说明：  电力系统的频率反映了发电机组所发出的有功功率与负荷所需的有功功率之间的平衡情况。当系统发生较大事故时,系统出现严重的功率缺额,其缺额值超出了正常热备用可以调节的能力,这时即使令系统中运行的所有发电机组都发出其设备可能胜任的最大功率,仍不能满足负荷功率的需要,所引起的系统频率下降值将远远超出系统安全运行所允许的范围。 在这种情况下从保障系统安全运行的观点出发,为了保证电网安全和对重要用户的供电,不得不采取应急措施,切除部分负荷,以使系统频率恢复到可以安全运行的水平内。
(The frequency of the power system reflects the balance between the active power generated by the generating unit and the active power required by the load. When the active power from the power plant does not meet the requirements of users, the system frequency will decrease. Frequency fluctuation caused by unplanned load in normal operation of the system. At this time, the system uses the hot standby capacity of the power plant, that is, the generator capacity in the system operation is enough to meet the needs of users. However, when the system has a major accident, the system has a serious power shortage, which is beyond the adjustable capacity of normal hot standby. At this time, even if all the generating units operating in the system send out the maximum power that their equipment may be competent for, they still cannot meet the demand of load power rate, and the resulting system frequency drop value will be far beyond the allowable range of safe operation of the system.)