Reassessing Self-Healing in Metallized Film Capacitors: A Focus on Safety and Damage Analysis

Metallized film capacitors (MFCs) are known for their self-healing (SH) properties, enabling efficient and reliable operation, even under challenging conditions. These SH events have the potential to inflict damage on both the polypropylene (PP) film and the electrode layer. However, not all types of SH damage lead to catastrophic failure of the capacitor. Thus, finding the threshold of SH that has little impact on the reliability of the capacitor is important. This article classifies SH events based on their SH energy, ranging from safe to risky, and establishes thresholds for safe SH. We investigate the correlation between SH energy and critical factors, such as peeling stress (adhesion between films), damage to internal components, and the number of damaged layers. For instance, at safe SH levels (< 100 mJ), peeling stress on metallized films remains below 8 N/m, while risky SH events (>250 mJ) result in peeling stress as high as 14 N/m. Furthermore, this article associates the equivalent parallel resistance ( ${R}_{P}$ ) with SH safety, realizing the correlation between external measurable parameters of capacitor and internal damage caused by SH events. ${R}_{P}$ serves as a valuable tool for evaluating the safety of MFCs with an unknown SH history, contributing to the assessment of their reliability.

I. Introduction

In recent years, the evolution of power electronics has placed increasingly higher demands on capacitor performance. In response, the film capacitor has emerged as a solution to meet the growing requirements for both enhanced power capabilities and reliability [1], [2]. One of the most distinctive attributes of metallized film capacitors (MFCs) is their self-healing (SH) capabilities, which enable them to endure multiple breakdown events under varying conditions [3]. This SH phenomenon is influenced by several factors, including operating voltage, mechanical pressure applied to the winding layer, and electrode thickness [4], [5], [6]. While the ability of capacitors to restore their insulation under high voltage is remarkable, it is important to note that the reliability of the capacitor may diminish significantly under high-frequency SH discharges caused by continuous over-voltage.