1. Quality and Security Assessment of Protection Systems
Prof. Dr. Rainer Krebs
Principal Expert Power Technologies
Siemens Energy

2. Industrial Power System
Transmission
Distribution
Public &
Private
Utilities
Industrial Power System
Primary Systems
Protection &
Control Systems – ~
Contents
Protection Systems
Power System Influences on Protection Systems
Cascading Protection Trips
Quality and Security Assessment
Conclusion
26-28 May 2009
R. Krebs

3. Protection Systems From Primary Energy Sources to Consumers
Windparcs Onshore/Offshore
Double fed ASM
Voltage Source Converters
Industries
Large Motors, Generators
Power Electronics
Dynamic Loads
Transmission
Short and long lines, cables
Transformers
Diff. Busbar Configs
FACTS / HVDC
Oil and Gas, Harbor-
and Special Systems
MVDC-SIPLINK
LNG
Power Plants
Large Generators
Large Motors
Auxiliary Systems
Distribution
Various Switching Situations
DGs
Short-circuit Current Limiters
26-28 May 2009
R. Krebs

4. Protection Systems Consist of Relay Types of Nearly All Eras
SIPROTEC V4
SIPROTEC V1-V3
1950
1960
1970
1980
1990
2000
2010
Control
Numerical Protection Relays
Analog Relays
Electromechanical Relays
26-28 May 2009
R. Krebs

5. Protection Systems Consist of Relay Types of all Nearly All Manufacturers
26-28 May 2009
R. Krebs

6. Protection Systems Standard Structure
signal
sampling
processing
analysis
Trip signal
formation
Protection Equipment
System
kV, kA
protection
object
System
V, A
signal
adaption
circuit
breaker
control
circuit
breaker
auxiliary
power
26-28 May 2009
R. Krebs

7. Protection Systems Power System Influences
Frequency
‚Very Fast
Transients‘
Transients &
Equipm. Interactions
Switching Voltages Surge Voltages
Power Converters Ferro-Resonances Transformer Switching System Resonances
40 MHz
10 MHz
5 kHz
1 kHz
100 Hz
10 kHz
Power Plant > System > Load
50 Hz fn
E-Generation
E-Transmission
Control &
Protection
Subsynchronous
Resonances
Power Swings
Oscillations of the Turbine-Generator Multimass System (Power Plants > 300MW)
Rotor Oscillations of Generators
10 Hz
5 Hz
0 Hz
26-28 May 2009
R. Krebs

8. Protection Systems Power System Influences
Inrush currents
Transformer overexcitation
CT saturation
Variable system impedances with FACTS
Non system frequent voltages with capacitive voltage transformers
Sub-synchronous frequencies with series compensation
Power swings
Inter-area oscillations
High equipment and route capacity utilization
26-28 May 2009
R. Krebs

9. Protection Systems Involvement in Cascading Outages
Practically there was no blackout without involvement of protection relays!
- Zone 3 trips of distance relays, often used for overload protection instead of use of thermal models in numerical relays - Trip of Distance relays due to missing load and power swing blocking - Uncoordinated protection / or overload settings across borders between diff. Utilities
- Too low synchro-check settings
- OC backup in parallel to distance or differential without delay
- Development of primary system without adaption of relaying design and relay settings - Wrong settings, no system measurements like zero-sequence impedances
Analysis and recommendations for improvement is mandatory!
26-28 May 2009
R. Krebs

10. Protection Systems Development of Selectivity over Years
Problem area ‚short-circuit‘ can often not clearly be confined towards the problem areas ‚overload‘, ‚power swing‘ or other system disturbances.
Design of the protection system and equipment selection follows standard company rules despite of new requirements defined by modern power systems
No consideration of system emergency situations during settings calculation
No consideration of system changes and extensions during settings calculations
Distance
Protection
New Protection Concept !
Short-Circuit
Emergency
Operation,
Overload
26-28 May 2009
R. Krebs

