Basic insulation characteristics of perfluorocarbon for large power transformers

Abstract

To evaluate performance of non-flammable high voltage large power transformers, the effects of pressure and dissolved SF6 g,as on the AC and lightning impulse insulation characteristics of perfluorocarbon were studied. With current flows of up to 300A in the conductor of an inter-coil insulation model, phenomena relating to SF gas bubble release from the conductor surface were studied. Then, relationships between the bubble release phenomena and the basic insulation characteristics of perfluorocarbon were clarified. I~O W C T I O NIn recent years, demands for non-flammability of power apparatus in urban area substations have been increasing in Japan. This is due to the employment of more underground substations in buildings and programs to introduce extra high voltage power systems in crowded urban areas. As such, there is a growing tendency to use SF6 gas insulated transformers or dry-type transformers instead of relatively small capacity, oil-immersed transformers. However, since it is very difficult to realize non-flammable, extra high voltage large power transformers with only SF6 gas insulation, a new type of non--flammable power transformer is required. Non-flammable transformers, in which the roles of transformer cooling and insulation are complete1 separated, have been conceptually presented(' ) ( 2 f 7 and trial produced(3). In these transformers, Freon or another fluorocarbon was used for transformer cooling and SF6 gas was used for insulation. Other new non-flammable power transformers with two-phase cooling, which are wholly insulated with SF6 gas and sprayed with fluo T%~@J. liquid for cooling, have also been trial made Perfluorocarbon is an excellent coolant with non-flammability which additionally has good insulation properties. Therefore, transformers insulated with perfluorocarbon should be desirable. A two-phase insulation of perfluorocarbon liquid and SF6 gas would be advantageous, because perfluorocarbon is very expensive. Consequently, the basic insulation characteristics of perf luorocarbon (C8F1 6O as the main component) are investigated in this paper, including the influence of the existence of dissolved SF6 gas. The following subjects are considered.(1) The boiling point of perfluorocarbon is as low as 100OC at atmospheric pressure. Since the insulation strength of the vapor phase is much lower than that of liquid phase, no boiling of perfluorocarbon necessitates an increased pressure on the liquid surface.58 CPl 048-1 oy t h e IEEE T r a n s f o r n e r s C o l n i t t e e of t h e I E F E Power E n g i n e e r i n g S o c i e t y f o r p r e s e n t a t i o n a t t h e IEEE/ PES 1185 Winter Y e e t i n g , New York, *Jew York, J a n u a r y 31 -F e b r u a r y 5 , 1988. M a n u s c r i p t s u b m i t t e d August 28, 1 9 5 7 ; made a v a i l a b l e f o r p r i n t i n g December 2 , 1987. 4 n a p e r recommended and approved Therefore, it is necessary to clarify the AC an3 lightning impulse insulation strength of perfluorocarbon at elevated pressures of the liquid.(2) When SF^ gas is ...

Study on decomposition gas for faults diagnostic of electrical equipment using fluorocarbons

“…Decomposition Experiment 0/ Fluorocarbon Liquid 1) Heating Tests: 4 Compared the Chromatogram of the gas sampled before and after the overheating, we found C2F 4' C2F 6' C3F 6 ' C3F s, C4F 10' CsF 12 ' C� 14 and other unknown elements generated [5]. In the same manner, decomposition by-products as C3Fs, C4FIO are found generated in the liquid sample.…”

AC breakdown voltage of thermal bubble induced two-phase flow condition of inflammable fluorocarbon by self-heating electrode

“…As inflammable insulating and cooling dielectrics, some fluorocarbons could be used in power transformers and other electrical equipments [1]. Therefore series of experiments have been implemented to study the AC breakdown voltage (BDV) of the fluorocarbons under the boiling two-phase flow condition [1][2][3].…”

“…Therefore series of experiments have been implemented to study the AC breakdown voltage (BDV) of the fluorocarbons under the boiling two-phase flow condition [1][2][3]. The authors have carried out the BDV test with plane-plane electrodes at 50Hz, proving that the dielectric strength of the boiling two-phase flow increases with the working pressure, which is controlled by the applied heat power [2][3].…”

“…However, the bubbles in the experimental models in previous literatures are all generated by auxiliary heater and then introduced into the electrode gap, instead of the electrode heating the liquid by itself [1][2][3][4][5][6]. Hence It is doubted that if the test methods above displayed the actual working condition precisely because the electrodes don't generate bubbles by self-heating, which is not the exactly situation occurring in the windings of transformers or superconducting apparatuses.…”