Large numbers of failures occur in coaxial line repeaters which are located in areas subject to high thunderstorm activity. J. Kemp [3] has calculated the voltage induced in coaxial cables which undergo direct lightning strokes, but it has been found that the failure rate that occurs in actual installations may, in some cases, be as great as 100 times the failure rate calculated by Kemp's method. Transient phenomena are generally calculated by means of transforms using Heaviside's operational method, but in the case of transmission lines, because of the need to employ approximations, very significant errors can be introduced. In particular, many of the buried cables installed in recent years have metallic sheaths which are insulated from the earth and it has become necessary to take this fact into account to arrive at accurate results. Using line constants which take into account the skin effect, the induced voltage is here determined by numerical computation of the inverse Laplace transform and from this the failure rate is computed. The results are in almost perfect agreement with actual conditions. In addition, comparing the results obtained by this method with those obtained by the conventional method, we see that when the metallic sheath is insulated from earth the induced voltage becomes large because the lightning wave flowing into the metallic sheath is not attenuated very much and a high excitation voltage is therefore distributed over a long distance. Since this method permits quite complicated computations, it is expected that its application will facilitate development of suitable lightning protection methods.
When a direct lightning stroke hits a cable in which the metallic sheath is insulated from ground a high voltage is induced between the metallic sheath and the cable core and this may result in multiple insulation breakdowns in the cable and associated equipment. Compared to the case in which the sheath is in direct contact with the ground, attenuation of the lightning current in the cable is relatively small and it has been found that this is the reason for the low attenuation of the distributed electromotive force in the circuit formed by the core and the metallic sheath. If the metallic sheath is grounded to cause a distributed flow of lightning current into the earth, attenuation of the sheath current can be greatly increased and it can be expected that the induced voltage will be lowered, reducing the failure rate. Using the inverse Laplace transformation, the sheath current and induced voltage are computed for the case where the coaxial cable is grounded at equal intervals in a repeater section. It is found that grounding at 450‐m intervals results in induced voltage between the inner and outer conductors of the coaxial pair which is about 60% of the voltage for grounding at 3600 m intervals and the failure rate is reduced to about one‐fourth. This method permits accurate determination of the crest value of the inflowing current which will not cause insulation breakdown failure in the cable and permits us to devise lightning countermeasures which will hold the failure occurrence rate to allowable limits.
In regions experiencing intense thunderstorm activity, there are frequent failures of communication lines and equipment due to direct lightning strokes. For the effective application of lightning protection measures, it is extremely important that we have a good understanding of lightning current distributions. The magnetic link is known to be a convenient method of measuring lightning currents at a large number of grounding points. However, when currents of different sign are flowing, due to fluctuation in residual magnetism of the magnetic link, in regions experiencing concentrated lightning strokes it has not been possible to measure the lightning current by means of magnetic links. Using the nonlinearity of the magnetization curve, this paper examines the measurement of currents of different signs using magnetic links. We place magnetic links at two locations having magnetic fields of different strengths and when currents of different signs are present, from the measured values of the residual magnetism in the two magnetic links, we prepared a calibration curve from which we can determine the magnitudes of the currents in each direction. In addition, this method was used in the west central region of Africa to measure cable sheath currents, obtaining lightning crest value distributions which can be considered to be essentially the same as the distributions in Europe and America. This work has verified the effectiveness of this method of lightning current measurement.
Based on the educational experimental method, we investigated the effectiveness of instruction programs for learning fundamental throwing movements. There were 58 participants who were second-graders(28 boys and 30 girls). Using the program that was developed(10 instructions of physical education), we instructed participants in"the active play of throwing."We analyzed their throwing activities from the viewpoints of throwing motion and softballthrowing distance. Throwing motion significantly improved in four of four criteria, and improvement in softball-throwing distance was significant. Participantsʼ feelings about sprints and this programʼs practice had become significantly favorable.
We attempted to investigate the effectiveness of instruction programs for learning fundamental movements in sprint based on educational experimental method.Our subjects were 56 of 2nd graders(experimental group 28:boys 12, girls 16. Control group 28:boys 11, girls 17)at Chiba Pref.. We instructed them in Sept. -Oct. 2009 utilizing the program(8 instructions of physical education) "the active play of sprint and jump" , that we developed. We considered their sprint activities from three viewpoints. We compared these before and after the program. ①movements on 50 m sprints:We evaluated their sprint movements on 14 criteria using VTRs recorded from three directions. ② records of 50 m sprints:We tested records of each 10 m interval, calculated and compared their velocities. ③We conducted surveys on the changes of feelings on sprints and practice of this program through formative evaluation of instructions. The results are as follows: ①Sprint movements were significantlly improved in 9 out of 14 criteria. ②Velocities of interval sprint in each three intervals from 20 m to 50 m speeded up significantlly.③The pre-test highest velocity interval was 10-20 m, but the post-test was 30-40 m. It became the part in the 50 m race where their maximum speed was recorded.④We compared the velocity in 40-50 m interval with the one in the interval where their highest speed was recorded. The relative velocity increased to 97%(post-test)from 88%(pre-test). This shows the reduction of the deceleration in the last interval. ⑤Feelings of the subjects for sprints and practice of this program had became significantlly favorable. However in the control group, the significant change was not found with either the sprint movement or sprint records.A program for lower graders elementary school in physical education"the active play of sprint and jump" utilized in this research was verified effective for learning fundamental movements on a sprint of children.
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