Electromagnetic Relations of Induction Machine Systems and Analyses of Some Operating Modes

Abstract

Induction machine systems are widely used in practice, so their operating behavior, especially transient performance, must be paid attention to. Firstly, we introduce the basic relations and parameters of induction machines in d, q, 0 axes, and then analyze the starting process of induction motors, in which d _c , q _c , 0 axes with synchronous speed are preferable to d, q, 0 axes due to variable rotor speed. The relations in d _c , q _c , 0 axes can be found out according to basic equations in d, q, 0 axes together with the conversion formulas in Section 3.1. By using the 4th order Runge-Kutta Method, we calculate the starting characteristics for different fly-wheel moments and loads, compare the transient starting characteristics with the steady-state ones, which are quite different, especially during no-load and small rotating inertia, and then illustrate why the transient starting characteristics are quite different from the steady-state ones. Furthermore, some fault is often temporary, so the production loss caused by failure in power supply can be decreased with the reswitching of the induction motors as quickly as possible after supply recovery. Transients of reswitching of the induction motors include two stages, one is the disconnection process due to source fault, and the other is the reclosing process after supply recovery, whose main problems are surge current and large electromagnetic torque; therefore we analyze them using α, β, 0 axes. As you know, the reclosing surge current is more serious than the direct starting current, which can be diminished in two ways: monitor the stator voltage phase-angle at the reclosing instant and use the extinguishing-flux method to make rotor current decay quick at the disconnecting instant. Moreover, induction motors in series with capacitance can keep the supply voltage constant, but sometimes self-excitation may occur, which is analyzed by using the D-domain partition method to get two self-excitation regions during lower compensation degree that is a new discovery, because some scientists pointed out only one self-excitation region before. In addition, a special generator is introduced as an important part of ship’s integrated power system, in which the stator has two suits of windings, one is a 12-phase power winding connected to a rectifier load and another is a 3-phase control winding connected to a static excitation regulator, and there is a squirrel-cage solid rotor. There are also the capacitors for self-excitation and inter-phase reactors in the system for performance improvement. It can be divided into two sub-systems: one consisting of 12-phase power winding with a rectifier load calculated by the circuit method, and another consisting of dual-stator-winding and squirrel-cage solid rotor analyzed by the electromagnetic field finite element method, the simulative results being approximate to experimental data.