A Contribution to Thermal Ageing Assessment of Glass Fibre Insulated Wire Based on Partial Discharges Activity

Abstract

This paper aims to evaluate a Type-II insulated wire (i.e., Glass fibre insulated wire) as a function of thermal ageing time based on partial discharges (PD) activity. Partial discharge inception voltage (PDIV), partial discharge extinction voltage (PDEV), and repetitive partial discharge inception voltage (RPDIV) measurements have been performed on both unaged and thermally aged specimens. Each specimen modelled the turn-to-turn insulation; hence it was made by a pair of Glass fibre wires wrapped in PTFE tape for a mechanical purpose. The PD tests have been carried out under positive and negative unipolar square waveform excitations using different rise times: 80, 400 and 800 ns. The trend of PD quantities vs exposure time demonstrates that the effect of space charge accumulation under unipolar excitation must be taken into account when unaged and thermally aged specimens are compared. Results revealed that although sometimes thermally aged samples might show a temporary superiority in the short run, unaged ones always present a better performance after space charge accumulation, as expected. Following the statistic postprocessing of the collected data, shape/slope parameters of the Weibull distribution relevant to PDIV can be used as an ageing indicator for Glass fibre insulated wire. Finally, the permittivity evaluation vs thermal and electrical stresses have been performed, relying on the measured capacitance of each specimen just after every PD test. Such analysis revealed that thermal ageing increases permittivity in the long run. However, electrical stress has different impacts on permittivity depending on the rise time, polarity, and magnitude of the applied voltage.

Glass Fibre Insulated Wire Assessment Under Partial Discharges Activity via Dielectric Dissipation Factor Measurements

“…Regarding the impact of rise time under bipolar excitation at a constant frequency, a higher RPDIV is associated with a faster rise time for both switching frequencies. However, the effect of rise time under unipolar excitation seems to be frequency-dependent [3]. Indeed, while a faster rise time gives a higher RPDIV at a lower frequency (i.e., 50 Hz), the opposite holds at a higher switching frequency (i.e., 2.5 kHz).…”

“…Therefore, PTFE-wrapped pairs of Glass fibre insulated wires are used to model the turn-to-turn insulation system instead of twisted pairs. Indeed, the two insulated wires are held next to each other using a binding tape (i.e., PTFE tapes) to deliver a perfect contact between their insulation surfaces [3]. Hence, the PTFE tapes are employed for a purely mechanical purpose in the specimen assembly and do not play any electrical insulation role.…”

“…The measurements are performed at room temperature (21°C), atmospheric pressure (1013 mbar) and relative humidity (28±5%). First, the repetitive partial discharge inception voltage (RPDIV) is measured according to the approach described in [3]. Then, the voltage is kept constant to age the specimens electrically for different cycles: 15, 30, 45 and 60 minutes (Fig.…”

“…The technology of converter-fed electrical machines is moving toward using modern inverters (e.g., silicon carbidebased inverters) to increase the power density besides reducing losses [1]. Modern inverters are featured by faster rise times, enabling higher switching frequencies, voltages, and temperatures than those typical of standard silicon MOSFETs [2,3]. A shorter voltage rise time enhances the risk of partial discharges (PD) inception for the turn-to-turn winding insulation.…”

Investigation on combined effect of humidity–temperature on partial discharge through dielectric performance evaluation

“…Optical PD detection using a photomultiplier tube (PMT) is employed for direct PD measurement. Twisted pair is used as the test sample since it is a fair representation of turn‐to‐turn insulation and is easy to manufacture [17]. The tip‐up test is carried out by industrial insulation tester Megger 4110.…”