When technical engineers conduct inspections at 220kV substations, they often encounter situations where dissolved gases in main transformer oil need to be periodically sampled and sent for testing. The traditional offline chromatography analysis process includes on-site sampling, transportation, laboratory degassing, and injection analysis, typically taking about a week. During the interval between two tests, if latent overheating or discharge faults exist internally, they may not be detected in time. Online monitoring devices deploy the analysis process directly beside the transformer, automatically completing oil sample collection, gas separation, and detection at set intervals, with data uploaded to the backend via communication networks.
Laboratory gas chromatographs pursue multi-component, high-precision offline analysis capabilities, suitable for fault confirmation and arbitration testing. Their advantages lie in high component separation and flexible calibration, but they require manual sampling and sample pretreatment, making it difficult to avoid gas escape and contamination during transportation. Online monitoring devices focus on continuous trend tracking, typically monitoring characteristic gases such as hydrogen, carbon monoxide, carbon dioxide, methane, ethylene, and acetylene, with detection intervals of 6 hours, 12 hours, or 24 hours. The two are not substitutes but form a complementary system of "online screening, offline confirmation." For unattended substations or important hub transformers, online devices can provide continuous dissolved gas content curves in oil, assisting operation and maintenance personnel in determining whether abnormal gas production rates exist.
The device uses imported specially designed detectors, optimized for detection sensitivity and repeatability of various gases, with error range controlled within ± requirements. Oil samples enter the degassing module through a permeable membrane, with a membrane lifespan of about 8 years; the chromatographic column achieves gas component separation with a lifespan of about 6 years; the sensor lifespan is about 10 years. Data storage capacity is no less than 10 years, meeting long-term trend traceability requirements. The operating ambient temperature range covers -40°C to 65°C, adapting to outdoor installation conditions. The default detection interval is 24 hours per test, and users can adjust to 6 hours per test or 12 hours per test according to transformer voltage level and operating conditions.
The device is typically installed beside key oil-filled equipment such as main transformers in power plant booster stations, main transformers in grid hub substations, converter transformers, and reactors. For high-load industrial transformers, detection frequency can be set according to load rate and cooling method. At northern outdoor sites with large ambient temperature spans, low-temperature startup and heating unit configuration of the device need to be confirmed.
