Based on experiments and calculations, this paper describes the influence of the time constant of the DC starting voltage on the no-voltage time required for successful restarting and the time required to complete the restarting.
(1) The 300kV class DC tension insulator assembly tested in this study was composed of disc-type insulator units used for AC transmission lines. The insulation recovery characteristics of the DC tension insulator assembly after DC arc extinctions of 400 and 4, 000 A were obtained by the switching impulse voltage and simulated DC starting voltage. The results showed that both methods obtained the same minimum values for the required no-voltage time. Thus, we verified the validity of this method to calculate the minimum value of the no-voltage time required for successful restarting based on the insulation recovery characteristics obtained by the switching impulse voltage.
(2) Based on the insulation recovery characteristics obtained by the switching impulse voltage after arc extinction, we calculated the relationships between the required no-voltage time and restarting completion time versus the time constant of the DC starting voltage. As the rising time constant of the DC starting voltage increased, the required no-voltage time decreased and the restarting completion time increased. It was shown that reducing the rising time constant of the DC starting voltage was an effective measure to shorten the restarting completion time after the arc extinction.

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The internal voltage gradient and behavior of column on long gap DC free arcs were analyzed quantitatively. In the analysis, an image processing technique developed by us was applied to the images shot from two orthogonal views by two high-speed video cameras to estimate the three dimensional arc column paths. Objective free arcs were ignited between the rod electrodes with the current in the range of 100 to 2000A and the gap in the range of 1.6 to 3.2m. In addition, some of objective free arcs were placed in the external magnetic field brought about by a large coil. As a result, macroscopic changes with time in terms of the arc voltage gradient along the column path, the ratio of the arc column length to the gap length and the distance from the center axis between the electrodes to the furthest point were derived. All average characteristics were shown as the experimental equations. In addition, the effect of the external magnetic field on the macroscopic velocity of the expansion was studied.

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The insulation recovery characteristics of 500kV class DC insulator assemblies were measured. Switching impulse voltage was applied to a tension insulator assembly and three kinds of suspension insulator assemblies (V, Y and I-arranged) following arc extinction. Arc currents ranged from 400 to 4, 000 A and arc duration ranged from 0.1s to 0.4s.
(1) All insulator assemblies show slow insulation recovery after arc extinction up to an impulse withstand voltage of 100-200 kV. The insulation recovery rates increase at near the impulse withstand voltage of 500kV.
(2) At an arc current of 400 to 4, 000 A, for a duration of 0.1s, the recovery rate for all insulator assemblies decreases with increases in arc current. This is believed to be due to the increases in the temperature of post-arc gas caused by the increased arc currents.
(3) When the arc duration is increased from 0.1s to 0.2s at an arc current of 4, 000 A, the insulation recovery of the V and Y arranged assemblies is delayed by 0.05s. This is believed to be due to the increases in the temperature of post-arc gas caused by the longer arc duration.
(4) By measuring the insulation recovery characteristics of the tension insulator assembly and three kinds of the suspension insulator assemblies with an arc current of 4, 000 A and an arc duration of 0.1s, the minimum value of non-voltage time for a 500kV DC transmission line is calculated to be 0.17s.

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It is very difficult to analyze the behavior of a free arc column from a series of continuous images, e. g. the images obtained using a high-speed video camera. This paper presents a useful method for estimating the three dimensional path of the long gap free arc column using image processing technique without making any subjective judgments. In this method, first of all, a set of two orthogonal digital images of the arc column is entered as the first data. Next, this set of images is processed using a new extraction scheme in order to obtain automatically a linear shape as the extraction area, which is especially useful for arc images including indistinct or low contrast sections. Finally, a set of two linear shapes in the extraction images is transformed into the three dimensional path in the coordinate system at actual size. This paper also describes the results ofapplying this method to continuous images of the long gap free arcs obtained using high-speed video cameras. The change with time of the visualized path, the length and expansion for the arc column with the direct current of 100 and 2, 000A and the gap length of 1. 6m, were derived quantitatively.

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It has been important to maintain high reliability for supplying electric power in recent high- intelligent society. Overhead ground wires (GW) are installed at upper positions of overhead transmission lines in order to prevent lightning attack on conductors. As the sacrifice, GW sometimes gets certain damages including strand-breakage by a severe lightning attack. Recently, optical fiber composite ground wire (OPGW), which has arisen for development of strong GW against lightning attack, in particular for transmission lines passing through areas where “winter lightning” with enormous electric charge occurs, or areas where frequent lightning occurs.
We investigated materials and strand structures to get high lightning-resistant properties and verified by rockettriggered lightning experiments and DC arc tests. As the results, we have developed excellent lightning-resistant OPGW that has fundamental properties equivalent to conventional GW.

