1：Experimental Design and Method Selection:

The study used synchronous optical and electrical PD measurements with a fluorescent silicone optical fiber sensor, opto-electrical converters, and a CCD camera to detect PD and tree growth under DC voltage stress, comparing with AC conditions.

2：Sample Selection and Data Sources:

Cylindrical and cubic samples made of transparent silicone rubber with embedded needle/plate electrode configurations and a fluorescent silicone optical fiber sensor were used.

3：List of Experimental Equipment and Materials:

Equipment includes MPD 600 PD detection system, high voltage source, coupling capacitor, quadrupole impedance, avalanche photo diode converter, photon counter, CCD camera, pulse injection calibration unit, and specific electrodes and sensors. Materials include transparent silicone rubber and optical fibers.

4：Experimental Procedures and Operational Workflow:

Voltage was applied in steps (AC: 1-2 kV rms, DC: 5 kV up to 70 kV) with exposure times up to 30 minutes; PD inception was detected electrically and optically, with images recorded; some samples had pre-incepted AC trees.

5：Data Analysis Methods:

Data were visualized in PRPD plots, and coincidence of electrical and optical pulses was analyzed in time intervals.