# State Evaluation of Electrical Equipment in Substations Based on Data Mining
## 2 Methodology
### Equipment Status Characteristics  
A substation's high-voltage electrical equipment primarily consists of transformers, circuit breakers, voltage transformers, current transformers, surge arresters, and capacitor banks. These devices serve multiple functions: voltage transformation, circuit interruption or connection, high-voltage current/voltage measurement, and lightning overvoltage protection, collectively ensuring stable power transmission and distribution. Substation state evaluation focuses on defining and assessing the current condition of these devices, quantified through testing and online monitoring. Electrical testing methods evaluate equipment insulation and functionality to determine its operational viability within the system. The predominant method involves comparing current test values with those recorded at equipment delivery or manufacturer-specified ranges. Post-test analysis of deviations from these reference values, coupled with expert assessment, determines equipment condition. Online monitoring utilizes various sensors to capture real-time equipment parameters. The data are transmitted to a monitoring system for assessment by personnel or automated analysis systems. In a substation, the Supervisory Control and Data Acquisition (SCADA) system integrates online monitoring  
Figure 1: Flowchart of method process. data from various devices via specialized modules. Transformer monitoring data include winding and oil temperature (via temperature sensors), current and voltage (via current transformers and voltage transformers), dissolved gas analysis (via gas chromatography), and insulation status (via insulation monitoring systems). Switchgear monitoring data comprise: switch operation count and status (via position sensors), temperature (via temperature sensors), and operating current (via current transformers). Switchgear cabinet monitoring data encompass internal or external temperature (via temperature sensors), internal humidity (via humidity sensors), and partial discharge (via specialized monitoring devices). Lightning arrester monitoring data include leakage current (via leakage current tester) for performance evaluation and discharge frequency (via discharge counter) to track operational conduction events. Capacitor monitoring primarily focuses on the temperature of capacitors and their peripheral devices, measured via temperature sensors. Cable monitoring data encompass cable sheath and internal temperatures (via temperature sensors), partial discharge (via specialized monitoring devices). The substation environment influences internal equipment, necessitating regular inspections by operation and maintenance personnel. These inspections focus on aspects beyond automated monitoring, including temperature at contact and wire connection points, inspection of aluminum stranded wire integrity, assessing of plants or animals' interference environmental temperature and humidity recording, oil level checks in oil-filled equipment, and SF\({}_{6}\) equipment gas pressure monitoring [20; 21]. Substations typically employ two transformer types: main power transformer (oil-filled) for voltage exchange and energy distribution, and station power transformers (dry-type) for powering station equipment. Circuit breakers are mainly categorized as gas-insulated switchgear (GIS), SF\({}_{6}\) circuit breakers, oil circuit breakers, and vacuum circuit breakers. GIS or SF\({}_{6}\) circuit breakers are typically employed on the high-voltage side, while switchgear is utilized on the low-voltage side. The three primary transformer types are current transformers, electromagnetic voltage transformers, and capacitive voltage transformers [22; 23; 24]. Table 2 delineates the monitoring parameters for each equipment type.