Schematic diagram of spherical and needle electrodes made of stainless steel (SUS304). The spherical electrode is 62 mm in diameter, whereas the needle electrode has a length of 60 mm, a cross-sectional diameter of 1.2 mm, and a spherical tip of radius 0.6 mm. The inter-electrode gap length (d g) is maintained at a constant value of 20 mm, and the gap consists of air under normal atmospheric conditions.
Schematic diagram of experimental setup. A lightning impulse generator (LIG) with a standard lightning impulse waveform (e.g., an IEC standard of 1.2/50 μs) is connected to a spherical electrode, and a dc power supply (DCPS) consisting of a 0.1 μF charged capacitor and a 4.7 kΩ discharge resistor is connected to a needle electrode. The LIG and DCPS are commonly charged by the output voltage of a half-wave rectifier using diode D+ or D−. Streamer discharge waveforms are measured using a HVP: high-voltage probe and CP1 and CP2 high-resolution current probes.
Emission photographs of corona streamer path: (a) positive sphere-to-negative needle (pS−nN) discharge, (b) negative sphere-to-positive needle (nS−pN) discharge.
Discharge waveforms of voltage (V d) and current (I d) for (a) pS−nN electrodes, (b) nS−pN electrodes. The time difference between V d and I d represents the time lag (t d).
V d−t d as a function of electrode shape and polarity at V d = V 50, where S−S and S−N represent the positive sphere-to-grounded sphere and positive or negative sphere-to-grounded needle electrodes, respectively. Regressions of V IG, V IG+, and V IG− are shown as two solid and a dashed lines, respectively, with analytical expressions next to the curves.
V d−t d at V d > V 50 in positive sphere-to-grounded needle (pS−gN) and negative sphere-to-grounded needle (nS−gN) electrodes. Regressions of V IG+ and V IG− are shown as solid and dashed lines, respectively, with analytical expressions next to the curves.
V d , V IG+, and V DC− as functions of t d in a pS−nN electrode at V d > V 50, where the absolute voltages of V d, V IG+, and V DC− are related by V d = V IG+ + V DC−. Regressions of V d, V IG+, and V DC− are shown as solid, dashed, and short-dashed lines, respectively, with analytical expressions next to the curves.
V d, V IG−, and V DC+ as functions of t d for a nS−pN electrode at V d > V 50, where the absolute voltages of V d, V IG−, and V DC+ are related by V d = V IG− + V DC+. Regressions of V d, V IG−, and V DC+ are shown as solid, dashed, and short-dashed lines, respectively, with analytical expressions next to the curves.
Power exponent (k) as a function of electrode configuration and polarity, where S−N ⇒ pS−gS at V d = V 50, S−N (1) ⇒ pS−gN and nS−gN at V d = V 50, S−N (2) ⇒ pS−gN and nS−gN at V d > V 50, and S−N (3) = > pS−nN and nS−pN at V d > V 50.
Laue distribution based on survivor probability (p) and t d in (a) positive and (b) negative sphere sets representing the polarity combinations sphere-to-sphere and sphere-to-needle.
Values of t d (composed of t f and t s) in (a) positive sphere (pS) and (b) negative sphere (nS) sets, where (1) and (2) represent the conditions V d = V 50 and V d > V 50, respectively.
Dependence of t d on k for the polarity combinations “pS set” and “nS set.” The black-filled circles represent the pS–gS electrodes without corona generation.
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