Ryoichi Hanaoka

Demagnetization Analysis of Additional Permanent Magnets in Salient-Pole Synchronous Machines With Damper Bars Under Sudden Short Circuits

To improve output performance of salient-pole synchronous machines, permanent-magnet-assisted salient-pole synchronous machines (PMa-SMs) that have permanent magnets (PMs) between the field poles were previously developed. The PM effect of increasing the output power and the terminal voltage has already been confirmed by finite element analysis (FEA) and experiments under steady states. In this paper, demagnetization in the PMs due to sudden three-phase short circuits is evaluated by FEA. The results show that irreversible demagnetization arises in the PMs of a PMa-SM with relatively smaller circumferential PM length. Effects of the PM shape and damper bars on the irreversible demagnetization are also investigated. The results show that making the PM shape a rectangle and adding damper bars on the outer surfaces of the PMs are effective to reduce the demagnetization, while increasing the number of the conventional damper bars is not effective.

Properties of EHD pump with combination of rod-to-rod and meshy parallel plates electrode assemblies

A high pressure required to drive the liquid can be generated by the compact electrohydrodynamic (EHD) pumps with multiple pairs of the rod-to-rod and meshy parallel plates electrode assemblies arranged in series. In this work, the performance of EHD pumps with electrodes up to nine pairs has been examined as a function of the applied voltage using a semi-insulating liquid. The pressure generated by energized electrodes gives rise to the vigorous liquid flow and the liquid ejects from the pump outlet. The flow direction always is from the cathode toward the anode. The pressure increases with nearly the square of the applied voltage and in proportion to the number of electrode pairs. The maximum pressure head achieved with a series of nine electrode pairs is 25.3 kPa at 18 kV with maximum power consumption of 7.2 W. The generated pressure is maintained stably at constant level of the corresponding value. EHD pumping is attributed to conduction pumping based on an unbalance of heterocharges with single ionic polarity in the vicinity of the anode and cathode.

Creeping discharge developing on vegetable-based oil / pressboard interface under AC voltage

The behavior of creeping discharges developing on the pressboard surface was investigated experimentally in palm fatty acid ester oil, natural rapeseed oil and commercial mineral oil under variable ac voltages with 60 Hz, respectively. The oilimpregnated pressboard was used as the solid dielectric and it was immersed completely into the same oil. The tungsten needle electrode was installed in the one side of pressboard surface without the counter electrode as a high voltage electrode and a grounded fine copper rod was adhered tightly in the other side of pressboard as a back side electrode. The discharge shape, streamer extension, streamer velocity and tracking at the oil/pressboard interface were observed as a function of the time and voltage by using a still camera equipped with a night viewer. Simultaneously, the discharge current and dissipated energy were measured. The gas components dissolved in oils by the creeping discharge were also examined by the dissolved gas-in-oil analysis (DGA). In this paper, it is presented that there are distinctive events due to the occurrence of creeping discharges.

Steady-State Analysis of a Dual-Winding Reluctance Generator With a Multiple-Barrier Rotor

This paper presents the modeling and steady-state performance of a novel dual-winding reluctance generator (DWRG) that uses a multiple-barrier (MB) rotor. A simple mathematical model was developed, and the effects of external parameters (speed, field current, and load) on the steady-state performance were analyzed. Experimental results conducted on a prototype machine were also provided to justify the theoretical approach and performance calculations. The developed model takes into account the magnetic saturation and core loss and enables a quantitative prediction of load characteristics from the no-load test data.

Causes of increase in the terminal voltage of a permanent-magnet-assisted salient-pole synchronous machine

Permanent-magnet-assisted salient-pole synchronous machines (PMa-SMs) have the ability to increase the terminal voltages as compared with conventional salient-pole synchronous machines. This paper investigates the main cause of the voltage increase under no-load conditions. The rotor and the stator flux components produced by permanent magnets (PMs) in a PMa-SM are computed by linear finite element analysis with frozen permeability. The results show that most of the flux produced by the PMs remains in the rotor unless the field current is very large. Therefore the main cause of the voltage increase is reduction of magnetic saturation in the rotor field poles.

Creepage discharge characteristics over solid-liquid interfaces with grounded side electrode

The properties of streamers traveling over the surface of oil-immersed solid dielectrics were experimentally studied under lightning impulse conditions. Streamer polarity and the position of a grounded side electrode significantly affected the relationship between the streamer extension length and the applied voltage. The solid surface charging had also a large effect on the streamer propagation. However, the streamer propagation properties showed a consistent dependence on the potential at solid-liquid interfaces. In addition, the potential drop inside the streamer channel was found as a function of normalized streamer length. The streamer appeared to progress in a constant velocity.

Impulse creeping discharge along the surface of polyethylene wire immersed in transformer oil

The experimental study was performed to clarify the basic behaviour of streamers traveling over the surface of oil-immersed polyethylene insulated wire under a standard lightning impulse voltage application. The effect of the grounded side electrode on the characteristics of creepage discharges, such as discharge inception voltage, discharge extension length, discharge current and charge, discharge figure has been studied. There is a remarkable difference in these characteristics between positive and negative polarities of the streamer. Though the approach of the grounded side electrode to the wire restrains the generation and progression of streamers, it leads to the reduction of a punch-through breakdown voltage of the wire insulator. The authors also measured the electric potential along the streamer channel and the streamer propagation velocity by means of a capacitive probe. It is indicated that the streamer continues to progress in a constant velocity and the streamer channel is not equipotential. The propagation of streamers appears to be stopped by a finite potential drop along the streamer channel.

Effect of electrode ice layer on prebreakdown current in liquid nitrogen

The effect of ice on dc prebreakdown events was investigated using a needle-to-plane electrode system in liquid nitrogen at 77.3 K. It was found that H/sub 2/O ice has marked effects on prebreakdown current, corona onset voltage and breakdown voltage. The breakdown voltage at atmospheric pressure depends on microscopic cracks in H/sub 2/O ice. >

Creeping discharges in transformer oil under lightning impulse voltages over 100 kV peak value

This paper describes the experimental results on the creeping streamer progressing the surface of a bakelite board immersed in transformer oil under the application of a standard lightning impulse voltage with peak values of plusmn100~350 kV. The growth of streamers is significantly affected by the thickness of bakelite board and the streamers are extended longer exponentially for the applied voltage more than ~plusmn200 kV. These streamers leave the remarkable discharge scars on the bakelite surface. The discharge scars are different by the voltage polarity which influences strongly to the streamer growth. The mean streamer velocities in both polarities have also been examined.

Steady-state analysis of a permanent-magnet-assisted salient-pole synchronous generator

This paper presents a simple mathematical model for the steady-state analysis of a permanent-magnet-assisted salient-pole synchronous generator (PMa-SG). The PMa-SG is a new type of salient-pole SG that has PMs between the adjacent pole shoes. The developed model takes into account the magnetic saturation and core loss, and enables quantitative predictions of load characteristics from the no-load test data. The validity of the developed model is confirmed experimentally. The effect of the PMs on the performance characteristics of the PMa-SG is also investigated.