Analysis of Stator Winding Inter-Turn Short-Circuit Faults in Induction Machines for Identification

Department of Electrical and Computer Engineering Marquette University Milwaukee, Wisconsin USA
Abstract—The main objective of this paper is to develop and experimentally verify a method of identifying the faulty phase in a three-phase armature of an induction motor with concentric coil construction, when such an armature suffers from an inter-turn within one of its phases. This work leads to a new technique for identifying the faulty phase in concentric wound machines and estimating the associated fault severity without any requirement for additional sensors, wiring constrains, or knowledge of any other details of the machine design. The technique has been verified through several experimental test results. Index Terms—magnetic field pendulous oscillation, stator fault diagnostics, inter-turn shorts, induction motor winding faults
Behrooz Mirafzal, Member, IEEE
Rockwell Automation/Allen-Bradley Mequon, Wisconsin USA
amplitude of the angle of the magnetic field pendulous oscillation as an index for estimating the fault severity in a motor’s winding. In the fourth section, the theoretical development which was introduced in the second section is analyzed. This is carried out through a 2-hp, 460-volt, 60-Hz, 2-pole case study three-phase induction motor. The proposed technique is verified using experimental results obtained for this case study. The last section includes the main conclusion. II. MAGNETIC FIELD SPACE VECTOR ANALYSIS OF AN INTERTURN SHORT-CIRCUIT FOR IDENTIFICATION OF THE FAULTY PHASE Consider an ideal case of a healthy three-phase induction motor with a balanced sinusoidal three-phase voltage applied at its terminals, and sinusoidal three-phase currents passing through its windings. The voltage and the current space vectors can be accordingly expressed as follows [7]:
This paper is based upon work supported by the National Science Foundation under Grant No. ECS-0322974.
(1) (2)
Consequently, under healthy conditions, the resultant forward rotating field, f s , in space-vector form can be written as follows: G G f s (t ) = N se i s (t ) = N se I s e j (ωt +α −φ ) (3) In the above equations, V s and I s are the peak values of the instantaneousG voltage and G current waveforms, respectively. G Meanwhile, vs , is , and f s are the instantaneous space vectors of the polyphase voltages, currents, as well as the resultant rotating stator MMF waveform in the air-gap, respectively. Here, N se , is the equivalent number of stator turns per phase, α is an arbitrary phase shift from the reference, and φ is the power factor angle. It follows that when a motor winding encounters an inter-turn short-circuit, see Fig. 1, the previous formulations in (2) and (3) are no longer valid since the polyphase balanced currents condition would be violated. Hence, the faulty phase winding can be represented by a healthy winding and an additional shorted (faulty) one as shown in Fig. 2, [6]. The latter winding can be considered as a separate phase, the so-called shorted coil, which is magnetically coupled to the other coils of the phase windings.
G v s (t )பைடு நூலகம்= V s e j (ωt +α ) G i s (t ) = I s e j (ωt +α −φ )
I. INTRODUCTION Over the last decade, premature failures in the windings of electrical machines have led to various investigations concerning the detection of commonly occurring stator winding shorts. Several interesting techniques have been introduced in the literature for purposes of diagnosing such types of fault at their early stages [1-5]. However, to these authors’ knowledge, most of these techniques do not offer the capability of identifying the specific faulty phase unless the neutral point is accessible or intrusive sensors are installed inside the machine. In addition, these techniques lacked the capability of accurately estimating the extent of the fault severity. In some of these investigations, additional sensors and/or knowledge of the details of a machine design were required. This paper introduces a space-vector magnetic field analysis based technique in case of a one-phase fault event occurring in a concentric polyphase winding. The method utilizes a magnetic field pendulous oscillation phenomenon presented earlier in [6] in order to identify the specific faulty phase and estimate the fault severity in that faulty phase. Such are considered as vital information about the fault extent and location for purposes of devising a fault mitigation strategy. This paper contains four additional sections. In the next section, a space-vector analysis of the disturbance in a motor magnetic field due to an inter-turn short circuit is introduced. The result of this analysis will be utilized to extract a time domain correlation between the so-called magnetic field pendulous oscillation (MFPO), which was introduced in [6], and the applied phase voltage associated with the faulty phase. This analysis is extended in the third section to the use of the