Master in Advanced Power Electrical Engineering

Techno-economic aspects of power systems Ronnie Belmans Dirk Van Hertem Stijn Cole

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• • • • • • • • • • © Copyright 2005

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

Overview • Power system control Why? ƒ How? ƒ

• FACTS Voltage control ƒ Angle control ƒ Impedance control ƒ Combination ƒ

• HVDC Classic ƒ Voltage source converter based ƒ

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Power transfer through a line How? • Active power transfer: Phase angle ƒ Problems with long distance transport ƒ

o o

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

• Reactive power transfer Voltage amplitude ƒ Problems: ƒ

o o

Voltage has to remain within limits 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 Theory

X ~ distance

Power transfer through a line: (U ) ⋅ (U ) 2 P= 1 ⋅ sin ( δ ) X U1 ) ( Q=

2

X

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U1 ) ⋅ (U2 ) ( − ⋅ cos X

(δ)

European power flows transport France ==> Germany NL UK

F

E © Copyright 2005

34 %

B 34 %

D 35 % 18 % 13 %

20 % CH

8 %

11 % A

10 % 3 % I

Overview • Power system control Why? ƒ How? ƒ

• FACTS Voltage control ƒ Angle control ƒ Impedance control ƒ Combination ƒ

• HVDC Classic ƒ Voltage source converter based ƒ

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Divisions within FACTS • Implementation ƒ

Series

ƒ

Shunt

ƒ

Combined

ƒ

ƒ

HVDC

ƒ

• Energy storage ƒ

Yes or no

• Application ƒ ƒ

Voltage magnitude control Phase angle control Impedance Combination of the above

• Switching technology ƒ

Mechanical

ƒ

Thyristor

ƒ

IGBT/GTO: Voltage Source Converter

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Application domain FACTS Transmission level • Power flow control ƒ

Regulation of slow power flow variations

• Voltage regulation ƒ

Local control of voltage profile

• Power system stability improvement ƒ

Angle stability o

ƒ

Caused by large and/or small perturbations

Voltage stability o

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Short and long term

Application domain FACTS Distribution level

• Quality improvement of the delivered voltage to sensitive loads ƒ ƒ ƒ ƒ

Voltage drops Overvoltages Harmonic disturbances Unbalanced 3-phase voltages

• Reduction of power quality interferences ƒ ƒ ƒ ƒ

Current harmonics Unbalanced current flows High reactive power usage Flicker caused by power usage fluctuations

• Improvement of distribution system functioning ƒ

Power factor improvement, voltage control, soft start,...

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Voltage magnitude adjustment

U1) ⋅(U2 ) ( ⋅sin( δ) P= X

U ) (U ) ⋅(U ) ( − ⋅ cos δ Q= 2 1

X

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1

2

X

( ( ))

Static Var Compensation - SVC

• Variable thyristor controlled shunt impedance ƒ ƒ

ƒ ƒ

Variable reactive power source Provides ancillary services o Maintains a smooth voltage profile o Increases transfer capability o Reduces losses Mitigates active power oscillations Controls dynamic voltage swings under various system conditions

Different configurations: ƒ

Thyristor Controlled Reactor (TCR)

ƒ

Thyristor Switched Capacitor (TSC)

ƒ

Thyristor Switched Reactor (TSR)

ƒ

Mechanical Switched Capacitor (MSC)

ƒ

Mechanical Switched Reactor (MSR)

ƒ

Often a combination

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Static Var Compensation - SVC Variable thyristor controlled shunt impedance: TCR +Capacitor U U L

U

C

IL max L

L

C

IC

U

IC

IL U

U

m in L

s lo p e KS

s lo p e KS IL © Copyright 2005

IC

IL

IL

Static var compensator SVC characteristics: Ugrid

USVC X

Without B S VC

XC 1 ⎛ ⎞ BSVC = ⎜ XL − ⋅( 2⋅( π −α) ) ⎟ XL ⋅ Xc ⎝ π ⎠ USVC Q= ⋅ (UVSC −Ugrid ⋅ cos( δ) ) X © Copyright 2005

U

With System Characteristics

IL

Static Var Compensation - SVC SVC control

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STATic COMpensator STATCOM

• Shunt voltage injection ƒ ƒ ƒ ƒ ƒ

Voltage Source Convertor (VSC) Low harmonic content s lo p e K S Very fast switching More expensive than SVC Energy storage? (SMES, supercap)

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U

I

L

Price comparison voltage regulation • Cost of voltage regulation capabilities dependent on: ƒ ƒ ƒ

Speed Continuous or discrete regulation Control application

• 300 MVAr – 150 kV ƒ ƒ ƒ

Capacitor banks: 6 M€ (min) SVC: 9 à 17 M€ (# periods) Statcom: 31 M€ (ms)

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Phase shifting transformer Voltage angle adjustment.

