1 . occurrence of discharge
DESCRIPTION
1 . Occurrence of Discharge. 1.1 Partial discharge 1.2 Inception of internal discharge 1.3 Inception of surface discharge 1.4 Inception of corona discharge 1.5 Discharge by electrical treeing. 1.1 Partial discharge. - PowerPoint PPT PresentationTRANSCRIPT
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1 . Occurrence of Discharge
1.1 Partial discharge1.2 Inception of internal discharge1.3 Inception of surface discharge1.4 Inception of corona discharge1.5 Discharge by electrical treeing
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1.1 Partial discharge
Electric discharge that do not completely bridge the electrodes are called partial discharges.
방전크기는 작지만 점진적으로 발전하면 ultimate failure 로 유발가능 비파괴시험으로 방전의 진행을 detect 하는게 필수적이다 .
1.1.1 Classification 1) Internal discharge (Figures 1.1 and 1.2) 2) surface discharge (Figures 1.3) 3) Corona discharge (Figures 1.4) 4) Discharge in electrical trees (Figures 1.5)
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1.1.2 Terminology Partial discharge 대신에 미국 , 영국 (ionization) 프랑스 (ionisation gazeuse) 독일 (Ionisationsvorgange) 라고함 . 파생어로는 ionization point , ionization livel Corona 의 파생어
1.2 Inception of internal discharge 1.2.1 Gas-filled cavities Figure(1.2(a)- 고체 절연체 전계 배 , (b) 배 ( c) 유전체와 동일한 크기 ( 전계가 집중되는 위험이있음 )
)21/(3
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Breakdown strength of the cavities (dimensions , type of gas , gas pressure) Ex)a flat cavity of 0.1mm 인 폴리에틸렌의 , =2.2 1atm 일때 f
ig 1.7 에서 의 breakdown stress 는 6.8kV/mm 이다 . inception stress 는 6.8/2.2 ~~3kV/mm 부분방전 전계는 설계전계보다 낮아도 일어난다 .(3.5 to 7kV/mm) Breakdown voltage 에 미치는 여러가지 요소중 예측치보다 낮은 B
DS 를 보이는데 그 예로 static charge in wall of cavity 에 의해 예측치는 20% 만큼 감소한다 . 그의 방안으로 the wall 을 도전성을 갖게한다 .
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1.2.2 Inclusions Extruded plastics of cast resin 에는 various inclusions : dirt, paper of textile fibres and other foreign particles inclusions 에 의해 BDS 는 감소하고 breakdown gas is forme
d and gas discharges occur. Gooding and slade 의 metal splinters embedded in the dielectric
local field concentration
1.2.3 oil-filled cavities Oil-impregnated paper insulation 의 stress 는 gas-filled cavities
와 유사하다 .
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1.3 Inception of surface discharge Surface discharge may occur of there exists a stress component p
arallel to a dielectric surface. bushings, ends of cables,the overhang of generator windings and where a discharge from outside touches the surface.
1.3.1 Discharges in air Figure 1.8 과 figure 1.9 에서의 V 와 에 의한 paschen curve
를 볼수있다 .(table 1.1 dotted line)
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1.3.2 Surface discharge under oil Similar formula as for air Contamination , moisture greatly affect the breakdown stress. 공기중에서의 BDS 는 습도에 매우 민감하며 , 절연유내의
실혐결과보다는 대개 낮은 특성을 보인다 .
1.3.3 Surface discharge under sulphur hexafluoride gas 절연물에서의 particles 은 표면의 섬락과 부분방전의 원인이
된다 . Brokman 은 이러한 현상을 3 가지 변수로 만들어보았다 .
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(1) roughness of the surface (2) semiconducting areas - contamination of the dielectric surface(Fig 1.11) (3) Particle - shape and dielectric constant of particle(Fig 1.12) -particles with sharp edges are dangerous sources of discharge The flashover voltage decreased with increasing
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1.4 Inception of corona discharge Corona discharge occur in gases at sharp points in the electrical f
ield(Fig1.13) Sharp edges , HV sides, laboratory floor…
1.4.1 corona air 1.4.2 corona in sulphur hexafluoride gas. SF6 하에서는 코로나 발생시 그의 부산물은 독성이 있다 . 1.5 discharge by electrical treeing electrical trees start from defects in the insulation(Fig1.15)
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