FACTS IN POWER SYSTEMS AN INTRODUCTIONDepartment of Electrical and Electronics Engineering Coimbatore Institute of TechnologyCoimbatore 641 014email: vasantharathna@cit.edu.in

Dr.S.VASANTHARATHNA *

Long Ago Spiritual Torture Power Sanction

Past Era Physical Torture Effective Utilisation / Profit

This Era Mental Torture -- Power Reliability

*

ELECTRICITYThe BIG Player

THE POWER SYSTEM*

*Peculiarities of Regional Grids in IndiaDeficit Region delhiSnow fed run-of the river hydroHighly weather sensitive loadAdverse weather conditions: Fog & Dust Storm

Very low load ShillongHigh hydro potentialEvacuation problemsIndustrial load MumbaiLow load KolkataHigh coal reservesPit head base load plantsHeavy load Bangaluru Monsoon dependent hydroCHICKEN-NECK

*

SalakatiBongaigaonBirparaMaldaDehriSasaramSahupuriAllahabadNorth-EasternEasternNorthernBelgaumKolhapurBudhipadarRourkelaKorbaRaipurAuraiyaMalanpurWesternSouthernBalimelaUpper SileruChandrapurRamagundamJeyporeGazuwakaSingrauliVindhyachal400kV220kV220kV500MW500MWW220kV1000MW500MW220kV400kV220 kV220kV TalcherKolar2500MWGorakhpur/LucknowMAJOR INTER REGIONAL LINKS-8000 MW CAPACITY*NEW is a major grid

INDIAN TRANSMISSION NETWORK 20083708 CKM 19505.7 million circuit km - 2011*

VOLTAGEUNDER CENTRALUNDER STATETOTAL CKM+500KV HVDC566815047172765 KV27094093118400KV61800276968949622OKV10066112894122960TOTAL80243142503222746

ENERGY IN INDIA - FACTS SWOT ANALYSIS

Demand and Supply gap5.8% June 2012

Per capita consumption818.9 KWh (by 2011)

GDP growth rate9-11% per annum

Installed Capacity2,05,340.26 MW

Proposed capacity addition200,000 MW by 2012

*

Power for AllMaximum Customer Satisfaction*

Eliminate service interruptionsMeet individualized consumer needsEnable DG and energy smart appliancesAchieve universal demand responseMinimize the cost of smart electric service GOAL: A Power System That Will Not Fail Consumers*

EYEING THE SILVER LININGIncreasing the Generation CapacityImproving The Power QualityMeteringRestructuringDeregulationDistributed GenerationEnergy ConservationAutomation

*

INCREASE IN GENERATIONThermal Power - installed 24,000 MWTarget 66000 MW by 2017NLC Tamilnadu Power Ltd. 1000 MW coal based plant at Tuticorin by 2011SAIL 1000 MW coal fired plantHydro installed 1,48,700 MW Target 6000 MWNuclear 2720 MWTarget 20,000 MW by 2020

*

CONGESTIONWhile load growth has occurred, Even with increased generating capacity

still the same prevails*

EYEING THE SILVER LININGIncreasing the Generation CapacityImproving The Power QualityMeteringRestructuringDeregulationDistributed GenerationEnergy ConservationAutomation

*

POWER QUALITY*a serious issue that touches almost all industrial,commercial andresidentialcustomers in some way.

POWER QUALITYIn view of an equipment designer or manufacturer might be that power quality is a perfect sinusoidal wave, with no variations in the voltage, and no noise present on the grounding system. In view of an electrical utility engineer might be that power quality is simply voltage availability or outage minutes.

In view of an end-user, is that power quality or quality power is simply the power that works for whatever equipment the end-user is applying.

While each hypothetical point of view has a clear difference, it is clear that none is properly focused.

*

Challenges to Secure Operation of Today's Power Systems*

Mechanical AnalogyBalls GeneratorsStrings- Interconnection linesFill a glass with the water to quarter of its capacity. The dropping of the marble is akin to a disturbance in the power system. In this situation no water from the glass will splash out, indicating the system is stable.

Now fill the glass with water close to its brim and drop the same marble into the glass. In this case, water will splash out, indicating the system is unstable

Limitations for Loading Capacity of Transmission SystemsThe ability of the transmission system to transmit power becomes impaired by one or more of the following steady state and dynamic limitations: (a) angular stability, (b) voltage magnitude, (c) thermal limits f{temperature,wind, conductor, ground clearance} (d) transient stability, (e) dynamic stability. These limits define the maximum electrical power to be transmitted without causing damage to transmission lines and electrical equipment. In principle, limitations on power transfer can always be relieved by the addition of new transmission lines and generation facilities.

