Development of Compact 500 kV 8000 a Gas Insulated Transmission Line-Dust Control during Field Jointing and Method for Detecting Conductive Particles

This paper describes the results of studies made on dust control during field jointing and a method for detecting conductive particles after installation in the development of a compact 500 kV 8000 A gas insulated transmission line (GIL). The study on dust control during field jointing proved that field jointing of the compact GIL can be done like conventional GIL in an easily fabricated vinyl shelter without a clean air flow. Harmful conductive particles can be detected with an Acoustic Emission (AE) sensor. This sensor is effective in improving the reliability of the compact GIL when used with a suitable ac voltage during field test. A 120 m long test line of compact 500 kV 8000 A GIL was constructed and, in a long-term field test, proved to have properties sufficient for practical use.     

An ultrasonic linear motor using ridge-mode traveling waves

A new type of ultrasonic linear motor is presented using traveling waves excited along a ridge atop a substrate. The ridge cross section was designed to permit only the fundamental mode to be excited during operation of the motor, with a Langevin transducer used as the source of vibration in this study. The ridge waveguide was first made of lossy media to avoid reflecting vibration energy back toward the vibration source, forming a traveling wave. A 5-mm-wide, 15-mm-tall rectangular acrylic ridge was used to move a slider placed upon it toward the vibration source, in opposition to the direction of the traveling wave transmitted along the waveguide ridge. Using a low-loss 3 x 6-mm aluminum rectangular ridge combined with a damper clamped onto the far end of the waveguide, similar results were obtained. To obtain bidirectional operation, the damper was replaced with a second Langevin transducer, giving a pair of transducers located perpendicularly to the ends of the ridge and driven with an appropriate phase difference. The moving direction of the slider was reversed by shifting this phase difference by about 180 degrees. With this simple configuration, it may soon be possible to fabricate a linear micromotor system on a silicon substrate or other semiconductor wafer adjacent to other electronic and optoelectronic devices.     

Prediction of turbulent flow structure in a fully developed rib-roughened narrow rectangular channel

Fully developed turbulent water-flow structure over one-side repeated-ribs in narrow two-dimensional rectangular channels was investigated experimentally by Particle Image Velocimetry (PIV) and analytically by the standard κ-ɛ and nonlinear κ-ɛ turbulent models. Two rib-pitch to height ratios (p/k) of 10 and 20 were investigated while the rib height was held constant at 4 mm. The rib height-to-channel equivalent diameter ratio (k/De) was 0.1. The streamwise mean velocity and turbulent kinetic energy distributions at six selected axial stations from the center rib for the two Reynolds number (Re) of 7,000 and 20,000 were obtained and compared with the predicted one. The performance ability in predicting separating and reattaching turbulent water-flow between the standard κ-ɛ and nonlinear κ-ɛ models had yielded no clear conclusion. A large-scale turbulent eddy was generated by the rib promoter and then propagated into the mainstream flow, which led to the deformation of the velocity profile. The turbulent kinetic energy was increased about two times higher at p/k = 20 than that at p/k =10 under the two Reynolds numbers. The effect of the p/k value and the Reynolds number (Re) on reattachment length (XR) was investigated and showed that the p/k and Re had no significant effect on the reattachment length beyond a critical value of Re = 15,000 where XR was found to be approximately 4 times of the rib height under water-flow condition.     

Heat transfer characteristics in a condenser of closed two‐phase thermosyphon: Effect of entrainment on heat transfer deterioration

Condensation heat transfer in a closed two‐phase thermosyphon is experimentally examined using two different types of test section. Test Section 1 is a straight‐pipe‐type thermosyphon, whereas Test Section 2 has a large‐diameter evaporator compared with a condenser to minimize entrainment at the evaporator. Condensation heat transfer in Test Section 1 shows much lower heat transfer coefficients than those estimated by a Nusselt theory. This low condensation heat transfer occurs due to a working fluid entrainment. It is confirmed from a result of Test Section 2 that the condensation heat transfer is similar to the values predicted by the Nusselt theory as far as the effect of the working fluid entrainment is negligible and flooding does not occur. A new correlation for the heat transfer coefficient considering the effect of entrainment is proposed. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(3): 212–225, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10030     

Development of 500-kV XLPE cables and accessories for long-distanceunderground transmission lines. V. Long-term performance for 500-kV XLPEcables and joints

