Bridge Inductance of Closed Slot Induction Motor for Design Process

Abstract

In the design of the induction motor, the equivalent circuit is used to predict its performance. The equivalent circuit consists of the magnetizing reactance and iron loss resistance, primary and secondary resistance and primary and secondary leakage reactance.The secondary leakage reactance of the closed slot rotor is not easy to calculate, because the closed slot rotor has a thin magnetic steel sheet bridge, through which the leakage flux passes. The inductance of the bridge changes depending on the B-H characteristics of the magnetic steel sheet.In this paper, a new equivalent B-H characteristics method is developed to calculate the bridge inductance of the closed slot. First, the bridge inductance of the closed slot is examined with experiments, flux by FEM and magnetic energy and magnetic coenergy by FEM. Then, magnetic energy and magnetic coenergy by FEM yields the bridge inductance of the closed slot for a wide slip range characteristics. From the bridge inductance and bar currents, the magnetomotive force and flux density are calculated for the equivalent B-H characteristics.This equivalent B-H characteristics method is able to respond to the inductance of the closed slot bridge from the unsaturated (small ampere-turn) zone of the magnetic steel sheet to the saturated (large ampere-turn) zone accurately. This yields the proper value of the bridge inductance, for which the conventional equations give a value of infinity.

A research trend of electric machines with development of finite element analysis

“…In Ref. [1], the authors propose a novel design method for the IM by using the calculated B-H characteristics with the equivalent circuit. They showed that the bar currents change from about 4 to 580 A when the slip sifts from 0 to 100%.…”

“…These achievements have been highlighted by many researchers who have proposed novel approaches to improve motor performance. Three groups of topics will be introduced in this paper: optimal design methods [1][2][3][4][5][6][7][8][9], novel motor structures [10][11][12][13][14][15][16], and novel control methods [17][18][19][20].…”