Steady-State Power Transfer Limit

Voltage Stability Limit Dynamic Voltage Limit Transient Stability Limit Power System Oscillation Damping Limit Inadvertent Loop Flow Limit Thermal Limit Short-Circuit Current Limit

*

Causes of BlackoutApart from natural disturbances, Lightning, Fog, Storm etc

Whether individually or in combination with one another, such as: Unavailability of individual generators or transmission lines High power flows across the region Low voltages earlier in the day or on prior days System frequency variations Low reactive power output from independent power producers (IPPs).

The outage must conform to these criteria:The outage must not be planned by the service provider. The outage must affect at least 1,000 people and last at least one hour. There must be at least 1,000,000 person/customer hours of disruption.

*

Blackout due to decrease in power factorI increasesHeat IncreasesLength increasesSag increasesFlashover on treesCrosses the safe limitTransients increase*

Power Angle Curve*X =XG + XL + XMEG = EM + jXI

ExampleA Generator having Xd=0.7 pu delivers rated load at a pf of 0.8 lagi) find Pe,Qe,E and dV=1+j0 I=1(cos f j sin f) = 1(0.8 j0.6) E=V+jXdI=1.53 L21.5

*

ii) The steam valve of the prime mover is opened further so that Pe increases by 20%. Find new values of Pe,Qe,E and d. ( 20% increase)Pe=0.8 x 1.2 = 0.96E=1.53 No change

Qe=0.535 pu*

Iii) The steam valve is restored to the original position. The exciter is adjusted to raise E by 20%. Find new values of Pe,Qe,E and dPe=0.8E=1.53x1.2 (20% increase) = 1.84

Qe=1.07 pu*

A 100 MVA synchronous generator operates on full load at a frequency of 50Hz. The load is suddenly reduced to 50 MW. Due to time lag in governor system, the steam valve begins to close after 0.4 sec. Determine the change in frequency that occurs on this time. given Kinetic Energy 5 x 105 kWs.Excess energy input to rotaing parts in 0.4 sec is 50 x 0.4 = 20, 000 kWs.Stored Kinetic Energy square of frequency.

Therefore frequency at the end of 0.4 sec = 51 Hz

*

Low FrequencyN Magnetic Induction Harmonic Effects Overheat of Machines B Core Loss Efficiency Fault Current Machine Saturates Motor Burnsout High FrequencyN B heat pf*

Two generators rated 200 MW and 400 MW are operating in parallel. The droop characteristics of their governors are 4% and 5% respectively from no load to full load. Assuming that the generators are operating at 50Hz at no load, how would a load of 600 MW be shared between them? What will be the system frequency at this load? *Frequency in %% loadAt 100 % load

60 % load

As the generates run in parallel, they operate at same frequency.Let load on G 1 ( 200MW) = x MWLoad on G2 (400MW)= (600 x) MWReduction in frequency = Df

Equating Df we get x=231 MWTherefore load on G1 is 231 MW and that of G2 is 369MW

*

As the droop characteristics is of different, G1 is overloaded and G2 is underloaded.

If both the governors are of droop 4% then they will share the load as 200 MW and 600 MW respectively. *

Equal Area Criterion*

Transient Stability Limit*

*

Objectives of FACTS controllers

1. Regulation of power flows in prescribed transmission routes.2. Secure loading of transmission lines nearer to their thermal limits.3. Prevention of cascading outages by contributing to emergency control.4. Damping of oscillations that can threaten security or limit the usable line capacity.

The implementation of the above objectives requires the development of high power compensators and controllers.

The technology needed for this is high power electronics with real time operating control.

The realization of such an overall system optimization control can be considered as an additional objective of FACTS controllers

Sequence of Events12:15 p.m. Incorrect telemetry data renders inoperative the state estimator, a power flow monitoring tool operated by the Indiana-based Midwest Independent Transmission System Operator (MISO). An operator corrects the telemetry problem but forgets to restart the monitoring tool.

1:31 p.m. The Eastlake, Ohio generating plant shuts down. The plant is owned by FirstEnergy, an Akron, Ohio-based company that had experienced extensive recent maintenance problems

2:02 p.m. The first of several 345 kV overhead transmission lines in northeast Ohio fails due to contact with a tree in Walton Hills, Ohio.

2:14 p.m. An alarm system fails at FirstEnergy's control room and is not repaired.

3:05 p.m. A 345 kV transmission line known as the Chamberlain-Harding line fails in Parma, south of Cleveland, due to a tree.

