FACTS for Cost Effective and Reliable Transmission of Electrical Energy

8/2/2019 FACTS for Cost Effective and Reliable Transmission of Electrical Energy

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FACTS Flexible Alternating Current Transmission Systems

For Cost Effective and Reliable Transmission of Electrical Energy

ABSTRACT

lexible alternating current transmissionsystems (FACTS) devices are used for theynamic control of voltage, impedance and phase angle of high voltage AC lines. FACTSevices provide strategic benefits for improved transmission system managementhrough: better utilization of existing transmission assets; increased transmissionystem reliability and availability; increased dynamic and transient grid stability;ncreased quality of supply for sensitive industries (e.g. computer chip manufacture);nd enabling environmental benefits.Typically the construction period for a factsevice is 12 to 18 months from contract signing through commissioning.

n order to increase the reliability of the nations power grid, this paper proposes using an Evolutionary Algorithm (EA)o optimize the placement of a limited number of Flexible AC Transmission System (FACTS) devices on power lines.We benchmark against a brute-force placement and compare our EA approach with a greedy algorithm approachuggested by previous research to show that the EA approach results in superior placements.

This paper starts by providing definitions of the most common application of FACTS devices as well as enumeratesheir benefits (focussingon steady state and dynamic applications). Generic information on the costs andbenefits ofACTS devices is then provided as well as the steps for identification ofFACTS projects. The paper then discusses twopplications of FACTS devices in Brazil and Indonesia.

ntroductionOur nation is becoming ever more dependent on its electrical power grid, while at the same time the power grid is becomingncreasingly vulnerable to both natural and intentional disruption . Increasing the reliability of our power grid is therefore ofaramount importance.

The need for more efficient electricity systems management has given rise to innovative

echnologies in power generation and transmission. The combined cycle power stations a good example of a new development in power generation and flexible AC transmissionystems, FACTS as they are generally known,are new devices that improve transmissionystems.

Worldwide transmission systems are undergoing continuous changes and restructuring. They are becoming more heavily loadednd are be in operated in ways not originally envisioned. Transmission systems must be flexible to react to more diverseeneration and load patterns diverse generation and load patterns. In addition, the economical utilization of transmission systemsset is of vital importance to enable utilities in industrialized countries to remain competitive and to survive.In developingountries, the optimized use of transmission systems investments is also important to support industry, create employment andtilize efficiently scarce economic resources.


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Flexible AC Transmission Systems (FACTS) is a technology that responds to these needs. Itignificantly alters the way transmission systems are developed and controlled together with improvements in asset utilization,ystem flexibility and system performance

What are FACTS devices?

ACTS devices are used for the dynamic control of voltage, impedance and phase angle of higholtage AC transmission lines. Below the different main types of FACTS devices are described:

Static Var Compensators (SVCs):-

he most important FACTS devices, have been used for a number of years to improve transmission economics by resolvingynamic voltage problems. The accuracy, availability and fast response enable SVCs to provide high performance steady statend transient voltage Control compared with classical shunt compensation. SVCs are also used to dampen power swings,mprove transient stability, and reduce system losses by optimized reactive power control.

Thyristor controlled series compensators (TCSCs):-


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hese are an extension of conventional seriescapacitors through adding a thyristor-controlled reactor. Placing a controlledeactor in parallel with a series capacitor enables a continuous andapidly variable series compensation system.The main benefits of TCSCs are increased energy transfer, dampening of powerscillations, dampening of subsynchronous resonances, and control of line power flow.

STATCOMs :-

hese are GTO (gate turn-off type thyristor) based SVCs. Compared with conventional SVCs (see above) they dont requirearge inductive and capacitive components to provide inductive or capacitive reactive power to high voltage transmissionystems. This results in smaller landequirements. An additional advantage is the higher reactive output at low system voltages where a STATCOM can beonsidered as a current source independent from the system voltage. STATCOMs have been in operation of approximately 5ears.

Unified Power Flow Controller (UPFC):-

Connecting a STATCOM, which is a shunt connected device, with a series branch in the transmission line via its DC circuit

esults in a UPFC. This device is comparable to a phasehifting transformer but can apply a series voltage of the required phase angle instead of aoltage with a fixed phase angle. The UPFC combines the benefits of a STATCOM and a TCSC.


