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### Abstract

In this study of corona streamer discharges from an impulse generator using a dc power supply, the relationship of the discharge time-lag with the dc bias voltage between the sphere-to-needle electrodes under atmospheric conditions is investigated. Devices utilizing corona discharges have been used to purify air or water, destroy bacteria, and to remove undesirable substances, and in order to achieve fast response times and high power efficiencies in such devices, it is important to minimize the time-lag of the corona discharge. Our experimental results show that (a) the discharge path of a negatively biased needle electrode will be straighter than that of a positively biased needle and (b) the discharge threshold voltage in both the positive and the negative needle electrodes is nearly equal to 33 kV. By expressing the discharge voltage as a power function of time-lag, the extent of corona generation can be quantitatively specified using the exponent of this power function. The observed behavior of a corona streamer discharge between the negative spherical and the positive needle electrodes indicates that the largest power exponent is associated with the shortest time-lag, owing to the reduction in the statistical time-lag in the absence of a formative time-lag.

This work was supported in part by KAKENHI (no. 23560339) from the Japan Society for the Promotion of Science (JSPS) in the Ministry of Education, Culture, Sports, Science and Technology (MEXT).

I. INTRODUCTION

II. EXPERIMENTAL SETUP

III. EXPERIMENTAL RESULTS AND DISCUSSION

A. Discharge behavior

B. Time-lag in discharges

IV. CONCLUSION

### Key Topics

- Electrodes
- 50.0
- Corona discharges
- 47.0
- Direct current power transmission
- 11.0
- Lightning discharges
- 8.0
- Electrical resistivity
- 5.0

##### C02

## Figures

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 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 *μ*s) is connected to a spherical electrode, and a dc power supply (DCPS) consisting of a 0.1 *μ*F 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 CP_{1} and CP_{2} high-resolution current probes.

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 *μ*s) is connected to a spherical electrode, and a dc power supply (DCPS) consisting of a 0.1 *μ*F 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 CP_{1} and CP_{2} 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.

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}).

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} 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}−*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} 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.

*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}.

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.

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.

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.

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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