3:17 p.m. Voltage dips temporarily on the Ohio portion of the grid. Controllers take no action.

3:32 p.m. Power shifted by the first failure onto another 345 kV power line, the Hanna-Juniper interconnection, causes it to sag into a tree, bringing it offline as well. While MISO and FirstEnergy controllers concentrate on understanding the failures, they fail to inform system controllers in nearby states.

3:39 p.m. A FirstEnergy 138 kV line fails in northern Ohio

3:41 p.m. A circuit breaker connecting FirstEnergy's grid with that of American Electric Power is tripped as a 345 kV power line (Star-South Canton interconnection) and fifteen 138 kV lines fail in rapid succession in northern Ohio.

3:46 p.m. A fifth 345 kV line, the Tidd-Canton Central line, trips offline.

*

4:05:57 p.m. The Sammis-Star 345 kV line trips due to undervoltage and overcurrent interpreted as a short circuit. 4:064:08 p.m. A sustained power surge north toward Cleveland overloads three 138 kV lines. 4:09:02 p.m. Voltage sags deeply as Ohio draws 2 GW of power from Michigan, creating simultaneous undervoltage and overcurrent conditions as power attempts to flow in such a way as to rebalance the system's voltage. 4:10:34 p.m. Many transmission lines trip out, first in Michigan and then in Ohio, blocking the eastward flow of power around the south shore of Lake Erie. Suddenly bereft of demand, generating stations go offline, creating a huge power deficit. In seconds, power surges in from the east, overloading east-coast power plants whose generators go offline as a protective measure, and the blackout is on. 4:10:37 p.m. The eastern and western Michigan power grids disconnect from each other. Two 345 kV lines in Michigan trip. A line that runs from Grand Ledge to Ann Arbor known as the Oneida-Majestic interconnection trips. A short time later, a line running from Bay City south to Flint in Consumers Energy's system known as the Hampton-Thetford line also trips. 4:10:38 p.m. Cleveland separates from the Pennsylvania grid. 4:10:39 p.m. 3.7 GW power flows from the east along the north shore of Lake Erie, through Ontario to southern Michigan and northern Ohio, a flow more than ten times greater than the condition 30 seconds earlier, causing a voltage drop across the system. 4:10:40 p.m. Flow flips to 2 GW eastward from Michigan through Ontario (a net reversal of 5.7 GW of power), then reverses back westward again within a half second. 4:10:43 p.m. International connections between the United States and Canada begin failing. 4:10:45 p.m. Northwestern Ontario separates from the east when the Wawa-Marathon 230 kV line north of Lake Superior disconnects. The first Ontario power plants go offline in response to the unstable voltage and current demand on the system. 4:10:46 p.m. New York separates from the New England grid. 4:10:50 p.m. Ontario separates from the western New York grid. 4:11:57 p.m. The Keith-Waterman, Bunce Creek-Scott 230 kV lines and the St. Clair-Lambton #1 230 kV line and #2 345 kV line between Michigan and Ontario fail. 4:12:03 p.m. Windsor, Ontario and surrounding areas drop off the grid. 4:12:58 p.m. Northern New Jersey separates its power-grids from New York and the Philadelphia area, causing a cascade of failing secondary generator plants along the Jersey coast and throughout the inland west. 4:13 p.m. End of cascading failure. 256 power plants are off-line, 85% of which went offline after the grid separations occurred, most due to the action of automatic protective controls.

*

In IndiaOn 2nd January 2010, Northern Region experienced a partial grid disturbance on the night of 2nd January, 2010 at 03:01 hrs. in which power supply in Punjab, North Haryana, Himachal Pradesh, Jammu & Kashmir and UT Chandigarh sub-system were affected.with 14 x 400 kV lines and 79 x 220 kV lines out.Load affected in this area was about 7,500 MW and there was about 4,000 MW loss of generation. Dense fog mixed with pollution reduces the breakdown strength of insulators and increases the conductivity along the surface of insulators causing the flash over across insulators and tripping of lines on earth fault. It has been observed that whenever temperature is low i.e. below 9 degree and humidity is high, more than 90 degree, formation of sufficient smog takes place causing flash over across insulators strings. Evening peak hours of 1st Jan 2010 were normal, however low ambient temperature (below 100 C) and high relative humidity (above 90 %) were observed in the region. Such atmospheric condition was witnessed for the first time during this winter season. Situation was under alert condition as it has been experienced in the past that such atmospheric conditions are favorable for fog / smog formation and tripping of transmission lines may occur.

This was followed by another partial disturbance almost on the same pattern, during the late evening hours on the same day i.e. 2nd January, 2010 at 21:54 hrs.

