High Current AC Break Arc Contact Erosion
2008 Holm Award
John J. Shea, Senior Member IEEE
Eaton Corporation
170 Industry Drive
Pittsburgh, PA 15275
johnjshea@eaton.com
J.J. Shea
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J.J Shea 1
Factors Affecting AC Break Arc Contact Erosion
Electrical
Material
Material Properties
(mp, bp, H, λ, ρ)
Peak Current
Device
Gap
Opening Profile
Dimensions
(area, shape)
Arc Energy
Arc Motion
Heat Sinking
Arcing Time
Processing Method
(porosity, density)
Gas Flow
Part Current
J.J. Shea
Phases/Additives
(2φ, 3φ, )
Surface Morphology
After Arcing
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Arc Quenching
Gas Pressure
Impact
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J.J Shea 2
Electrical Parameters
Polarity
Current
Parting Current
Contact Part
Gap Voltage
J.J. Shea
to Arcing Time, Arc Energy
Phase Angle
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Contact Parameters
• Material Properties
• Processing
• Size and Shape
• Formulation
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J.J Shea 4
Device Parameters
• Opening Speed
• Arc Running
• Open Gap
• Arc Quenching
• Heat Sinking
• Gassing Material
• Venting
• Arc Shape
• Make or Break
• Surface Area
• Impact
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J.J Shea 5
Breakers and Contactors
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High Power Air Switches
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Example Circuit Breaker Test Standards
An Example of Test Requirements for a 600A Molded Case Breaker Test
Endurance
1,000 operations at 600Arated
5,000 no load operations
Overload
50 operations at 3600A
Short Circuit
3 operations at 100kAavailable
Typical let-through of 45kAp
J.J. Shea
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J.J Shea 8
High Speed Frames of Breaker Arc Interruption
26,000 frames/second
290
Current (kA)
190
1 0 .0 0
140
90
5 .0 0
40
0 .0 0
-1 0
0
2.20 ms
2
4
6
T im e (m s )
8
10
J.J. Shea
Arc Temperatures up to 30,000 oC
Chamber pressures reach 20 atmospheres
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J.J Shea 9
Sept. 00
Voltage (V)
240
1 5 .0 0
Overview
¼ A
Surface Area
½A
Erosion
A
Surface Area
Peak Arcing Current
Parting Current
Polarity
+
Material
Gap
• Learn about factors important for
developing numerical models and
providing useful data useful as guidance
for estimating quantities
Erosion
Factors Examined
• Gap (parting bridge and length)
• Current (arc root dimensions)
Contact Gap
• Polarity (anode and cathode)
• Contact Area (arc root dimensions)
© size,
Eatonprocess)
Corp.
• Material (type, particle
J.J Shea 10
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J.J. Shea
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AC Break Arc Contact Erosion
Anode
At high currents loss dominates
• Long arcing time
• Large gap
• Blow-off
TM
TB
R e d e p o s it
T ra n s fe r
Loss
TB
TM
C a th o d e
J.J. Shea
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J.J Shea 11
Arc Chamber
To Solenoid
Glass Polyester Walls
AgC
(Stationary)
Vent
J.J. Shea
AgW
Gap (Moving) 4.5 cm
½I
½I
3.2 cm
7 cm
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Circuit
Pulser
Solenoid
Capacitor
Bank
+
I
V
Arc
Chamber
Line Filter
J.J. Shea
(DAS BW= 200MHz)
Camera
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Initial Contact Part
Expanded region
Va
Vign
Vmin
Current
Elongation
Melting
tb
Parting Current
ta
tg
tm
Contact Part
Gap Voltage
J.J. Shea
to
t1
t2
t3
to
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Arc Property at Bridge Ignition
Vcol = 0
Va
{
Vmin
Vc
Va {
Vcol {
{
Va
Vcol
Vc
Vc
Cathode
Cathode Anode
- +
Anode
Cathode
- +
Initial Bridge Explosion
J.J. Shea
Short Bridge – No Column
V = Vmin ~ (Vi + φw)
Initial Bridge Explosion
Long Bridge – Column
V > Vmin
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-
