Dynamic analysis and testing of on-load tap changer (OLTC) by the dynamic resistance measurement (DRM)

Summary

Power transformers represent the most expensive chain links connecting generation to utilization. One very important component of a power transformer is the on load tap changer (OLTC). There are two common technologies of OLTC in the market. The so called inductive ones, which are typically used in North America on the low voltage side, and the resistive OLTCs, which are typically used in the rest of the world on the high voltage side. This paper focuses on the resistive OLTCs. As opposed to other more static components in a transformer, the OLTC consists of a lot of moving parts. Therefore, a typical maintenance cycle, mostly depending on the total number of switching operations, is given by the manufacturer. The switching time of the OLTC is typically below 100 ms. This is very fast and effects during the switching process cannot be detected by the static winding resistance measurement. In this paper the dynamic resistance measurement (DRM) is discussed to analyze the OLTCs switching process. A fast measurement methodology and novel analysis and comparison method is discussed for determining defects and possible failures in time. The paper considers which typical pattern of the DRM can be expected for the most common OLTCs. Failures which can occur in OLTCs include breaking of springs, worn or damaged mechanical parts, too high and irregular contact wear of the arcing contacts, broken leads (to the commutating resistors and auxiliary contacts), too long switching times and bouncing contacts which could have an accelerating effect on the contact wear.

Additional informations

Authors

Hanaoka Ryouichi, Alapati Sridhar, Abbasi Amirhossein, Saltzer Markus