11. Protection Systems Example for Non-Selectivity after Years
Sammis-Star
Example Canada-US-Blackout 2003 50
100
X/Ohm
R/Ohm
MHO-Characteristic
Blinders must be used for load impedance areas in normal and overload situation 
Load impedance during emergency operation Value during US-Blackout 2003 
Min. load impedance during normal operation, planning value
26-28 May 2009
R. Krebs

12. Protection Systems Quality and Security
Stability
avoids disconnections by false tripping
Speed
limits damages
maintains system stability
Modern
Protection System
avoids overfunction
avoids underfunction
Security
limits isolation area
increases availability
Selectivity
26-28 May 2009
R. Krebs

13. Quality and Security Assessment Check and Dimensioning of Instrument Transformers
Check of CTs und VTs for changed conditions
For relays of all manufacturers
Acc. to all international standards
For all protection systems
Simulation and documentation
CTDIM 3.2
26-28 May 2009
R. Krebs

14. Quality and Security Assessment with SIGUARD® - PSA Analysis of Backup O/C-Protection
Line No.
^1-phase-to-ground short-circuit: Fault location at % line length
Backup OC Protection-System Behavior p th 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
100 1 2 3 4 6 7 8 9 11 12 13 14 16 17 18 19 21 22 23 -1
unselective
No trip
t/s
Actual State of the System
SIGUARD® - Patents pending
26-28 May 2009
R. Krebs

15. Quality and Security Assessment with SIGUARD® - PSA Adapted Settings for Backup O/C Protection
Line No.
1-phase-to-ground short-circuit: Fault location at % line length
Backup OC Protection-System Behavior p th 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
100 1 2 3 4 6 7 8 9 11 12 13 14 16 17 18 19 21 22 23 -1
unselective
No trip
t/s
Actual State of the System
Revised Relay Settings
SIGUARD® - Patents pending
26-28 May 2009
R. Krebs

16. Quality and Security Assessment with SIGUARD® - PSA Analysis of Distance Protection for Diff. Fault Resistances
Fehlerwiderstand
< 2,5 Ohm
< 2,4 Ohm
< 2,3 Ohm
< 2,2 Ohm
< 2,1 Ohm
< 2,0 Ohm
< 1,9 Ohm
< 1,8 Ohm
< 1,7 Ohm
< 1,6 Ohm
< 1,5 Ohm
< 1,4 Ohm
< 1,3 Ohm
< 1,2 Ohm
< 1,1 Ohm
< 1,0 Ohm
< 0,9 Ohm
< 0,8 Ohm
< 0,7 Ohm
< 0,6 Ohm
< 0,5 Ohm
< 0,4 Ohm
< 0,3 Ohm
< 0,2 Ohm
< 0,1 Ohm
< 0,0 Ohm
26-28 May 2009
R. Krebs

17. Quality and Security Assessment with SIGUARD® - PSA Analysis of Distance Protection for Diff. Fault Resistances
SIGUARD® - Patents pending
26-28 May 2009
R. Krebs

18. Quality and Security Assessment with SIGUARD® - PSA Analysis of Distance Protection for Diff. Fault Resistances
SIGUARD® - Patents pending
26-28 May 2009
R. Krebs

19. Conclusion
Power systems are changing in Structure Generation Utilization
Quality and security of the protection system can be assessed continuously or from time to time with SIGUARD® - PSA
Settings have to be adapted where necessary to avoid wrong or cascading trips
Relay functionalities have to be adapted where necessary
Communication has to be installed where necessary
Measures can be validated with SIGUARD® - PSA
26-28 May 2009
R. Krebs

20. Thank you for your attention!
Prof. Dr. Rainer Krebs
Principal Expert Power Technologies
Head of System Protection and Power Quality
Siemens AG, E D SE PTI
Freyeslebenstr. 1
91058 Erlangen
Telefon: –
Fax: –
Mobil: –