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

Thank You for your Attention!

with HVDC & with HVDC &

FACTS from FACTS from

Siemens Siemens