Pressure and stress characteristics of transformer tank with power-frequency arc fault in oil

Transformer tanks typically have thin-walled structures. The internal power-frequency arc is one of the most serious transformer faults, which is likely to cause tank rupture and fire, and has attracted wide attention in recent years. In this study, a series of power-frequency arc experiments were conducted in oil to analyse the pressure and stress characteristics of the tank surface. Stress has not yet been reported and this pressure is a new form of pressure loading. The results show that the pressure wave generated by the arc comprises two parts: quasi-static pressure (0-500 Hz) and shock pressure (above 500 Hz). The arc energy affects the quasi-static pressure and can cause quasi-static stress, which increases slowly during discharge and peaks simultaneously when the arc is extinguished. Shock pressure can cause a dynamic response in the tank. The shock pressure peaked at approximately 0 ms and decayed rapidly, whereas the inertia of the tank and oil led to a maximum stress on the tank surface at 6 ms. In the 10 kA arc experiment, the peak shock stress was approximately 25 MPa, resulting in a maximum strain rate of approximately 0.680 s-1. However, in many transformer explosion accidents, the strain rate might have reached 20 s-1 or even higher. The dynamic and static stress simulations of the tank were conducted based on the measured pressures. The stresses obtained from the measurements and simulations indicate that the shock stress caused by the shock pressure may be higher than the final quasi-static pressure. Existing static stress simulation methods for transformer tanks are inappropriate. It may have underestimated the dynamic stress; therefore, the dynamic response of a tank with an arc fault must be considered in the future.