Effect of Pole Number on Generator End Winding Electromagnetic Force and Mechanical Response before and after RISC

This paper comparatively studies on the end winding electromagnetic force and mechanical response for generators with different numbers of poles. The analytical expression of the end winding electromagnetic force is derived under the rotor winding interturn short circuit (RISC) considering the pole number. Meanwhile, the three-dimensional transient finite element simulation is carried on two generators with one-pair poles and three-pair poles. Then, the frequency composition and amplitude variation characteristics of the radial, axial, and tangential electromagnetic forces are analyzed. Further, the maximum stress and deformation on the end winding are calculated and the similarity and difference of the coil failure law are obtained for two kinds of generators. It is found that RISC will bring odd harmonics to electromagnetic force for one-pair pole generators but it will bring odd and fraction harmonics for multipair pole generators. Moreover, the max mechanical response under RISC will decrease for one-pair pole generators but it will increase for multipair pole generators.

Improving the energy efficiency of electric drives for auxiliary units of traction rolling stock

The review of technical solutions and schematic characteristics of auxiliary drives for traction vehicles has shown that the most rational variant is an electric drive with an induction machine. Given the operating modes of the auxiliary drives and the share of their power consumption in the total locomotive power, the task of using scalar control systems for induction machines becomes relevant. Based on a mathematical model describing the dynamic energy conversion processes in the T-shape substitution circuit of an induction motor, taking into account stator steel losses and current displacement effects in the rotor winding and saturation along the main magnetic path, possibilities for reducing stator current have been investigated. In order to improve the energy efficiency of electric drives two variants of control system have been proposed. One based on search method of self-tuning to the stator current minimum and the other - on maintaining the power factor of induction motor at the level that ensures equality of active and reactive components of stator current. The hardware and software requirements for implementing control systems have been analysed. Modelling using Matlab has shown that both control systems work - power loss reduction can be as low as 50% and as high as 60% in certain modes.

METHOD OF VECTOR PRIVATE CONTROL OF ASYNCHRONOUS ELECTRIC DRIVE

Анализируется проблематика векторного частотного управления асинхронным электроприводом, широко применяемым в качестве исполнительного элемента в рамках современных средств построения обрабатывающих комплексов, разрабатываемых в машиностроительной отрасли. Предлагается вариант частотно-регулируемого асинхронного электропривода, управляемыми величинами которого являются полярные координаты вектора тока в обмотке статора. В данном варианте применяется закон управления, согласно которому угол между векторами тока в обмотке статора и потокосцеплением обмотки ротора не меняется. Управление скоростью вращения электропривода и электромагнитным моментом реализуется заданием модуля тока обмотки статора. При этом формирование угла поворота вектора тока обмотки статора, зависящего от модуля величины потокосцепления роторной обмотки и значения скольжения асинхронного двигателя, дает возможность сохранять постоянным угол между векторами тока обмотки статора и потокосцеплением обмотки ротора, что, в свою очередь, реализует направленное формирование переходных процессов в асинхронном двигателе. Рассматриваемый вариант частотно-регулируемого асинхронного электропривода может найти применение в производственных механизмах, в которых быстродействие не является определяющим критерием функционирования привода, а важно плавное регулирование электромагнитного момента и возможность его ограничения во всех режимах работы. Данный способ управления характеризуется тем, что электромагнитный момент определяется исключительно модулем тока обмотки статора, а контур регулирования скольжения используется для реализации закона поддерживания постоянства угла между током обмотки статора и потокосцеплением обмотки ротора The article analyzes the problems of vector frequency control of asynchronous electric drive, widely used as an executive element in the framework of modern means of constructing processing complexes developed in the machine-building industry. Here we propose a variant of a frequency-controlled asynchronous electric drive, in which the polar coordinates of the current vector in the stator winding are the controlled quantities. In this variant, the control law is applied, according to which the angle between the current vectors in the stator winding and the flow coupling of the rotor winding does not change. The control of the speed of rotation of the electric drive and the electromagnetic torque is realized by setting the current module of the stator winding. At the same time, the formation of the angle of rotation of the current vector of the stator winding, depending on the modulus of the magnitude of the flow coupling of the rotor coil and the sliding value of the asynchronous motor, makes it possible to keep the angle between the current vectors of the stator winding and the flow coupling of the rotor winding constant, which in turn implements the directional formation of transients in the asynchronous motor. The considered variant of a frequency-controlled asynchronous electric drive can be used in production mechanisms in which speed is not a determining criterion for the operation of the drive, but smooth regulation of the electromagnetic torque and the possibility of its limitation in all operating modes is important. This control method is characterized by the fact that the electromagnetic moment is determined exclusively by the current module of the stator winding, and the slip control circuit is used to implement the law of maintaining the constancy of the angle between the current of the stator winding by the flow coupling of the rotor winding

