Polyimide-Coated Fibre Bragg Grating (FBG) Sensors for Thermal Mapping of Electric Machine Windings

Abstract

This paper presents a design concept and a prototype of a polyimide-coated Fibre Bragg Grating (FBG) thermal sensor system based on a fast scan tunable laser source (up to 1kHz sensing frequency). This system was deployed to perform a comprehensive 2-D real-time radial and axial thermal profiling of an electromagnetic coilthe short duty cycle electric machine (EM) windings. The thermal measurements were performed using an equivalent prototype consisting of an FBG interrogator, a multi-FBG string temperature sensor, power resistors (thermal objects), and conventional thermocouples used for measurement comparison. The FBG measurements of copper windings were subsequently carried out using a copper coil with FBG sensors system to map the radial and axial temperature distribution of the coil. The experimental results show that Polyimide-coated FBG sensor can be used for multi-point temperature monitoring of electromagnetic coils with a sensing temperature range of 20-200℃, a spatial resolution of 6cm, and a measurement error of  2%. The obtained thermal maps can be used for the identification of hot spot locations in electromagnetic coil systems. I.

Fiber Optic Fiber Bragg Grating Sensing for Monitoring and Testing of Electric Machinery: Current State of the Art and Outlook

“…The conventional temperature monitoring approach in electric machines generally employs embedded temperature sensors, such as thermocouples (TCs) or resistance thermal detectors (RTDs), to measure the local temperature of the monitored parts [26]. However, the utilization of these sensors, especially for critical machine applications, can have considerable limitations due to the safety risks posed by the electrically conductive nature of the sensor material and the sensor installation complexity; further constraints arise from the physical dimensions of these sensors, which can prevent or significantly complicate the effective access to key thermal measurement locations of interest (e.g., windings slots) [27]. The conventional TC and RTD-based thermal sensing are additionally challenged where the monitoring of machine rotary components is concerned, suffering from installation and wiring complexity and challenges around data transmission between the rotating rotor and a stationary external sensing platform [28,29].…”

“…In addition, operating speed monitoring in electric machines is essential for their effective usage and control. This is usually measured using encoder and resolver sensors; however, these can be compromised in challenging environments [27]. There is a general interest, therefore, in employing the inherent ability of FBG sensing for conceiving speed sensing schemes in rotating machines which could yield gains in increased robustness, smaller sensor packages, etc.…”

Fibre optic sensors for the monitoring of rotating electric machines: a review

“…Furthermore, a design concept and a prototype of a polyimide-coated Fibre Bragg Grating (FBG) array thermal sensor system was presented to perform a comprehensive 2-D real-time radial and axial thermal profiling and mapping of short duty cycle electric machine windings. Such systems, based on tunable laser technology, successfully demonstrated the advantages for FBG thermal mapping of copper windings: broad temperature detection range (20-200 °C), adequate spatial resolution (6 cm) and fast wavelength sweeping frequency (up to 1 kHz) (Shang et al 2020). Simultaneous thermal maps can be used for real-time monitoring of the distribution and spatial localization of thermal hot spots within the EM copper windings (Fig.…”

“…The energy Fig. 4 Schematic of FBG thermal sensor array embedded together with a copper windings (left), and corresponding Radial and Axial thermal maps using data collected by FBG sensor array (Shang et al 2020) efficiency is also decayed by vibrations. The vulnerable EM components to vibrations are similar with those of thermal issues: bearing, winding, stator and rotor.…”