MODERN TRENDS IN OLTC DIAGNOSTICS THROUGH OIL ANALYSIS

The development of transformer component manufacturing technology is focused on producing parts that enhance the longevity and reliability of equipment. Consequently, improved components exhibit different performance characteristics, operating mechanisms, and degradation processes, which in turn influence diagnostic approaches and methods. Due to their specific function, on-load tap-changers (OLTCs) are subjected to increased stress, making them more prone to failures. As a result, they have undergone continuous improvements and structural modifications in recent years. One notable trend is the growing use of vacuum-type OLTCs instead of conventional ones, necessitating updates to diagnostic criteria and testing methods for assessing their condition. This paper presents a comparison of vacuum and oil-filled OLTCs, with a focus on their potential impact on test results. Special emphasis is placed on dissolved gas analysis (DGA) using gas chromatography (GC), a sensitive method for the early detection of failures, particularly those of thermal origin. Case studies from practical applications illustrate the differences in interpreting GC analysis results depending on the OLTCs type, complemented by electrical testing methods.