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Benefits of utilizing FACTS devices:-

he benefits of utilizing FACTS devices in electrical transmission systems can beummarized as follows:Better utilization of existing transmissionsystem assets

Increased transmission system reliabilityand availability

Increased dynamic and transient gridstability and reduction of loop flows

Increased quality of supply for sensitive industries

Environmental benefits

Better utilization of existing transmissionsystem assets :-

n many countries, increasing the energy transfer capacity and controlling the load flow ofansmission lines are of vital importance, especially in de-regulated markets, where the

ocations of generation and the bulk load centers can change rapidly. Frequently, adding newansmission lines to meet increasing electricity demand is limited by economical andnvironmental constraints. FACTS devices help to meet these requirements with the existingansmission systems.

ncreased transmission system reliability and availability :-

ransmission system reliability and availability is affected by many different factors. AlthoughACTS devices cannot prevent faults, they can mitigate the effects of faults and make electricityupply more secure by reducing the number of line trips. For example, a major load rejectionesults in an over voltage of the line which can lead to a line trip. SVCs or STATCOMsounteract the over voltage and avoid line tripping.

ncreased dynamic and transient grid stability :-

ong transmission lines, interconnected grids, impacts of changing loads and line faults canreate instabilities in transmission systems. These can lead to reduced line power flow, loopows or even to line trips. FACTS devices stabilize transmission systems with resultingACTS For cost effective and reliable transmission of electrical energy higher energy transfer capability and reduced risk ofne trips.

ncreased quality of supply for sensitive industries :-

Modern industries depend upon high quality electricity supply including constant voltage, andequency and no supply interruptions. Voltage dips, frequency variations or the loss of supplyan lead to interruptions in manufacturing processes with high resulting economic losses.ACTS devices can help provide the required quality of supply.

nvironmental benefits :-

ACTS devices are environmentally friendly. They contain no hazardous materials and produce no waste or pollutanse. FACTSelp distribute the electrical energy more economically through better utilization of existing installations thereby reducing theeed for additional transmission lines.


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Applications and technical benefits of FACTS devices:-


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xhibits 2 to 4 below describe the technical benefits of the principal FACTS devices including steady state applications inddressing problems of voltage limits, thermal limits, loop flows, short circuit levels and subsynchronous resonance. For eachroblem the conventional solution (e.g. shunt reactor or shunt capacitor) is also provided (as well as for dynamicpplications see below), as well as dynamic applications of FACTS in addressing problems in transient stability, dampening,

ost contingency voltage control and voltage stability. FACTS devices are required when there is a need to respond to dynamicfast-changing) network conditions. The conventional solutions are normally less expensive than FACTS devices- but limited inheir dynamic behavior. It is the task of the planners to identify the most economic solution.In Exhibits 3 and 4 information is provided on FACTS devices with extensive operationalxperience and widespread use such as SVC, STATCOM, TCSC and UPFC. In addition,nformation is provided on FACTS devices that are either under discussion, development or asrototype in operation such as the thyristor controlled phase-angle regulator (TCPAR); the thyristor controlled voltage limiterTCVL); and the thyristor switched series capacitor (TCSC).

echnical benefits of the main FACTS devices


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egend for Exhibit 3GH = Hingorani Damper TCSC = Thyristor Controlled Series Capacitor AR = Phase-Angle-Regulator TCVL = Thyristor Controlled Voltage Limiter CCL = Super-Conducting Current LimiterSBR = Thyristor Switched Braking Resistor

VC = Static Var Compensator TSSC = Thyristor Switched Series Capacitor TATCOM = Static Compensator UPFC = Unified Power Flow Controller CPAR = Thyristor Controlled Phase-Angle Regulatorxhibit 3: Steady state applications of FACTS

nvestment costs of FACTS devices.

he investment costs of FACTS devices can be broken down into two categories:a) the devices equipment costs, andb) the necessary infrastructure costs.

Equipment costs:-

quipment costs depend not only upon the installation rating but also upon special requirements such as:

redundancy of the control and protection system or even main components such as reactors,

seismic conditions,

ambient conditions (e.g. temperature, pollution level): and

communication with the Substation Control System or the Regional or National Control Center.

nfrastructure Costs

nfrastructure costs depend on the substation location, where the FACTS device should be installed. These costs include e.g.

land acquisition, if there is insufficient space in the existing substation,

modifications in the existing substation, e.g. if new HV switchgear is required,

construction of a building for the indoor equipment (control, protection, thyristor valves, etc)

yard civil works (grading, drainage, foundations etc.), and

connection of the existing communication system with the new installation.


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xhibit 5: Typical investment costs for SVC / Statcom

What are the financial benefits of FACTS devices?

here are three areas were the financial benefits could be calculated relatively easily.. Additional sales due to increased transmission capability.. Additional wheeling charges due to increased transmission capability.. Avoiding or delaying of investments in new high voltage transmission lines or even new

Power generation.

Maintenance of FACTS devices

Maintenance of FACTS devices is minimal and similar to that required for shunt capacitors, reactors and transformers. It can beerformed by normal substation personnel with no specialrocedures. The amount of maintenance ranges from 150 to 250 man-hours per year andepends upon the size of the installation and the local ambient (pollution) conditions.