500-kV XLPE-insulated cable with an insulation thickness of 27 mm and its joint have been developed for long distance transmission lines. First, in the basic research made from 1989 to 1992, elicited were the performance-determining factors of XLPE cables and joints. Their respective insulation designs were made in terms of these factors. On the basis of these designs, full-sized cables and joints were manufactured in the course of the development research performed from 1992 to 1993. The next step was to evaluate the initial electrical performance to estimate the suitability of our designs. As the final step of our series of researches so far carried out, a long-term loading cycle test was carried out by means of a model line with joints as installed and using the same techniques as employed in the actual commercial lines for full eight months. We could thus verify the long-term reliability for commercial use. The authors discuss EMI, performance dominating effects and quality control, and initial and long term electrical performance testing     

Current-pressure-position triple-loop feedback control of electro-hydrostatic actuators for humanoid robots

To overcome the tradeoff between torque density and response of the backdrivable actuators, actuation by electro-hydrostatic actuators (EHA) is effective. While their backdrivability and energy efficiency was shown in the previous studies, their closed-loop dynamic behavior was not discussed in detail. In this paper, we present the analysis and experimental evaluation of the force control performance of the electro-hydrostatic actuator for the humanoid robot ‘Hydra’. We first present a simplified model of EHA and show that EHA can be simplified as a mass-spring-damper model if all values such as pump torque/velocity and fluid pressure/flow-rate are expressed in the equivalent value seen from the actuator. We also show the comparison between the model and experimentally acquired open-loop dynamic behavior. Then, the evaluation on the force measurement and control performance is shown. The static friction on the rod-seal was 0.46% of the maximum piston force, and with additional strain gauge information, the error can be reduced to 0.28% of the maximum force. We also show that our developed EHA has a pressure control bandwidth of 100?Hz in the fixed piston configuration, which is higher than other state-of-the-art series elastic actuators. In the last of paper, the joint level position and torque control performance of Hydra is examined.     

Parameters determining water temperature of a proglacial stream: The Phelan Creek and the Gulkana Glacier,Alaska

The heat budget of a proglacial stream, Phelan Creek, from the Gulkana Glacier, Alaska, is estimated by using the hourly time series of stream water temperature, discharge and meteorology obtained in the summer of 2006. As an analytical result, the net shortwave radiation and bed friction occupied 32.1 and 38.2% of the total thermal input to the stream, respectively. The time series of the water temperature were simulated by a deterministic model with the coupling of the heat budget and the thermal advective diffusion equation. The simulated result is agreeable to the observed one with the Nash‐Sutcliffe efficiency (NASH) of 0.747 and the root‐mean‐square error (RMSE) of 0.236°C over the observation period. However, under condition that the rainfall of more than 1 mm h^?1 occurs continually for more than a day, the simulation was less reasonable with NASH = 0.225 and RMSE = 0.226°C. This is probably because the relatively warm subsurface flow input to the stream channel from the non‐glacial area. Copyright © 2009 John Wiley & Sons, Ltd.     

Critical heat flux at high velocity channel flow with high subcooling

A quantitative analysis of critical heat flux (CHF) in heated channels under high mass flux with high subcooling was successfully carried out by applying a new flow model to the existing CHF model of a macro-water-sublayer on the heated wall and steam blankets over it. The CHF correlation proposed could correctly predict the existing experimental data for circular tubes of 0.33–4 mm in diameter with mass flux of 124–90 000 kg (m² s)⁻¹ and inlet water subcooling of 35–210 K at 0.1–7.1 MPa, resulting in CHF of 4.2–224 MW m⁻², and for rectangular channels of 3–20 mm gap with a mass flux of 940–27 000 kg (m² s)⁻¹ and inlet water subcooling of 13–166 K at 0.1–3.0 MPa, resulting in CHF of 2.0–62 MW m⁻². An error of the CHF correlation has also been estimated.     

Development of 3-DOF wrist mechanism for electro-hydrostatically driven robot arm

Electro-hydrostatic actuator (EHA) has backdrivability and is suitable for a robot system that cooperates with human. However, its design methodology to miniaturize and to generate high pressure has not been established. We develop a robotic arm, all joints of which are actuated by EHAs. This paper reports the development of the vane motor type EHA and a wrist mechanism using the EHA. We employ a single vane motor for a wide motion range. In order to suppress internal leakage, we carefully set the clearance of the EHA and made the rigid casing by using ceramics disks. It is confirmed that the internal leakage of the new EHA is significantly reduced compared to that of the previous model. The wrist mechanism has three degrees of freedom, consisting of three vane motors in series. The flow path between a hydraulic pump and a vane motor is designed using metal pipings, swivel joints and manifolds are presented for a compact wrist mechanism. We validated the fundamental performance of the developed wrist mechanism through experiments.