Voltage measuring device and gas-insulated switching apparatus

A voltage measuring device comprising:

• a light source;
• a polarizer to polarize light emitted from the light source;
• a grounded conductor provided in such a way as to be separated from a high-voltage conductor, the grounded conductor being grounded;
• a crystal end face electrode having a floating potential, the crystal end face electrode being out of contact with the grounded conductor and the high-voltage conductor;
• a Pockels cell to transmit the light emitted from the polarizer, the Pockels cell being provided between the crystal end face electrode and the grounded conductor;
• an analyzer to transmit the light reflected by the Pockels cell;
• a photodetector to detect the light emitted from the analyzer;
• an intra-crystal electric field measurer to convert a voltage output by the photodetector into an intra-crystal electric field and output the intra-crystal electric field;
• a bias electrode provided between the high-voltage conductor and the crystal end face electrode in such a way as to be out of contact with the crystal end face electrode;
• a bias supply connected to the bias electrode;
• a bias supply controller to control the bias supply so as to keep an internal electric field of the Pockels cell at zero, the bias supply controller being connected to the intra-crystal electric field measurer;
• and
• a measurement voltage calculator to obtain a voltage of the high-voltage conductor based on results output by the intra-crystal electric field measurer and the bias supply controller.