Stray Flux Sensor Core Impact on the Condition Monitoring of Electrical Machines

Abstract

The analysis of the stray flux for electrical machine condition monitoring is a very modern and active research topic. Thanks to this technique, it is possible to detect several types of failures, including stator and rotor inter-turn faults, broken rotor bars and mechanical faults, among others. The main advantages are that it involves a non-invasive technique and low-cost monitoring equipment. The standard practice is to use coreless flux sensors, with which the stray flux of the machine is not perturbed and there are no problems due to saturation or nonlinear behavior of the iron. However, the induced voltage in the coreless coil sensor may be very low and even, in some cases, have a similar amplitude to the noise floor. This paper studies the use of iron core stray flux sensors for condition monitoring of electrical machines. The main advantage of iron core flux sensors is that the measured electromotive force is stronger. In the case of large machines in noisy environments, this can be crucial. Two different types of iron core stray flux sensors and a coreless flux sensor are tested. A comparison of the three sensors is presented. Extensive experimental testing with all sensors shows the superiority and greater sensitivity of sensors with core versus the coreless ones.

Torque estimation in three-phase induction motors under broken bars and voltage variations using airgap flux measurement and a machine learning model

“…This technique requires a phase angle determination and some motor parameters to estimate the torque with a good accuracy. Note that the cited method applied a coreless flux sensor, being the induced voltage in this type of core very low and quite similar, in some cases, to the amplitude of the noise floor, as mentioned by [14]. As described by [12], other studies have shown the use of internal sensor for condition monitoring of rotating electrical machines [15,16].…”

Detection of Field Winding Faults in Synchronous Motors via Analysis of Transient Stray Fluxes and Currents

“…The total dimensions are 60x25x40 mm (length x width x height) and it had 200 turns. Further information about this flux sensor are detailed in [20]. The first set of starting tests were performed with the machine unloaded, that is the induction machine stator was disconnected.…”

Methods of Condition Monitoring and Fault Detection for Electrical Machines

“…Monitoring magnetic flux has become a widespread and effective method for fault detection in electrical machines, as many early failures create a magnetic asymmetry that can be detected [86]. Electromagnetic measurement can be efficiently used to monitor the electrical machine as an additional or alternative tool to stator current monitoring.…”