【正文】 ly a year, we went to work on the development of the overhead contact line system taking into account shortening of the work period.2. Overhead Contact Line System Suitable for Increased Speed As is widely known, improving the wave propagation velocity of the overhead contact line shown in formula (1) is effective for increasing the running speed. For that reason, we have increased the tension of and decreased the weight of the contact wire. c= (T / r) 1/2 [km/h] (1)T: Tension of the overhead contact line [N], r : Weight per unit length of the overhead contact line [kg/m]Table 1 and Fig. 1 shows the pound catenary equipment deployed for JR East Shinkansen. The “Higher tension heavy pound catenary equipment” in Table 1 is the overhead contact line system that was improved when we increased the speed of the Tohoku Shinkansen to 275 km/h, and the “CS heavy pound catenary equipment” is the system that was improved in tests 15 years before where we successfully increased the speed to 425 km/h using the STAR21 test train on the Joetsu Shinkansen. In the high speed running tests this time, performance equivalent to that of the CS heavy pound catenary equipment was required. We were concerned, however, that development and construction could not be done in time, because the section that needed improvement was as long as approx. 60 km (60 drums) between Sendai and Kitakami.3. Issues in Improvement of the Overhead Contact Line System Issues in Current Collection Performance In running tests in 2003 using an operating train to get basic data for tests with FASTECH360, we measured remarkable strain (stress) on the contact wire over 1,000 μst at 360 km/h. We presumed the cause to be the pound effect of short intervals of 50 m for pantographs of the test train, singlearm contact strips and heavy pulloff arms. Also, we thought that another cause was that wave propagation was prevented because sufficient wave propagation velocity was not secured due to loose tension of the auxiliary messenger wire. Issues in Construction When we conducted improvement work of the CS heavy pound catenary equipment for the running tests of STAR21, for example, it took three days to improve one drum length (see Table 4). It was clear that if applying the same work method to the improvement this time, work would take more than half a year. Considering that and a balanced schedule with other maintenance work, we had to drastically shorten the work period.4. Development of Overhead Contact Lines with Good Current Collection Performance and Easy Improvability In improvements to enable a higher tension heavy pound catenary equipment to handle 360 km/h running, we set the following targets as requirements to improve the current collection performance and,at the same time, to allow effective work.1) Approx. 500 km/h1)* wave propagation velocity for the contactwire2) No change of the total tension of the overhead contact linesystem to avoid modification of support ponents3) Shortening the work period to 2/3 that of past work1Train speed ≤ wave propagation velocity multiplied by approx. or is desirable. In order to achieve 1), we made the diameter of the contact wire thinner (lighter in weight), from 170 mm2 to 110 mm2, and increased the tension from kN to kN. Regarding 2), to maintain kN total tension of the overhead contact line system, the total tension of the messenger wire and the auxiliary messenger wire needed to be decreased. As for the CS system, we decided to decrease the tension of the auxiliary messenger wire while keeping the tension of the messenger wire the same。 but that could result in insufficient wave propagation velocity of the auxiliary messenger wire. And, since we kept the tension of the messenger wire asis in spite of the lighter contact wire, we had to replace all droppers to maintain the height of the contact wire. That work took a lot of time and manpower.Accordingly, we tested a method of reducing the tension of the messenger wire according to the reduced tension of the messenger wire, to eliminate the replacement work of droppers. Also, we added thatreduced weight of the contact wire to the auxiliary messenger wire to improve the wave propagation velocity up to the test speed (360 km/h) with an aim of improving the current collection performance.Formula (2) shows the calculation of the dip in the catenary curve D (see Fig. 2).D=x (SX) r /2T (2)S: Span length, T and r : As in Formula (1) Since the unit weight of the overhead contact line system is changed from kg to kg due to the introduction of 110 mm2 diameter contact wire, approx. kN tension of the messenger wire is desirable based on Formula (2).Table 2 shows the specs of the improved pound catenary equipment for the tests this time.5. Verification of Workability and Current Collection Performance of the Overhead Contact Lines Workability First, we verified the dropper length of the higher tension heavy pound catenary equipment (before improvement) and the improved pound catenary equipment. Table 3 indicates the parison results at the 50 m span length. The difference of the dropper length is within a few millimeters at other span lengths also. Therefore, replacement of droppers is not required. In this way, we could drastically simplify the improvement work pared to the CS heavy pound catenary equipment, as shown in Table. As shown in the above table, we could shorten the improvement work time of almost three days to two days. For the change of the tension of the messenger wire (replacement of anchor yokes), one of our partner panies developed a special jig to shorten the work time. The parison of before and after the improvement work using the data of an electric and track inspection car proved that the status before the improvement such as the height and d