Известия Томского политехнического университета: Инжиниринг георесурсов (Aug 2018)
Problem of induction motors rotor winding overheating in starting modes of high inertia electric drives of oil and mining industry
Abstract
The relevance of the research is caused by the need to increase the reliability and reduce the fault rate of asynchronous electric drives of high-inertia mechanisms of the oil and gas industry and the mining industry, such as main oil pipeline pumps, ventilator installations of mining enterprises and others. A cross-line starting of such electric drives, as well as when starting with the use of thyristor voltage converters, strong heating of the rotor winding takes place, which leads to negative consequences of thermomechanical effects with the electric motor failure. The main aim of the research is to reveal the regularities relating the parameters of induction motors and the start-up modes with the level of the rotor winding heating; to determine the possibility of influence of accelerating time defined by the stator current limit set point at start-up with a thyristor voltage converter on the rotor heating. Object of the research is an electric drive of high inertia mechanisms of the oil and gas industry and the mining industry with an induction motor, starting at a constant rotational speed of the stator magnetic field. Methods: analytical methods, as well as computer simulation using thermodynamic models of an induction motor based on thermal circuits with lumped parameters. Results. Analytically, and also with the help of computer simulation it is shown that when the dimensions of the electric motor increase (ceteris paribus), the problem of the rotor winding overheating becomes more and more urgent. If the number of motor poles is increased (at the same nominal power, in the case when it is possible to use the gear ratio of the gearbox corresponding to the rated motor speed and the required speed of the mechanism), the heating of the rotor winding decreases. It is also shown that by increasing the duration of starting an induction motor due to the use of a thyristor voltage converter, it is possible to solve the problem of the rotor win-ding overheating only when starting without load. In other cases, an increase in duration of the start-up either does not allow a signify-cant reduction in heating, or leads to an increase in heating. In this situation, the use of thyristor voltage converters makes sense if it is predetermined only by the limitations associated with the network voltage drop during start-up, and the only solution to the problem of overheating is the use of a frequency converter.
