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Development of a Circuit Breaker Condition Monitor - The most common primary electric power distribution voltage in Japan is 6 kV. Each feeder must have a circuit breaker (CB) for switching and protection. If the lubricating grease of a CB solidifies, its operation becomes slower, and this may eventually cause switching failure. This failure in turn causes expansion of the power outage area and slower power recovery. Grease solidification occurs more often when a CB has not functioned for a long period of time. Comparison between measured and expected (or normal) operation times is a very effective method of detecting grease solidification at an early stage and thus a very effective method of condition monitoring.