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Operation of FACTS devices

ACTS devices are normally operated automatically. They can be located in unmannedubstations. Changing of set-points or operation modes can be done locally and remotely (e.g.rom a substation control room, a regional control centre, or a national control centre).

Steps for the Identification of FACTS Projects

. The first step should always be to conduct a detailed network study to investigate the criticalonditions of a grid or grids connections . These conditions could include: risks of voltageroblems or even voltage collapse, undesired power flows, as well as the potential for powerwings or subsynchronous resonances.. For a stable grid, the optimized utilization of the transmission lines e.g. increasing thenergy transfer capability could be investigated.

. If there is a potential for improving the transmission system, either through enhancedtability or energy transfer capability, the appropriate FACTS device and its required rating can be determined.

. Based on this technical information, an economical study can be performed to compareosts of FACTS devices or conventional solutions with the achievable benefits.

f the FACTS

Worldwide Applications

hree projects are described below, where FACTS devices have proven their benefits overeveral years. These descriptions also indicate how the FACTS devices were designed to meethe different requirements of the three transmission systems. The investment costs forhese devices are consistent with the information presented in Exhibits 4 and 5 above.

BRAZIL: North South Interconnection

n Brazil there are two independent transmission grids, the North grid and the South grid. Thesewo grids cover more than 95% of the electric power transmission in the country. Detailed studies demonstrated the economicttractiveness of connecting the two grids. Interalia they compared the attractiveness of building an AC or a HVDC (Higholtage Direct Current) connection of more than 1.000 km long passing through an area with a fast growing economynd also with a high hydropower potential. As it is technically much easier and more economicalo build new connections to an AC line than to an HVDC line it was decided to build a new ACline.


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xhibit 10: BRAZIL: TCSC, Serra de Mesa


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NDONESIA: Containerized Design

Load flow and stability studies of the Indonesian power system identified the need for a SVC withcontrol range of 25 MVAr to + 50 MVAr at Jember Substation(Bali). The SVC provides fastoltage control to allow enhanced power transfer under extreme system contingencies, i. e. lossf a major 150 kV transmission line. Fast implementation of the SVC was required to ensure safe system operation within thehortest time achievable. To achieve the tight schedule, a unique approach was chosen comprising a SVC design based onontainerization to the greatest extent possible to allow prefabrication, pre-installation and pre-commissioning of theVC system at the manufacturers workshop.


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Future Developments in FACTS

uture developments will include the combination of existing devices, e.g.combining a STATCOM with a TSC (thyristor switchedapacitor) to extend the operational range. In addition, more sophisticated control systems will improve the operation of FACTSevices. Improvements in semiconductor technology (e.g. higher current carrying capability, higher blocking voltages) couldeduce the costs of FACTS devices and extend their operation ranges. Finally, developments in superconductor technologypen the door to new devices like SCCL (Super Conducting Current Limiter) and SMES (Super Conducting Magnetic Energytorage).

here is a vision for a high voltage transmission system around the world to generate electricalnergy economically and environmentally friendly and provide electrical energy where itsneeded. FACTS are the key to makehis vision live.

Design, Implementation, Operation and Training Needs of FACTS Devices

etwork studies are very important for the implementation of a FACTS device to determine theequirements for the relevant installation. Experienced network planning engineers have to evaluate the system including futureevelopments. Right device right size right place right cost. Reliable operation of FACTS devices require regularmaintenance in addition to using equipment of the highest quality standards. Maintenance requirements are minimal butmportant.Optimal use of FACTS devices depend upon well-trained operators. Since most utility operators are unfamiliar with FACTSevices (compared with for example switched reactors or capacitors), training on the operation of FACTS devices is thereforeery important. What is important for the operators to know is are the appropriate settings of FACTS devices, especially thepeed of response to changing phase angle and voltage conditions as well as operating modes. This training would normally lastne to two weeks.

5 Conclusions

he increasing dependence of our nation on its power grid makes the robustness and integrity of the power grid ever moreritical. The placement of power regulation devices, such as FACTS devices, is an important tool for protecting power grids fromatastrophic failures. Placement is critical for obtaining optimal benefits from these devices. Prohibitively high costs for FACTSevices make it essential to obtain the maximum benefit from the minimum number of devices.

The EA (evolutionary algorithm) presented in this paper was demonstrated to be superior to the Iterative Greedy FACTSlacement algorithm suggested in previously published work. The customized recombination and mutation operators provedffective for this particular placement problem and are expected to be similarly effective on other placement problems.

Documents

FACTS for Cost Effective and Reliable Transmission of Electrical Energy