Mikimasa Iwata

Arc voltage characteristics of high current fault arcs in long gaps

This paper describes the arc voltage characteristics of high current arcs simulating fault arcs on 500 kV class transmission lines and the simulation result of the 50 kA rms class fault arcs. A high power arc test was carried out and the arc voltage in a 3.4 m gap and the voltage of the arc jet near the electrode were measured. The voltage gradient of the arcs and arc jets and the voltage-current characteristics of arcs were investigated. The test results showed that the voltage gradient of the arc jet was larger than that of the arc column. The high current fault arc voltages were calculated using numerical arc models and the arc parameters for the numerical arc model of 50 kA rms class ultra high current arcs were investigated. The calculated values were in good agreement with the measured data.

Synthesis of purified AlN nano powder by transferred type arc plasma

Nano powder of aluminium nitride (AlN) is one of the materials necessary for developing solid insulating materials with high thermal conductivities. This paper describes the results of chemical equilibrium composition calculations and the results of experiments in synthesizing AlN nano powder using transferred type arc plasma. In order to increase the AlN content in synthesized powder, ammonia was recommended as a reacting/quenching gas, to be blown into aluminium gas in a temperature range between 2000 and 2400 K. The AlN content increased by more than 99% on passing the synthesized powder through ethanol.

Development of arcing horn device for interrupting ground-fault current of 77 kV overhead lines

This paper describes an arcing horn device for interrupting the ground-fault current of 77-kV overhead lines. The main characteristics of the device are as follows. The arcing horn device interrupted the ground-fault current 445A within a half cycle without replacement ten times. The arcing horn device did not interrupt short-circuit current. However, even when a short-circuit current of 10 kA flowed through the interruption portion, the device did not explode and damage any surrounding apparatus, such as insulators and conductors. The arcing horn device flashovered perfectly in the interruption portion when a lightning impulse voltage of 1400 kV was imposed under dry, water-sprayed and contaminated conditions. The arcing horn device was installed on a 77-kV overhead line belonging to the KANSAI Electric Power Co, Osaka, Japan, and was found to interrupt the ground-fault current.

CFD Calculation of Pressure Rise Due to Internal AC and DC Arcing in a Closed Container

Computational fluid dynamics calculation results of pressure rise and propagation due to high-current arcs in a closed container are described. The pressure developments at different locations within the container are calculated by changing the current frequency (ac of 50 and 60 Hz, and dc) and the electric arc energy input (up to approximately 1000 kJ). The local pressure oscillation amplitude for AC/50 Hz within the container exceeds that for dc. From the pressure oscillation period and the sound speed distribution in the container, the following conclusions are made. With growing electric arc energy, the pressure amplitude increases because of the resonance effect between the arc power oscillation and pressure waves reflected on the walls. When the electric arc energy reaches a value of around 500 kJ, the pressure amplitude rises significantly. This is considered attributable to superimposition of pressure waves near the container wall caused by low propagation velocity of the pressure waves near the wall. It is necessary to consider this phenomenon for public safety when designing electric power equipment.

Development of an EMTP Simulation Model of Arcing Horns Interrupting Fault Current

Arcing horns interrupting fault current is a new type of arcing horns installed on transmission-line towers, which act to interrupt fault current independently within one cycle of commercial frequency. In this paper, we have developed an Electromagnetic Transients Program (EMTP) simulation model of the arcing horns interrupting fault current to ascertain the application effects and devise an installation strategy. The EMTP simulation model can consecutively simulate the entire process, from fault occurrence to fault clearing, by integrating two different kinds of macroscopic arc models, and is capable of dealing with the entire short-circuit current range by taking into account the characteristics of the arc parameters. Finally, we have verified the validity of the EMTP simulation model by comparing simulation and experimental waveforms, and have shown the simulation of current and voltage waveforms in the event of a system fault by using the Japanese Power System Model as an application example of the EMTP simulation model.

Development of a Method of Calculating the Melting Characteristics of OPGW Strands Due to DC Arc Simulating Lightning Strike

Some strands of composite fiber-optic ground wire (OPGW) are sometimes melted and broken by high-energy lightning strikes. DC arc tests simulating lightning strikes have been performed to obtain the melting and breaking characteristics of OPGW strands. The tests have to be performed under many conditions concerning the arc (e.g., current, duration, polarity, gap length) and the OPGW (e.g., size, type, and number of strands) to clarify the melting and breaking characteristics of the strands. In this paper, the calculations regarding the melting characteristics of strands are performed considering the transferred heat and its area from the arc to the strands under the aforementioned conditions. The melting characteristics of strands are calculated with an arc current of 1-100 kA considering the measured current of actual lightning. The calculation results of the strand melting duration depending on arc current show good agreement with the experimental values obtained in dc arc tests.

Analytical investigation on OPGW strands melting due to DC arc discharge simulating lightning strike

Some metal strands of OPGW (composite fiber-optic ground wire) are sometimes melted and broken by lightning strikes. DC arc tests simulating lightning strikes have thus been performed to obtain their melting and breaking characteristics. In this paper, calculations regarding these melting characteristics are performed considering the transferred heat and its area from the arc to the strands. The melting characteristics of strands are calculated with an arc current of 0.1 - 100 kA, considering the current prescribed in the IEC standard and the measured actual lightning current. The calculation results of the strand melting duration depending on the arc current show a good agreement with the experimental values obtained in DC arc tests.

Effect on transferred ac arc plasma stability of increasing ambient temperature and superimposing pulse at current zero point

The use of alternating current (ac) arc plasma involves a problem of instability of the arc plasma at current zero point. This paper describes the effects of ambient temperature and of superimposing a pulse current on stability of the ac argon arc plasma; the pulse current (10 A) is superimposed on an ac current only at each current zero point. The ac arc plasma is generated between a tungsten electrode of a plasma torch and a copper counter electrode in a chamber. The ac current is 100-500 Arms and the arc plasma length is 40 mm. As the ambient temperature increases from 300 K to 900 K, the stored energy in the arc plasma increases and the required supply voltage to stabilize the arc plasma decreases by about 20% (from 270 to 220 Vrms). Additionally, superimposing a pulse current on an ac current causes the required supply voltage to decrease by about further 20% (from 220 to 180 Vrms).

Reduction in Pressure Rise Due to Internal Arcing Using Melting and Vaporization of Metal

Summary form only given. When an arc is ignited between the electrodes in a closed chamber, the internal pressure rises. In this paper, the reduction in the pressure rise due to internal arcing using the melting and vaporization of a de-energized metal plate was investigated experimentally. The results showed that allowing a Cu or Fe plate placed near the electrodes to be melted and vaporized by the arc, the reduction in the pressure rise increased as the amount of mass loss of the plate increased. The decrease level of the maximum pressure rise was more than 20% on average in our experiments. On the basis of these experimental results, the energy balance in the closed chamber was estimated in order to clarify the mechanism behind the reduction in the pressure rise. The dominant cause of the reduction in the pressure rise for the Cu plate was the increase in energy consumption by the melting and vaporization of the plate. For the Fe plate, it was the increase in the energy of consumption by the arc radiation.

Influence of Current and Electrode Material on Fraction

The fraction k_p of electric arc energy leading to pressure rise in its surroundings is determined in dependence on arc current and electrode material for an arc occurring in a closed container. It is shown that the kp values for closed containers depend apart from the electrode material on the level of arc current, which, in turn, affects the energy balance.