Sadayuki Yuasa

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms - method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms -

To lower the lightning impulse withstand voltage of gas insulated switchgear (GIS) while maintaining the high reliability of its insulation performance, it is important to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the preceding researches, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five to six kinds of non-standard lightning impulse waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. Then, the dielectric breakdown voltage iquest time characteristics were measured under several different conditions on the quasi-uniform SF6 gas gaps and partly the coneshaped insulating spacers that represent insulation elements of GIS for six kinds of nonstandard lightning impulse waveforms. In this paper, the resultant breakdown voltages were evaluated in terms of the overvoltage duration, which led to their formulation in a unified way. On the basis of these insulation characteristics and their unified formulation, the paper investigated a method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms with equivalent stress for the insulation. When the constructed algorithm was applied to five examples of representative two type waveforms in the lightning surge time region, they were converted into standard lightning impulse waveforms with crest values reduced by 20% to 34%, suggesting potentiality for reduction of lightning impulse insulation specifications of GIS.

Simulation of propagation characteristics of higher order mode electromagnetic waves in GIS

Numerical simulation of electromagnetic fields was performed to investigate the transmission and reflection characteristics of electromagnetic waves excited by partial discharge through spacers, L-shaped sections of a GIS bus structure. The resonance frequencies of a cavity between spacers agreed roughly with the experiment. The modes of electromagnetic wave are shown to transform to different modes, e.g., from TE11 to TE21 mode, after transmission and reflection through L-shaped sections of a GIS. The frequency intervals of the resonance in tanks longitudinal direction for a L-shaped section are different between horizontal and vertical excitation of partial discharge source. The two characteristics, mode transformation and the dependence of resonance frequency on excitation direction, were confirmed experimentally

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms - analysis and generation circuit of non-standard lightning impulse waveforms in actual field

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of a gas insulated switchgear (GIS) and thus cut the equipment cost while maintaining the high reliability of its insulation performance, it is necessary to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In this paper, first, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five non-standard lightning surge waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. Next, high-voltage circuits that generate these non-standard lightning surge waveforms were designed and constituted using EMTP (electro magnetic transients program) based on a circuit with a gap, inductors, and resistors connected in series and resistors and capacitors connected in parallel. Further, circuits were actually constructed, to obtain voltage waveforms approximately equal to those designed. Finally, the dielectric breakdown voltage-time characteristics were measured under several different conditions for the quasi-uniform SF6 gas gap that represents an insulation element of a GIS. As a result, it was found that, in the tested range, the dielectric breakdown values for non-standard lightning impulse waveforms were higher than for the standard lightning impulse waveform by 6% to 32%

Evaluation of Breakdown Characteristics of Gas Insulated Switchgears for Non-Standard Lightning Impulse Waveforms - Breakdown Characteristics for Non-Standard Lightning Impulse Waveforms Associated with Lightning Surges

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of a gas insulated switchgear (GIS) and thus cut the equipment cost while maintaining the high reliability of its insulation performance, it is necessary to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the preceding paper, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five to six non-standard lightning surge waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. In this paper, the dielectric breakdown voltage - time characteristics were measured under several different conditions mainly for the quasi-uniform SF6 gas gaps that represent an insulation element of a GIS toward four kinds of non-standard lightning impulse waveforms associated with lightning surges. As a result, in the tested range, the dielectric breakdown values for nonstandard lightning impulse waveforms were higher than for the standard lightning impulse waveform by 3% to 32%.

