s
Reliabilty of the Electrical Systems
Elimination of Bottlenecks in Transmission Systems using FACTS and HVDC
Mario Lemes – Siemens Brazil
Dietmar Retzmann – Siemens Germany
The Blackout – A spread of Cascading Events
A brief Summary of the RoutCauses:
n Lack of Investments into the Grids (high CostPressure for the AssetOwners due to Deregulation), leading to Bottlenecks in Transmission
n Need for more Regulatory Works (Rules, Gridcode etc.) for the Operation of Transmission Systems and Power Plants in Case of Cascading Events
n Weak Points in the Energy and Demand Side Management EMS, DSM
The Final Report - Direct Causes and Contributing Factors
Source: USCanada Blackout Final Report April 2004
The Blackout: Conclusions and Recommendations - an Excerpt
Source: USCanada Blackout Final Report April 2004
3T: Trees Tools Training
System Enhancement & Elimination of Bottlenecks
● OnLine Monitoring and RealTime Security Assessment ● Increase of Reserve Capacity
What can be done ? Are other large Systems in the World Safe ?
n Enhancement of Communication and Monitoring with IT (EMS & DSM)
n Review of Generator and Load Trip Strategy (UnderVoltage and UnderFrequency Trip Levels and Times)
n Use of FACTS for ReactivePower Compensation, PowerFlow Control and Prevention of Voltage Collapse
n Active Damping of Power Oscillations with FACTS & HVDC
n Possibly more HVDC in the interconnected USCanada Areas: HVDC is a Barrier against cascading events (Voltage Collapse and Frequency decline): Quebec was not affected !
n Increase of Reserve Capacity (HVDC, new Generations)
Task Forces are “ looking into” their Systems all over the World
Quebec Canada was not affected – Why ?
The Reasons are very clear:
n Québecs major Interconnections to the affected Areas are DCLinks
n These DCLinks are like Barriers against Cascading Events
n They split the Systems at the right Point in the right Time, only if necessary
n Hence, Quebec was “ saved”
n In addition, for the USSystem Restoration, the DCs assisted by “ Power Injection”
Spain-France Interconnections: A weak Link
“ Stable” Power Flow: 1500 2000 MW. Stability Limit: 0 MW.
System unstable in Case of Power Reversal.
However, in UCTE, bottlenecks are well known. Looking into details …
Waiting for a new 400 kV Line ?
Summary of Root Causes for Italian Blackout
Source: UCTE Interim Report 27.10.2003
Source: UCTE Interim Report 27.10.2003
Blackout in Italy: Conclusions
Summary: Ø There is congestion in the UCTE System Ø Too high phase angle difference between UCTE main grid and Italy Ø Voltage collapse in Italy Ø Loss of generation Ø Blackout in Italy
Evaluation of Countermeasures: Ø Avoidance of Congestion Ø System Enhancement
by means of: Ø Studies
Source: UCTE Interim Report 27.10.2003
System Enhancement - How to use HVDC & FACTS
U U 1 1 U U 2 2
U U 1 1 U U 2 2
Parallel Compensation
X X
X X
Series Compensation
G ~ G ~
, , δ 1 , , δ 2
sin ( sin (δ 1 δ 2 )
LoadF low Control
P P
P P = =
Elimination of Bottlenecks in Transmission – Prevention of Overloads and Outages
Source: National Transmission Grid Study; U.S. DOE 05/2002
Load Displacement (by Impedance Control)
Short Circuit Current Limitation for Connection of new Power Plants
The FACTS & HVDC “ Application Guide”
Load Management by PowerFlow Control
Avoidance of Loop-Flows by means of Power-Flow Control
360 km
400 MW
Loads
Loads
3 ~
Power Flow Controller
3 ~
Restoration of the initial Power Flow
200 MW
… Quite Easy
A B
UCTE: Load-Flow Improvement with FACTS/HVDC
DE CZ
Uncontrolled LoadFlow
DE
Power Flow Controller
CZ Control of LoadFlow
Benefits: Directing of LoadFlow
Basis for Power Purchase Contracts
Voltage Collapse – without and with Reactive-Power Compensation
No Reactive Power Support
Voltage remains low
Reactive Power Support
Voltage recovers
Voltage Collapse - How to explain it
n During the Fault, the Induction Machines Slip increases
n This is like a Starting Conduction: high Currents 5 x I nominal
n High Reaction Power Consumption decreases the Recovery Voltage
n ReactivePower Compensation is essential
The Solution: SVC + MSC. Option: STATCOM. However, the
required Reaction Time is only 100 ms =
Voltage Collapse – What are the “Parameters” ?
Fault Duration: here 150 ms
Initial Recovery Voltage ~ Σ S Machines
SCC System
SCC System + 5 x
Very High Reactive Power Consumption
A Study Example: SVC Muldersvlei, RSA
No SVC Voltage Collapse leads to Protection Trip and System Blackout
With SVC System recovers*
The test Case : AC System with large Induction Machine Loads
Fault Duration: 150 ms*
* In this Simulation (RTDS), both Fault duration & Machine Rating have been selected to “ hit” the Stability Limit → “ Slow Recovery”
Classification of Stability Problems in Power Systems
Overview about basic physical Problems, which are related to a high loading of Transmission Systems by Transport of electrical Energy.