Anode
+
Arc Elongating
Cathode and Anode
Sheaths + Column
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Minimum Voltage Dips
AgW35/65
25
Vmin
AgNi60/40
AgW50/50
Vmin
20
Voltage (V)
Vmin
Vmin
AgW50/50
15
AgW35/65
Ag100
10
AgW35/65
3x106 V/s
AgW50/50
5
J.J. Shea
0
0.0
0.5
1.0
1.5
2.0
2.5
Time (ms)
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3.0
3.5
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Bridge Voltage
Vignition
Vmin
Voltage, V, (V)
20
Longer bridge
Vcolumn >0
15
Vi + φw
}
10
5
Increasing Ag content on contact surface
J.J. Shea
0
Cathode: AgW35/65 AgW50/50 AgW50/50 AgW35/65 AgNi60/40
Anode: AgW35/65 AgW50/50 AgW50/50 AgW35/65 AgNi60/40
1st operation 1st operation
Material Type
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Ag100
Ag100
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J.J Shea 17
Metallic Phase
Varc
tm
Density, δ
tm
Gas Ions
Metallic Ions
Time
Time
-
- +
+
Initial ignition – metal vapor only Longer time – air ion + metal vapor
tm depends on bridge geometry, material, current, and contact motion
J.J. Bridge
Shea
Short
– less metal, short gap ! #$ tm
Long Bridge – more metal, long gap ! #$ tm
Blow-off (I) – more metal, short gap ! #
tm
Sliding
– more metal, short gap ! # tm
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Metallic to Gaseous Phase Transition
AgW35/65
AgW50/50
tm
Voltage (V)
20
15
AgW35/65
AgW35/65
tm
10
5
J.J. Shea
0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Time (ms)
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1.6
1.8
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J.J Shea 19
Metallic Phase Times
Time (µs)
300
200
100
J.J. Shea
0
Cathode: AgW35/65 AgW50/50 AgW50/50 AgW35/65 AgNi60/40
Anode: AgW35/65 AgW50/50 AgW50/50 AgW35/65 AgNi60/40
1st operation 1st operation
Material Type
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Ag100
Ag100
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J.J Shea 20
Instability at Part
24
22
20
Bridge
AgNi60/40
Instabilities
AgW50/50
Voltage (V)
18
16
14
AgW35/65
1.2x106 V/s
12
10
AgW50/50
8
6
4
2
J.J. Shea
0
0.9
1.0
1.1
1.2
Time (ms)
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1.3
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J.J Shea 21
Erosion Measurement
1.8 cm gap
8
0.8 cm2 area
Current (kA)
6
60
Voltage
4
40
2
20
Charge (C) or Voltage (V)
80
Current
Arcing Charge
0
0
J.J. Shea
0
2
4
6
8
Time (ms)
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J.J Shea 22
Contact Mass Loss
200
Weight Change (mg)
0
Cathode (stationary)
AgWCC(70/27/3)
-200
-400
-600
Anode (moving)
AgW(50/50)
-800
-1000
Surface Area
A= 0.8 cm2
-1200
5kAp
Gap= 1.8 cm
J.J. Shea
0
10
20
30
40
50
Number of Arcing Operations (#)
K= Slope/Arcing Charge
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Polarity
Average Erosion Rate, k, (mg/C)
3.0
Surface Area
A= 0.8 cm2
Gap= 1.8 cm
2.5
2.0
Typically anode
higher erosion
1.5
AgW 35/65
Anode
Moving
1.0
AgW 35/65
0.5
Cathode
Stationary
0.0
J.J. Shea
0
5
10
15
20
Current (kA)p
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Alternating Polarity
50
0
Weight Change (mg)
-50
-100
-150
-200
Stationary (Alternating)
AgWCC(70/27/3)
Moving (Alternating)
AgWCC(70/27/3)
-250
-300
-350
5kAp
-400
-450
-500
Surface Area
A= 0.8 cm2
Gap= 1.8 cm
J.J. Shea
0
10
20
30
40
Number of Arcing Operations (#)
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50
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J.J Shea 25
Average Erosion Rate, k, (mg/C)
Asymmetric Materials
Alternating Polarity
Surface Area
A= 0.8 cm2
AgC 95/5 (stationary)
Gap= 1.8 cm
2
AgW 35/65 (moving)
1
0
J.J. Shea
0
2
4
6
8
10
12
Current (kA)p
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J.J Shea 26
Contact Gap
Anode
Cathode
0.8
AgW 50/50 cathode (moving)
AgW 50/50 anode (stationary)
Contact Erosion rate (mg/C)
