This paper presents the Root Cause Failure Analysis (RCFA) and the solution of the broken lever problems on 230 kV unit circuit . The mentioned circuit breakers are Alstom high voltage circuit breakers: Model "FXT15" Mechanism Type "FK3-4", which are used at the Sirikit Hydro Power Plant and Rachaprapa Hydro Power Plant, under responsibility of Electricity Generating Authority of Thailand (EGAT). Penetrant test and observing oil dashpot function were utilized to collect the data for the Root Cause Failure Analysis to find the main cause. It results that the main cause came from non-center movement of oil dashpot. Moreover, when the FXT15 model was compared with other models, it was found that the FXT15 model did not contain the supporter of piston rod. To solve this problem, the modification of the piston rod's shelter is required to support the symmetry movement of oil dashpot. After completion of modification, the several circuit breaker mechanism tests have been repeatedly carried out to observe its movements. The result shows that the circuit breaker pistol rod movement is in balance and symmetry. The benefits of the modification are the reduction of operation cost due to unit tripped by the circuit breaker malfunction and improvement of the EGAT power plant reliability.
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