vacuum technology in electrical switches presented by zhenxing wang from xi’an jiaotong university...
TRANSCRIPT
Vacuum Technology in Electrical Switches
Presented by Zhenxing Wang
From Xi’an Jiaotong University
Now at University of Helsinki
29 January, 2015
April 19, 2023 Zhenxing Wang 2
Content
I Background of Vacuum Switch
II Vacuum Breakdowns in 126kV Vacuum interrupter
III Vacuum Arc and Its Effect
IV Post-arc Breakdowns
V Conclusion and Future Plan
April 19, 2023 Zhenxing Wang 3
I Background
Stationary Contact
Movable Contact
Movable Conducting Rod
Stationary Conducting Rod
Main Shield
Porcelain Envelope
Porcelain Envelope
132mm
471.5mm
Vacuum technology is one good solution for electrical insulation, and the environment-friendly merit makes it suitable for substituting SF6 gas switches.
Now vacuum switches dominate the medium voltage level of power system(3kV - 40.5kV).
We would like to develop a vacuum switch can be used in the power system above 70.5kV - 126kV or above.
This is a 126kV vacuum circuit breaker designed by my group in XJTU
Vacuum Interrupter
April 19, 2023 Zhenxing Wang 4
I Background: The Interrupting Processes
Schade, E. and E. Dullni, "Recovery of breakdown strengthof a vacuum interrupter after extinction of high currents".Ieee Transactions on Dielectrics and Electrical Insulation,2002. 9(2): p. 207-215.
Vacuum arc can destroy the contact surfaces severely.
There are three stages in the post –arc stage:
Residual plasma dissipates from the gap.
Metal vapor dissipates from the gap.
The gap recovers to vacuum.
If the contacts can withstand the transient voltage and turn to be vacuum again the current is interrupted successfully. Otherwise the contact gap will restrike.
April 19, 2023 Zhenxing Wang 5
I Background: Three Major Problems
Vacuum Breakdown
Vacuum ArcInterruption
Post-arcBreakdown
The breakdown mechanism in long vacuum gap (>10mm). Does the same mechanism dominate breakdowns between the processes in short and long vacuum gap?
The arc burning process and erosion of contact material. How to get a more precise plasma arc model and calculate the erosion of the arc on the surfaces?
The breakdown mechanism in low-pressure metal vapor on the destructed surfaces.How to give a more reliable estimation to dielectric recovery strength?
Problem I Problem II Problem III
April 19, 2023 Zhenxing Wang 6
To Impulse Generator Gap Spacing
Adjuster (0~50mm)
Insulation Gas SF6
Vacuum InterrupterPorcelain Envelope
To Earth
d=10~50mm
15mm
Contact Diameter:60mm or 75mm
Radius of Contact Edge: R2mm or R6mm
Contact Material:CuCr40
Surface Roughness: 3.2um or 1.6um
VI Radius of Contact Edge(mm) Roughness(μm) Contact
Radius(mm)
No.1 6 1.6 60
No.2 2 1.6 60
No.3 6 3.2 60
No.4 6 1.6 75
Adopting 126kV vacuum interrupters to study the behaviors of breakdowns with a contact gap of 10~50mm
Voltage type:1min AC voltages impulse voltages
II Vacuum BDs in 126kV VIs: Experimental Setup
April 19, 2023 7
Gap Length(mm)
AC
Bre
akd
own
Vol
tage
(kV
) UB=89d0.25
The relation between contact gaps and AC breakdown voltages can be expressed as
behaviors of UB=89d0.25
The possibilities of impulse voltage breakdowns in a vacuum interrupter satisfy Weibull distribution.
The discrepancies between the contact with roughness 1.6um and the one with 3.2um are within 3%.
The discrepancies between the contact with a diameter of 60mm and the one with 75mm are within 10%.
AC Voltage breakdowns
Impulse Voltage breakdowns
The Effect of roughness
The Effect of Contact Diameter
II Vacuum BDs in 126kV VIs: Results
Zhenxing Wang
April 19, 2023 Zhenxing Wang 8
Materials
Region I %
Region II %
Before %
Cr 31 18 25
Cu 69 82 75
Composition of Melt Layer in Different Regions
III High Current Vacuum Arc: ExperimentsResults from Electron Scanning Microscope
April 19, 2023 Zhenxing Wang 9
Physical Process:Melting/Solidification, Free Surface, Heat Flux from Arc Column, Arc pressure.
Arc ColumnAnode Region
Mathematical ModelPhysical Model
III High Current Vacuum Arc: Simulation Model
d( ) 0
d
F FV F
t t
Boundary Condition Adopting pressure and heat from arc calculation as the boundary of anode surface
Free Surface
April 19, 2023 Zhenxing Wang 10
III High Current Vacuum Arc: Simulation ResultsVelocity Pressure
Current Density Temperature
Evolution of Temperature and Surface
This process reshapes the contact surface and energy distribution.
Pressure from arc can be a dominant force to shape the surface of anode contact.
The influence of the process has a significant impact on the post-arc period.
