Uwe Riechert
10/04/2012
IEEE PES Switchgear Committee, 2012 Fall Meeting
September 30 – October 4, 2012
Catamaran Resort Hotel, San Diego, CA, USA
Uwe Riechert, ABB Switzerland Ltd, High Voltage Products, 2012-10-04
Very Fast Transient Overvoltages (VFTO) in
Gas-Insulated EHV & UHV Substations
Tutorial of CIGRÉ Working Group A3.22 / A3.28
Technical Requirements for UHV and EHV Substation Equipment
© ABB Group
September 28, 2012 | Slide 1
Contents



VFTO

Rise time

Amplitude
Simulation

Simulation methods

Verification
Insulation Co-ordination
Approach

Trapped charge voltages

Damping measures

Summary

Conclusions
© ABB Group
September 28, 2012 | Slide 2
IEEE PES Switchgear Committee, 2012
Fall Meeting
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Uwe Riechert
10/04/2012
Very Fast Transient Overvoltages (VFTO)
Switching of Small Capacitive Currents with
Gas-insulated Metal-Enclosed Disconnector Switches
600
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
[kV]
Opening
400
200
0
-200
-400
0,0
Fixed Contact
0,2
[s]
0,3
500
[kV]
350
Closing
Moving Contact
0,1
200
50
-100
-250
-400
0,4
0,5
0,6
0,7
0,8
0,9 [s]
1,0
© ABB Group
September 28, 2012 | Slide 3
Very Fast Transient Overvoltages (VFTO)
Rise Time
Time duration tb of spark ignition in gas such as SF6 is
given by TOEPLER equation:
10000
Rise Time [ns]
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
Air
1000
Measured values
100
SF6
Measured values
10
Field Utilization Factor
1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Gas Pressure [MPa]
© ABB Group
September 28, 2012 | Slide 4
IEEE PES Switchgear Committee, 2012
Fall Meeting
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Uwe Riechert
10/04/2012
VFTO - Amplitude
Principle – Case A
Characteristic Impedance Z
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
Case A
5m
Wave Travel Time τ
U
R=0Ω
UTC = -1 pu
© ABB Group
September 28, 2012 | Slide 5
VFTO - Amplitude
Principle – Case B
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
Case A Case B
5m
5m
10 m
U
U
20 m
R=0Ω
UTC = -1 pu
© ABB Group
September 28, 2012 | Slide 6
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Uwe Riechert
10/04/2012
VFTO - Amplitude
Principle – Damping Effect
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
Case A Case B
5m
5m
10 m
U
U
20 m
R = 10 Ω
UTC = -1 pu
© ABB Group
September 28, 2012 | Slide 7
VFTO - Amplitude
Principle – Real Trapped Charge
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
Case A Case B
5m
5m
10 m
U
U
20 m
R = 10 Ω
UTC = -0.45 pu
© ABB Group
September 28, 2012 | Slide 8
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Fall Meeting
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Uwe Riechert
10/04/2012
VFTO - Amplitude
Traveling wave reflection – open end
Impedance
matching
ZS=Z0
Open end
ZL= ∞
u(t,x)
uL=u(x1)
uS=u(x2)
x
Coaxial line 2D model
Conductor
uL=u(t,x=x1)
Open end reflection
 2D model
 Coaxial line
 Vs= +1 V, ZS= Z0
 ZL= ∞, (VL= 0 V)
 Simulation time: 100 ns
uS=u(t,x=x2)
© ABB Group
September 28, 2012 | Slide 9
VFTO
VFTO versus Rated Voltages
5
4
Voltage [pu]
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
Rated lightning impulse withstand voltage
Rated switching impulse withstand voltage
Rated power frequency withstand voltage (peak)
3
GIS
GIS
GIS
2
1
0
300
Hybrid-IS
Hybrid-IS
Japan
500
South Africa
700
900
Rated voltage Ur [kV]
China
1100
Source: CIGRE TB 456, WG A3.22
© ABB Group
September 28, 2012 | Slide 10
Dependency of rated withstand voltages and calculated
VFTO on rated voltage as per IEC 62271-203
IEEE PES Switchgear Committee, 2012
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Uwe Riechert
10/04/2012
VFTO
Classification in High Voltage GIS Substation
Origin
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
switching operation in gas-insulated HV substations
Very fast transients in gas-insulated substations
VFTO
Propagation
Internal transient voltages
Travelling waves
between inner conductor and
enclosure
Effect
Leader branching
Stresses in insulation
design,
free moving particles,
DC stress
External transient voltages
Transient
enclosure
voltage
TEV
Transient
electromagnetic
fields
EMF
Stresses in
secondary
equipment
control circuits, EMC,
personnel safety
Travelling
waves on
overhead lines
Stresses in airinsulated
operating equipment
Transformer, bushings
© ABB Group
September 28, 2012 | Slide 11
IEC 62271-102 Annex F
Requirements for switching of bus-charging currents by
disconnectors for rated voltages 72.5 kV and above
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion

Test Duty TD 1: Switching of a very short section of busbar duct

Normal type test and mandatory for DS

The circuits for DS testing were chosen in such a way, that
maximum pu (per unit) values for VFT peak were generated and it
was assumed that they would also be the highest possible in the
GIS.

