Detection Of Inter-turn Short Circuits Research Articles

Introductory notes for the Acta IMEKO Special Issue on "Technical Diagnostics : New Perspectives in Measurements, Tools and Techniques for Industrial Applications"

The concept of Quality has undergone important transformations over time. In a first assumption, sometimes passed in many industrial contexts, the term “product quality” was essentially associated with “compliance”. Nowadays, the term “conformity to specifications” is widely used but this has to be considered only as an aspect in the measurement of the quality level. In fact, referring to the ISO Standard 9001 Quality management systems, the term Quality corresponds with the degree to which a set of characteristics of an object fulfils requirements. Concerning characteristics, such Standard proposes a classification in physical (e.g. mechanical, electrical, etc.), temporal (e.g. reliability, availability, etc.), and so on. It is interesting to observe that also the concept of product changed over time. Now, it is usual to assume the product as the result of a manufacturing process in which a series of activities transforms raw materials, technologies and resources into the output – that is the product. So, it is mandatory to implement different activities concerning monitoring, as well as to collect and analyse appropriate data with the aim to demonstrate the suitability and the achievement of a desired quality levels. The analysis of data provides information about conformity to product requirements but also related to characteristics and trends of processes and products, including opportunities for preventive actions. This last aspect – the preventive action – depends also on the ability to monitor both the functionality of the product and the capability of the process to fulfil requirements. In this scenario IMEKO TC 10 aims to represent a reference point for scientists and researchers. It can be regarded as a forum for exchanging knowledge and sharing ideas concerning methods, principles, instruments and tools, standards and industrial applications on Technical Diagnostics as well as their diffusion across the scientific community. In this issue two main aspects are considered as a result of different research activities presented in the Workshop. First, the impact of technical diagnostics on the product performances is considered. For this topic different points of view and proposals in the field of fault diagnosis are presented by the authors. B. Aubert et al. deal in [1] with an Extended Kalman Filter based fault detection in Permanent Magnet Synchronous Generators. Being such equipment used often in high technology contexts, it is fundamental to guarantee high performances in terms of reliability and safety. Authors propose a method for inter-turn shortcircuit detection based on the identification of the shortcircuited turns ratio in a faulty PMSG model expressed in Park frame. Several tests are also implemented in order to demonstrate robustness and sensitivity of the approach. In the field of testing for electronic devices an interesting contribution is proposed by D. Zaleski and R. Zielonko in [2]. The paper concerns the testing of analog circuits and blocks in mixed-signal Electronic Embedded Systems (EESs) by means of the Built-in Self-Test (BIST) technique. In particular, two testing functions are performed:

Detection of inter-turn short-circuit in induction motors using Park–Hilbert method

In this paper, a new method, called Park–Hilbert (P–H), is presented and used to detect inter-turn short circuit in three-phase induction motors. This technique is based on spectral analysis, via the FFT, of a new generated signal called PVMP–H which represents the Park’s vector modulus computed starting from the analytical signals obtained from the three-phase current by the Hilbert transform. A theoretical analysis is performed in order to show how the proposed method works. Various experimental tests carried out on a 3 kW three-phase induction motor, illustrate the efficiency of this new method and show that some spectral components of the PVMP–H are extremely sensitive to the occurrence of shorted turns. However, it is shown that the information about the motor state is distributed on many spectral components and in order to gather these useful information, the present paper suggests the monitoring of a new fault indicators computed starting from the most sensitive harmonics (basing on the multiple signature processing). This technique is applied on the proposed signal PVMP–H; and the experimental tests confirm that a small number of shorted turns can be effectively detected using these new fault indicators even under low load. A comparative study with the conventional MCSA and EPVA methods is also performed. The obtained results show the superiority of the P–H method and prove the effectiveness of the proposed fault indicators for extracting useful information from any motor signal.

WAVELET ANALYSIS FOR STATOR FAULT DETECTION IN INDUCTION MACHINES

The main objective of the proposed analysis is the detection of inter-turn short circuits in the stator windings of an induction machine. The analysis of the space vector current modulus of an induction motor is presented in this paper. This analysis is based on Daubechies 8 wavelet with seven decomposition levels. The 5th decomposition-level detail signal for a 4 kHz sampling frequency is chosen as a fault indicator, based on simulation results that show different behaviors of the energy contained in the detail signals independent of the percentage of load and fault levels. Experimental results that validate the proposed strategy are also presented. These results also show that the strategy is in addition immune to load variations as well as to feeding voltage unbalances.

Detection of stator winding faults in induction motors using three-phase current monitoring

The objective of this paper is to propose a new method for the detection of inter-turn short circuits in the stator windings of induction motors. In the previous reported methods, the supply voltage unbalance was the major difficulty, and this was solved mostly based on the sequence component impedance or current which are difficult to implement. Some other methods essentially are included in the offline methods. The proposed method is based on the motor current signature analysis and utilizes three phase current spectra to overcome the mentioned problem. Simulation results indicate that under healthy conditions, the rotor slot harmonics have the same magnitude in three phase currents, while under even 1 turn (0.3%) short circuit condition they differ from each other. Although the magnitude of these harmonics depends on the level of unbalanced voltage, they have the same magnitude in three phases in these conditions. Experiments performed under various load, fault, and supply voltage conditions validate the simulation results and demonstrate the effectiveness of the proposed technique. It is shown that the detection of resistive slight short circuits, without sensitivity to supply voltage unbalance is possible.

A current monitoring system for diagnosing electrical failures in induction motors

Induction motors are critical components in industrial processes. A motor failure may yield an unexpected interruption at the industrial plant, with consequences in costs, product quality, and safety. Many of these faulty situations in three phase induction motors have an electrical reason. Among different detection approaches proposed in the literature, those based on stator current monitoring are advantageous due to its non-invasive properties. One of these techniques resorts to spectrum analysis of machine line current. Another non-invasive technique is the Extended Park's Vector Approach, which allows the detection of inter-turn short circuits in the stator winding. This article presents the development of an on-line current monitoring system that uses both techniques for fault detection and diagnosis in the stator and in the rotor. Based on experimental observations and on the knowledge of the electrical machine, a knowledge-based system was constructed in order to carry out the diagnosis task from these estimated data.

The detection of inter-turn short circuits in the stator windings of operating motors

This paper develops a winding-function-based method for modeling polyphase cage induction motors with inter-turn short circuits in the machine stator winding. Analytical consideration which sheds light on some components of the stator current spectra of both healthy and faulty machines is developed. It is shown that, as a result of the nature of the cage rotor, no new frequency components of the line current spectra can appear as a consequence of the fault. Only a rise in some of the frequency components which already exist in the line current spectra of a healthy machine can be observed. An experimental setup comprising a 3 kW delta-connected motor loaded by a generator was used to validate this approach. The experimental results obtained clearly validate the analytical and simulation results.