External Partial Discharge Analysis in Design Process of Electrical Space Components

Abstract

External Partial discharges (PDs) can occur in strong non-uniform electrical fields on electrical equipment. Usually, PDs are only considered in the design process of high voltage applications, where ionization is more likely to occur. Under certain ambient conditions, i.e. under low gaseous pressures, the dielectric strength of an insulation might be weakened, leading to onset of partial discharges - even at voltages below 1 kV. PDs are responsible of insulation deterioration, due to bombardment of ions formed by PDs, as well as chemical reactions by compounds formed during discharge process. Additionally, PDs can cause interference in communication systems. Therefore, PDs are also highly unwanted on electronics for space applications, where reliability is utmost important. The European Cooperation for Space Standardization issued a design handbook for electronics for space applications, in which PD magnitude limits are given. It discards the importance of external PDs, since it argues that no atmosphere will be present in outer space. While that is true, equipment that is under operation during launch of the space vessel, will experience a pressure drop from standard atmospheric pressure to near vacuum. Given a corona onset, an enhancement of the field in the vicinity of the cathode might occur, due to the relative low mobility of the formed positive ions, thereby transitioning the corona into a self-sustained PD. This paper therefore presents both predictive analytical tools for external PDs, applicable in the design process of equipment, as well as an experimental measurement setup to measure PDs in compliance with IEC 60270. Flux A/S design and manufacture magnetic components for space applications. They were unable to analyze a prototype design for PDs before manufacturing, and unable to measure PDs on manufactured prototypes. Collaboration was established between Flux A/S and Aalborg University to enable Flux to do so.