| The problems of comprehensive protection and the soft-starting andpower-saving operation of asynchronous motor are studied in this thesis . With the high function micro-computer, the comprehensive protection and the soft-starting and power-saving operation of asynchronous motor are corresponding unified . It can not only protect the motor, but also control the motor. The following is the main work of thesis :1. The fault current characteristics of the asynchronous motor and corresponding relations of fault reasons are analyzed in this paper. Based on the detection of the positive-sequence and negative-sequence and zero-sequence current , a new criterion for asynchronous motor protection is proposed . This paper presents the comprehensive protection principle and analyses core algorithm of realization of multi-function protection by micro-computer.2. The paper analyses the relation of the starting-time and the multiple of starting current and voltage in the current-limited starting process of motor with different character load . And it presents a novel digital phase-control method based on three-phase thyristor voltage regulation by micro-computer . In addition , the principle and designs of digital phase-shifting and the digital trigger system are described.3. hi this paper , the power-saving operation of asynchronous motors with step-down voltage is analyzed theoretically . Taking control measure of the ratio between the stator voltage and the stator current , the method of low-load power-saving operation by regulating-voltage is presents . And it is analyzed theoretically that the control measure is defined.4. The paper presents the hardware drawing of motor control center, which the comprehensive protection and control are corresponding unified with microcomputer. The comprehensive control can not only protect the motor, but aslo be power-saving operation control and soft-starting control.
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