Breakdown strength of perfluorocarbon liquid/vapor and mixtures of the liquid with SF6

Abstract

In the insulation design for power apparatus which use perfluorocarbon (PFC) liquid, it is necessary to study the breakdown strength of the liquid/vapor under a uniform field. Particularly for devices with SF6, the breakdown strength is an important factor in insulation engineering. This paper presents an investigation on the insulation characteristics of PFC liquid/vapor with and without SF6, when the temperature is varied from 20 °C to 80 °C. Experiments are performed using plane–plane electrode geometry in a closed system under ac and lightning impulse voltages. Results are as follows: (1) in the case of PFC vapor pressure above the liquid without SF6, the breakdown strength in the liquid phase is little affected by the temperature rise, whereas it increases greatly in the vapor phase under the same condition; (2) in the other case of a mixture pressure above the liquid with SF6 under ac voltage, the breakdown strength of the mixture vapor phase is given by adding the contribution of the two components (PFC vapor and SF6). © 2000 Scripta Technica, Electr Eng Jpn 134(1): 1–9, 2001