The test circuit has to be arranged in such a way, that the measured
peak voltage to ground without a trapped charge voltage at the load
side and 1 pu at the source side is higher than 1.4 pu. The time to
first peak should be less than 500 ns.
© ABB Group
September 28, 2012 | Slide 12
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Fall Meeting
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Uwe Riechert
10/04/2012
VFTO Measurement
Test Set-up TD 1
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
10.7m
1.5m
© ABB Group
September 28, 2012 | Slide 13
VFTO Simulation
Calculation and Measurement of VFTO
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion

Conventional single spark
approach

EMTP- electromagnetic
transient program

The accuracy of the simulation
model must be verified

VFTO calculation and
measurement when switching
busbars with a GIS DS as per IEC
62271-102


without pre-charging

with pre-charging
The measured voltage
progressions coincide very well
with the simulation.
© ABB Group
September 28, 2012 | Slide 14
IEEE PES Switchgear Committee, 2012
Fall Meeting
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Uwe Riechert
10/04/2012
VFTO Simulation
Extended Disconnector Model
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion



Simulation of the entire
process

Consideration of the dielectric
behavior of the DS

Simulation of all pre-strikes
and re-strikes
ATP/EMTP
MODEL
Calculation

Trapped Charge (DC)

Pre- and Re-strike duration

Number of strikes
As basis for the insulation
coordination
i
r = r(t,uS,uL,i)
uS
uL
DC Trapped Charge
© ABB Group
September 28, 2012 | Slide 15
VFTO – Full DS Operation
Comparison of Calculation and Measurement (Tests)
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion

A comparison between simulation and measurement can verify the
accuracy of the simulation.
400
400
*10 3
*10 3
300
300
200
200
100
100
0
0
-100
-100
-200
-200
-300
-300
-400
0,0
-400
0,0
0,1
0,2
(f ile disconnector_03_v erif ication_test_duty .pl4; x-v ar t) v :U2
0,3
0,4
0,5
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
(f ile disconnector_03_v erif ication_test_duty .pl4; x-v ar t) v :U2
factors:
1
-1
offsets:
0,00E+00 0,00E+00
© ABB Group
September 28, 2012 | Slide 16
IEEE PES Switchgear Committee, 2012
Fall Meeting
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Uwe Riechert
10/04/2012
VFTO Simulation – Extended Model
Calculation of Number of pre-strikes during one Closing
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
VFTO (Peak Value, abs.) [pu]
2.0
1.5
1.0
0.5
TCV -1 pu
TCV -0.3 pu
0.0
0.5
0.75
1
Time [s]
1.25
1.5
© ABB Group
September 28, 2012 | Slide 17
VFTO Simulation – Extended Model
Trapped Charge Voltage TCV
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion

Use of real trapped charge behavior of the disconnector, if known.

Otherwise the worst case assumption of a trapped charge voltage of
-1 pu should be used for the simulation.
20%
Simulated
Measured
10%
Probability
15%
5%
0%
0.0
0.2
0.4
0.6
0.8
1.0
Trapped charge voltage (abs.) [pu]
© ABB Group
September 28, 2012 | Slide 18
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Fall Meeting
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Uwe Riechert
10/04/2012
VFTO Simulation – Extended Model
TCV Distribution

The TCV distribution depends strongly on the contact speed.

The TCV is specific for each design and could be analyzed during type
testing or simulated with high accuracy.
1
Trapped charge voltage (abs.) [pu]
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
calculated
90% probability
95% probability
99% probability
measured
0.8
0.6
0.4
0.2
0
0
0.5
1
1.5
2
2.5
3
3.5
Contact speed [m/s]
© ABB Group
September 28, 2012 | Slide 19
VFTO 3D Simulation
Full-Maxwell Simulation Approach
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion

Full-Maxwell simulation approach (vector FEM implemented in
COMSOL)

Full-Maxwell time-domain simulation approach offers the following
advantages:

Very fast transients can be visualized and its wave character can be
better understood

