T. Nitta

Diamond park and spline: Social virtual reality with 3d animation, spoken interaction, and runtime extendability

Diamond Park is a social virtual reality system in which multiple geographically separated users can speak to each other and participate in joint activities. The central theme of the park is cycling. Human visitors to the park are represented by 3D animated avatars and can explore a square mile of 3D terrain. In addition to human visitors, the park hosts a number of computer simulations, including tour buses and autonomous animated figures. Diamond Park is implemented using a software platform called Spline, which makes it easy to build virtual worlds where multiple people interact with each other and with computer simulations in a 3D visual and audio environment. Spline performs all the processing necessary to maintain a distributed, modifiable, and extendable model of a virtual world that is shared between the participants. For more information visit http://www.merl.com.

Factors Controlling Surface Flashover in SF6 Gas Insulated Systems

Various factors controlling the flashover of solid insulators in pressurized SF6, are reviewed and their influences in gas insulated systems are discussed from a practical point of view. Flashover voltage of clean insulator surface is under the influence of the insulator-metal contact as well as the macroscopic electric field distortion due to the high dielectric permittivity of solid insulator. Conducting particles or even fine metal powder can reduce the flashover voltage. Their effects are strongly dependent on the position they are located, the size of the insulator and gas pressure. Humidity of SF, gas should be strictly governed in SF, gas insulated apparatuses, since the condensation of water can decrease flashover voltage considerably. Decomposition products of SF6 due to the arcing in switchgears are deleterious to epoxy insulators particularly when silica is used as their filler. The decomposition products decrease the leakage resistance on the insulation surface. The field strength near positive electrode is enhanced by the electrolytic effect in the surface conduction layer. In some extreme condition, it initiates tracking on the insulator surface.

Static Electrification by Forced Oil Flow in Large Power Transformer

Static electrification phenomena in forced oil cooled large power transformer are studied on two full scale models of EHV transformer and some other supplemental models. The dc field due to the static charge separation by the flow of oil can possibly exceed the dielectric strength of oil to produce a discharge in oil. The important factors in the streaming electrification and the precautions for the static charge problem are discussed in this paper.

Stability and Long Term Degradation of Metal Oxide Surge Arresters

The thermal runaway process and the long term degradation of metal oxide blocks for a surge arrester are investigated both experimentally and analytically. The critical condition of a thermal runaway of the blocks is formulated. The dynamic stability after surge absorptions is also studied. The stability limit is given as a function of the temperature rise of the blocks due to the surge absorptions. A kind of degradation of metal oxide proceeds under ac stress even at the level lower than that required for the thermal runaway. The life of a metal oxide surge arrester is evaluated combining the degradation process with the above thermal runaway condition. The Arrhenius relation which has been proposed to evaluate the life of metal oxide blocks is discussed in the light of the analysis.

Evaluation of Surge Degradation of Metal Oxide Surge Arrester

The surge degradation of zinc oxide elements under a constant ac stress is investigated experimentally. The results are summed up in a set of formulae and figures from which the degradation of any given condition can be evaluated. The increase ratio of leakage current from the initial value is successfully sed as the indicator of degradation of elements. The two types of elements are investigated concurrently-Formation I being used in production and Formation II a new material. Formation II is found to be remarkably resistant to surges and particularly to ac stress. The influence of degradation on the life of metal oxide surge arrester is discussed on the basis of a dynamic thermal stability. The permissible number of surges during the life is determined for the two types of elements. The performance of arrester is expected to be greatly improved by the use of Formation II.

Statistical Property of the Breakdown of Vacuum Circuit Breakers and its Influence on the Surge Generation in Capacitive and Reactive Current Interruption

The statistical property of the breakdown of a contact in vacuum has been studied experimentally. The results are summarized so as to express the cumulative probability of breakdown as a function of the applied voltage and the spacing of the contact. The expression of the probability distribution is applied to analyze the switching surge generation by a vacuum circuit breaker in the load current interruption of capacitive and inductive circuits. It was shown that a completely restriking -free condition is quite difficult to realize particularly at high system voltages. The statistics of the switching surges due to the restrikings and the problems of circuit protection for them are given based on the analysis.

Model Approach to the Static Electrification Phenomena Induced by the Flow of Oil in Large Power Transformers

Static electrification phenomena induced by the flow of oil have been studied using a model duct of a forced oil cooled power transformer. The discharge observed in full scale model transformers at an excessive flow rate of oil was reproduced in the model duct. The leakage current to the ground induced by the flow of oil is a practical measure of the static electrification process.

Surge Propagation in Gas Insulated Substation

Surge propagation performance in a 550 kV gas insulated substation is studied experimentally and by computer simulation using the Electro-Magnetic Transients Program. Extra capacitance added to the system by the components of GIS such as potential devices, branch buses, circuit breakers deform the wave shape of the travelling surges. Because of the effect of those extra capacitances, experimental values of the surge impedance and the travelling velocity are considerably different from the theoretical values. If we take these extra capacitances into account, however, surge phenomena in GIS can be analyzed properly using the theoretical surge impedance determined by physical dimensions of the GIS and the travelling velocity of light. A simple modeling technique to represent GIS in surge analysis is proposed and its applicability is proved in this paper.

Characteristics of Short Circuit Electromagnetic Forces in Three Phase Enclosure Type Gas Insulated Bus

The effects of the enclosure material to the electromagnetic force and the dynamic performances of the force have been measured in case of 3¿ fault and ¿-¿ fault, using three phase enclosure type gas insulated bus (GIB) models. The analysis for the electromagnetic force has been performed and compared with the experimental results. Mild steel and stainless steel enclosure have little influence to the electromagnetic forces between the phase conductors, whereas the forces are fully reduced by the existence of aluminum alloy enclosure.

Spectroscopic study of high current discharges

A high current arc was developed between carbon electrodes in H 2 , SF 6 , He, Ar, and air at an initial pressure higher than 1 atm. The current peak was above 5 kA and the duration of the current was 250 µs. The temporal and spatial changes of plasma parameters were measured by time-resolved spectrography and high-speed framing camera. The electron density of the plasma was estimated from the Stark broadening of the lines, H β , C II 4267 A, He I 4471 A, and He I 5876 A. Our observations show the following: The arc space is divided into two regions, the bright narrow core and the broad outer flame. The electron density of the core is estimated to be of the order of 1018cm-3and an electron temperature of the order of 104°K is obtained at current peak. Even after current zero, the electron density keeps the order of 1017cm-3regardless of the kind of gas.