High voltage measuring apparatus based on kerr effect in gas

In testing and monitoring electric power systems, a high voltage measuring system which covers wide frequency range is required. In this study, high voltage measuring apparatus based on Kerr effect in gas is developed. Parallel plate electrodes are placed in a chamber filled with gaseous material up to 0.5 MPa and the electric field between the electrodes is optically measured by Kerr effect in gas. Since the Kerr constant of gas is very small, a White cell structure is utilized to multiply the optical path length and an optical phase modulation technique is also introduced to improve the sensitivity of the measuring system. With the prototype system whose modulation frequency is 50 kHz, ac power-frequency voltage up to 130 kV is measured by using SF6, N2, CO2, and CF3I as the Kerr material. With the modified system whose modulation frequency is raised above 200 MHz, lightning impulses up to 160 kV are measured by using CF3I whose Kerr constant is relatively high.