U1) ⋅(U2 ) ( P= ⋅sin( δ+α) X

U ) (U ) ⋅(U ) ( Q= − ⋅ cos δ+α 2 1

X

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1

2

X

( (

))

Phase shifting transformer

• Allows for some control over active power flows • Mechanically switched ==> minutes P=

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(U 1 ) ⋅ (U 2 ) ⋅ s in X + X

PST

(δ + α )

Phase shifting transformer (II) Principles

• Injection of a voltage in quadrature of the phase voltage

• One active part or two active parts Asymmetric ΔU 25 ° ==> 10 % voltage rise ==> 40 kV @ 400 kV

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Symmetric

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) 3'

1'

2'

3

1 1 © Copyright 2005

2

3

3' Voltages over coils on the same transformer leg are in 2 phase

Phase shifting transformer (V) Two active parts 0 ==> α=0 3

3' 3

3'

1'

2

2

1' 1 © Copyright 2005

2'

1

2'

Phase shifting transformer (V) Two active parts

• Series voltage injection • In quadrature to the phase voltage

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Phase shifting transformer (II) Principles

• Current influence: ƒ

The phase shifter consists of an impedance ƒ The current causes an additional phase shift U2 (-α)

U2 (+α)

Us α α

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IZ

Us

α α Ur

IZ

Ur

Phase shifting transformer Regulating • Changing injected voltage: Tap changing transformer ƒ Slow changing of tap position: ½ min ƒ

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

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Phase shifter influence Base case 1018 MW A

500 MW B G

G

Slack bus

1000 MW

500 MW 344.3 MW

173.5 MW

170.4 MW

G

losses: 18 MW © Copyright 2005

800 MW

C 800 MW

Flow of A to B gets distributed according to the impedances

Phase shifter influence 1 phase shifter placed 1024.6 MWA

500 MW B G

G

1000 MW

500 MW 491.8 MW

15 ° 32.8 MW

33 MW

G

losses: 24.6 MW © Copyright 2005

800 MW

C 800 MW

Flow of A to B is taken mostly by line A-B

Phase shifter influence 1 phase shifter placed: overcompensation 1034 MW A

500 MW B G

G

1000 MW

500 MW 580 MW

30 ° 42.3 MW

41.4 MW

G

losses: 34 MW © Copyright 2005

800 MW

C 800 MW

Overcompensation causes a circulation current

Phase shifter influence 2 phase shifters: cancelling 1052.3 MWA

500 MW B G

G

500 MW 15 ° 313.9 MW

1000 MW

15 ° 221 MW

238.4 MW

G

losses: 52.3 MW © Copyright 2005

800 MW

C 800 MW

The phase shifting transformers can cancel their effects

Phase shifter influence 2 phase shifters: cancelling 1052.3 MWA FLOWS G

MW (no PS) relative to base500 case B G 1000 MW

500 MW 15 ° -8.8 % 313.9 MW

15 ° 221 MW

+14.6 %

238.4 MW

+18.8 % Additional losses: + 34.4 MW © Copyright 2005

G

800 MW

C 800 MW

When badly controlled, little influence on flows, more on losses

Phase shifter influence 2 phase shifters: fighting 1054 1052.3 MW MWA FLOWS G

MW (no PS) relative to base500 case B G 1000 MW

500 MW 30 ° -8.8 % 15 259.7 MW 313.9

15 ° 259.7 221 MW MW

+14.6 %

294.3 MW 238.4

+18.8 %

G

Additional losses:+54 losses: 34.4 MW MW © Copyright 2005

800 MW

C 800 MW

The When phasebadly shifting controlled, little transformers can influence on flows, `fight' more on losses

Phase shifter influence 2 phase shifters: fighting 1054 MW A FLOWS G

MW (no PS) relative to base500 case B G

500 MW 15 ° -24.5 % 259.7 MW

1000 MW

30 ° 259.7 MW

294.3 MW

+28 %

+35 % G

losses: 54 MW © Copyright 2005

800 MW

C 800 MW

The phase shifting transformers can `fight'

Thyristor Controlled Phase shifting transformer

• ms switching • Reliability? • No practical

implementation

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Phase shifters in Belgium • Zandvliet – Zandvliet • Meerhout – Maasbracht (NL) • Gramme – Maasbracht (NL) ƒ ƒ ƒ ƒ

400 kV +/- 25 ° no load 1400 MVA 1.5 ° step (34 steps)

• Chooz (F) – Monceau B ƒ ƒ ƒ ƒ

220/150 kV +10/-10 * 1.5% V (21 steps) +10/-10 * 1,2° (21 steps) 400 MVA

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Overview • Power system control Why? ƒ How? ƒ