*

*

Power FactorProblems due to Power Factor-

Increased line losses- I2RWasted generation capacityWasted distribution/transformer capacityWasted system capacity Reduced system efficiencyIncreased maximum demand and related chargesPossible power factor chargesIncreased maintenance of equipment and machineryWasted energy/High electric billWasted investment and operating capital

Power factor is the ratio of watts to VA: apparent power to real power.*

*Active and Reactive Power

kVA = (KW)2 + (KVAR)2*The lower the load power factor, the more reactive power is consumed by the load. For example,a 100 MW load with a load power factor of 0.92 consumes 43 MVAr of reactive power, whilethe same 100 MW of load with a load power factor of 0.88 consumes 54 MVAr of reactive power.Under depressed voltage conditions, the induction motors used in air-conditioning units and refrigerators, which are used more heavily on hot and humid days, draw even more reactive power than under normal voltage conditions.

*The power factor impact can be quite largefor example, for a metropolitanarea of 5million people,

the shift from winter peak to summer peak demand can shift peak loadfrom 9,200 MW in winter to 10,000 MW in summer

that change to summer electric loads canshift the load power factorfrom 0.92 in winter down to 0.88 in summer

and this will increasethe MVAr load demand from 3,950 in winter up to 5,400 in summer

*Power Factor Correlation*

Loss Reduction through var compensationPower Losses due to current transmission can be reduced with power factor improvement

%loss reduction = 1 [100 x (original pf / improved pf)2]

Assume a pf improvement from 0.7 to 0.95% loss reduction = 1- (0.7/0.95)2 x100= 45.7%

Load CompensationManagement of Reactive Power to improve Power QualityInstalling Shunt Compensating devices

Line CompensationFerranti effect is minimisedUnderexcited operation of synchronous generators is not requiredThe power transfer capability of the line is enhanced.

Compensating DevicesCapacitorsCapacitors and InductorsActive Voltage Source (Synchronous generator)

Controlling the sending and receiving end voltagesControlling the angle between sending and receiving end voltagesControlling the series reactance

Conventional Equipment For Enhancing Power System Control

Series Capacitor -Controls impedance Switched Shunt-Capacitor and Reactor -Controls voltage Transformer LTC -Controls voltage Phase Shifting Transformer -Controls angle Synchronous Condenser -Controls voltage Special Stability Controls -Typically focuses on voltage control but can often include direct control of power Others (When Thermal Limits are Involved) -Can included reconductoring, raising conductors, dynamic line monitoring, adding new lines, etc. *

FACTS Controllers for Enhancing Power System Control

Static Synchronous Compensator (STATCOM) -Controls voltage Static Var Compensator (SVC) -Controls voltage Unified Power Flow Controller (UPFC) Convertible Series Compensator (CSC) Inter-phase Power Flow Controller (IPFC) Static Synchronous Series Controller (SSSC) - impact voltage, impedance, and/or angle (and power) Thyristor Controlled Series Compensator (TCSC) -Controls impedance Thyristor Controlled Phase Shifting Transformer (TCPST) -Controls angle Super Conducting Magnetic Energy Storage (SMES) -Controls voltage and power *

Classification of FACTS devices*

GUPFCGeneralized unified power flow controllerIPC Interphase power controller IPFCInterline power flow controllerSSSC Static synchronous series compensatorSTATCOMStatic synchronous compensatorSVCStatic var compensatorTCBRThyristor controlled braking resistorTCPAR Thyristor controlled phase angle regulatorTCPST Thyristor controlled phase shifting transformerTCRThyristor controlled reactor

TCSCThyristor controlled series capacitorTCSRThyristor controlled series reactorTCVLThyristor controlled voltage limiterTCVR Thyristor controlled voltage regulatorTSCThyristor switched capacitorTSRThyristor switched reactorTSSC Thyristor switched series capacitor

TSSRThyristor switched series reactorUPFCUnified power flow controller

*

*

*

Series Controller Series controllers include

SSSC, IPFC, TCSC, TSSC, TCSR, and TSSR.

StorageFCVariable Impedance- capacitor/ Reactor/ Power Electronics based variable source of main frequency, subsynchronous and harmonic frequencies (or a combination) to serve the desired load

It injects voltage in series with the line

If the voltage is in phase quadrature with the line current, the series controller only supplies or consumes variable reactive power

Any other phase relationship will involve handling of real power as well.

V

Shunt ControllerFCIvariable impedance, variable source, or a combination of these.

In principle, all shunt controllers inject current into the system at the point of connection.

