**3. Theoretical Background**

In this section, we introduce the relevant theoretical background of the study. Firstly, we introduce the alarm reduction algorithm based on hierarchical clustering, including the concept of generalization level, the calculation method of distance and the basic process of the algorithm. Second, we introduce the main ideas and basic process of WOA. Table 1 shows the list of notations used in this paper.

**Table 1.** Table of notations used in this paper.


#### *3.1. Alarm Reduction Algorithm Based on Hierarchical Clustering*