EXPERIMENTAL STUDY OF STATIC CHARACTERISTICS ASYNCHRONOUS MACHINE IN DYNAMIC BRAKING MODE WITH INDUCTION RESISTANCE IN THE ROTOR WINDING

The article discusses the results of a study of the static electromechanical characteristics of an asynchronous machine (AM) when prototypes of induction resistances (IR) with improved parameters are included in its rotor circuits. The dynamic braking (DB) of asynchronous machines, which is widespread in practice, provides for the dissipation of the kinetic energy of the rotating parts in the resistance boxes included in the rotor winding. In the process of stopping, to maintain a constant average braking torque AM, a bulky relay-contactor circuit for shunting rotor resistances is used. However, it is not possible to eliminate significant fluctuations in the electromagnetic torque in this way. To optimize the DB AM process, it is proposed to include a three-phase IR in the rotor winding instead of resistance boxes, the value of which automatically decreases along with the rotor current frequency. This approach allows you to abandon contact equipment and ensure smooth braking of the machine with fluctuations in the electromagnetic moment in narrower limits. The known IR designs are designed for starting modes of induction motors with a wound rotor, but they cannot ensure the constancy of the torque on the AM shaft in the DB mode. Therefore, the purpose of the study is to develop and experimentally confirm the effectiveness of simple control circuits of an induction machine in the specified mode with improved contactless induction rheostats in the rotor. The paper presents a diagram of a pilot plant and a figure explaining the design features of the IR. The studies were carried out for an asynchronous machine of the MTB-412-8 type, equipped with a thyristor exciter and a tachogenerator. The three phases of the AM rotor included ICs connected by a "star". The experiments were carried out in the direction of obtaining the necessary braking characteristics of the AM by varying the switching circuit of the stator phases and the value of the current supplying them. The figures show the mechanical characteristics of AM, obtained in the process of studying the influence on them of three typical circuits for switching on the phases of the stator winding and two values ​​of the fixed supply current. The research results show that the desired form of the mentioned AM characteristics is achieved only when using the stator phase switching in a function of the rotor speed and a constant supply current value.

Study of the Thermal Conductivity of Soft Magnetic Materials in Electric Traction Machines

The power density of traction drives can be increased with advanced cooling systems or reduced losses. In induction machines with housing and shaft cooling, the produced heat in the stator and rotor winding system needs to be extracted over the rotor and stator lamination. The influence of soft magnetic material parameters, such as texture, thickness or alloy components on the magnetization and loss behavior, are well studied. Studies about influencing factors on the thermal conductivity are hard to find. Within this study, eight different soft magnetic materials are analyzed. An analytical approach is introduced to calculate the thermal conductivity. Temperature-dependent measurements of the electric resistivity are performed to obtain sufficient data for the analytical approach. An experimental approach is performed. The thermal diffusivity, density, and specific heat capacity are determined. An accuracy study of all measurements is performed. The analytical and the experimental approach show good agreement for all materials, except very thin specimens. The estimated measurement error of those specimens has high values. The simplified case study illustrates the significant influence of the different soft magnetic materials on the capability to extract the heat in the given application.