DC Voltage Endurance of Capacitor BOPP Films at High Temperature

A large-area method for determining the voltage endurance of capacitor films is presented. The method was used to characterize the high field - high temperature performance of a commercial biaxially oriented polypropylene film. Following IEC standard 61251, an inverse power law model was fitted to the Weibull-distributed times-to-breakdown data. The insulation life increased rapidly as either field or temperature was decreased. Even at mildest stresses used, the failure rate was still increasing with time, implying that the conditions were above reasonable design limits. Determining the threshold conditions below which the failure rate starts to decrease with time may open up new paths for development of dielectric for higher energy density film capacitors.

I. Introduction

High voltage direct current (HVDC) transmission is indispensable in utilizing distant renewable energy sources, such as offshore wind power. Voltage source converters (VSCs) offer a smart, new way to connect HVDC networks to the existing AC power transmission grid. Especially when combined with stationary energy storage both power quality and grid stability are improved. Capacitors are key components in VSC systems, thus ensuring extreme technical performance and uncompromised reliability is of great importance. New high energy density dielectrics could open up paths to improved VSC systems. However, the reliability and long-term properties of any new dielectrics needs to be verified before their use in these often reliability-critical applications. Repeatable and reliable voltage endurance test methods are needed for early screening of novel would-be dielectrics, before expensive industrial scale production, which is the prerequisite for tests using wound capacitor elements.