As long as the injected current is in phase quadrature with the line voltage, the shunt controller only supplies or consumes reactive power.

Any other phase relationship will involve handling of real power as well.

Shunt controllers include STATCOM, TCR, TSR, TSC, and TCBR.

Unified Series - Series ControllerThis could be a combination of separate series controllers, which are controlled in a coordinated manner, in a multiline transmission system.

Or it could be a unified controller in which series controllers provide independent series reactive compensation for each line but also transfer real power among the lines via the proper link.

The real power transfer capability of the unified series-series controller, referred to as IPFC, makes it possible to balance both real and reactive power flow in the lines and thereby maximize the utilization of the transmission system.

The term unified here means that the dc terminals of all controller converters are all connected together for real power transferFCFCDc link ac lines

Coordinated Series and Shunt ControllerCombined series-shunt controllers. This could be a combination of separate shunt and series controllers, which are controlled in a coordinated manner or a UPFC with series and shunt elements.

In principle, combined shunt and series controllers inject current into the system with the shunt part of the controller and voltage in series in the line with the series part of the controller.

However, when the shunt and series controllers are unified, there can be a real power exchange between the series and shunt controllers via the proper link.

Combined series-shunt controllers include UPFC, TCPST, and TCPAR.VFCI FCLineCoordinated Control

Generalized Unified Power Flow ControllerGUPFC can effectively control the power system parameters such as bus voltage, and real and reactive power flows in the lines A simple scheme of GUPFC consists of three converters, one connected in shunt and two connected in series with two transmission lines terminating at a common bus in a substation.

It can control five quantities, i.e., a bus voltage and independent active and reactive power flows in the two lines.

The real power is exchanged among shunt and series converters via a common dc link.

*

Interphase Power Controller

IPC is a series-connected controller of active and reactive power consisting, in each phase, of inductive and capacitive branches subjected to separately phase-shifted voltages.

The active and reactive power can be set independently by adjusting the phase shifts and/or the branch impedances, using mechanical or electronic switches.

In the particular case where the inductive and capacitive impedance form a conjugate pair, each terminal of the IPC is a passive current source dependent on the voltage at the other terminal.

*

Thyristor Controlled Braking ResistorTCBR is a shunt-connected thyristor- switched resistor, which is controlled to aid stabilization of a power system or to minimize power acceleration of a generating unit during a disturbance

*

THYRISTOR-CONTROLLED REACTORA reactance which is connected in series with a bidirectional thyristor valve. The thyristor valve is phase-controlled. Often the main TCR reactor is split into two halves, with the thyristor valve connected between the two halves. This protects the vulnerable thyristor valve from damage due to flashovers, lightning strikes etc. In parallel with the circuit consisting of the series connection of the reactance and the thyristor valve, there may be an opposite reactance, usually consisting of a permanently connected, mechanically switched or thyristor switched capacitor.

By phase-controlled switching of the thyristor valve, the value of delivered reactive power can be set.

Thyristor-controlled reactors can also be used for limiting voltage rises when circuits are open. A TCR is usually a three-phase assembly, normally connected in a delta arrangement to provide partial cancellation ofHarmonics.

This is often the optimum solution for sub transmission and distribution networks supplying industrial loads such as electric arc furnaces, rolling mills and mining processes.

The characteristics of a TSC/TCR combination are:Continuous controlNo transientsElimination of harmonics by tuning the capacitorsCompact design

Thyristor Switched CapacitorTSC is a shunt-connected thyristor-switched capacitor whose effective reactance is varied in a stepwise manner by full- or zero-conduction operation of the thyristor valve

Static Var Compensator The application of SVC was initially for load compensation of fast changing loads such as steel mills and arc furnaces. Here the objective is to provide dynamic power factor improvement and also balance the currents on the source side whenever required

In seventies only it is used in power systemsIncrease power transfer in long lines Improve stability with fast acting voltage regulation Damp low frequency oscillations due to swing (rotor) modes Damp subsynchronous frequency oscillations due to torsional modesControl dynamic overvoltages*

Static Var Compensator * SVC is a shunt-connected static var generator or absorber

whose output is adjusted to exchange capacitive or inductive current so as to maintain or

control specific parameters of the electrical power system (typically bus voltage).

SVC*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

STATCOM- A VSC interfaced in shunt to a transmission line

STATCOM is a static synchronous generator operated as a shunt-connected static var compensator whose capacitive or inductive output current can be controlled independent of the ac system voltage.

