influence of surface charges on alumina dielectrics …...influence of surface charges on alumina...
TRANSCRIPT
Surface charge
60
50
40
30
20
10
0
Fla
sh
ove
r e
lectr
ic f
ield
-10 -8 -6 -4 -2 0 2 4 6Surface charging potential [kV]
str
en
gth
Ep [
kV
/mm
]
100
102
104
106
Se
co
nd
ary
ele
ctr
on
50403020100Distance from center of electrode [mm]
No charge
Negative charge (Vs = 9.5kV) Positive charge (Vs = +5.0kV)
en
erg
y E
n [
eV
]
10-4
10-3
10-2
10-1
100
Flig
ht
dis
tan
ce
S [
mm
]
50403020100Distance from center of electrode [mm]
No charge Negative charge (Vs = -9.5kV) Positive charge (Vs = +5.0kV)
Influence on development of surface discharge
Influence of Surface Charges on Alumina Dielectrics
on Impulse Flashover Characteristics in VacuumHidenori Kato1, Katsumi Kato1, Ayumu Morita2, Hitoshi Okubo1
1Nagoya University, Japan 2Hitachi, Ltd., Japan
In order to enhance the electrical insulation performance of vacuum circuit breakers (VCBs), the surface flashover mechanism on soliddielectrics in vacuum needs to be clarified. We investigated the surface flashover characteristics under the existence of surface charge onalumina ceramic insulator in vacuum. We investigated the dependence of the location and magnitude of surface charge on surface flashovercharacteristics. The experimental result revealed the influence of surface charges on surface flashover characteristics in vacuum.
Surface charge generation
Introduction
Influence on inception of surface discharge
Vacuum circuit breaker
2tan2cos4tancossin41
0nE
nE
tan
tan12sin02
zEn
ES
The surface charge is critical factors to the
surface flashover phenomena.
When surface charge located near the
cathode electrode (Case A), positive
charge made surface flashover voltage
lower and negative charge made surface
flashover voltage higher. We could explain
the results by the change of electric field
at flashover by surface charge.
When surface charge located at the way
of discharge path (Case B), either positive
or negative charge made surface flashover
voltage lower. We could explain the results
by the role of surface charge for making
the secondary electron energy higher for
satisfying the condition of secondary
electron emission avalanche.
Vacuum gap length
Back electrode(Grounded)
H.V. electrode
GND electrode
H.V. dc
(negative or positive)
Alumina(150mm×150mm×5mmt)
75
0
-7575-75 0
(a) Negative charge (b) Positive charge
-8
-6
-4
-2
0
Surface potential [kV]
75-75 0
-8.0 -4.0 0 0 1 2 3 4
75
0
-75
0 2.0 4.0Surface potential [kV]
H.V. electrode
Alumina
GND electrode
1.0mm
Negative impulse (1.2/50ms)
H.V. electrode
1.0mm
Negative impulse (1.2/50ms)
Alumina
Surface charge
Case B
Case A
H.V. electrode
GND electrode
Alumina
En0= 4 [eV]
Vacuum
En
S
Alumina
-Ex
-Ez
GND electrode
GND electrode
SEE coefficient is higher than 1
Charging area
Negative charge(relax electric field)
Positive charge(enhance electric field)
= 5°
Surface flashover generation
Conclusion
1.
2.
3.
Key points
on insulation designStationary rod
Electrodes
Contacts
Shield
Moving rod
Bellows
Insulation of
shield-electrode
and shield-rod
Insulation
between contacts
Creepage insulation
of solid insulator
Alumina
dielectrics
External insulation
Negative impulse (1.2/50ms)
Negative impulse (1.2/50ms)
Case A
-30
-25
-20
-15
-10
-5
Surf
ace fla
sh
ove
r voltage
[k
V]
-10 -8 -6 -4 -2 0 2 4 6Surface charging potential [kV]
Case A Case B
-30
-25
-20
-15
-10
-5
Su
rfa
ce
fla
sh
ove
r vo
lta
ge
[k
V]
-10 -8 -6 -4 -2 0 2 4 6Surface charging potential [kV]
Case A Case B
50mm
50mm
GND electrode