New Approach to Breakdown Study by Measuring Pre-Breakdown Current in Insulating Materials

Abstract

A technique of measuring current prior to breakdown was introduced. The breakdown mechanism was discussed on the basis of results obtained for polythylene (PE) and polymide (PI) by applying dc ramp voltage. At 90°C the pre-breakdown current of PI sharply increased from about 1 msec before breakdown. For PE, the sharp current increase could not be detected till about 100 ns before breakdown, which is the resolution limit of the measuring system. If this sharp increase is due to the temperature rise of the sample, thermal breakdown may be dominant in the case of PI but not of PE.

Thermal breakdown modeling in polyimide films by solving the heat balance equation

“…Thus, while Cv is around 1.3×10 6 J/m 3 K at room temperature, its values is close to 2.8×10 6 J/m 3 K at 390 °C. In previous studies, all the authors always modeled the heat balance equation considering the heat capacity as a constant, probably obtained at room temperature [2,3,8,9,11]. Moreover, Zebouchi et al has pointed out in the case of PET the possible influence that this parameter could have on the obtained difference between experimental and modeling results [11].…”

“…Although electrical properties of PI films have been investigated since many years, their operating limit under high electric field at high temperature remains unknown up to now. As PI are known to break down via a thermal process [2,3], it is fundamental to use them below the temperature run away when high electric fields are applied to their bulk. Moreover, even if PI films own a high dielectric strength [4], the electric field range for high temperature operation should be limited to keep the thermal balance in order to avoid the breakdown.…”

“…In a previous paper, the extreme high temperature (320 °C to 400 °C) electrical conduction of PI films has been investigated highlighting a space-charge limited currents mechanism using pre-breakdown current measurements [5]. In the past, Hikita et al have measured the pre-breakdown currents in PI films and calculated the temperature rise, but only for an initial sample temperature of 90 °C [2]. In the present paper, and based on our previous results of pre-breakdown currents [5], we have modeled the temperature rise and runaway inside PI films for extreme temperatures by solving the heat balance equation in order to derive the theoretical thermal breakdown field.…”

Thermal runaway in polyimide at high electric field probed by infrared thermography

“…In the past, Hikita et al have measured the pre-breakdown currents in PI films at 90 C and calculated theoretically the induced temperature rise. 10,15 However, up to now, such temperature increase has never been confirmed by experimental measurements. Earlier attempts to detect the temperature increase using infrared (IR) thermography of insulating samples at room temperature and under high field have been reported by Nagao et al on polyethylene films in the 90s and later by Torimoto et al on polyethylene naphthalate thin films.…”

“…[2][3][4] Although the electrical properties of PI films have been largely investigated since many years, 5-9 their operating limit under high electric field at high temperature still remains unknown up to now. As PI is known to fail via a thermal process, 10,11 resulting from the formation of a spacecharge-limited-current mechanism, 12,13 they have to be used below the temperature runaway when high electric fields are applied to their bulk. Moreover, even if PI films show a high dielectric strength, 14 the electric field range for high temperature operation should be limited to keep the thermal balance in order to avoid breakdown.…”