An optical measurement method of DC total electric field with space charges based on probe self-rotation modulation.

• An optical measurement method for total electric field with space charge has been proposed. • The problem of internal polarization and external charge accumulation are solved through self-rotation modulation. • The rotation mode and its impact on sensitivity are studied. • The tests are completed using a small model of a unipolar HVDC transmission line. Researching the measurement of DC total electric field with space charges (Poisson field) can help establish a monitoring system for the electromagnetic environment of UHVDC transmission lines and protect the health of the ecological environment. This paper proposes a DC total electric field optical measurement method based on the Pockels effect and probe self-rotation modulation. It can address the issues of internal charge drift and external charge accumulation in traditional optical probes when measuring DC electric fields with space charges. Theoretical analysis was conducted on measurement under probe rotation, and the optical modulation system was integrated into a probe with dimensions of 60 mm × 30 mm × 20 mm. A self-rotating platform for the probe was designed, and the influence of rotation mode on the results was analyzed. It was found that the sensitivity was higher when using the horizontal-horizontal mode. The signal processing system was tested, showing that the probe retained around 50 % of its original output when rotating at low speeds (frequency 1–3 Hz), fully meeting the measurement requirements. The test platform has been constructed, and the probe's sensitivity was assessed under an AC electric field and validated under a DC electric field. Finally, the optical method proposed in this paper was used to measure the DC total electric field with space charges under a small model of a unipolar HVDC transmission line. Five locations under the line were selected as measurement points, and the results were compared with those obtained from a field mill probe and numerical simulation. This comparison indicates that the proposed method agrees with experimental and simulation results. The average sensitivity of the self-rotating optical probe was 3.71 mV/(kV/m). The error did not exceed 5 % in high-field strength areas (above 20 kV/m) and was also controlled within 15 % in low-field strength areas (below 20 kV/m). [ABSTRACT FROM AUTHOR]