Katsuharu Iwamoto

Liquid-level sensor with optical fibers

A liquid-level sensor, consisting of three optical fibers, is described. A light is projected onto an oil surface through a transmitting fiber. A receiving fiber picks up the light reflected from the oil surface. A reference fiber transmits the light from a light-emitting diode back and forth along the same path as that of the transmitting fiber and the receiving fiber. Division is accomplished by using the reflected signal and the reference signal, so it becomes possible to eliminate apparent distance variations that are due to the variations in light intensity, which may be caused by external forces and temperature changes. The distance range is 100 mm.

Pressure sensor using optical fibers

A diaphragm-type pressure sensor consisting of three optical fibers is described. A light is projected onto a pressure-receiving diaphragm via a transmitting fiber. A receiving fiber receives the reflected light from the diaphragm. A reference fiber transmits light from an LED back and forth along the same path as the transmitting fiber and the receiving fiber. Division is accomplished by using the reflected signal and the reference signal, so it becomes possible to eliminate apparent pressure variations due to variations in light intensity, which may be caused by external forces and temperature changes. The maximum pressure is 39.3 MPa.

Gas-flow Simulation with contact moving in GCB considering high-pressure and high-temperature transport properties of SF/sub 6/ gas

This paper addresses a thermal gas-flow simulation in gas circuit-breaker (GCB) chambers, introducing SF/sub 6/ gas constants up to a pressure of 10 MPa and to a temperature of 30 000 K. In the simulation, moving parts, such as nozzle, movable arcing contact, and operating rod, are moved with the opening motion of GCB to see if different results are produced from the conventional simulation method, in which fixed parts in the real GCB are moved. As a result, as far as the pressure profile in the puffer chamber is concerned, it is confirmed that this simulation method can produce better results than the conventional method for the hybrid-puffer-type chamber.

Preliminary investigation for application of MEMS acceleration sensor to SF 6 gas circuit breaker

With an aim of applying a MEMS (micro electrical mechanical system) acceleration sensor as a diagnosis tool for a mechanical degradation of a SF6 gas circuit breaker, we investigated the fundamental characteristics. It is confirmed that the MEMS acceleration sensor with a maximum acceleration number of 250 G and a frequency band width up to 400 Hz can be applied to measure an acceleration number of the model GCB, while all tests were carried out under no electromagnetic stresses on the GCB. In addition an optical acceleration sensor by using a photo-reflector was developed to be applied in a severe electromagnetic field. The first model of the optical sensor showed insufficient frequency band width for the purpose.

Numerical Simulation of Unsteady Behavior of Rotary Arc Plasma under Magnetic Field

We are currently developing a time-dependent, three-dimensional computational magneto-plasma-dynamics (MPD) code for simulating a rotary gas circuit breaker utilizing an external applied magnetic field. In order to test the computational code under development, we have conducted the numerical simulation of arc plasma in a cylindricalshaped chamber filled with SF6 gas in the presence of externally applied magnetic field. The present paper describes details of the MPD model in the computational code, and also shows numerical simulation results.

Time-dependent Magnetohydrodynamic Simulation of SF6 Rotary-arc Plasma with Consideration of Electromotive Force

We have carried out time-dependent three-dimensional magnetohydrodynamic numerical simulations of rotary arc plasma in a simple chamber filled with SF6 or CO2 gas under an externally applied magnetic field. In the numerical simulations for both the gas conditions, the arc current and the strength of applied magnetic field are set to DC 2 kA and 1.2 T, respectively. In this paper we show that the rotation of arc plasma induced by applying the magnetic field increases the arc voltage and the gas pressure in the chamber, and also these phenomena with applying the magnetic field are much clearly observed in CO2 gas than SF6 gas. Furthermore, we show from the numerical simulations of rotary arc plasma in SF6 gas that the rotational speed of arc plasma becomes slow by accounting for the electromotive force induced by the MHD interaction, but the induced electromotive force has only a little influence on the arc voltage and the gas pressure in the chamber.

Research on acceleration phenomena with test equipment of simulating puffer type gas circuit breaker

The diagnosis was investigated by using the acceleration measurement for mechanical failure and degradation of a SF6 gas circuit breaker (GCB). The mechanical model GCB was fabricated to produce similar acceleration characteristics to a real GCB. The MEMS (Micro Electro-Mechanical System) sensor was adopted for the purpose of confirming its applicability with the well-established piezoelectric accelerometer. The acceleration characteristics of the model GCB was generally similar to the real GCB of 300kV class, except the high frequency component. The MEMS sensor application was feasible with some limitations. It was indicated a mechanical failure could be detected by the acceleration measurement.

Flow Visualization of Flow in Nozzle Used in Gas Circuit Breaker.

It is important to understand the aerodynamic characteristics of a circuit breaker nozzle with a complicated inner shape. Therefore, the experimental apparatus was fabricated with air instead of SF6 as the working fluid. Experiments were conducted using an acrylic nozzle model and a glass nozzle. The flow visualization of flow in the acrylic nozzle model was conducted using the laser light sheet technique, and the flow visualization of flow in the glass nozzle model was conducted using the laser shadowgraph method. Moreover, the flow velocity in the glass nozzle model was measured using a laser velocimeter. Judging from the experimental results, the weak shock is formed in front of the electrode in the circuit breaker nozzle.

Free Convection Cooling in Large Cabinet.

A large cabinet model(812 by 812 by 1856 mm) containing a heater was fabricated. Experiments were conducted using this cabinet model for free convection cooling and for forced convection cooling by a fan. The measured internal temperature distribution of the cabinet model was compared with the prediction on the basis of flow network method. This calculation method assumes the flow to be one-dimensional, while friction, buoyancy and radiation effects are taken into account. The results of calculation agree well with the experimental data in the case of forced convection cooling, however a discrepancy of about 5% between the experiment and the prediction was observed in the case of free convection cooling.