The main types of Instability Concerns are: Ø Cascading Line Tripping by Overload Ø Loss of Synchronism due to Angle Instability Ø Oscillatory Instability causing self exciting InterArea Oscillations Ø Exceeding of the allowed Frequency Range (Over and Under Frequency)
Ø Voltage Collapse
Source: UCTE Interim Report 27.10.2003
Alternatives of Power System Interconnections
System 1 System 2
a) AC Interconnection: many Lines “ at the Beginning”
c) Hybrid AC/DC Interconnection: The flexible synchronous Solution
b) DC Interconnection: 1 Link sufficient for stable Interconnection
HVDCLDT 9 GW: TAGG
Tomorrow:
Power Exchange today: Western Eastern 700 MW Western ERCOT 200 MW Eastern ERCOT 800 MW
US Grid: DC Energy Bridges - more in the Future ?
Eastern Interconnection
Western Interconnection
Power River Basin, WY Chicago, IL
DCLinks Today:
TAGG TransAmerica Generation Grid: “ Coal & Wind by Wire”
ERCOT Los Angeles, CA
Planning the Future
New DCs from Canada ?
System A
AC double-link 1
1200 MW
Ac double-link 2 7
System B
200 GW Grid A 200 GW Grid B
System Stability: Comparison of AC & Hybrid Interconnection (Study for 400 kV Grids)
System A System B
AC double-link 2
DC-link 1
7 1200 MW
AC & Hybrid Interconnection - Test Results
Only AC System instable after Fault Hybrid AC/DC System remains stable
AC Link 1
AC Link 2 AC Link 2
DC Link 1
m With DC Solution, Interconnection Rating is determined only by the real Demand of Transmission Capacity
m With AC solution, for System Stability Reasons, AC Rating must be higher than the real Demand on Power Exchange
m Increase of Power Transfer: With DC, staging is easily possible
m With DC, the Power Exchange between the two Systems can be determined exactly by the System Operator
m DC features Voltage Control and Power Oscillation Damping
m DC is a Barrier against Stability Problems and Voltage Collapse
m DC is a Barrier against cascading Blackouts
m Predetermined mutual Support between the Systems in Emergency Situations
Benefits of DC Solution for System Interconnection
How large can a synchronous System be ?
Effor ts, Benefits
Interconnected Operation
Benefits
Efforts
Advantages of
Size of inter connected Gr id
Optimum
Effor ts, Benefits
Interconnected Operation
Benefits
Efforts
Advantages of
Size of inter connected Gr id
Optimum
Interconnected Systems
o Load Flow Problems (needs Management of Congestion)
o Frequency Control
o Voltage Stability
o Oscil lation Stability
o InterArea Oscillations
o Blackout Risk due to cascading Effects
o Physical Interactions between Power Systems
When the Synchronous System is very large – Advantages diminish
Long Distance Transmission Systems
o Voltage Stability
o Reactive Power Problems
o SteadyState Stability
o Transient Stability
o Subsynchronous Oscillations
Limitations of large AC Systems
FACTS & HVDC - The Result
Influence: *
¡ low or no l l small l l l l medium l l l l l l strong
* Based on Studies & practical Experience
HVDC (B2B, LDT)
UPFC
(Unified Power Flow Controller)
SVC (Static Var Compensator)
STATCOM (Static Synchronous Compensator)
Load-Flow Control
Voltage Control: Shunt Compensation
l l l l l l
l l l l l l
FSC (Fixed Series
Compensation)
TPSC (Thyristor Protected Series Compensation)
TCSC (Thyristor Controlled Series Compensation)
Variation of the Line Impedance: Series Compensation
Voltage Quality
Stability Load Flow
Scheme Devices Principle
l l
l l
l l
l l l l l l
l l l l l l
l l l l
l l l l l l
l l l l l l
l l l l
l l l l l l
l l l l
l l
l l l l l l
l l l l l l
¡
l l
l l l l
¡
Impact on System Performance
l l l l l l
System Interconnections: The “Extended“ HVDC & FACTS Application Guide
System A
System B
System C
System E
System F
HVDC LDT
B2B GPFC
FACTS
Voltage Power Flow
Control of Limitation of
Faults SCC
Power Swing Damping
Barrier x x
x TCSC
x
SVC* SVC* SCCL
x
x
x
x Barrier
Spread of Voltage Collapse
x
x
x Risk
Risk of Spread of Voltage Collapse Barrier Barrier Risk
System D
*or STATCOM
Lessons learned: HVDC and FACTS are essential for Transmission
Need for Advanced Transmission Solutions
This is This is unavoidable unavoidable ... but ... but HVDC & FACTS HVDC & FACTS can support can support Recovery Recovery
Reduction Reduction of Outage of Outage Times & Times & more more Stability Stability
Blackout Blackout Increasing Increasing Oscillations Oscillations
If there is no If there is no HVDC HVDC, , no no FACTS FACTS ... ...
Intelligent Solutions for Power Transmission
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