Dielectric loss of insulating materials

Under the action of electric field, the energy loss of insulating materials is caused by leakage and polarization. In general, the dielectric loss is expressed by the tangent of loss power or loss angle.

Under the action of DC voltage, the instantaneous charging current, absorbing current and leakage current will be adopted. When AC voltage is applied, the instantaneous charging current is reactive current (capacitive current); the leakage current is active current in phase with the voltage; and the absorption current has both reactive current component and active current component. The main factors affecting dielectric loss of insulating materials.

Frequency. When the temperature is constant, the tangent of loss angle reaches a peak at a certain frequency, and the dielectric loss value P increases fastest in unit volume.

Because there are different dielectric losses at different frequencies, a certain frequency must be selected when measuring the tangent value of the loss angle. Usually the materials used in the motor are the tangent of the dielectric loss angle when measuring its power frequency.

Temperature. When the frequency is constant, the tangent of the loss angle will peak at a certain temperature, and the absorption current will cause the greatest loss. In the low temperature region, the active components of leakage current and absorption current are very small, so the tangent of loss angle is very small; in the high temperature region, the loss caused by absorption current disappears, which is determined by leakage loss.

For some organic insulating materials, the tangent of loss angle may have several peaks at different temperatures or frequencies. Therefore, in high-frequency or high-voltage electrical equipment, appropriate insulation materials should be carefully selected according to the relationship between tangent of loss angle and temperature and frequency, so as to avoid peak tangent of loss angle at working frequency and temperature, in order to prevent accelerated aging or thermal breakdown of materials.

The electric field intensity increases. The tangent of loss angle also increases. When the voltage increases to a certain value, the bubble or the edge of the electrode in the medium will appear local free phenomenon, and the tangent of loss angle will suddenly increase significantly. This voltage value is called the initial free voltage. In engineering, the measurement of initial free voltage is often used to check the air gap in the insulation structure to control the insulation quality.