The withstand voltage of outdoor oilimmersed transformers is specified by standards and depends on voltage class and insulation type.

　　Core Withstand Voltage Requirements

　　Power frequency withstand voltage: For 10kV class, the phasetoground withstand voltage of the winding is usually 35kV/1min (effective value), and phasetophase is the same as phasetoground. For 35kV class, it is typically 85kV/1min.

　　Lightning impulse withstand voltage: 10kV class is about 75kV (peak value), 35kV class is about 185kV (peak value), to resist lightning overvoltage.

　　Oilpaper insulation performance: The transformer oil and insulating paper together form the main insulation system, whose withstand voltage directly affects the overall performance.

　　Key Influencing Factors

　　Voltage class: Higher voltage transformers require higher withstand voltage to ensure insulation safety.

　　Insulation state: Aging of transformer oil (moisture, impurities) or damage to insulating paper will reduce withstand voltage.

　　Operating environment: Outdoor conditions (moisture, temperature changes) may affect insulation performance, so the design has additional environmental adaptability considerations.