or the thermal current protection do not take into account the ambient temperature and the different variants of electric motors heat removal in mining machinery and installations caused by conditions of their operation. In addition, in case of motor shutdown after overload-caused overheating, when the load normalizes, both these protection types will allow the motor to start even if it has not chilled yet, because these in-situ methods control the current of the supply circuit, but not the heating of the motor. Thus, the electric drive thermal protection for such installations as chain-and-flight or belt conveyors, drill rigs, shearers and road headers, compressor units, slime pumps and similar could be built only on the basis of indirect methods one of which is considered in this paper. Implementation of the research results could decrease the amount of failure for electric drives in the mining industry, will ensure the longer operating life of electrical equipment and in addition the mining safety. The main aim of the research is the development of thermal protection device for the stator winding of noncontrolled induction motor drives for mining machinery and installations based on an indirect method. Objects of the research are the induction motor in the noncontrolled electric drives of mining machinery and installations; the thermal protection device based on an indirect method. Methods: basics of electric drive theory; computer simulation of dynamic processes; experimental design techniques and results processing. Results. The authors have verified the relation between the pulsations of motor starting current and the stator temperature. In intermittent periodic duty, it was found out that the dependence of the number of pulsation on the stator temperature is linear in a range up to 200 С. The authors prescribed the motor capacity limit within the boundaries of which the stator temperature is calculated with inaccuracy up to 2 %.
