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Bertenshaw D.R.,ENELEC Ltd | Smith A.C.,Singapore Institute of Manufacturing Technology | Ho C.W.,Singapore Institute of Manufacturing Technology | Chan T.,Aurecon Australia Pty Ltd | Sasic M.,Iris Power LP
IET Electric Power Applications | Year: 2012

Monitoring the health of large electrical machines, especially power station generators, is now an integral part of their operation to maintain and extend life. This work studies the use of electromagnetic sensors to detect inter-lamination insulation faults in the stator cores of large generators before they propagate to a level that can lead to catastrophic failure. The work develops a deeper understanding of the electromagnetic behaviour of core faults so that condition-monitoring sensors can be more specific about the location and severity of the fault. The study develops two new three-dimensional (3D) analytical models, one for predicting the fault current distribution in a stator core fault and the second for predicting the varying detection of such current by air-cored sensors. This further analysed the 3D detection efficiency of typical short fault lengths to compare with the two dimensional (2D) default of infinite-length faults. Different fault positions were modelled so that a clearer understanding of the location and severity of the fault is possible. These were validated on a specially constructed experimental test core that can impose controlled fault currents. The study also demonstrates how small core faults can escalate then self-limit radially, but may propagate axially into longer more damaging faults. © 2012 © The Institution of Engineering and Technology. Source

Bertenshaw D.R.,ENELEC Ltd | Smith A.C.,University of Manchester | Chan T.,Aurecon Australia Pty Ltd | Sasic M.,Iris Power LP
IET Electric Power Applications | Year: 2014

Faults in the stator cores of large electrical machines can both damage local winding insulation and propagate to catastrophic failure. This study develops three-dimensional finite element models of inter-laminar insulation faults in order to obtain a deeper understanding of the electromagnetic behaviour of core faults and the sensitivity of sensing systems. The problem of developing a model that adequately reflects the laminar constraints of the structure, while remaining computable is addressed, together with eliminating images from boundaries. The model was validated by experimental measurement and results shown to be closely matched, with the fault current distribution also predicted. The sensitivity profiles for various fault positions and lengths were determined, which enables condition-monitoring sensors to be more specific about the location and true threat that a fault signal may pose to the machine. © The Institution of Engineering and Technology 2014. Source

Iris Power MDSP3 Detecting motor rotor cage-winding faults and air gap eccentricity The Iris Power MDSP3 is a portable instrument specifically designed to monitor squirrel-cage induction motors. The Iris Power MDSP3 detects rotor cage winding faults i ...

Stone G.C.,Iris Power LP | Sasic M.,Iris Power LP | Dunn D.,Aramco Services Company | Culbert I.,Iris Power LP
IEEE Industry Applications Magazine | Year: 2011

In many respects, Large Motors and generators in petrochemical plants have become a commodity product with intense competition to secure orders among manufacturers from around the world. This has resulted in pressure on machine designers to reduce manufacturing costs. Many design and processing innovations have been successfully implemented. However, there are both anecdotal and statistical data that indicate that there are more problems with machines made in the past ten years when compared with machines made earlier. Engineering firms and end users perhaps need to provide comprehensive, yet reasonable, purchase specifications that allow all manufacturers to compete on a level-playing field. Stator windings rated greater than 6 kV and rotors of various-sized machines are the main topics of discussion. © 2006 IEEE. Source

Sasic M.,Iris Power LP | Stone G.C.,Iris Power LP | Stein J.,EPRI | Stinson C.,Air Liquide
IEEE Industry Applications Magazine | Year: 2013

The rotor windings of synchronous motors and generators are usually very reliable. However, the turn insulation in such machines will eventually degrade and puncture due to thermal aging, load cycling, and/or contamination. Although turn shorts do not directly lead to machine failure, they can lead to high bearing vibration, may damage synchronizing systems within brushless motors, and may limit output. Offline tests are available to detect rotor-winding shorted turns, but they may be unreliable because the rotor is not spinning for the test, and, if only a few shorts are present, the shorts may disappear once the rotor is spinning (or vice versa). With funding from the U.S. Electric Power Research Institute (EPRI), a new type of online magnetic flux test has been developed that is suitable for salient pole machines, in particular the salient pole rotors in four- (or more) pole hydrogenerators and synchronous compressor motors that are widely used for air separation. The test requires retrofitting a small magnetic flux probe to the stator core and instrumentation to interpret the small voltage signals that are measured from the probe. This article describes the aging processes of salient pole turn insulation and briefly presents the off line method that has been used to detect turn shorts. © 1975-2012 IEEE. Source

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