Flashover Characteristics on the Gap of Rod to Plane Applied Bipolar Impulse Voltage

This paper describes the fifty percent flashover voltage and the V-t curve for a rod-plane gap applied bipolar impulse voltage, and the behaviour of the space charge in the gap. In the distribution line, the bipolar impulse voltage had been observed frequently when lightning hit near it. Then, the bipolar impulse wave used in the experiment was decided as the composite voltage wave made from the preceding wave of positive (or negative) polarity, 20/500 μsec. and the following wave of negative (or positive) polarity, 2/60 μsec. The connecting time of the abovementioned two pulses was decided as 20±5 μsec.. The test gap was the rod-plane gap with a gap length of 6.0cm, and the rod diameter of 1.0cm as a non-uniform field, mainly. As for the experimental results, when the applied preceding impulse voltage was positive polarity and a corona occurred, the fifty percent flashover voltage was up by 15%. And, when the preceding impulse voltage was negative polarity and with a corona, the fifty percent flashover voltage was down by 10%. The space charge phenomena as the cause given by the abovementioned results were observed by using an image converter camera

The development of hypothesis testing behaviour in children

This experiment investigated whether six, eight, and ten year-old children are capable of simultaneously using more than one hypothesis at a time, or whether children can test only one at a time in a discrimination learning situation

Experimental Approach to Shielding and Reducing Effects on Ion Currents and Electric Fields at Earth Level under a DC Transmission Line

Use of a d. c. transmission line to find a way to reduce ion currents and electric fields at earth level is a most important matter for environmental safety. This paper discusses the relation between the ion currents and the electric fields at earth level, measured by using a unipolar d. c. transmission line scale model and a bipolar d. c. transmission line. Electric fields at earth level were calculated by means of the image charge method without taking into consideration the space charge caused by the d. c. line. The middle scale models for the unipolar and the bipolar d. c. lines were set at the height of the d. c. lines at 2m. Both types of scale models were set up in a sufficiently spacious room. Two small scales for the unipolar and the bipolar d. c. lines, with the height of the d. c. lines set at 20cm above the earth and the separating distance between the two d. c. lines set at 35 to 75cm, were placed in a suitable roomo. Both the experimental results are discussed here in comparison with the calculated fields. As a conclusion, in using the model unipolar d. c. line with a shielding wire, the shielding effects for both the electric fields and the ion currents at earth level nearly coincided with the calculated fields. However, in using the model bipolar d. c. lines, the reducing effect for the ion currents dind't coincide with the ealculated fields, actually not quite half of the calculated fields. In particular, the ion currents, at earth level on the positive voltage side were reduced very well, relative to those on the negative voltage side. They were measured in relation to the ratio of the separating distance of the bipolar d. c. lines to the the height of the d.c. line from earth level

Discharge Phenomena of the Insulator Assembly and Occurrence of Critical Cascading Flashover Phenomena

This paper describes conditions for an occurrence of cascading flashover phenomena on the insulator assembly with the use of a high voltage transmission line by experiments in a laboratory room. The 154 kV suspension insulator assembly is employed as testing apparatus which consists of a chain of 9 standard suspension insulators equipped with an arcing horn. In the experiments, the apparatus is separated into two parts consisting of a bare insulator chain and a pair of arcing horns. The lightning impulse with positive polarity or negative are applied to the test pieces, and the over-voltage is used in those tests. Thus, the creeping flashover occurred with short lag time. The V-t curves and the 50% cascading flashover voltage were obtained and the prebreakdown phenomena were observed from the tests, then, it is concluded that the critical cascading flashovers occur with short time lag (T₀＝1.8 μ sec. or less) and a high steepness (1833 kV/μ sec. or more), and corona on the insulator surface starts from negative side electrode

Space Charge Measurement Using a Small Sphere as a Probe

A method for measuring the space charge produced by impulse corona in an air gap has been developed, using a small sphere as a probe. The probe is located far from the corona volume, and is connected to earth through resistance or capacitance. The probe induces a current or charge by electrostatic induction from the space charge. Since the induced charge on the probe is proportional to the space charge, it is possible to analyze the magnitude and polarity of the space charge from the probe signal. It is also possible to analyze the temporal variation caused by corona growth or movement of the space charge