其次是求机组同时发生事故的或然率。因为仅仅知道了电力系统每台机组的事故停用平均持续时间(即事故率乘以动转时间),还不能求得事故备用容量及事故备用电量值。系统的每台机组可能在一定的时间内发生事故停电,但是不应该假定系统所有机组发生事故的时间,会互相重合,因而也就不应该假定所需的事故备用值等于全部工作机组的容量。 The second is to find the possibility of accident occurred at the same time. Because only the average duration of incidents (ie accident rate multiplied by the turn-around time) for each unit of power system is known, it is not possible to find the accidental reserve capacity and the accidental reserve value. Each unit in the system may have a power outage within a certain period of time, but it should not be assumed that the time of occurrence of all units in the system will coincide with each other. Therefore, it should not be assumed that the required reserve for an accident is equal to the capacity of all working units.