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When a fault occurs on transmission or distribution systems due to lightning or overvoltage, there is often an arc discharge at the fault point. The arc discharge, which is caused by a fault current, has a high current, high temperature, strong light emission etc., so it sometimes causes heavy damages to the electric power equipment.
The arc discharge is influenced by the conditions around the arcs: gas, insulation materials, gap length, weather etc. And the arc voltage along the arc column indicates the characteristics of the arc. If the voltage waveforms of the arcs caused by the fault on transmission or distribution systems are classified, it is possible to find the location and the equipment where the fault occured.
This time, the arc voltage data in 6kV class XLPE cables and 6kV class overhead lines were analyzed and an artificial neural network method is applied to classify the arc voltage waveforms. The results obtained from the six artificial neural networks developed show that the artificial neural network method is effective for classification of arc voltage waveforms if adequate input parameters are selected.

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An arc occurred between a pair of parallel conductors is driven by the electromagnetic force. Such traveling phenomena of arcs are found in low voltage circuit breakers, switch boxes or panel boards at accidental condition. Until now, these study have been reported only for relatively low current level, and there are few study for short circuit large current level. Also, the traveling velocity of the arc reported was an average value through whole arcing time. This paper describes the experimental results on the traveling arc between a pair of parallel conductors for alternating current from 600 to 1, 100 A(rms.) with a frequency of 60Hz. The material of conductors is copper and the gap of the two conductors is 15mm. The arc velocity and the arc extinguishing properties are studied. Measurements were made on the average velocity through traveling period and also the instantaneous velocity at each phases of the sinusoidal current. The instantaneous velocity ranged from 2 to 65 m/s and showed a proportional expression to the power of current, same as the average velocity case. Influences of shape of the electrode especially its width upon the arc length, traveling velocity and extinguishing properties were clarified.

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Experimental investigation was performed on an electromagnetically driven arc burning between the edges of parallel flat electrodes in atmospheric pressure. A pair of parallel flat electrodes having a length of 640mm, a width of 20mm and a thickness of 1.2mm is set up horizontally with a gap length of 13mm. After new electrodes were arranged, the arc was sequentially ignited either 100 or 200 times in interval of 30 seconds. The result revealed that after reaching the local maximum at iteration number N_test of 10-15, the travelling velocity of the arc slightly decreased with an increase in N_test for all of the d. c. arc current la in the range from 36.5 to 117 A. The skipping number N_skip of an anode spot per unit length proved to lessen gradually with Ntest for I_a=36.5 and 48 A and to remain constant for I_a=65, 90 and 117 A. For instance, N_siap decreased from 102 to 80 m^-1 with increasing N_test from 10 to 100 times for I_a=36.5 A, while N_sbp was kept at 36 m^-1 for I_a=117 A. Accumulated amounts M_a of the anode erosion and M_c of the cathode erosion, respectively, were found to rise almost proportionally with N_test for all of I_a and to reach 118 and 65 mg at N_test of 200 times in case of I_a=117 A, respectively.

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In the analysis of the particular commercial firm like company, bank and so forth, it is necessary to use the first hand documents such as account books or diaries, so that we can penetrate into their real activity or inner structure in their totalty. Such way of analysis has been frequently used in the cases in Japanese and Western economic history. This is also true with cases of Chinese economic history. This paper tries to show the activities of the Sheng-Tai Hao (生泰号) Company in Nagasaki, by way of the author's detailed research into the account books it possessed, in the hope of filling the gap which has been studied so little. The founder of the Sheng-Tai Hao was a merchant who lived in the last days of the late Ch'ing period and came over to Nagasaki from Fu-chou of Fu-Kien province. Nagasaki has been a sole trading port opened for the sea-trade between China and Japan since the early Tokugawa era. With the opening of that port as one of treaty-ports in 1858, the Chinese merchants had to dwell in the quarters assigned as foreign residence, at that time, the Sheng-Tai Hao establishd its firm im Shinchi-cho within that quarters and remained to stay there until 1948. After the Second World War it changed its business and became a Chinese restaurant. The Sheng-Tai Hao was a firm owned and operated by the Chen family, slong with their relatives and the persons recruited from their hometowns who amounted to about twenty members in all. The Sheng-Tai Hao was a whole-sale dealer, dealing the import of goods from China such as silk, furniture, writing brush, cosmetics, etc. and export of marine-products. In addition, it dealt retail business only partially (about 20% in the sales). The sphere of its business spread very extensively; from Kyushu to Tokyo, Shang-hai, Taiwan, Korea, having had about 970 customers at its heyday. Its gross annual sales of about 90,000 yen plus annual profits of about 20,000 yen which could be ranked as a middle scale firm among the Chinese companies therein. Only a part of the books possessed originally by the Sheng-Tai Hao, nevertheless, the eighteen different kinds of books extant which compose a series of documents ranging from daily records to ledgers of the main and the subsidiary books, are of particular importance. Generally, the Sheng-Tai Hao books could be defined as those compiled by the single entry book keeping method. Its mode of book keeping also could be grouped into such localized one as that prevailed in Amoy area in Southern Fukien. It should be noted that it was kept without any influence from western double entry book keeping technique. The books can be devided into two kinds in size: the larger one, 24 cm by 18.5 cm, and the smaller one, 15 cm by 22 cm. Every entry was writtern by Chinese brush and by use of Shuchou numerals. A line in the midde divides the space into two parts, the upper shows Debtor and the under shows Creditor. All in all, this management and book keeping method should be regarded as a typical example of the old-style Chinese trading companies.

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