The design of the sensor in electronic voltage transformer

A sensor of electronic voltage transformer (EVT) was designed for the purpose of measurement in the medium/low voltage grids. Among which, a metal electrode was fixed into the center of a polytetrafluoroethylene (PTFE) cylinder, and stuck a double-sided flexible printed circuit board (FPCB) on the cylinder surface. With this arrangement, the metal electrode, the PTFE cylinder and the double-sided FPCB constituted two equivalent capacitors which acted as a capacitive voltage divider. The emphasis of the design was laid on the structure and the size of the capacitive voltage divider. Using FPCB, a pre-amplifier and a filter were installed inside the senor to improve the ratio of signal-to-noise. Compared with the EVTs used in the high-voltage grids, conventional SF₆ gas insulating materials was replaced by PTFE to improve the stability of the measurement system. Further, the operation and maintenance costs of EVTs could be reduced.