SSSC- A VSC interfaced in series to a transmission lineStatic Synchronous Series Compensator Generator operated without an external electric energy source as a series compensator whose output voltage is in quadrature with, and controllable independently of, the line current for the purpose of increasing or decreasing the overall reactive voltage drop across the line and thereby controlling the transmitted electric power.

The SSSC may include transiently rated energy storage or energy absorbing devices to enhance the dynamic behavior of the power system by additional temporary real power compensation, to increase or decrease momentarily, the overall real (resistive) voltage drop across the line

UPFC- Coupling of converters' DC terminals offers a fundamentally different range of control optionsUPFC is a combination of STATCOM and a SSSC which are coupled via a common dc link to allow bidirectional flow of real power between the series output terminals of the SSSC and the shunt output terminals of the STATCOM

controlled to provide concurrent real and reactive series line compensation without an external electric energy source.

The UPFC, by means of angularly unconstrained series voltage injection, is able to control, concurrently or selectively, the transmission line voltage, impedance, and angle or, alternatively, the real and reactive power flow in the line.

The UPFC may also provide independently controllable shunt reactive compensation.

TCSC is a capacitive reactance compensator, which consists of a series capacitor bank shunted by a thyristor-controlled reactor in order to provide a smoothly variable series capacitive reactance.

HVDC LIGHT TECHNOLOGY

Unified Power Flow ControllerThe unified power flow controller is a second generation FACTS device, which enables independent control of active and reactive power with the unique capability of controlling power flow among multi-lines.

It is a multifunction power flow controller with capabilities of terminal voltage regulation, series line compensation and phase angle regulation.

The UPFC primarily injects a voltage in series with the line whose phase angle can vary between 0 to 2 with respect to the terminal voltage and whose magnitude can be varied from 0 to a defined maximum value (depending on the rating of the device).

Hence, the device must be capable of generating and absorbing both real and reactive power.

This controller can be realized by using two Voltage Source Converters (VSCs) employing GTOs

The signal washout is the high pass filter that prevents steady changes in the speed from modifying the IPFC input parameter.

The value of the washout time constant w T should be high enough to allow signals associated with oscillations in rotor speed to pass unchanged.

From the viewpoint of the washout function, the value of w T is not critical and may be in the range of 1s to 20s.

Interline Power Flow Controller

Thyristor Controlled Phase Shifting TransformerCPST is a phase-shifting transformer adjusted by thyristor switches to provide a rapidly variable phase angle

Thyristor Controlled Voltage RegulatorThe basic concept of voltage regulation is the addition of an appropriate in-phase or a quadrature component to the prevailing terminal voltage in order to change (increase or decrease) its magnitude to a desired value.

In thyristor based approach of voltage regulation, the insertion of voltage is obtained by selection of appropriate tap of a regulating transformer (insertion transformer), in series with the line.TCVR. TCVR is a thyristor-controlled transformer that can provide variable in-phase voltage with continuous control

The power circuit scheme of a thyristor tap changer with a RL load arrangement can give continuous voltage magnitude control by initiating the onset of thyristor valve conduction.

The voltage obtainable at the upper tap and lower tap are V2 and V1 respectively.

The gating of the thyristor valves is controlled by the delay angle , with respect to the voltage zero crossing of these voltages.

At = 1, valve sw2 is gated on, which commutates the current from the conducting thyristor valve sw1 by forcing a negative anode to cathode voltage across it and connecting the output to the upper tap with voltage V2. Valve sw2 continues conducting until the next current zero is reached. Thus, by delaying the turn-on of sw2 from zero to , any output voltage between V2 and V1 can be attained, as shown in Fig.

Self-tuning Controller for Damping of Power System Oscillations with FACTS Devices

*MATHEMATICAL MODELLING OF THE PQ SIGNALS

S.No.

Event

Controlling Parameters

Equations

1

Pure Sine

F = 50 Hz

V= 230 V

V(t) = sin(t)

2

Sudden Sag

0.1

0.9

t

t2-t1

9t

V(t)=A[1-(u(t2)-u(t1))] sin(t)

3

Sudden Swell

0.1

0.9

t

t2-t1

9t

V(t)=A[1+(u(t2)-u(t1))] sin(t)

4

Harmonics

0.1

0.9

0.1

0.9

0.1

0.9

V(t)=A[ sin(t) + sin(3t) + sin(5t) + sin(7t)]

5

Flicker

0.1

0.2

0.1

0.5

V(t)=A[1+sin(t)] sin(t)

6

Oscillatory Transients

0.1

0.9

0.5t

t2-t1

3t

0.1

0.2

V(t)=A[sin(t)+ e-(t-t1)/ sin(n (t-t1)) (u(t2)-u(t1)) ]

