EXPERIMENTAL INVESTIGATION OF ELECTROMECHANICAL CHARACTERISTICS OF ASYNCHRONOUS MOTOR WITH INDUCTION RHEOSTATS IN ROTOR’S CIRCUIT

Abstract

The article deals with the results of the study of static electromechanical characteristics of an asynchronous motor with a wound rotor (AM) with the inclusion of advanced samples of induction rheostats (IR) with improved parameters in its rotor circuits. In many enterprises, induction motors with wound rotor and rheostatic starter are used to drive mechanisms and their bridging is carried out with bulky contactor-relay equipment which requires constant continuous maintenance and periodic repairs. In this situation, the equipment reliability increasing, which uses a wound rotor AM, is an important task that can be solved by switching induction rheostats (IR) into the circuit of the wound rotor AM. This approach gives the possibility to sharply reduce the amount of contact equipment, as well as due to the nonlinearity of electromagnetic parameters of IR - to ensure a smooth acceleration of the engine with a given starting current. If you divide the shielded coil with an additional ferromagnetic insert, you can increa­se the variation value in the electro-magnetic parameters changing the direction of current in the semi-coils. The use of analytical methods for such constructs gives only approximate results. Therefore, the task of the work is to clarify geometrical dimensions of ferromagnetic elements and obtain electromechanical characteristics with the help of experimental studies. The paper presents drawings of the scheme of the experimental installation and the half-phase IR coils inclusion. The investigations were performed for the MTB-412-8 engine when the stator win­dings are switched on in the star and powered by a linear voltage U 1 = 220 V. Experiments were carried out both in the direction of the mass-size indicatorsreducing and in the direction of obtaining the required AM characteristics. Therefore, in the course of the experiment, all IR constructions have been modified several times. In this case, the thickness of the inner plates varied from 2 to 16 mm, as well as the thickness and length of the inner rings. The choice of the indicated geometric design parameters is due to the necessity of increasing the IR production efficiency. The figures below show the mechanical characteristics and the AM starting currents obtained as a result of the effect investigation of the switching methods of IR half-phase coils and the thickness of the middle sheet. The results of the study show that the ferromagnetic insert (middle sheet) affects the electromechanical characteristics of AM and IR by the form of mechanical characteristics can be adjusted by changing the insert thickness. AM has the best mechanical characteristics with IR at inclusion of parallel-oncoming coils and with 4 mm insertion thickness for this type of engine.