23/04/2017 TITRE PRESENTATION 1.

23/04/2017 TITRE PRESENTATION 1

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

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 FACTS HVDC Why? How? Voltage control
Angle control Impedance control Combination HVDC Classic Voltage source converter based FACTS = flexible AC transmission systems HVDC = high voltage direct current transmission

Power transfer through a line How?
Active power transfer: Phase angle Problems with long distance transport Phase angle differences have to be limited Power transfer ==> power losses Reactive power transfer Voltage amplitude Problems: Voltage has to remain within limits Only locally controlled By changing voltage, impedance or phase angle, the power flow can be altered ==> FACTS Limit phase angle differences to avoid losing synchronism (in de laatste zin heb ik nog ‘impedance’ toegevoegd) (ik heb in alle figuren V door U vervangen (maar niet in de formules))

Power transfer through a line Theory
This is an approximation of P and Q. The series conductance is neglected. For the full calculation see e.g. :Power System Analysis: short-circuit load flow and harmonics, J.C. Das

European power flows transport France ==> Germany
UK F CH I E B D 35 % A NL 18 % 13 % 8 % 34 % 20 % 10 % 3 % 11 % transfer of energy from France to Germany will cause power flows all over Western Europe

Angle control Impedance control Combination HVDC Classic Voltage source converter based

Divisions within FACTS
Application Voltage magnitude control Phase angle control Impedance Combination of the above Implementation Series Shunt Combined HVDC Energy storage Yes or no Switching technology Mechanical Thyristor IGBT/GTO: Voltage Source Converter Energy storage can extend the application range of the FACTS devices. IGBT = insulated gate bipolar transistor GTO = gate turn-off thyristor

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 Caused by large and/or small perturbations Voltage stability Short and long term

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,... at the distribution level, FACTS are often used to solve power quality problems. Similar devices can get a different name in transmission systems and distribution systems. For instance a SSSC (solid state series compensator) and a DVR (dynamic voltage regulator). Another noteworthy remark is that also different companies will give similar technology different terminology. For instance the VSC HVDC technology (HVDC using voltage source converters) is called HVDC light by ABB and HVDC plus by Siemens... Somethimes is the power electronic different, also the control techniques applied is generally speaking different. The system behavior however is comparable.

Voltage magnitude adjustment
The same formula is used throughout this lesson. The voltage has to remain around 1 pu (only small variations are allowed within a high voltage grid), therefore, changing the voltage will influence on the active power is limited. The influence on reactive power can be much bigger as the cosine can result in a positive or a negative value, and (|U_1|-|U_2|) determines the outcome significantly

Static Var Compensation - SVC
Variable thyristor controlled shunt impedance Variable reactive power source Provides ancillary services Maintains a smooth voltage profile Increases transfer capability Reduces losses Mitigates active power oscillations Controls dynamic voltage swings under various system conditions 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 The SVC is a robust and well proven technology with worldwide application on distribution and transmission systems, to control system voltage and hence to a lower lower extend the power flows. The control of power flows by SVCs is especially important when long power lines with one generation point and a distant load area are considered. With additional voltage support the voltage sag over the line is limited, and the available power transfer capability of the line will be enhanced. There are over 1000 SVC in service, based on thyristor technology. This is by far the most numerous of FACTS devices. The first FACTS were built about 30 years ago.

STATic COMpensator STATCOM
Shunt voltage injection Voltage Source Convertor (VSC) Low harmonic content Very fast switching More expensive than SVC Energy storage? (SMES, supercap) A statcom has the same system behavior as the synchronous compensator, and is somethimes also called a synchronous condensor or static condensor (statcon). Several topologies are possibles, but in general there is the IGBT convertor (ABB) and a series topology based on GTOs (Areva) There are about 30 STATCOM installations worldwide. SMES = superconducting magnetic energy storage

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)

Phase shifting transformer Voltage angle adjustment.

Phase shifting transformer
Allows for some control over active power flows Mechanically switched ==> minutes The phase shifting is often not considered as a FACTS device because of the fact that it is mechanical switched, and therefore have limited dynamic performance. They enable however power flow control and add flexibility to the grid control.

Phase shifting transformer (II) Principles
Injection of a voltage in quadrature of the phase voltage One active part or two active parts Asymmetric Symmetric D U 25 ° ==> 10 % voltage rise ==> kV Asymmetric phase shifters are used when voltage difference between the end terminals can vary. The phase angle is limited. Asymmetric phase shifters are cheaper because there is no midpoint tap-changer connection needed. The symmetric phase shifter configurations have equal voltage at the terminals.

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 3' Voltages over coils on the same transformer leg are in phase line voltages from the opposite side of the triangle are injected in series with the phase voltage causes a phase shift between the input and output of the phase shifter 1 2 1 2 3

Phase shifting transformer Regulating
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 WAMS = Wide Area Measurement System WACS = Wide Area Control System

Phase shifter influence Base case
1018 MW 500 MW A B G G G G G G G G 500 MW 1000 MW Slack bus 344.3 MW 173.5 MW 170.4 MW Flow of A to B gets distributed according to the impedances (suppose no losses) There are three countries A, B, and C. Demand equals supply in country C. In country A there is a production surplus of 500 MW. In country B there is a production shortage of 500 MW. A and B agree upon a flow of 500 MW from A to B. However, electricity follows the laws of Kirchoff. A part of the flow goes through line AC and CB MW from A to B: 2/3 * 500 MW through line AB, 1/3 * 500 MW through line AC and CB. Non-contracted flows are flowing on the interconnections of country C. C G G G 800 MW losses: 18 MW 800 MW

