Diagnostic Magnetic Shunt Anomaly of Power Transformer 150/20 kV 60 MVA at Tambun Substation

Power transformer is the heart of power system and critical equipment in transmission line grid. Reliability of power transformer is the most important thing in transmission system. UIT JBT (Unit Induk Transmisi Jawa Bagian Tengah) as a unit of PLN that operates and maintains the middle section of java transmission system is responsible for ensuring power system reliability. Dissolved Gas Analysis (DGA) is widely used for interpreting condition and faults diagnostic of power transformer that depend on concentrations and composition of gases in transformer’s oils. It can be used to identify the type of pending or occurring faults and estimate it’s severity that will be used to determine the appropriate action and avoid unexpected failure. Transformer 150/20 kV 60 MVA at Tambun Substation has special case, which has only been operating since 2012 but in 5 years of operation detected anomaly (infant failure). Diagnosis of defects is obtained by DGA test and the interpretation indicated thermal fault 700°C. DGA trend showed a significant increase in gas concentration was detected which was suspected due to an internal fault of the transformer. The transformer followed up with shutdown investigation, and insulation test measurement between core and frame of the transformer indicated a short circuit which is further detected as a result of the displacement of the magnetic shunt that slide and shorting the core and the frame. Further corrective action taken by on site repair.