Master in Advanced Power Electrical Engineering

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Techno-economic aspects of power systems

Ronnie BelmansDirk Van Hertem

Stijn Cole

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• Lesson 1: Liberalization

• Lesson 2: Players, Functions and Tasks

• Lesson 3: Markets

• Lesson 4: Present generation park

• Lesson 5: Future generation park

• Lesson 6: Introduction to power systems

• Lesson 7: Power system analysis and control

• Lesson 8: Power system dynamics and security

• Lesson 9: Future grid technologies: FACTS and HVDC

• Lesson 10: Distributed generation

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• Power system control Why? How?

• FACTS Voltage control Angle control Impedance control Combination

• HVDC Classic Voltage source converter based

Overview

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Power transfer through a lineHow?

• Active power transfer: Phase angle Problems with long distance transport

o Phase angle differences have to be limitedo Power transfer ==> power losses

• Reactive power transfer Voltage amplitude Problems:

o Voltage has to remain within limitso Only locally controlled

By changing voltage, impedance or phase angle, the power flow can be altered ==> FACTS

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Power transfer through a line:

distanceX ~

1 2

2

1 1 2

P = sin

Q = cos

U Uδ

X

U U Uδ

X X

Power transfer through a lineTheory

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UK

F CH

IE

B

D35 %

A

NL

18 %13 %

8 %

34 %34 %

20 %

10 % 3 %

11 %

European power flowstransport France ==> Germany

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Overview

• Power system control Why? How?

• FACTS Voltage control Angle control Impedance control Combination

• HVDC Classic Voltage source converter based

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• Application Voltage magnitude control Phase angle control Impedance Combination of the above

Divisions within FACTS

• Implementation Series Shunt Combined HVDC

• Energy storage Yes or no

• Switching technology Mechanical Thyristor IGBT/GTO: Voltage Source Converter

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Application domain FACTS

Transmission level• Power flow control

Regulation of slow power flow variations

• Voltage regulation Local control of voltage profile

• Power system stability improvement Angle stability

o Caused by large and/or small perturbations Voltage stability

o Short and long term

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Application domain FACTS

Distribution level• Quality improvement of the delivered voltage to sensitive loads

Voltage drops Overvoltages Harmonic disturbances Unbalanced 3-phase voltages

• Reduction of power quality interferences Current harmonics Unbalanced current flows High reactive power usage Flicker caused by power usage fluctuations

• Improvement of distribution system functioning Power factor improvement, voltage control, soft start,...

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1 2

21 1 2

P= sin

Q= cos

U Uδ

X

U U Uδ

X X

Voltage magnitude adjustment

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Different configurations:

Thyristor Controlled Reactor (TCR)

Thyristor Switched Capacitor (TSC)

Thyristor Switched Reactor (TSR)

Mechanical Switched Capacitor (MSC)

Mechanical Switched Reactor (MSR)

Often a combination

Static Var Compensation - SVC

• Variable thyristor controlled shunt impedance Variable reactive power source Provides ancillary services

o Maintains a smooth voltage profileo Increases transfer capability o Reduces losses

Mitigates active power oscillations Controls dynamic voltage swings under various system

conditions

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STATic COMpensatorSTATCOM

• Shunt voltage injection Voltage Source Convertor (VSC) Low harmonic content Very fast switching More expensive than SVC Energy storage? (SMES, supercap)

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Price comparison voltage regulation

• Cost of voltage regulation capabilities dependent on: Speed Continuous or discrete regulation Control application

• 300 MVAr – 150 kV Capacitor banks: 6 M€ (min) SVC: 9 à 17 M€ (# periods) Statcom: 31 M€ (ms)

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1 2

21 1 2

P= sin

Q= cos

U Uδ+α

X

U U Uδ+α

X X

Phase shifting transformer Voltage angle adjustment.

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1 2 sinPST

U UP= δ+α

X + X

Phase shifting transformer

• Allows for some control over active power flows

• Mechanically switched ==> minutes

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U

25 ° ==> 10 % voltage rise ==> 40 kV @ 400 kV

Phase shifting transformer (II)Principles

• Injection of a voltage in quadrature of the phase voltage

• One active part or two active parts

Asymmetric Symmetric

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2

1'

311

2

32'3'3'

Voltages over coils on the same transformer leg are in phase

Phase shifting transformer (III)One active part

• Series voltage injection

• In quadrature to the phase voltage

• One active part: low power/low voltage (high shortcircuit currents at low angle)

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Phase shifting transformerRegulating

• Changing injected voltage: Tap changing transformer Slow changing of tap position: ½ min

• Control of the injected voltage: Centrally controlled calculations Updates every 15 minutes Often remote controlled Can be integrated in WAMS/WACS

system

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GGGGGGGG

GGG

A B

C

1018 MW

Flow of A to B gets distributed

according to the impedances

173.5 MW 170.4 MW

344.3 MW

800 MW800 MW

500 MW

500 MW

1000 MW

losses: 18 MW

Slack bus

Phase shifter influenceBase case

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GGGGGGGG

GGG

A B

C

1024.6 MW

Flow of A to B is taken mostly by

line A-B

33 MW32.8 MW

491.8 MW

800 MW800 MW

500 MW

500 MW

1000 MW

losses: 24.6 MW

15 °

Phase shifter influence1 phase shifter placed

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GGGGGGGG

GGG

A B

C

1034 MW

Overcompensation causes a

circulation current

41.4 MW42.3 MW

580 MW

800 MW800 MW

500 MW

500 MW

1000 MW

losses: 34 MW

30 °

Phase shifter influence1 phase shifter placed: overcompensation

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GGGGGGGG

GGG

A B

C

1052.3 MW

The phase shifting transformers can

cancel their effects

238.4 MW221 MW

313.9 MW

800 MW800 MW

500 MW

500 MW

1000 MW

losses: 52.3 MW

15 °

15 °

Phase shifter influence2 phase shifters: cancelling

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GGGGGGGG

GGG

A B

C

1052.3 MW

238.4 MW221 MW

313.9 MW

800 MW800 MW

500 MW

500 MW

1000 MW

Additional losses: + 34.4 MW

15 °

15 ° -8.8 %

+14.6 %+18.8 %

FLOWS relative to base case (no PS)