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms under diverse conditions

To lower the lightning impulse withstand voltage of gas insulated switchgear (GIS) while maintaining the high reliability of its insulation performance, it is important to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the preceding researches, the dielectric breakdown voltage-time characteristics were measured under several different conditions on the quasi-uniform SF6 gas gap and partly the cone-shaped insulating spacers that represent an insulation element of GIS for six kinds of non-standard lightning impulse waveforms associated with lightning surges and disconnector switching surges. As a result, in the tested range, the dielectric breakdown values for non-standard lightning impulse waveforms were higher than those for the standard lightning impulse waveform by 3% to 36%. In these experiments, parameters other than waveforms were fixed to standard conditions. In this paper insulation characteristics on quasi-uniform SF6 gas gaps were examined while changing conditions on gas pressures, gap lengths, electrode surface roughness, voltage polarities, and bias voltages. As a result, it was confirmed that the results under standard experimental conditions in the preceding experiments can be applied widely to the GIS actual equipment conditions.

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms - breakdown characteristics for non-standard lightning impulse waveforms associated with disconnector switching surges -

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of a gas insulated switchgear (GIS) and thus cut the equipment cost while maintaining the high reliability of its insulation performance, it is necessary to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the preceding paper, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five to six non-standard lightning surge waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. In this paper, the dielectric breakdown voltage - time characteristics were measured under several different conditions for the quasi-uniform SF6 gas gap that represents an insulation element of a GIS toward two kinds of non-standard lightning impulse waveforms associated with disconnector switching surges. As a result, in the tested range, the dielectric breakdown values for non-standard lightning impulse waveforms were higher than for the standard lightning impulse waveform by 6% to 36%.

Dielectric Properties of Gas Mixtures with Carbon Fluoride Gases and N2/CO2

With excellent insulation and current interruption characteristics, SF6 gas has been applied since the 1960’s in electric power equipment, and is finding a wide range of applications today in GIS, GCB and GIL of classes from several kV to 1OOOkV. In COP3 of 1997, however, it was designated a greenhouse gas and since then there has been demand for alternative insulating gases to pure SF6 gas.(1)

Insulation Characteristics of Gis for Non-Standard Lightning Surge Waveforms

Evaluation of lightning surge waveform, which actually enter into substations, is important when investigating the test voltage of equipment. The waveform of the standard lightning impulse waveform (1.2/50 µs) is used for testing; however, the lightning surge waveforms in actual fields are complex waveforms in which various different oscillations are superimposed1,2). Investigation of the insulation characteristics of the equipment against the complex waveforms and standard one has significant importance. The insulation characteristics of Gas Insulated Switchgear (GIS) were investigated for these waveforms.

PD Inception and Breakdown Voltage Characteristics in PFC and SF6 gas mixtures

Since SF6 gas has excellent properties like a high dielectric strength, and is chemically inert, nontoxic, and so on, it has been widely used as an insulation material for gas insulated switchgears (GIS) and insulated transmission lines (GIL)(1,2). However, SF6 gas is a potent green house gas and its global warming potential (GWP) is estimated as a very large at 23,900. Accordingly, SF6 gas was designated as one of the emission gases to regulate at COP3. It is necessary to decrease the use of SF6 gas, design techniques to retrieve SF6 gas and reduce its emission into the atmosphere and develop alternative gases having much lower GWP values. SF6/N2 gas mixtures have been proposed as a promising alternative to SF6. To date, the authors have shown that adding a small amount of CO2 to an SF6/N2 gas mixture results in a prominent increase in the insulation performance under both uniform and nonuniform electric fields(2,3).

Breakdown Characteristics of SF6 Gas under Non-Standard Lightning Impulse Voltage-Insulation Characteristics for Gas Gap under Oscillatory Waveforms-

Evaluation of lightning surge waveforms that actually enter into substations is important to investigating the test voltage of gas insulated switchgear (GIS). The actual lightning surge waveforms in substations are different from the standard lightning impulse voltage because they are complex and are usually superimposed with various oscillations. This paper describes insulation characteristics in SF6 gas gap under the waveforms including oscillation (called waveforms B, C and D). The minimum breakdown voltages (Vmin) under experimental waveforms are higher than Vmin under the standard lightning impulse voltage. The evaluation method, which deals duration applied over 80% of peak voltage and conversion factor for second waves of waveform B, can estimate the insulation characteristics under waveforms B, C and D.