Nils P. Basse, UPB International Seminar in Electronics Engineering, May 2009
Physics of arc interruption
in circuit breakers
© ABB Group
April 16, 2009 | Slide 1
Outline
© ABB Group
April 16, 2009 | Slide 2
1.
Circuit breakers
2.
Mixing experiment
Outline
© ABB Group
April 16, 2009 | Slide 3
1.
Circuit breakers
2.
Mixing experiment
What is a circuit breaker?
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A circuit breaker is an automatically-operated
electrical switch
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It is designed to protect an electrical circuit from
damage caused by overload or short-circuit
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A circuit breaker is
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a device used to open/close electric circuits
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an ideal conductor in closed position
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an ideal insulator in open position
Why use a circuit breaker?
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Fault current switching
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Load current switching
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April 16, 2009 | Slide 4
Unplanned events initiated by the network’s protection system
Planned events initiated by the system operator
Where does one use circuit breakers?
HV circuit breakers
GENERATION
TRANSMISSION
DISTRIBUTION
System voltage: 12-24 kV
Rated current: 6000-24000 A
Max. short-circuit current: 50-500 kA
System voltage: 72-800 kV
Rated current: 2500-4000 A
Max. short-circuit current: 25-63 kA
MEDIUM AND LOW
VOLTAGE
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April 16, 2009 | Slide 5
Arcs do not extinguish by themselves...
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April 16, 2009 | Slide 6
Typical circuit breaker design
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April 16, 2009 | Slide 7
High voltage (HV) circuit breakers are key components in
all power systems. They are the final link in protection of
the power system from short-circuits.
Transient flow effects
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April 16, 2009 | Slide 8
Pressure scaling of current interruption
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Significant scatter in the measurements:
- Is this important for interruption performance?
25
dI/dt limit [A/μs]
20
15
10
Hold
Late fail
Early fail
Fit
13% error
5
0
0
© ABB Group
April 16, 2009 | Slide 9
5
10
15
20
25
30
Heating volume pressure [bar]
35
Pressure measured close to the arc zone
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Flow reversal induces transient pressure oscillations in the
heating channel and arc zone
30
pheating volume 1
pheating channel
Pressure [bar]
25
20
15
10
-5
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April 16, 2009 | Slide 10
-2.5
0
Time [s]
2.5
5
x 10
-3
Computational fluid dynamics (CFD) simulations
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April 16, 2009 | Slide 11
Research and development
Validation
EXPERIMENTS
SIMULATIONS
(e.g. CFD)
• Detailed understanding of the physical processes
• Optimisation of design through simulation
• Reduction of development tests/costs
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April 16, 2009 | Slide 12
Measurements and CFD simulations compared
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Temporal behaviour closely matched
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Absolute values within ± 20 % (in this case)
Meas. pheating volume 1
30
Sim. pheating volume
Meas. pheating channel
Pressure [bar]
25
Sim. pheating channel
20
15
10
-5
© ABB Group
April 16, 2009 | Slide 13
-2.5
0
Time [s]
2.5
5
x 10
-3
Outline
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April 16, 2009 | Slide 14
1.
Circuit breakers
2.
Mixing experiment
Setup of the mixing experiment
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Hot gas mixing in the heating volume of gas circuit
breakers determines the current interruption performance
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A simplified small-scale test device with a 2D transparent
heating volume was constructed to visualise the mixing
Mirror
Test object
Lens
Mirror
Lens
Filter
Pin hole (schlieren)
CCD camera
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April 16, 2009 | Slide 15
Laser source
Heating volume and arc zone
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The heating volume consists of 2 Plexiglas plates
enclosing Teflon parts
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Arc ignition wire through hollow contacts
Heating
volume
Pressure
sensor HV
Heating
channel
Hollow
plug
Hollow
plug
Pressure
sensor arc
Arc zone
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April 16, 2009 | Slide 16
Arc discharge overview
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Left-hand plot: Arc current
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Right-hand plot: Arc pressure and heating volume pressure
Shot 19
Shot 19
2.2
10
Arc zone
Heating volume
2
Pressure [bar]
Current [kA]
8
6
4
1.8
1.6
1.4
1.2
2
1
0
0.8
-10
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April 16, 2009 | Slide 17
-5
Time [s]
0
5
x 10
-3
-10
-5
Time [s]
0
5
x 10
-3
Auto correlation analysis
x 10
-3
Auto correlation signal a
1
1.5
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Determines the frequency of an
oscillating signal
Timelag [s]
1
0.5
0.5
0
0
-0.5
-1
Signal a = 500 Hz
-0.5
-1.5
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Signal b = 1 kHz
2
4
6
Time [s]
-1
8
x 10
-3
2.5
x 10
-3
Auto correlation signal b
1
1.5
1
1.5
Timelag [s]
Amplitude [a.u.]
2
Signal a
Signal b
1
0.5
0.5
0.5
0
0
-0.5
-1
0
-0.5
0
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April 16, 2009 | Slide 18
-0.5
-1.5
2
0.002
0.004
0.006
Time [s]
0.008
0.01
4
6
Time [s]
-1
8
x 10
-3
Frequency of heating volume pressure oscillation
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The pressure wave propagation in the heating volume
can be used to estimate the average temperature:
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Average speed = 2 × volume width × oscillation frequency
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Early average speed = 396 m/s
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Corresponds to 391 K
Late average speed = 792 m/s
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April 16, 2009 | Slide 19
Corresponds to 1683 K
Refraction of light: Visualising the invisible
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April 16, 2009 | Slide 20
Robert Hooke first described methods to observe
inhomogeneous media in 1665 in his treatise on optics,
Micrographia
Shadowgraphy
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April 16, 2009 | Slide 21
Shadowgraphy uses the free propagation of a collimated
beam a small distance beyond the object to create patterns
of increased and decreased light intensity
Shadowgram of bullet at Mach 1.5
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April 16, 2009 | Slide 22
„Focused“ shadowgraphy
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April 16, 2009 | Slide 23
How to extract the flow velocity field
1.
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April 16, 2009 | Slide 24
Pick two sequential frames
Cross correlation analysis
2.
Cross correlate subwindows of the two frames
x 10
2.5
2
Time 1
Time 2
-3
Cross correlation (1 and 2)
1
1.5
Distancelag [m]
Amplitude [a.u.]
1
1.5
1
0.5
0.5
0.5
0
0
-0.5
-1
0
-0.5
0
© ABB Group
April 16, 2009 | Slide 25
-0.5
-1.5
0.002
0.004
0.006
Distance [m]
0.008
0.01
2
4
6
Distance [m]
-1
8
x 10
-3
Velocimetry
3.
Plot the velocity vectors
Shot 19, time = -0.00250 s
70
Height [mm]
60
50
40
30
20
20
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April 16, 2009 | Slide 26
40
60
Width [mm]
80
100
Speed
4.
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April 16, 2009 | Slide 27
Convert velocity to speed
Example: Flow speed at a fixed position
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The flow speed at the bottom of the heating volume
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Outflow from heating volume clearly visible
Shot 19
30
Speed [m/s]
20
10
0
-10
Speed at bottom
X-component
Y-component
-20
-30
© ABB Group
April 16, 2009 | Slide 28
-10
-5
Time [s]
0
5
x 10
-3
Acknowledgements
© ABB Group
April 16, 2009 | Slide 29
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Margarita Abrahamsson
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Riccardo Bini
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Christian Franck
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Javier Mantilla
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Felix Rager
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Michael Schwinne
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Martin Seeger
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Torsten Votteler
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Benjamin Wüthrich