Phase shifter influence 1 phase shifter placed
MW 500 MW A B G G G G G G G G 500 MW 1000 MW 491.8 MW 15 ° 32.8 MW 33 MW Flow of A to B is taken mostly by line A-B Country C installs a PST. The power flow is changed by adaption of the phase angle. The flow is now taken mostly by line AB C G G G 800 MW losses: 24.6 MW 800 MW

Phase shifter influence 1 phase shifter placed: overcompensation
1034 MW 500 MW A B G G G G G G G G 500 MW 1000 MW 580 MW 30 ° 42.3 MW 41.4 MW Overcompensation causes a circulation current C G G G 800 MW losses: 34 MW 800 MW

Phase shifter influence 2 phase shifters: cancelling
MW 500 MW A B G G G G G G G G 500 MW 1000 MW 15 ° 313.9 MW 15 ° 221 MW 238.4 MW The phase shifting transformers can cancel their effects Country A installs a PST to push the current through the ACB path. Losses increase significantly C G G G 800 MW losses: 52.3 MW 800 MW

Phase shifter influence 2 phase shifters: cancelling
MW FLOWS relative to base case (no PS) 500 MW A B G G G G G G G G 500 MW -8.8 % 1000 MW 15 ° 313.9 MW 15 ° 221 MW 238.4 MW +14.6 % +18.8 % When badly controlled, little influence on flows, more on losses C Additional losses: MW G G G 800 MW 800 MW

Phase shifter influence 2 phase shifters: fighting
1054 MW MW FLOWS relative to base case (no PS) 500 MW 500 MW A A B B G G G G G G G G G G G G G G G G 500 MW 500 MW -8.8 % 1000 MW 1000 MW 15 ° 30 ° 259.7 MW 313.9 MW 15 ° 15 ° 221 MW 259.7 MW 238.4 MW 294.3 MW +14.6 % +18.8 % The phase shifting transformers can `fight' When badly controlled, little influence on flows, more on losses Two phase shifters try to push power through the other line, resulting in enlarged losses, but almost no difference in power flow. C C G G G G G G 800 MW 800 MW Additional losses: MW losses: 54 MW 800 MW 800 MW

Phase shifter influence 2 phase shifters: fighting
1054 MW FLOWS relative to base case (no PS) 500 MW A B G G G G G G G G 500 MW -24.5 % 1000 MW 15 ° 259.7 MW 30 ° 259.7 MW 294.3 MW +28 % +35 % The phase shifting transformers can `fight' C G G G 800 MW losses: 54 MW 800 MW

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 The three phase shifters in the North will have the same properties (construction during )

Series compensation Line impedance adjustment
Basic idea: decrease the overall effective series impedance

Series Compensation – SC and TCSC
Balances the reactance of a power line Can be thyristor controlled TCSC – Thyristor Controlled Series Compensation Can be used for power oscillation damping The number of TCSCs in service is probably still less than 10 projects. Although Fixed Series Capacitors (FSCs) have been in service for many years as a means of reducing transmission impedances the use of thyristor control only dates from the first project in the mid 1990's. Installation is a series device, and must be isolated from the earth voltage: therefore placed on poles. The TCSC allows both power flow control and power oscillation damping (transient stability, voltage stability and sub-synchronous resonance). First installation was built in 1993, commissioned (after testing) in 1995, in Slatt (USA). Picture: todo: source

Unified Power Flow Controller Ultimate flow control
The UPFC is able to control all the parameters that affect power flow simultaneously.

UPFC - Unified Power Flow Controller
Voltage source converter-based (no thyristors) Superior performance Versatility Higher cost ~25% Concurrent control of Line power flows Voltage magnitudes Voltage phase angles Benefits in steady state and emergency situations Rapid redirection power flows and/or damping of power oscillations Todo: source figure Other advanced (VSC) FACTS are: StatCom - Static Compensator SSSC - Solid State Series Compensator UPFC - Unified Power Flow Controller IPFC - Interline Power Flow Controller

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 1 2 A UPFC is a combination of a SSSC and a STATCOM, connected with their DC link

Interline Power Flow Controller IPFC
Two voltage source converters 2 Series flow controllers in separate lines 1 2 A UPFC is a combination of two SSSCs, connected with their DC link 3

High Voltage Direct Current HVDC
High voltage DC connection No reactive losses No stability distance limitation No limit to underground cable length Lower electrical losses 2 cables instead of 3 Synchronism is not needed 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 Connecting different frequencies. E.g. Japan and Brasil: 50Hz grid connected to 60Hz grid by back-to-back (BTB) HVDC. Connecting two non-synchronous networks. E.g. UCTE and the Russian grid, France and UK Losses: R*I², but I is lower because no Q

History of HVDC

HVDC Configurations: Transmission modes (I)
Monopolar Back to back (Sea) Multiterminal Bipolar + Multiterminal costly and difficult to obtain with classical hvdc. -

HVDC Configurations: Transmission modes (II)

LCC HVDC Thyristor or mercury-arc valves Reactive power source needed
Large harmonic filters needed

VSC HVDC IGBT valves P and Q (or U) control
Can feed in passive networks Smaller footprint Less filters needed

HVDC Example Norned cable
700 MW LanguageCode=en&DocumentPartID=&Action=Launch

HVDC Example Norned cable: schema
Source ABB

HVDC Example Norned cable: sea cable
Partly single core cable, partly double core cable Source: ABB

HVDC Example Garabi back to back

HVDC Example Garabi back to back (4x)
Source ABB

VSC HVDC example: Murray link
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 HVDC example: 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

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 New developments: 1) VSC up to kV 2) LCC up to ±800 kV

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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