大型汽轮发电机组突然甩负荷,会使汽轮机组超速、发电机变压器组过电压.利用发电机有功功率作为特征量,通过判断发电机机端有功功率值在极短时间内从一高值(PF>)降至一低值(PF<).有功功率高值(PF>),以机组快速减负荷(RB)工况有功功率的1/3为参考值;有功功率低值(PR<)以发电机组厂用电作为参考值,再加上发电机低电压与主汽门关闭闭锁判据,就能正确区分发电机组是否发生了甩负荷工况.由此判据构成的发电机零功率保护可在发电机组甩负荷初始时间内做出快速反应,能够在发电机突然甩负荷时关闭主汽门、灭磁,将机组转速、端电压升高幅度降至最低.结合某电厂在送出系统中断导致发电机功率不能送出,发电机零功率保护快速动作于全停来保障机组安全的实例,论证了发电机组装设零功率保护的必要性.%Sudden load rejection will lead to the overspeed of turbo-generator and the overvoltage of unit-generator. The sudden drop of generator output active power from PF＞ to PF＜ is taken as the criteria,together with the blocking condition of low voltage of generator or close of main steam valve,to detect the load rejection. The PF＞ is set as onethird of the active power of unit in RB operation and the PF＜ as the plant power consumption. According to it,the zero power protection can response at the very beginning of load rejection. It shuts down the main steam valve and deexcites the generator to limit the increase of generator rotating speed and terminal voltage. Site operation shows its necessity for the secure operation of unit.
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