• FACTS Voltage control ƒ Angle control ƒ Impedance control ƒ Combination ƒ

• HVDC Classic ƒ Voltage source converter based ƒ

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Series compensation Line impedance adjustment

U1) ⋅(U2 ) ( P= ⋅sin( δ) X

U ) (U ) ⋅(U ) ( Q= − ⋅ cos δ 2 1

X

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1

2

X

( ( ))

Series Compensation – SC and TCSC

• Balances the reactance of a power line ƒ

Can be thyristor controlled o

ƒ

TCSC – Thyristor Controlled Series Compensation

Can be used for power oscillation damping

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Series Compensation TCSC Z Resonance

α

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SSSC: Solid State Series Compensator

• Voltage source convertor • Series voltage injection • DVR for distribution level ƒ ƒ

Voltage dips mitigation Harmonic compensation

• Power oscillation damper ƒ ƒ ƒ

SSR Angle Stability Voltage stability

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Unified Power Flow Controller Ultimate flow control

U1 ) ⋅ (U2 ) ( P= ⋅ sin X

( δ)

U ) (U ) ⋅ (U ) ( Q= − ⋅ cos δ 2 1

X

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1

2

X

( ( ))

ΔU

UPFC - Unified Power Flow Controller ƒ

ƒ

ƒ

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

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Rapid redirection power flows and/or damping of power oscillations

Unified Power Flow Controller (II) Ultimate flow control

• • • •

Two voltage source converters Series flow control Parallel voltage control Very fast response time ƒ

Power oscillation damper

P s h u n t = − P se rie s 1

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2

Interline Power Flow Controller IPFC

• Two voltage source converters • 2 Series flow controllers in separate lines P se rie s 1 = − P se rie s 2

1

2

3 © Copyright 2005

Overview • Power system control Why? ƒ How? ƒ

• FACTS Voltage control ƒ Angle control ƒ Impedance control ƒ Combination ƒ

• HVDC Classic ƒ Voltage source converter based ƒ

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High Voltage Direct Current HVDC • High voltage DC connection ƒ

No reactive losses o o o

No stability distance limitation No limit to underground cable length Lower electrical losses

2 cables instead of 3 ƒ Synchronism is not needed ƒ

o o o

ƒ

P =U DC ⋅ I DC

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

Power flow (injection) can be fully controlled

• Renewed attention of the power industry

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High Voltage Direct Current (II) HVDC • Classical HVDC ƒ ƒ

Thyristor based (or mercury valves) Triggering: Electrical or light? o o

ƒ ƒ

==> light has galvanic separation ==> electrical is robust and reliable

6 pulse ==> 12 pulse (==> 24 pulse) CCC HVDC: capacitor commutated HVDC o o

capacitors placed between transformer and bridge less filtering needed

• Voltage source converter HVDC (e.g. HVDC light) ƒ ƒ

IGBT or GTO switches ==> PWM signal No (less) harmonic filtering needed

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HVDC Configurations: Transmission modes (I)

• Back to back

• Monopolar

(Sea)

• Bipolar

+

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• Multiterminal

HVDC Configurations: Transmission modes (II)

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HVDC classic Reactive power/compensation

• Converters absorb reactive power ƒ

Phase delay

ƒ

(Q = 50 à 60 % P)

• Harmonic filters have to be installed • Reactive power absorption increases (superlinear) with transmitted power

• Need for harmonic compensation increases (supra-linear) with transmitted power

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HVDC classic Working principle Ud

Voltage drop Stable operation point

Inverter

I 02

Rectifier

I 01

ΔI = current margin © Copyright 2005

Id

• • • • • •

Rectifier ==> current setting ==> constant current control (feedback) Inverter ==> voltage setting ==> constant excitation angle (tap changer + controller)

U di 0 N U d = U di 0 ⋅ cos α − d xN ⋅ ⋅ Id I dN

HVDC Example Norned cable

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HVDC Example Norned cable: schema

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HVDC Example Norned cable: sea cable

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HVDC Example Garabi back to back

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HVDC Example Garabi back to back (4x)

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VSC HVDC example: Murray link

• Commissioning • • • • •

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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 HVDC example: Troll

• Commissioning year: •

• • •

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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

HVDC: Current sizes

Classic VSC Voltage (kV)+/- 600 +/- 150 Current (kA) 3.93 1.175 Power (MW)2x3150 350 Length (km) 1000 2x180

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Other new technologies for transmission systems • Energy storage ƒ

Existing technologies o o o

Pumped storage Pressurized air Battery?

Supercapacitors / Ultracapacitors ƒ SMES (Superconducting Magnetic Energy Storage) ƒ Fuel Cells ƒ

• Cables New techniques ƒ HTS Cables (High Temperature Superconductor) ƒ

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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

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