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Does electric motor reactance at given speed is constant according to rotor position (angle)?

For switched reluctance it is not. But for three phase induction motor? Considering there is no any noise.

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    \$\begingroup\$ depends on the machine, its saliency and how much it is loaded \$\endgroup\$
    – user16222
    Commented Jun 20, 2018 at 17:24

2 Answers 2

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Induction motors are designed to avoid reluctance variation according to rotor position. That also avoids reactance variation with rotor position. To avoid reluctance variation, it is necessary to avoid variations in the air gap that would occur if the rotor bar slots in the rotor iron and the stator winding slots in the stator iron are aligned with each other at specific rotor positions. The number or rotor and stator slots must be selected to avoid alignment as much as possible. In addition the rotor slot are configured so that they are not parallel to the shaft, but "skewed" at an angle with the shaft.

With all types of synchronous motors, the rotor is aligned with the rotating stator magnetic field. In that case, the effective reactance is constant because of the nature of than alignment.

Here is a question about skew with answers:

Skew angle in squirrel cage induction motor

The diagram below is from Phillip L. Alger The Nature of Polyphase Induction Machines Copyright, 1951 by General Electric Company. It shows a cross section view of "a typical small induction motor, with a 4-pole, 3-phase 36-slot stator winding." While not discussed in the chapter containing the diagram, the diagram shows that relatively few rotor bars are aligned with stator slots for any given angular rotor position. Also, the stator slots are shaped to maximize the iron path for magnetic flux and minimize the effect of air-gap variations. The copper, aluminum and insulating materials in the air spaces is effectively equivalent to air in the spaces in terms of magnetic permeability, reluctance and reactance.

enter image description here

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  • \$\begingroup\$ thanks. so in solid rotor motor . we have constant inductive reactance of the motor ? \$\endgroup\$
    – xcs
    Commented Jun 23, 2018 at 6:05
  • \$\begingroup\$ If an induction motor stator and rotor could be completely homogeneous (solid), there would be no variation in inductive reactance with rotor position. Since an induction motor must have both iron and conductors in the stator and rotor, the design features described are used to make the magnetic path as homogeneous as possible thus minimizing the variation in inductive reactance. \$\endgroup\$
    – user80875
    Commented Jun 23, 2018 at 13:39
  • \$\begingroup\$ if we put solid rotor within standart stator windings in three phase induction motor there would be almoust no variations in reactance/reluctance ? \$\endgroup\$
    – xcs
    Commented Jun 23, 2018 at 20:56
  • \$\begingroup\$ With a rotor and stator that have been designed as described above, the variations in reactance/reluctance are sufficiently small that they are of no significant concern. If that is not what you consider to be a solid rotor, you are not asking about a rotor that is functional as a rotor for an induction motor. \$\endgroup\$
    – user80875
    Commented Jun 23, 2018 at 22:08
  • \$\begingroup\$ I am deleting my comments to answer that should be deleted. \$\endgroup\$
    – user80875
    Commented Jun 25, 2018 at 13:53
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enter image description hereso considering coreless induction motor three windings with solid rotor (iron copper) only there should be almost no variations in reactance at certain speed or at any speed

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  • \$\begingroup\$ so if the rotor on the right has solid core (from iron/copper), it is "älmost " constant reluctance/reactance/inductive resistance ? Thanks a lot \$\endgroup\$
    – xcs
    Commented Jun 24, 2018 at 17:10
  • \$\begingroup\$ ok. i'll consider above right picture on the motor to be a constant reluctance/reactance motor at certain rotation speed. \$\endgroup\$
    – xcs
    Commented Jun 25, 2018 at 6:15
  • \$\begingroup\$ lets consider it solid steel/copper rotor. I took the first picture i've found. thanks \$\endgroup\$
    – xcs
    Commented Jun 25, 2018 at 11:55
  • \$\begingroup\$ permanent or not permanent reactance ? \$\endgroup\$
    – xcs
    Commented Jun 25, 2018 at 13:17

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