Cable accessories are significant and weak part of cable system. Silicon Rubber (SR) and Ethylene Propylene-Diene Monomer (EPDM) are commonly used in insulation of cable accessories for their high elasticity, great corona and electricity-erosion resistance and mature manufacturing technology. But there is a controversy on which one is better in China. Under the influence of structure, installation and operation conditions, the insulation main body and interface of cable accessories are subjected to multi-stresses, including electrical stress due to operation voltage, thermal stress caused by conducting current and mechanical stresses as a result of expanding of insulation main body, which cause aging and deterioration of the insulation materials and eventually lead to the breakdown of accessories. Thus, It is of great theoretical and engineering significance to research the aging characteristics and mechanism of SR and EPDM under multiple stresses. In this work, SR and EPDM used as insulation of 110 kV cable joints were selected as test samples. Flat samples were made by tableting, put together with flat XPLE sample and placed in the coupling electrical-mechanical stress aging device. In this way, the insulation interface in cable accessory and its stresses were simulated, and different mechanical tension and/or electrical stresses were applied to the rubber samples in the interface composed of XLPE-SR/XLPE-EPDM. After being stressed for preset time periods, the samples were observed by scanning electron microscope (SEM), and their mechanical property, volume resistivity, degree of crosslinking, attenuated total reflectance Fourier infrared spectrum (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) are measured. The results indicate that the volume features of aged SR decrease a lot, including mechanical strength, volume resistivity and crosslinking ratio, while EPDM's stayed almost unchanged. Besides, according to the chemical analysis, under electrical stress or the coupling electrical-mechanical stresses, some chemical bonds of new SR and EPDM are destroyed, while oxidation groups such as -OH and C=O are formed and the destruction of surface chemical structure is more serious when mechanical stress is coupled. Above all, it's proposed that some molecular chains of SR and EPDM are broken by ion bombardment under electrical stress, producing free radical, which could react with each other or reactive species to produce micro-molecule and oxides. And mechanical stress is able to facilitate this process by weakening intermolecular entanglement, destroying physical crosslinking and triggering before-dissociation active state. The destruction of SR already goes deep to the volume, while EPDM's still remained at the surface during experiment period, presumably due to their different chain structure and amount of fillers in polymer systems.
In un sistema elettrico le parti che compongono un cavo sono una parte significativa e nello stesso tempo, la parte debole in quanto sono presenti difetti dovuti alla produzione, installazione e operazione. Gomma di Silicone (SR) e Monomero di Etilene Propilene-Diene (EPDM) sono comunemente impiegati per la realizzazione degli accessori dei cavi perché hanno elevata elasticità, ottima resistenza sia all’effetto Corona che all’erosione elettrica e hanno una avanzata tecnologia di produzione. Esistono controversie su quale dei due materiali sia il migliore. Inoltre, l’isolamento e l’interfaccia degli accessori dei cavi sono sottoposti a multi-stress, affetti da strutture complicate, installazione improprie e cattive condizioni dell’ambiate in cui si opera. Per esempio, ci sono stress elettrici causati dalla tensione alla cui sono sottoposti, stress termici introdotti dalla corrente e stress meccanici nell’interfaccia e nell’isolamento dovuti dalla espansione degli dell’isolamento degli accessori durante l’installazione. Quindi, l’invecchiamento e la degradazione dell’isolamento degli accessori sono affetti a diversi fattori, la cui possono provocare l’eventuale rottura di quest’ultimo. Dunque, per SR e SPDM, è importante conoscere la teoria e analizzare l’aspetto ingegneristico delle caratteristiche meccaniche ed elettriche dopo un’invecchiamento dovuto ad uno stress multiplo. In questa tesi, gli campioni utilizzati per gli esperimenti sono il SR e il EPDM che sono usati come isolanti per i giunti dei cavi di 110kV. Campioni piatti sono fatti da pastigliatura, assemblati con un campione di XPLE piatto e collocati nel dispositivo di invecchiamento da stress elettrico-meccanico. In questo modo, l'interfaccia di isolamento nell'accessorio del cavo e le sue sollecitazioni vengono simulate applicando stretching meccanici e sollecitazioni elettriche su campioni di gomma. I campioni SR ed EPDM sono invecchiati in tempi e