April 19, 2023 Zhenxing Wang 11
2D3V PIC-MCC model of post-arc breakdown
e
Cathode Anode
e
eIe
10mm
Negative Voltage Ground
Cu e Cu e *Cu e Cu e
Cu Cu Cu Cu
Cu Cu Cu Cu
Postarc cathode
Postarc anode
U = 0
U = UR(t) positive space
sheath
Neutral plasma
ds
A 1D3V PIC-MCC model of sheath development
Physical Process:
Plasma transportation under TRV.The effect of existing background neutral vapor.
Physical Process:
Breakdowns in a low density metal vapor. The effect of destructed surface.
IV Post-arc BDs : Simulation Model
April 19, 2023 Zhenxing Wang 12
The distribution of electron
Sheath thickness
0 1 2 3 4 5
5.0x1016
1.0x1017
1.5x1017
2.0x1017
2.5x1017
150ns300ns450ns600ns750ns
Postarc CathodePostarc Anode
Ele
ctro
n D
ensi
ty(/
m3 )
Axial Position(mm)
0 1 2 3 4 5
0.0
2.0x1016
4.0x1016
6.0x1016
8.0x1016
1.0x1017
1.2x1017
150ns300ns450ns600ns750ns
Postarc Anode Postarc CathodeIo
n D
ensi
ty(/
m3 )
Axial Position(mm)
0 1 2 3 4 5
-1400
-1200
-1000
-800
-600
-400
-200
0
150ns
300ns
450ns
600ns
Postarc Cathode
Vo
ltag
e(V
)
Axial Position(mm)Postarc Anode
750ns
The distribution of ion
The distribution of voltage across gap
0.0 0.5 1.0 1.5 2.0 2.5 3.00
1
2
3
4
5
n0=1018
n0=1020
n0=1021
Sh
eath
Th
ickn
ess(
mm
)
Time(s)
n0=1022
Sheath development can last for several microseconds.
The existing of metal vapor can affect the development of residual plasma only in a high density situation.
IV Post-arc BDs : Sheath Development
April 19, 2023 Zhenxing Wang 13
0 50 100 150 200 250 300
01x10112x10113x10114x1011
0 50 100 150 200 250 30002468
10
0 50 100 150 200 250 3000
1x1011
2x1011
3x1011
4x1011
The Number of Copper Ion
Time(ns)
Time(ns)
Time(ns)
The Current Absorbed by Cathode
Time(ns)
The Number of Electron
0 50 100 150 200 250 300-12-10
-8-6-4-20
The Current Absorbed by Anode
The evolution of particles during a breakdown
Paschen curve for copper
The paschen curve for copper are only limited available from experiments.
PIC-MCC is helpful for estimating the breakdowns in a low-density metal vapor.
0 2 4 6 8 10 12 140
25
50
75
100
(pd=5.52Pam, Vb=30V)
(pd) / Pam
Bre
akd
ow
n V
olt
age
/ V
(pd=1.01Pam, Vb=11.7V)
IV Post-arc BDs : Metal Vapor BD
April 19, 2023 Zhenxing Wang 14
0 1 2 3 4 5 60
2
4
6
8
10
12
14
16
(2) (1)
Heig
ht o
f ape
x (u
m)
Time (us)
220MV/m (1) 240MV/m (2) 260MV/m (3)
(3)
0 1 2 3 4 5 60
500
1000
1500
2000
2500
3000(2) (1)
Elec
tric
field
(MV/
m)
Time (us)
220MV/m (1) 240MV/m (2) 260MV/m (3)
(3)
0 1 2 3 4 5 610-3
10-2
10-1
100
101
102
103
104
105
106
107
(2) (1)
Ther
mo-
field
ele
ctro
n em
issi
on (A
/m2 )
Time (us)
220MV/m (1) 240MV/m (2) 260MV/m (3)
(3)E0
0
Vacuum
Liquid metal
Height of apex
Surface tension force
Electric stress
Initial shape
d
Viscosity force
0 1 2 3 4 50
2
4
6
8
10
12
14
16
(2) (1)
Hei
ght o
f ape
x (u
m)
Time (us)
1356K (1) 1700K (2) 2300K (3)
(3)
0 1 2 3 4 50
500
1000
1500
2000
2500
3000(1)(2)
Elec
tric
field
(MV/
m)
Time (us)
1356K (1) 1700K (2) 2300K (3)
(3)
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.510-310-210-1100101102103104105106107108109
(1)(2)
Ther
mo-
field
ele
ctro
n em
ssio
n (A
/m2 )
Time (us)
1356K (1) 1700K (2) 2300K (3)
(3)
IV Post-arc BDs : Micro Tip Induced by Electric Field
Tip Formed Electric Field Enhanced Current Emission Increased
The existence of micro tip can reduce the BD voltages significantly.
1515
Conclusion & Future Plan
Breakdowns in vacuum and low density metal vapor are the most fundamental issues in designing a high voltage interrupter.
The mechanism of vacuum breakdowns with a large contact gap (10mm~60mm) still does not be understood.
It is necessary to integrate the process of vacuum arcs and post-arc breakdowns for the purpose of better understanding the interrupting processes.
We plan to model breakdowns with a several millimeters contact gap and verify the model by observing the evolution of vacuum breakdowns adopting a steak camera.
A integrated post-arc breakdown model is being developed.
Thanks For Your Attention!