The safe operation and service life of dry-type transformers largely depend on the safety and reliability of the transformer winding insulation. The temperature of the winding exceeding the insulation withstand temperature causes insulation damage, which is one of the main reasons why transformers cannot operate normally. Therefore, monitoring and alarm control of the operating temperature of transformers are very important.
⑴ Automatic control of the fan: Temperature signals are measured using Pt100 thermistor resistors embedded at the hottest point of the low-voltage winding. The transformer load increases and the operating temperature rises. When the winding temperature reaches 110 ℃, the system automatically starts the fan for cooling; When the winding temperature drops to 90 ℃, the system automatically stops the fan.
⑵ Overtemperature alarm and tripping: The winding or iron core temperature signal is collected through PTC nonlinear thermistor embedded in the low-voltage winding. When the temperature of the transformer winding continues to rise and reaches 155 ℃, the system outputs an over temperature alarm signal; If the temperature continues to rise to 170 ℃, the transformer cannot continue to operate and an over temperature trip signal must be sent to the secondary protection circuit to quickly trip the transformer.
⑶ Temperature display system: The temperature change value is measured by a Pt100 thermistor embedded in the low-voltage winding, and the temperature of each phase winding is directly displayed (three-phase inspection and maximum value display, and historical highest temperature can be recorded). The highest temperature can be output as an analog quantity of 4-20mA, and if it needs to be transmitted to a remote (up to 1200m distance) computer.
