91_optical - IEEETransectiom on Power Delivery Vol. 6 ,...

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524 IEEE Transectiom on Power Delivery Vol. 6, No. 2, April 1991 DC-PROBES FOR ELECTRIC FIELD DISTRIBUTION MEASUREMENTS Sven P. Hornfeldt High Voltage Research Swedish Transmission Research Institute Box 107, 5-111 01 LUDVIKA, Sweden Abstract It is desired to measure the external electric field distribution of components for high voltage DC transmission. This information is useful in the development of such components. By measuring the field under a variety of ambient conditions, the performance of both the external and the internal insulation of the component can be assessed. The principles of how DC fields can be measured using an isolated probe coupled by fiber optics to a separate receiver are discussed. The construction of some practical systems are described. We have measured the electric fields around a full size wall bushing energized to 600 kV in rain. The results of this and other measurements are presented. They demonstrate the usefulness of isolated DC field measurements. Keywords: High Voltage DC, Field Measurements, Fiber-Optics. 1. Introduction High voltage direct current (HVDC) has been utilized for power transmission for more than 30 years. Today about 3% of the transmitted electric power is carried by DC lines. This fraction is expected to increase during the coming years. HVDC systems for voltages up to 600 kV are now in opera- tion; the voltage levels are expected to increase in the future. In order to develop improved insulation systems for HVDC components it has become evident that it is desirable to have methods to measure the electric field distribution in the vicinity of the components and under a variety of ambient conditions, follow the field variations with time. It is of special interest to investigate the field pattern just before a flashover is initiated. A system to measure electric fields in a variety of environmental conditions could be designed such that the measuring signal is transmitted by means of an optical fibre from a field sensing probe at high potential to a registering unit at ground potential. Building the meter in two parts allows the probe, which has no galvanic contact with the other components of the system, to have the form of a sphere, with a diameter as small as possible to make the distortion of the field to be determined minimal and easy to calculate. The probe may be metallic or dielectric. Any stationary probe will collect charge when exposed to a DC field in open air. In time, all parts of the probe will reach the same potential, and the 90 SW 325-1 PWRD by the IEEE Power System Instrumentation & Measure- ments Committee of the IEEE Power Engineering Society for presentation at the IEEE/PES 1990 Summer Meeting, Minneapolis, Minnesota, July 15-19, 1990. Manuscript submitted January 27, 1989; made available for printing May 18, 1990.
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91_optical - IEEETransectiom on Power Delivery Vol. 6 ,...

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