7

Notch

Vb=230 V, fb=50Hz, Vn = Notch Signal

V(t)=

Vb sin(2 fb t) + Vn

8

Outage

0.9

1

t

t2-t1

9t

V(t)=A[1-(u(t2)-u(t1))]

9

Sag with harmonics

0.1

0.9

t

t2-t1

9t

0.05

0.15

0.05

0.15

V(t)=A[1-(u(t2)-u(t1))]

(sin(t)+ sin(3t) + sin(5t) +]

10

Swell with harmonics

0.1

0.8

t

t2-t1

9t

0.05

0.15

0.05

0.15

V(t)=A[1+(u(t2)-u(t1))]

(sin(t) + sin(3t) + sin(5t) +]

_1159643394.unknown

_1159644255.unknown

_1159643340.unknown

* Impulsive TransientsMomentary Interruptions Voltage Sag Capacitor Switching

*Voltage Imbalance Momentary Interruption with Sag HarmonicsHarmonics with Swell

*Fault Simulation Model

*Harmonic Simulation Model

*Circuit Breaker Operation Model

3-machine 9-bus system*

COMPLETE CLASSICAL SYSTEM MODEL FOR TRANSIENT STABILITY STUDY IN SIMULINK *

COMPUTATION OF ELECTRICAL POWER OUTPUT BY G1(SIMULINK MODEL) *

COMPUTATION OF ELECTRICAL POWER OUTPUT BY G2 (SIMULINK MODEL) *

COMPUTATION OF ELECTRICAL POWER OUTPUT BY G3(SIMULINK MODEL) *

Phases of power system studies for FACTS installation project

Phase 1Initial Feasibility Studies to Determine System Constraints and Reinforcement Needs Phase 1 type studies are typically performed by the transmission owner or its consultant. The main study tools and FACTS model requirements for Phase 1 type studies are: Load Flow Programs Stability Programs Positive Sequence Modeling Only Full Scale Model of the Power System Simple Device Models are Adequate for Study Phase 1

*

Identify Characteristics of the Power System

Identify System Performance Problems -Transient instability -Oscillatory instability -Dynamic voltage instability -Voltage collapse -Thermal ratings (power flow)

Identify which Transmission Constraints that can be Examined Independently and which Require a Coordinated Analysis

Identify the Reinforcement Needs (Shunt vs. Series and Fast vs. Slow)

Phase 2

Studies to Determine Type of Equipment, Location, and RatingsPhase 2 type studies are typically performed by the transmission owner or its consultant.*

key objectives for Phase 2 type

Identify Solution Options, both Conventional and FACTS and Combinations Thereof Evaluate Performance of Solution Options (Consider Other Issues )-Location -Economics of the solution options -Losses -Interaction with other devices Evaluate Economics of Each Options Costs vs. Value of Power System Benefits

The main study tools and FACTS model requirements for Phase 2 type studies are: Load Flow Programs Stability Programs Positive Sequence Modeling Only Full Scale Model of the Power System Device Models -Load flow models -Stability models -Control modelsElectromagnetic transients analysis is typically not required at this stage.

If the analysis of Phase 1 indicates that the system has a problem with voltage, then in Phase 2 it is necessary to identify solution options for system voltage control. These include:

For Dynamic (fast) Voltage Instability, Consider: -Shunt capacitor banks -Static shunt compensators (e.g., STATCOM, SVC) -Combination

For Voltage Collapse (slow), Consider: -Shunt capacitor banks -Series capacitors -Static shunt compensators (e.g., STATCOM, SVC) -Static series compensators (e.g., SSSC) -Combination

If the analysis of Phase 1 indicates that the system has a problem with rotor angle stability, then in Phase 2 it is necessary to identify solution options for this type of problem. For Transient Instability, Consider: -Series capacitors -Static shunt compensators (e.g., STATCOM, SVC) -Static series compensators (e.g., SSSC) -Combination For Oscillatory Instability, Consider: -Power system stabilizers (PSS) -Damping controls added to static shunt or series compensators

The end results (deliverables) of Phase 2 type studies are: Identification of Viable Solution Options -Consider both conventional and FACTS and combinations thereof -Rank all viable solutions in terms of system benefits Identification of Suitable Location to Install the Solution Options -Choice may be obvious or depend on the solution to be implemented -Site work and permitting etc. may be a key factor Evaluation of Economics of Each Options Overall Costs vs. Value of Power System Benefits -Rank all viable solutions in terms of overall economics

Phase 3

Pre- Specification Studies for Defining Equipment RequirementsTo be Able to Write a Technical Specification and RFP to Submit to Potential Bidders Phase 3 type studies are typically performed by the transmission owner or its consultant.

