A comparative study of insulator materials exposed to high voltage AC and DC surface discharges

[摘要] The rising worldwide popularity of HVDC applications for power transmissionpurposes increases the need to study the performance of commonly used insulationmaterials when exposed to this voltage type. The aim of this study is thus to compareseveral insulation materials according to their resistance to erosion and tracking whenexposed to surface discharges of HVAC and HVDC voltages of both polarities. Thematerials are tested according to the Incline Plane Test method described in the IEC60587 standard, using a test voltage of 4.0 kV (rms).An important aspect of this project is the development of a bipolar DC source capableof delivering the required test voltage and current for both positive and negativepolarities, while performing in accordance with the specifications set down in thestandard. The design is intentionally kept modular in order to make it adaptable forfuture installations.Since the standard describes two different test methods, i.e. the constant trackingvoltage method and the stepwise tracking voltage method, a comparison is donebetween the two methods in order to determine which one delivers best results for thetest samples. The comparison shows that the methods deliver comparable results, butthe constant tracking voltage method is preferred due to its superior test procedure.Finally, four different polymer insulator materials are tested and successfullycompared under the effects of HVAC and HVDC of both polarities. The test materialsinclude a RTV silicone rubber coated ceramic, two different HTV silicone rubbersand an EPDM rubber. The comparison is done according to the results obtained for anumber of evaluation criteria. The results show that the RTV silicone rubber coatingexhibits the least erosion for an AC voltage, but shows extensive erosion for anegative DC voltage. The HTV silicone rubbers exhibit only minimal erosion whenexposed to an AC test voltage, but develop strong erosion under a positive DC voltagewhich can result in sample failure. The EPDM experiences its least erosion for anegative DC voltage, but shows maximum erosion severity for the AC voltage.

[发布机构] Stellenbosch University