| Summary: | 碩士 === 國立勤益科技大學 === 電子工程系 === 106 === Traditional methods to protect the electric-driven facilities from overload or short circuit usually use electronic breaker or fuse. However, the reaction time for these devices normally require more than 0.1 sec that may be not sufficiently fast to disconnect the power supply for protection, and higher rating size of breakers or fuses is demanded than expected due to lack of a surge current suppression mechanism. For this reason, this thesis proposes a fast large current electronic breaker based on the integration of current-divider sensing and surge suppressing methods and develops a fast and simple electronic over-current protection circuit based on the current-adjustable sensing method. Firstly, the load surge current can be effectively suppressed by series negative temperature coefficient (NTC) thermistors, the load current is sensed and converted to a voltage signal using Hall sensor. Then, the signal is amplified and compared with the predefined threshold value, i.e., the maximum tolerance current, using amplifier and comparator, respectively. The timer will generate a pulse signal input to the trigger circuit for rapidly switching off AC power once the load current exceeds the tolerance value. The AC power disconnection can continue for a period of time set by the timer in advance. The experimental results prove that the proposed circuit takes less than 10ms and it is significantly fast to react for facility protection in time.
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