Impedance matrix analysis technique in wound rotor induction machines including general rotor asymmetry

Abstract

A steady state analysis is developed for a wound rotor induction machine. In this paper the authors derive simple expressions for the mutual and coupling impedance in order to build impedance matrix. The analysis can be used in two ways when dealing with a symmetrical and asymmetrical rotor. The method is verified using an inverted-geometry wound motor; the analysis is then used to investigate an asymmetry fault on a 4 pole wound rotor. Experimental results (torque and current characteristic) are compared with computer predictions for the machine with both open-circuit and short-circuit faults.

Analysis of DFIG machine with rotor-wound faults

“…This paper develops a method for the steady-state analysis of a WRIM or DFIG capable of including rotor asymmetry. The proposed technique has been already investigated in [8] and [9], and here the rest of the experimental work and simulation results are presented and discussed. The main contribution of this work is the application of the proposed technique to the diagnosis and detection of rotor imbalances faults while the fault at an early stage of development.…”

“…The presented analysis will also derive such quantities as power and torque. The authors have put the derivation of the coupling and mutual impedances in [9] and the rest of the experimental work and simulation results are presented here. This technique was used successfully in [8] and [I OJ to study cage rotor machines with any number and distribution of bar and/or eccentricity faults.…”

“…The rotor of a WRIM has a group of three-phase windings that are similar to those on the stator although the rotor slot number will vary and so will the rotor coil turn number. The derivation will be straightforward because the rotor loop currents do not share any common paths down bars [9]. The main feature of the method is that any asymmetrical winding can be taken into account.…”

“…It can be expanded to incorporate eccentricity faults and the condition monitoring of wound rotor machines [14]. The impedance matrix includes all impedances in [9] which are functions of the three-phase windings on the stator and rotor: In a healthy machine, there will be a magneto-motive force (MMF) wave on the rotor rotating at slip frequency sfm in the rotor coordinates. If there is asymmetry, then there will be a backward rotating MMF wave.…”

“…The impedance matrix technique described in [9] is used to find the steady state equivalent circuit for the wound rotor. As mentioned early, all the derivations of the mutual and coupling impedance can be found in [9].…”