Local field values are available over the 3D GIS geometry

Critical places of the GIS design can be reliably detected

Sensitivity study with small geometrical changes is possible

Design optimization is possible
© ABB Group
September 28, 2012 | Slide 20
IEEE PES Switchgear Committee, 2012
Fall Meeting
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Uwe Riechert
10/04/2012
VFTO 3D Simulation
Example
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
© ABB Group
September 28, 2012 | Slide 21
VFTO 3D Simulation
Simulation Results
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
© ABB Group
September 28, 2012 | Slide 22
IEEE PES Switchgear Committee, 2012
Fall Meeting
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Uwe Riechert
10/04/2012
VFTO 3D Simulation
Experimental Verification of the Results
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
© ABB Group
September 28, 2012 | Slide 23
VFTO Simulation
Comparison of Simulation Methods
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
Conventional
Model
One Strike
„Worst case“
Extended EMTP
3D Model
Model
Entire process
Detailed Calculation
of GIS
Description
Insulation
coordination
Considaration of
Design
Amplitude
Rise Time
Accuracy > 95%
Trapped Charge
Pre- and Re-striking
Times
Visualization
Local Field Strength
Internal Mitigation
Studies
Optimization
© ABB Group
September 28, 2012 | Slide 24
IEEE PES Switchgear Committee, 2012
Fall Meeting
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Uwe Riechert
10/04/2012
Insulation Co-ordination Approach
Overview according to IEC 60071-1
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
Step 1 Calculation of VFTO (peak
value and rise time)
Trapped charge voltage
(TCV) behavior
known
NO
YES
System analysis
VFTO calculation
(verified calculation
method)
YES: UTCV = - 0.3 … - 1.0 pu
NO: UTCV = - 1.0 pu
Evaluation of trapped
Maximum
calculated VFTO
Umax_VFTO
charge behavior
Insulation characteristic

Statistical distribution

Inaccuracy of simulation
KC = 1.05
Co-ordination factor KC
Selection of the insulation
meeting the
performance criterion
Correction factors

Atmospheric correction
factor Kt

Aging in service

Quality of installation
Co-ordination withstand
voltage
Ucw_VFTO
KS
Application of factors to
account for the
differences between
type test and actual
service conditions
Safety factor KS
External
insulation
YES: Kt
Required withstand
voltage
Urw_VFTO
Step 2 Comparison of calculated
VFTO values with LIWV
level for the different
equipment by using:

Co-ordination factor Kc

Safety factor Ks

Test conversion factor Ktc
Test conditions
Test conversion factor Ktc
Ktc ≤ 1
Comparison with LIWV
LIWV ≥ Urw_VFTO
Standard lightning
impulse withstand voltage
(LIWV)
NO
Definition of required
damping measures



Trapped charge behavior
Resistance value for
damping resistor
Other mitigation methods
YES
Step 3 Definition of measures
according to the insulation
co-ordination
No damping measures
necessary
© ABB Group
September 28, 2012 | Slide 25
VFTO Co-ordination: Step 2
Comparison of calculated VFTO values with LIWV level
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion

Calculation of the required VFTO withstand voltage UCW_VFTO for the
different equipment by using:
Co-ordination factor Kc (statistical distribution, inaccuracy of simulation,
frequency of occurrence)  1.05 ( 1.0 … 1.1)

 Safety factor Ks (atmospheric correction, aging behavior in service,
quality of installation)  1.15 (1.05 for air insulation)
 Test conversion factor Ktc (for a given equipment or insulation
configuration, describes the different withstand behavior under VFTO stress
compared to the stress with standard LI voltages)  1.0 (0.95 for SF6)

Comparison of calculated required VFTO withstand voltage values
with LIWV level
© ABB Group
September 28, 2012 | Slide 26
IEEE PES Switchgear Committee, 2012
Fall Meeting
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Uwe Riechert
10/04/2012
Insulation Co-ordination Approach
Definition of Damping Measures
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion

Definition of measures according to the insulation co-ordination

No damping measure required

Damping measure required

DS with low TCV

Damping resistor
Definition of required resistance value

Other mitigation methods
Magnetic damping or resonators
© ABB Group
September 28, 2012 | Slide 27
VFTO Mitigation – Damping Resistor
Principles
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion

Arc commutation

Series resistor (contact)
(2)

Parallel resistor (contact)
(1)
(2)
(1)
© ABB Group
September 28, 2012 | Slide 28
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Uwe Riechert
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VFTO Mitigation – Damping Resistor
Effect
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion

Italy: 110 Ω

China, Japan, Korea: 500 Ω
© ABB Group
September 28, 2012 | Slide 29
VFTO Mitigation – Damping Resistor
Working Principle and Structure
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
© ABB Group
September 28, 2012 | Slide 30
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Uwe Riechert
10/04/2012
VFTO Mitigation – Damping Resistor
Requirements for the Resistor
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion

Voltage withstanding characteristic and energy absorption
capability of the resistor in case of re-strikes and pre-strikes
between the moving contact and the arcing electrode of the
resistor.

