What are the impacts of temperature on AIS voltage transformers?

Impact on Insulation Performance

• Changes in Insulating Material Properties: AIS voltage transformers rely on air as the insulating medium, and they also contain some solid insulating materials, such as insulating paper and insulating bushings. When the temperature rises, the migration and evaporation of moisture in solid insulating materials like insulating paper will accelerate, resulting in a decrease in the electrical strength of the insulating materials and an increased risk of insulation breakdown. When the temperature drops, the insulating materials may become brittle, with reduced mechanical properties. When subjected to electrical or mechanical stress, cracks are likely to occur, which in turn affects the insulation performance.
• Changes in Air Insulation Performance: When the temperature rises, the density of air decreases, the distance between gas molecules increases, and the insulation strength of air will decline. This means that under the same voltage, gas discharge phenomena such as corona discharge and spark discharge are more likely to occur, affecting the normal operation of the voltage transformer. When the temperature drops, the insulation strength of air will increase to some extent. However, extremely low temperatures may cause condensation on the surface of the equipment. Moisture adhering to the surface of the equipment will greatly reduce the surface insulation performance and cause faults such as flashover.

Impact on Electrical Parameters

• Change in Transformation Ratio: Changes in temperature will cause changes in the winding resistance of the voltage transformer. According to the temperature characteristics of resistance, the resistance of general metal materials increases with the increase in temperature. The change in winding resistance will affect the transformation ratio accuracy of the voltage transformer. For example, when the temperature rises, the resistance of the primary winding increases. Under the same primary voltage, the primary current will decrease. According to the principle of electromagnetic induction, the secondary voltage will also change accordingly, resulting in deviations in the measured voltage value and affecting the accuracy of metering and protection devices.
• Change in Capacitance Parameters: There are capacitive components inside the voltage transformer, such as bushing capacitance. Changes in temperature will cause changes in the properties of the capacitance medium, resulting in changes in the capacitance value. Changes in capacitance parameters will affect the voltage distribution and phase characteristics of the voltage transformer, and have an impact on the correct operation of the relay protection device.

Impact on Mechanical Structure

• Thermal Expansion and Contraction: AIS voltage transformers are composed of a variety of materials, and different materials have different coefficients of thermal expansion. When the temperature changes, various components will undergo different degrees of thermal expansion and contraction. If this thermal stress cannot be effectively released, it may cause loosening of the connections between components, such as the connection between the winding and the iron core, and the connection of the secondary terminal, which in turn causes faults such as poor contact.
• Sealing Performance: Temperature changes will also have an impact on the sealing structure of the voltage transformer. High temperatures may cause aging and deformation of the sealing material, reducing the sealing performance and causing external dust, moisture, etc. to enter the interior of the equipment, affecting the normal operation of the equipment. Low temperatures may cause the sealing material to become hard and brittle, losing its elasticity and similarly damaging the sealing effect.