Probe for measurements of the DC electric field in air around high voltage apparatus

Knowledge of the external field distribution around high voltage apparatus is of vital importance. As a part of the effort to improve the physical understanding of the DC field distribution outside high voltage apparatus, a small probe that can measure DC electric fields has been developed and a first version of this probe has been tested. The probe is 26 mm long and 12 mm in diameter. It is designed to measure electric fields in the range 10 - 500 V/mm. Results from calibration measurements show that the accuracy of the field measurement (both magnitude and direction) is better than ±5%. As an example of measurements on high voltage apparatus, some results from measurements of the DC field around an HVDC transformer bushing are presented. The results confirm that the probe can give valuable contributions to the understanding of the external field distribution around high voltage apparatus, for existing and future generations of HVDC.