An electret transducer for impulse voltage measurements

A method for detecting impulse voltages in transmission and distribution lines that uses an electret as the element of transduction is proposed. The sensor consists of two metallic electrodes separated by a piece of dielectric (Teflon FEP) and an air gap. The impulse voltage produces an electric discharge in the gap and charges are transferred from the electrode to the dielectric surface, forming the electret. For a sensor with planar electrodes, a linear relationship between the applied peak voltage V_p and the electret potential was found, and the sensor can be used in the range of 0.8<V _p<1.9 kV. For a sensor with a cylindrical electrode, the experimental results show a well-defined relationship between the charged area of the electret and V_p, and this was employed to measure V_p in the range between 0.8 and 6 kV