Effects of electric partial discharges on the rheological and chemical properties of polymers used in HV composite insulators after railway service

Abstract

The origin and the consequences of the electric failure of in-service composite hollow insulators used in railway transportation were investigated. Direct electrical measurements made it possible the detection of partial discharges (PD) and UV emissions allowed of identifying the location of the PD at the interface between metal braids and a silicone liner. To investigate the effects of the damaging PD activity, physicochemical properties of the different polymers were investigated and compared to new samples. The thermomechanical properties of the HTV and RTV silicones showed important alterations in the polymers structure. The chemical analyses of the silicones and nitrile rubber conducted using ATR-FTIR spectroscopy revealed that the polymers were oxidized after electrical failure. The results indicated that the ozone production and UV emission were due to the surface electrical activities. The breakdown of alumina trihydrate (ATH) in the inner HTV silicone liner demonstrated that undesired electrical discharges induced an significant increase of temperature and the formation of moisture in the air present in the hollow insulator. Laboratory artificial aging performed on the silicones and nitrile rubber showed similar degradation as in service. Further electrical experiments conducted on empty hollow insulators enabled the detection of internal PD located in micro-voids present in the adhesive used to bond the HTV silicone liner to the inner composite tube.

An Experimental Study Followed by a Development and a Comparison of Regression Models for Predicting TJ Electric Discharge in Insulators

“…In other words, porcelain has a weak bonding force between its molecules, unlike heat tempered glass and silicone (silicone has a strong bonding force between its molecules made from oxygen and silicon). Thus, this chemical structure plays a main role in the electrical and dielectric properties of these materials [25].…”

Degradation and Stability of Polymeric High-Voltage Insulators and Prediction of Their Service Life through Environmental and Accelerated Aging Processes

“…In fact, during surface electrical discharge due to a significant increase in temperature, both degradation of the matrix polymer and dehydration of the ATH-like filler present in the compound can happen. 44,89−92 Therefore, it may be concluded that the second stage decomposition temperature measured through TGA for a housing material is related to its service life.…”

“…However, the housing material may be exposed to a much higher temperature well beyond 170 °C, the highest aging temperature for a very short duration during electrical discharges. 44,89−92…”

Assessment of the resistance to tracking of polymers in clean and salt fogs due to flashover arcs and partial discharges degrading conditions on one insulator model

“…This could be the main reason that leads to tracking due to its lowest activation energy. Furthermore, a reduction in the percentage of C‐H and pyrolysis of sulphuric components (‐S) are likely to facilitate the ignition of a conducting path and gas by‐products such as SO 2 and H 2 S [26]. As concerns HDPE, its resistance to tracking in salt fog is better than that in clean fog probably due to a higher leakage current magnitude that dries quickly the moisturised surface and inhibits FOV arcs.…”