Direct Electrical Field Strength Distribution Determination on Electrical Apparatus by Means of an Electro-optical Miniature Field Sensor

Summary

Numerical field calculations are an important tool during the design process of high voltage devices and relating products with high electric field strengths. Although the accuracy of these simulations can be increased with modern computers, measurements are often necessary to verify certain model assumptions and to get information about required but unknown material properties. During manufacturing or operation of cost-intensive apparatus, a monitoring of the electric field strength could be advantageous for the prevention of critical conditions, which would result in a reduced lifetime or even a damage of the device. In both cases, small potential free sensors with a neglectable influence on the electric field distribution are needed. Conventional E-field sensors cannot be used, because they contain electronic components together with an energy storage device or units for energy transfer so that they become too large, consequently. Miniature probes, which are used in EMC-tests, are connected by cables and therefore they are not potential-free. In addition, as they are based on the measurement of displacement currents, their sensitivity is only small for low frequencies. However, a suitable sensing principle is given by the electro-optic Pockels effect. Although the measuring principle is not new and has already been investigated for voltage sensors it can be used with a similar setup for measurements of the electric field strength, as well. Although the focus of this paper is set on the application as miniature electric field probe and not on the measuring principle itself, a repetitive introduction of the mathematical background is first given, to get a comprehensive overview of the sensor's design and fabrication process and to have a base for comparisons with experimental results. Although the Pockels effect normally can´t be used to measure direct voltages or field strengths, a method is presented how to use this device for DC-apparatus is also given.

Additional informations

Authors

Shengtao Li, Banda Cedric Amittai