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.