v= 5 m/s
tarcing= 7 ms
Surface Area
A= 0.8 cm2
I= 10 kAp
0.6
6 ops. total
0.4
0.2
50 C/oper.
40 C/oper.
40 C/oper.
J.J. Shea
0.0
0.00
0.25
0.50
0.75
1.00
1.25
1.50
Contact Gap (cm)
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1.75
2.00
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J.J Shea 27
Small Contact Gap
Ip= 8.5 kAp
25
42 C/shot
θpart= 15o
Erosion Rate (mg/C)
1.0
Surface Area
A= 0.8 cm2
Gap= 0.25 cm
tarcing= 7 ms
v= 5 m/s
Fc= 30 N
0.8
20
Anode (stationary)
15
0.6
10
Cathode (moving)
0.4
Erosion Rate (mg/kJ)
1.2
5
0.2
AgW 35/65 anode (stationary)
AgW 35/65 cathode (moving)
J.J. Shea
0.0
0
0
1
2
3
4
5
6
7
8
9
Number of Arcing Operations (n)
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High Speed Imaging of the Arc at 5 kAp
Anode
Moving
Contact
Arc Root
Diameter
Arc Column
J.J. Shea
Cathode
Cathode
Stationary
Contact
J.J Shea
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Arc Root Diameter and Current Density
I (t)
D(t) = 2
πJ
J = 5,000 to 38,000 kA/cm2 at bridge explosion
(using r = 50µm to 130µm parting at 3kA)
Arc root diameter tends to
follow current - maintain
constant J except at part
J = 200 kA/cm2 at initial part
Area (A)
J = 10 kA/cm2 (constant)
Diameter (D)
J=I/A
J.J. Shea
I
Arc
Contact
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J.J Shea 30
Arc Characteristics - Current Effect
Ag/W 50/50
Cathode
Cathode
2.9kAp
0.8cm2
Anode
Anode
Ag/W 50/50
8.0kAp
0.8cm2
Anoderoot
root jumps
Anode
jumps
Anode attachment
Anode attachment
Anode
root
Anode
root forms
Gap
Gap
1.27cm
Dual Column
column
Dual
Arc roots
cover total
contact surface
surface
Arc
roots
cover
Diffuse
Arc
Diffuse
arc
+
Arc rootscover
cover contact
surfaces surface
Arc roots
contact
Ag/W 50/50
15.5kAp
0.8cm2
J.J. Shea
+
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Arc Root Transition at Different Contact Part
8
AgW35/65 (cathode)
AgW35/65 (anode)
A= 0.8cm2
Gap= 1.1cm
Current (kA)
7
6
1.2
1.0
Current
0.8
5
0.6
4
0.4
2
Dc
1
0
J.J. Shea
0
1
0.2
Gap
2
4
5
Time (ms)
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6
Arc Root Diameter, Dc, Gap (cm)
10
1.4
0.0
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J.J Shea 32
Arc Characteristics – Contact Area
Contact
Contact
Ag/W 50/50
Cathode
3.3kAp
Cathode 0.8cm2
Anode
Anode
Ag/W 50/50
3.3kAp
0.4cm2
Copper
Copper
Mount
mount
Cathode Jet
Cathode Jet
Anode Jet
+
-
Anode Jet
Copper
mount
Cathode
Contact
Strong Anode
+
0.635cm
Anode
Anode
Jets
Jet
Strong Anode and CathodeJets
Strong Anode and Cathode Jets
Ag/W 50/50
3.2kAp
0.2cm2
Cathode
Contact
J.J. Shea
Anode
+
0.457cm
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J.J Shea 33
Percent of Arc Root Area Covering Contact
Dc: Cathode arc root diameter
Ac= 0.2 cm2
Current
8
Current (kA)
AgW50/50 (cathode)
200
AgW50/50 (anode)
Gap= 1.8 cm
>100% arc covers
attachment
6
150
100
4
Ac= 0.4 cm2
50
2
Ac= 0.8 cm2
J.J. Shea
0
0
1
2
4
5
6
Time (ms)
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7
0
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J.J Shea 34
Dc/Ac (%)
10
Arc Jet Characteristics
µo I 2
Farc =
4πAarcl
I
Cathode
Cathode Root Diameter
Moving
l
Arc Area
Cathode Jet
Anode Root Diameter
Anode
J.J. Shea
Anode Jet