A flashover across the resistor may lead to high VFTO and has to
be avoided. A higher resistance value leads to a higher voltage
stress across the switching resistor. The rate of rise of the voltage
across the resistor could be very high and depends on the set-up
and the capacitances on the load and source side.

The thermal absorption capability of damping resistor is defined to
withstand the thermal stress of one close-open operation. During
the switching a lot of re-strikes or pre-strikes occur. The absorption
energy of each strike must be added to get the whole absorption
energy for one operation.
© ABB Group
September 28, 2012 | Slide 31
Insulation Co-ordination Approach
New Mitigation Methods
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
High frequency RF resonator

Low quality factor designed
to cover a wider frequency
range

Tuned to the dominant
harmonic component

20 % damping
Nano-crystalline material

Placed around the conductor

Depending on number,
material and size of the rings

20 % damping
© ABB Group
September 28, 2012 | Slide 32
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Uwe Riechert
10/04/2012
Summary
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
Summarizing the different experiences an insulation co-ordination
procedure with three steps is proposed, following the general insulation
co-ordination approach.
The trapped charge voltage is specific for each design and could be
analyzed during type testing or simulated with high accuracy and has to
be used for the insulation coordination.
Required damping measures could be defined for the specific project.
© ABB Group
September 28, 2012 | Slide 33
Conclusions
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
Everything should be as simple as it is
but not simpler.
Albert Einstein
© ABB Group
September 28, 2012 | Slide 34
IEEE PES Switchgear Committee, 2012
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Uwe Riechert
10/04/2012
CIGRÉ
UHV Working Groups
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
(1) CIGRÉ WG A3.22: Technical Requirements for Substation Equipment
Exceeding 800 kV – TB 362 & TB 456
(2) CIGRÉ WG B3.22: Technical Requirement for Substations Exceeding 800 kV –
TB 400
(3) CIGRÉ Ad Hoc TF of SC D1: VFTO in UHV GIS Systems
(4) CIGRÉ WG D1.36: Special Requirements for Dielectric Testing of Ultra High
Voltage (UHV) Equipment
(5) CIGRÉ WG C4.306: Insulation Coordination for UHV AC Systems
(6) CIGRÉ WG A3.28: Switching phenomena and testing requirements for UHV &
EHV equipment
(7) CIGRÉ WG B3.27: Field tests technology on UHV substation during
construction and operation
© ABB Group
September 28, 2012 | Slide 35
Summary
Outlook – EHV & UHV AC World Map
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion
Canada
Russia
USA
Italy
China
Japan
South Korea
Venezuela
India
Brazil
South Africa
1050 kV – 1100 kV
735 kV – 800 kV
735 kV – 800 kV and 1100 kV – 1200 kV
Source: CIGRÉ WG C4.306 / highest voltages
© ABB Group
September 28, 2012 | Slide 36
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Uwe Riechert
10/04/2012
Author
CV Dr.-Ing. Uwe Riechert
Content
Introduction
VFTO
Simulation
Insulation
Co-ordination
Damping
Summary
Conclusion

Studies in electrical engineering at the Dresden Technical University

Research assistant at the Dresden Technical University


© ABB Group
September 28, 2012 | Slide 37


Diagnostics and dielectric properties of polymeric insulated
cables for ac and dc applications

PhD on the topic of polymeric insulated HVDC cables in 2001
Since 1999 ABB Switzerland Ltd

Up to 2001: test engineer in the high voltage laboratory

Since 2001: switchgear development, responsible for partial
discharge diagnostic and monitoring, solid insulating materials,
dielectric design, patents, testing, product certification and
cooperation with research centers and universities

Since 2004: development project manager (e.g. 1100 kV circuitbreaker)

2008: senior manager

2009-2011: high current systems (generator circuit breaker)
development

Since 2011: gas insulated switchgear development
Membership

DKE (German Commission for Electrical, Electronic & Information
Technologies of DIN and VDE)

Swiss Electrotechnical Committee (CES) TK42 (convener) and
TK115 (convener)

CIGRÉ working groups (AG D1.03, WG A3.28, WG D1.25, WG
D1.28, WG C4.306).

Convener of CIGRÉ working group D1.36: Special requirements
for dielectric testing of Ultra High Voltage (UHV) equipment

IEC TC42/WG19
email: uwe.riechert@ch.abb.com
© ABB Group
September 28, 2012 | Slide 38
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