Static and dynamic eccentricity fault diagnosis of large salient pole synchronous generators by means of external magnetic field

Abstract

Although synchronous generators are robust and long-lasting equipment of power plants, consistent electricity production depends on their health conditions. Static and dynamic eccentricity faults are among the prevalent faults that may have a costly effect. Although several methods have been proposed in the literature to detect static and dynamic eccentricity faults in salient pole synchronous generators (SPSGs), they are non-sensitive to a low degree of failure and require a predefined threshold to recognise the fault occurrence that may vary based on machine configuration. This article presents a detailed magnetic analysis of the SPSGs with static and dynamic eccentricity faults by focusing on the external magnetic field. The external magnetic field was measured using two search coils installed on the backside of the stator yoke. Also, advanced signal processing tools based on wavelet entropy were used to analyse the induced electromotive force (emf) in search coils to extract the fault index. The proposed index required no threshold to recognise the starting point of fault occurrence and was sensitive to a low degree of fault. It was also non-sensitive to load variation and noise that may induce a false alarm. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Advanced Fault Detection of Synchronous Generators Using Stray Magnetic Field

“…Some recent work has suggested the analysis of stray flux data for the detection certain faults in SPSGs, such as field winding faults [23], [24], damper faults [24], [25], eccentricities [9], [26] or even stator faults [27]. This work has verified the potential of this technique for reliable detection of these faults and for their discrimination from other faults or nonfaultârelated phenomena.…”

“…1) ITSC and DE faults detection based on the application of FFT on the stray magnetic field in a SPSG are proposed in [9], [30]. The method compares the frequency spectrum of the faulty SPSG with a healthy SPSG in order to determine the health status of the machine.…”

“…Although the method was able to introduce a new pattern that can detect the fault at an early stage, the pattern for DE and ITSC fault were similar that makes fault type detection difficult. 3) A highly sensitive method using DWT is proposed to detect the DE fault based on the differential stray magnetic field [9]. In this method, at least two sensors are required to embed on the stator core exactly opposite of each other.…”

“…The amplitudes of the signals captured by the four sensors installed with a mechanical distance of 90 degrees are checked to inspect the possibility of a static eccentricity fault. The amplitude of one pair of sensors installed in front of each other must differ in a way that ensures that the amplitude of the induced voltage in one of the sensors is high and that of the other sensor is low for a static eccentricity fault to occur [9]. However, the amplitudes of the induced voltages in this pair of sensors are similar, which indicates the absence of a static eccentricity fault in the 22 MVA SPSG.…”

“…The number of reported broken damper bar failures in the synchronous motor compare with the synchronous generator is higher, however, faults due to broken dampers may have serious implications concerning the starting of synchronous machines [7]. Other faults, such as eccentricities [8], [9], shaft current discharges [10], and field winding [11] and stator turn faults [12], have also been reported in hydro generators. The negative effects of most of these failures can eventually lead to forced synchronous generator outages; therefore, an intensive effort has been devoted to the development of intelligent techniques that are able to detect these faults when they are in their early stages of development [11]- [13].…”