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A separable connector is used for the power cables and apparatuses in renewable energy systems. The shield of the collector cable is sometimes an open circuit at one end to reduce power loss due to the shield current. However, this has a disadvantage from the viewpoint of lightning protection. The semiconductive part of the separable connector is grounded for safety. The ground potential rise due to a direct lightning strike to a wind tower sometimes damages the collector cables and power apparatuses in the wind tower. Combustion in a cable is one of the most serious types of lightning‐caused damage. This paper describes an experimental study on fire ignition in a collector cable caused by a ground potential rise due to a direct lightning strike to a receptor. The mechanism leading to fire ignition is discussed based on the experimental results. This paper also proposes a countermeasure against such fire ignition. [ABSTRACT FROM AUTHOR]

The Tokyo Electric Power Company had conducted field research of voltages and currents in actual distribution lines due to lightning strokes between 1997 and 2001. These results confirm that the distribution line faults are mainly caused by direct lightning strokes to the line. Thus, it is important to simulate lightning performance for direct strokes to establish a lightning protection design of distribution lines. In this paper, statistical data of the observed voltages and currents are analyzed, and the validation of the observation results for the direct lightning strokes using a lightning surge analysis model is conducted. The observation results and the simulation model are useful in clarifying lightning performance in distribution lines. Index Terms--Direct lightning stroke, distribution line, lightning current, lightning protection design, lightning surge analysis model, soil ionization.

Soil ionization occurs around a grounding electrode when current density in the soil exceeds a critical value and reduces grounding resistance. This paper proposes a current- dependent grounding resistance model considering the soil ionization. The proposed model is derived on the basis of energy balance of the soil ionization. The resistivity of the ionization zone depends on energy stored in the zone. Analytical expressions of the model are proposed to estimate the zone resistivity. The model is verified by comparing it with experimental results. Index Terms--Current dependence, energy balance, grounding resistance, hysteresis effect, soil ionization.

This paper investigates the charge versus voltage (q-v) curves of surge corona on transmission lines. Two measurement methods of the q-v curves are proposed, and field test results are shown to validate the methods. Since the new methods do not require a charge-measuring conductor, such as a corona cage, the q-v curves are measured in the real electric-field distribution. One of the methods obtains the amount of charges q by numerically integrating the digitally stored waveform of injected current, assuming that the line is short in length and open ended. Thus, it is suitable for measurement using an experimental setup. The other calculates q from voltage and current waveforms based on the traveling-wave theory, assuming that the line is long enough to expect no reflected waves, and it is applicable to existing 'real' transmission lines. Measured q-v curves are compared with simulated ones, and their physical properties are discussed in the paper. Index Terms--Charge measurement, corona, power transmission lines, space charge, surges.

In this article, lightning-induced overvoltages due to inclined lightning are investigated by a finite-difference time-domain (FDTD) method for distribution lines of a single conductor and a multiphase line (three-phase conductors with a shield wire, utility poles, groundings, and arresters). The FDTD model is validated in comparison with results of circuit-theory-based analytical and numerical calculation methods. In the single conductor line, the influences of inclined lightning on the induced voltage waveform, peak voltage, and voltage profile along the line are investigated with several combinations of lightning distances, earth resistivities, and lightning current waveforms. The induced voltage is significantly influenced by the lightning inclination toward the line (angle θ). The increased ratio of the peak voltage by the angle θ becomes larger with lower earth resistivity and shorter rise time of the lightning current. While the inclination along the line (angle ϕ) makes only minor differences on the peak voltage, the voltage profile along the line becomes asymmetric. In the multiphase line, the influence of the angle θ on the voltage becomes similar to that in the single conductor line. These results clearly indicate that the lightning inclination should be considered for an accurate evaluation of lightning-induced voltages. [ABSTRACT FROM AUTHOR]