Tsuneharu Teranishi

Breakdown Characteristics of Moving Transformer Oil

As a result of investigating breakdown characteristics of moving oil, it has become clear that the breakdown voltage of ac and dc for moving oil is higher than that for stationary oil by 10-15 % at a moving velocity of 5 cm/s region; the former voltage becomes almost equal to the latter voltage in the region of 25 cm/s, and the former is reduced to lower than 90 % of the latter when the moving velocity exceeds 100 cm/s. However, for impulse voltage, the breakdown voltage of moving oil is the same as that of stationary oil.

Development of key components and technologies for a high repetition rate and high-power excimer laser

Key components and technologies have been developed for an ultrahigh repetition rate XeCl excimer laser of 5 kHz to be used for industrial applications. A compact axial blower having a revolution rate of up to 10 000 min−1 and a maximum pressure of 16.2 kPa in air was made with a canned magnetic coupler to circulate a laser gas at a flow velocity of over 150 m/s in a discharge region. Materials constituting a laser chamber were tested to prevent discharge instability by gas contamination to enable long time operation. The dominant cause of the instability was investigated by a simple simulation. For a preionization, a novel sealed-off x-ray tube was developed to compare the suitability in a high repetition rate operation with that of conventional UV preionization. The gas due to the shock and acoustic waves generated by discharge pulses was measured to design the damper, which enabled the suppression of the gas turbulence by around a tenth. To simplify cumbersome laser maintenance, a new power supply prov...

DC creepage breakdown characteristics of oil-immersed insulation

This paper deals with dc creepage breakdown characteristics of oil-immersed insulation in HVDC transformers. The authors investigated dc breakdown characteristics using element insulation models and a full-scale model with a high creepage electric field on the insulation surfaces. The results are as follows: The dielectric strength of creepage insulation in non-contact with electrodes was more than twice higher that of creepage insulation in contact with bare electrodes. The dielectric strength is dependent on the creepage distance of surface insulation and decreases to about 45% in case of surface insulation with ten times creepage distance.

Local Voltage Oscillation in Interleaved Transformer Windings

In this paper, local voltage oscillation of each turn within sections of interleaved transformer winding are discussed. Because of interlacing of turns, each turn within a pair of sections of the winding has initial voltage distributions quite different from final voltage distributions. This difference brings about local oscillation when a steep impulse voltage enters the winding.

Design concept and performance considerations for fast high power semiconductor switching for high repetition rate and high power excimer laser

A semiconductor switching power supply has been developed, in which a novel structure semiconductor device, metal-oxide-semiconductor assisted gate-triggered thyristor (MAGT) was incorporated with a single stage magnetic pulse compression circuit (MPC). The MAGT was specially designed to directly replace thyratrons in a power supply for a high repetition rate laser. Compared with conventional high power semiconductor switching devices, it was designed to enable a fast switching, retaining a high blocking voltage and to extremely reduce the transient turn-on power losses, enduring a higher peak current. A maximum peak current density of 32 kA/cm2 and a current density risetime rate di/dt of 142 kA/(cm2×μs) were obtained at the chip area with an applied anode voltage of 1.5 kV. A MAGT switching unit connecting 32 MAGTs in series was capable of switching on more than 25 kV–300 A at a repetition rate of 5 kHz, which, coupled with the MPC, was equivalent to the capability of a high power thyratron. A high repe...

Development of insulation technology for high-voltage gas-insulated transformer

Insulation technology development for 275 kV 300 MVA class SF/sub 6/ gas-insulated transformers is described. The main area of development is turn-to-turn insulation using polymer film in sheeting winding. It was experimentally demonstrated that two sheets of film, several tens of micrometer in thickness, had sufficient insulation strength for impulse and short/long-term AC voltage application. Sufficient insulation performance for coil end insulation was demonstrated by a full-scale impulse model, taking into consideration the results of three-dimensional electric field analysis. A 275 kV 50 MVA prototype with an insulation structure equivalent to that of 275 kV 300 MVA units was developed, and a three-month reliability test was conducted. >

Dielectric characteristics of static shield for coil-end of gas-insulated transformer

The impulse breakdown characteristics of insulation models simulating static shields for coil ends of SF/sub 6/ gas-insulated transformers are studied. The static shield is composed of a double-covered electrode and a filler between the coverings. If a filler made of elastomer material is fitted closely on the covered electrode to eliminate gas gaps between the filler and the covered electrode, the impulse breakdown voltage of the static shield is higher than with gas gaps. If a low-permittivity filler is used, the impulse breakdown voltage of the static shield is still higher. The breakdown voltage can be explained by considering that the breakdown is caused by small gas gaps between the filler and the covered electrode. The dielectric strength of the coil end can be increased by applying a static shield with an elastomer filler. >

A high‐frequency model of an oil‐immersed transformer, and its use in lightning surge analysis

A circuit model of an oil-immersed transformer for use in surge analyses in the high-frequency region is proposed, and its effectiveness is evaluated by comparison with measurements on a model winding. The circuit model is used for lightning surge analyses of a 500-kV substation, and the effect of transformer modeling on the lightning surge voltage at the transformer terminals is investigated. When the new circuit model is used for transformer modeling, the peak value of the surge voltage is lower but the rate of voltage rise is higher than in conventional transformer modeling by a lumped capacitance. This difference can be explained in terms of the charging of capacitances in the transformer model.

Barrier effects of surface discharge propagation in SF/sub 6/ gas

The effects of a barrier with PET film on surface discharges in a composite insulating system in SF/sub 6/ gas were investigated. The relationship between surface discharge propagation characteristics and the protection effect of barriers was clarified. If a barrier has a right-angle bottom, the positive breakdown voltages are higher but the negative breakdown voltages remain unchanged. If a barrier having a bottom is installed near the high-voltage electrode, positive breakdown voltages are higher under a higher gas pressure, but are nearly the same under a lower gas pressure as without a barrier. If a barrier having a bottom is installed near the high-voltage electrode, a barrier effect is also observed with negative discharges, allowing breakdown voltage to rise.<<ETX>>

Dielectric Study and Develpment of Gas-Insulated Transformer

In Japan, demand for electric power has been concentrating in large cities recently, but it has been becoming increasingly difficult to build substations in urban areas because of the difficulty in obtaining land and fireproofing related to them. This has been inviting rapidly growing demand for large-capacity underground substations. Gas-insulated transformers have been finding growing applications primarily in power distribution, and a large number have been installed in densely populated buildings and underground. Recently, large-capacity gas-insulated transformers have been developed and today gasinsulated transformers are coming to be used not only for power distribution but also in large-capacity substations.