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x
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J.J Shea 35
Arc Characteristics – Vapor Jet Pressure
Strong Anode and CathodeJets
Anode
and Cathode Jets
Ag/W 50/50
3.2kAp
0.2cm2
Contact
Contact
Cathode
Cathode
0.457cm
Anode
Anode
Ag/W 50/50
8.4kAp
0.4cm2
Vapor disk
Vapor disk
+
Equally Strong Anode and Cathode Jets
Equally strong anode and cathode jets
Cathode
Anode
J.J. Shea
High-Speed Video
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J.J Shea 36
Method for Arc Temperature Estimates
T1
Gap= 1.1 cm
A= 0.8 cm2
AgW35/65
I Gap
σ (t ) =
V Aarc
8
T2
I1
T = 76σ
P1
6
2
30
25
20
3
15
I2
4
10
2
5
J.J. Shea
0
Arc Temperature x103 (oK)
Current (A) or Power x105 (W)
10
0
2
P2
AgW50/50
4
6
Time (ms)
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8
0
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J.J Shea 37
Arc Characteristics - Splatter
Ag100
8.1kAp
0.8cm2
-
Molten Ag
+
• Large amount of molten Ag removed by vapor jet force and magnetic force
• Relatively low viscosity molten silver is easily splattered away – large losses
• A high temperature refractory matrix (i.e. tungsten) greatly reduces silver
loss
J.J.mixtures
Shea
• Also, oxide particle
can increase pool viscosity reducing erosion
due to splatter
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J.J Shea 38
Processing Effects
Anode
Cathode
0
Weight Change (mg)
-20
-40
-60
Type 2
-80
-100
AgW 35/65
-120
Anode (Stationary)
8 kAp
30 C/oper.
-140
-160
-180
J.J. Shea
0
38
76
Type 1
Surface Area
A= 0.8 cm2
Gap= 0.9 cm
114
152
190
228
266
304
Charge, q, (C)
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342
380
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J.J Shea 39
Particle Size Effects
0
AgW 50/50 (v)
-100
Weight Change (mg)
AgW 50/50
-200
-300
-400
AgC 95/5 (f)
-500
AgC 95/5 (c)
5kAp
-600
Shea
Gap= 1.8J.J.cm
0
100
200
Surface Area
A= 0.8 cm2
300
400
500
Anode (Moving)
600
700
800
900 1000
Charge, q, (C)
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J.J Shea 40
Surface Morphology Changes from ½
Cycle Arcing
AgW35/65
10kAp
2kAp
22kAp
J.J. Shea
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J.J Shea 41
Ag Depletion from Surface
100
90
80
Weight %
70
W
Ag
60
50
40
30
O2
20
10
0
J.J. Shea
0
5
10
15
20
Current (kA)p
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J.J Shea 42
Conclusions
• High current AC break arc contact erosion has many factors to
consider.
• This data can be useful for developing erosion models and for
guidance regarding general trends.
•
•
•
•
•
•
Highlights include:
Bridge ignition voltage increased with increasing Ag content.
Short gap (blow-off) has high erosion rate.
When arc root diameter approached contact surface dimension.
erosion rate significantly increased (smaller area higher erosion)
Arc root diameter was proportional to current.
Current density transitions from 4x107 A/cm2 at bridge ignition to a
constant 1x104 A/cm2 independent of current.
Synchronized data with high-speed optical images of the arc can be
J.J. Shea
used to estimate
arc properties.
• Products need to be tested under actual conditions.
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J.J Shea 43