Analysis of oil leakage anomaly in a 220kV current transformer

This paper analyzes an oil leakage anomaly in a 220kV vertical current transformer (CT) at a substation, where oil leakage was found at the connection between the expander and flange of the 2nd bus tie CT phase C during a power outage maintenance. Through factory disassembly, sealing performance tests, X-ray detection, and process analysis, the root cause is identified as shrinkage porosity in the oil conservator due to poor casting process control. The shrinkage porosity, initially non-penetrating, gradually formed an oil leakage path under long-term micro-positive pressure operation. Corresponding conclusions and suggestions are proposed to prevent similar anomalies.