Analysis of Electromagnetic Transient Process Under Lightning Impulse Voltage for Silicone Rubber Cast Dry-type Transformer

Dry-type transformer cast with recyclable silicone rubber materials has high overload capacity, low vibration and noise. It is also environment friendly. However, the transient potential and electric field distribution in the winding when exposed to lightning impulse voltage has rarely been reported for this type of transformer. In this paper, the electromagnetic transient process of a 10 kV silicone rubber cast dry-type transformer is analyzed. First, a two-dimensional(2D) axisymmetric finite element model is established. By dividing the high voltage winding into 35 disk coils, the resistance, inductance and capacitance parameters of each disk coil are extracted, and a lumped parameter equivalent model is constructed. Then, the disk to ground and interdisk voltages under the lightning impulse voltage are calculated. By assigning the voltage data to the 2D simulation model, transient potential and electric field distribution in the silicone rubber and the air channel can be calculated, therefore the weak insulation area can be identified. The presented approach allows for fast and accurate calculation of the electromagnetic transient process in transformer windings, which can benefit the insulation structure design and optimization for silicone rubber cast drytype transformers.