Mechanical properties of transformer insulations under DC bias condition

In a traditional vibration model of transformer windings, the insulations are regarded as a linear spring. However, the windings are subjected to dynamic electromagnetic forces during operations. The electromagnetic force has a low frequency component of 50 Hz under the condition of DC bias. In this study, the dynamic mechanical properties of the insulations are extracted from the collected stress and strain data, and a Bouc-wen model is selected to fit the sequential data. In the experiment, a new platform was designed to acquire the stress and strain of the insulations under sinusoidal forces at different frequencies. It is proved that the stiffness and damping are the function of the clamping force. The mechanical parameters of the insulations under normal conditions are different from those under DC bias.