rapporti di allungamento diversi, mentre lo stress elettrico è invariante. Quindi l'aspetto, le caratteristiche meccaniche, elettriche e chimiche di quei campioni invecchiati vengono misurati per analizzare il loro meccanismo di invecchiamento e confrontare la loro capacità di anti-invecchiamento. I risultati mostrano che le caratteristiche del volume degli SR invecchiati diminuiscono molto, come per la resistenza meccanica, la resistenza volumetrica e il rapporto di reticolazione, mentre gli SPDM sono stabili. Inoltre, secondo l’analisi chimica, sotto stress elettrico, alcuni legami chimici nei nuovi campioni SR e SPDM vengono distrutti, mentre gruppi di ossidazione come –OH e C=O sono generati e la distruzione della struttura chimica superficiale è più grave quando lo stress meccanico è combinato allo stress elettrico. Dagli esperimenti si vede che alcune catene molecolari di SR e RPDM vengono spezzate da particelle energetiche durante la scarica, producendo radicali liberi, che potrebbero reagire tra loro o attivare gli ossidi per creare micro-molecole e ossidi. Invece lo stress meccanico è in grado di facilitare questo processo alleviando l’entanglement (correlazione) molecolare, innescando lo stato attivo prima della dissociazione del legame. Inoltre, durante il periodo di esperimento, si vede che la distruzione di SR giunge già in profondità mentre per EPDM rimane ancora in superficie e questa differenza è correlato alla loro diversa struttura della catena e alla loro frequenza di addizione.
Research on performance change and failure mechanism of silicone rubber and EPDM rubber under interfacial multi-stresses
WANG, XING
2018/2019
Abstract
Cable accessories are significant and weak part of cable system. Silicon Rubber (SR) and Ethylene Propylene-Diene Monomer (EPDM) are commonly used in insulation of cable accessories for their high elasticity, great corona and electricity-erosion resistance and mature manufacturing technology. But there is a controversy on which one is better in China. Under the influence of structure, installation and operation conditions, the insulation main body and interface of cable accessories are subjected to multi-stresses, including electrical stress due to operation voltage, thermal stress caused by conducting current and mechanical stresses as a result of expanding of insulation main body, which cause aging and deterioration of the insulation materials and eventually lead to the breakdown of accessories. Thus, It is of great theoretical and engineering significance to research the aging characteristics and mechanism of SR and EPDM under multiple stresses. In this work, SR and EPDM used as insulation of 110 kV cable joints were selected as test samples. Flat samples were made by tableting, put together with flat XPLE sample and placed in the coupling electrical-mechanical stress aging device. In this way, the insulation interface in cable accessory and its stresses were simulated, and different mechanical tension and/or electrical stresses were applied to the rubber samples in the interface composed of XLPE-SR/XLPE-EPDM. After being stressed for preset time periods, the samples were observed by scanning electron microscope (SEM), and their mechanical property, volume resistivity, degree of crosslinking, attenuated total reflectance Fourier infrared spectrum (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) are measured. The results indicate that the volume features of aged SR decrease a lot, including mechanical strength, volume resistivity and crosslinking ratio, while EPDM's stayed almost unchanged. Besides, according to the chemical analysis, under electrical stress or the coupling electrical-mechanical stresses, some chemical bonds of new SR and EPDM are destroyed, while oxidation groups such as -OH and C=O are formed and the destruction of surface chemical structure is more serious when mechanical stress is coupled. Above all, it's proposed that some molecular chains of SR and EPDM are broken by ion bombardment under electrical stress, producing free radical, which could react with each other or reactive species to produce micro-molecule and oxides. And mechanical stress is able to facilitate this process by weakening intermolecular entanglement, destroying physical crosslinking and triggering before-dissociation active state. The destruction of SR already goes deep to the volume, while EPDM's still remained at the surface during experiment period, presumably due to their different chain structure and amount of fillers in polymer systems.File | Dimensione | Formato | |
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Research on Performance Change and Failure Mechanism of SR and EPDM under Interfacial Multi-stresses.pdf
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https://hdl.handle.net/10589/148971