When badly controlled, little

influence on flows, more on losses

Phase shifter influence2 phase shifters: cancelling

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GGGGGGGG

GGG

A B

C

1054 MW

The phase shifting transformers can

`fight'

294.3 MW259.7 MW

259.7 MW

800 MW800 MW

500 MW

500 MW

1000 MW

losses: 54 MW

15 °

30 °

GGGGGGGG

GGG

A B

C

1052.3 MW

238.4 MW221 MW

313.9 MW

800 MW800 MW

500 MW

500 MW

1000 MW

Additional losses: + 34.4 MW

15 °

15 ° -8.8 %

+14.6 %+18.8 %

FLOWS relative to base case (no PS)

When badly controlled, little

influence on flows, more on losses

Phase shifter influence2 phase shifters: fighting

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GGGGGGGG

GGG

A B

C

1054 MW

The phase shifting transformers can

`fight'

294.3 MW259.7 MW

259.7 MW

800 MW800 MW

500 MW

500 MW

1000 MW

losses: 54 MW

30 °

15 °

+35 %

-24.5 %

+28 %

FLOWS relative to base case (no PS)

Phase shifter influence2 phase shifters: fighting

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Phase shifters in Belgium

• Zandvliet – Zandvliet

• Meerhout – Maasbracht (NL)

• Gramme – Maasbracht (NL) 400 kV +/- 25 ° no load 1400 MVA 1.5 ° step (34 steps)

• Chooz (F) – Monceau B 220/150 kV +10/-10 * 1.5% V (21 steps) +10/-10 * 1,2° (21 steps) 400 MVA

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• Power system control Why? How?

• FACTS Voltage control Angle control Impedance control Combination

• HVDC Classic Voltage source converter based

Overview

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1 2

21 1 2

P= sin

Q= cos

U Uδ

X

U U Uδ

X X

Series compensationLine impedance adjustment

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Series Compensation – SC and TCSC

• Balances the reactance of a power line Can be thyristor controlled

o TCSC – Thyristor Controlled Series Compensation

Can be used for power oscillation damping

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1 2

21 1 2

P= sin

Q= cos

U Uδ

X

U U Uδ

X X

ΔU

Unified Power Flow Controller Ultimate flow control

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UPFC - Unified Power Flow Controller

Voltage source converter-based (no thyristors)

o Superior performance

o Versatility

o Higher cost ~25%

Concurrent control of

o Line power flows

o Voltage magnitudes

o Voltage phase angles

Benefits in steady state and emergency situations

o Rapid redirection power flows and/or damping of power oscillations

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P shunt=− P series

21

Unified Power Flow Controller (II)Ultimate flow control

• Two voltage source converters

• Series flow control

• Parallel voltage control

• Very fast response time Power oscillation damper

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P series 1=− P series 21

3

2

Interline Power Flow ControllerIPFC

• Two voltage source converters

• 2 Series flow controllers in separate lines

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Overview

• Power system control Why? How?

• FACTS Voltage control Angle control Impedance control Combination

• HVDC Classic Voltage source converter based

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DC DCP=U I

• High voltage DC connection No reactive losses

o No stability distance limitationo No limit to underground cable lengtho Lower electrical losses

2 cables instead of 3 Synchronism is not needed

o Connecting different frequencieso Asynchronous grids (UCTE – UK)o Black start capability? (New types, HVDC light)

Power flow (injection) can be fully controlled

• Renewed attention of the power industry

High Voltage Direct CurrentHVDC

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History of HVDC

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• Back to back

• Multiterminal• Bipolar

• Monopolar

(Sea)

+

-

HVDC Configurations:Transmission modes (I)

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HVDC Configurations:Transmission modes (II)

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LCC HVDC

• Thyristor or mercury-arc valves

• Reactive power source needed

• Large harmonic filters needed

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VSC HVDC

• IGBT valves

• P and Q (or U) control

• Can feed in passive networks

• Smaller footprint

• Less filters needed

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HVDC ExampleNorned cable

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HVDC ExampleNorned cable: schema

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HVDC ExampleNorned cable: sea cable

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HVDC ExampleGarabi back to back

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HVDC ExampleGarabi back to back (4x)

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• Commissioning year:2002

• Power rating: 220 MW AC

• Voltage:132/220 kV

• DC Voltage:+/- 150 kV

• DC Current: 739 A

• Length of DC cable:2 x 180 km

VSC HVDCexample: Murray link

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VSC HVDCexample: Troll

• Commissioning year: 2005

• Power rating: 2 x 42 MW AC Voltage:132 kV at Kollsnes, 56 kV at Troll

• DC Voltage: +/- 60 kV

• DC Current: 350 A• Length of DC cable:4

x 70 km

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HVDC: Current sizes

LCC VSC

Voltage (kV) ±600 ±150

Current (kA) 3.93 1.175

Power (MW) 2 x 3150 350

Length (km) 1000 2 x 180

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References

• Understanding Facts: Concepts and Technology of Flexible AC Transmission Systems, Narain G. Hingorani, Laszlo Gyugyi

• Flexible AC transmission systems, Song & Johns

• Thyristor-based FACTS controllers for electrical transmission systems, Mathur Vama

• Power system stability and control, Phraba Kundur, 1994, EPRI