Finite Element Analysis of DC Partial Discharges in O-Ring applications

Inhalt:
There is an increasing need for direct current (DC) transmission and converters to reduce the issue of reactive power losses in various applications. The converters contain multiple semiconductor switching units. The present study focuses on the examination of a single switching unit within this converter system, specifically with respect to the electrical stress of the O-rings embedded in the cooling system. The O-rings are stressed by high DC voltages. By simulate the behavior of these O-rings under such conditions, valuable knowledge can be gained to enhance the overall reliability of the con-verter units. To address this goal, a model of an O-ring is created to calculate the electrical quantities, including potential, current and charge density, and electric field strength using Ansys Charge Plus. The inserted geometry is discretized using a finite element (FE) mesh. The electrical quantities are calculated by a quasi-static solver using the biconjugate gradient stabilization method. Furthermore, Ansys Charge Plus implements a stochastic tree model, which allows the accurate calculation of avalanche breakdown by enabling electrostatic discharge (ESD). The results show that EPDM and silicon O-rings lead to space charge accumulation and high electric field strength at the interfaces between cooling system and O-ring. Partial discharges (PD) occurred at the triple point of the O-ring in the air gap. That could be an indicator that partial discharges creep up on the edge of the O-ring and damage it. Based on simulation data, applying silicon grease to the O-ring prevent PD and is a potential solution. It is a cost-effective and easy countermeasure that does not require the replacement of any components. If silicon grease is applied immediately during the first assembly of the cooling system, it can prevent coolant leakage due to O-ring failure caused by partial discharge events.