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The key objectives for Phase 3 : There are a variety of technical items to be determined apriori by system studies. These include, but are not limited to, the following: Device Type, Rating, and Location (From Phase 2 Studies) System Descriptions -Minimum and maximum operating voltage for steadystate and transient conditions (MCOV, BSL, BIL, etc) -Minimum, maximum, emergency, and ultimate system strength and corresponding X/R ratios -Minimum and maximum frequency excursions -Maximum unbalance (negative and zero sequence) System Dynamic Performance Requirements To develop strategies for system steady-state and transient performance Harmonic Limits and System Characteristics-Maximum individual harmonic distortion (Dn) -Maximum total harmonic distortion (D) -Telephone interference limit (TIF) -Impedance envelopes for normal and contingency conditions

High-frequency Interference Issues and Limits -To determine maximum acceptable limits on power line carrier (PLC) noise and radio interference (RI) noise

Other Items to Prepare -System one-line diagram and impedance map -Load flow and stability data sets -Equipment performance requirements --Control objectives (steady state and transient) --Response times --Voltage imbalance --Availability/Reliability criteria --Acceptable Failure Rate of components -Loss evaluation criteria, formula, and associated cost/penalty -List of required system studies by vendor (See Phase 4 type studies)

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Phase 4Pre-Manufacturing and Equipment Design and Verification Studies Phase 4 type studies are typically performed by the vendor after an award of a contract for the FACTS installation. *

The key objectives for Phase 4 type To verify to the owner that the device described by the specification meets all system and equipment performance requirements to complete the detailed design for equipment Manufacturing and Procurement for: -Control and Protection (Hardware and Software) -Insulation Coordination -Inverters -Filters -High-voltage and low-voltage equipment -Etc

Phase 5Studies for post-commissioning system operation Studies are typically performed by the transmission owner.

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The key objectives and deliverables for phase 5 type To confirm the network load flow conditions are within benchmark limits To confirm installed equipment is effective to enhance network steady-state and dynamic performance To setup instrumentation and obtain measurements during staged fault tests and actual faults/dynamic events To ensure there are no adverse interactions with other system equipment To measure reliability/availability of equipment To establish operational losses algorithm

FACTS controllersControl attribute

STATCOMVoltage control, VAR compensation, damping oscillations, voltage stability

SVC, TCR, TSC, TSRVoltage control, VAR compensation, damping oscillations, transient and dynamic stability, voltage stability

TCBRDamping oscillations, transient and dynamic stabilitySSSC, TCSC, TSSC, TCSR, TSSRCurrent control, damping oscillations, transient and dynamic stability, voltage stability, fault current limiting

TCPSTActive power control, damping oscillations, transient and dynamic stability, voltage stability

UPFC, GUPFCActive and reactive power control, voltage control, VAR compensation, damping oscillations, transient and dynamic stability, voltage stability, fault current limiting

TCVLTransient and dynamic voltage limit

TCVR, IPFCReactive power control, voltage control, damping oscillations, transient and dynamic stability, voltage stability

Operating problemCorrective action FACTS controllers

Voltage limits:Low voltage at heavy loadSupply reactive power STATCOM, SVC

High voltage at low load Absorb reactive power STATCOM, SVC, TCR

High voltage following an outage Absorb reactive power; prevent overload STATCOM, SVC, TCR

Low voltage following an outage Supply reactive power; prevent overload STATCOM, SVC

Thermal limits:Transmission circuit overloadReduce overload TCSC, SSSC, UPFC, IPC

Tripping of parallel circuits Limit circuit loading TCSC, SSSC, UPFC, IPC

Loop flows:Parallel line load sharingAdjust series reactance IPC, SSSC, UPFC, TCSC

Post-fault power flow sharing Rearrange network or use thermal limit actions IPC, TCSC, SSSC, UPFC

Power flow direction reversal Adjust phase angle IPC, SSSC, UPFC

Issues Associated with Adding Distributed Generation to Distribution SystemsIssue 1Improper Coordination 2Nuisance Fuse Blowing 3Reclosing out of Synchronism 4Transfer Trip 5Islanding 6Equipment Over voltage 7Resonant Over voltage 8Harmonics 9Sectionalizer Miscount10Reverse Power Relay Malfunctions11Voltage Regulation Malfunctions12Line Drop Compensator Fooled by DRs13LTC Regulation Affected by DRs14aSubstation Load Monitoring Errors14bCold Load Pickup with & without DRs15 Faults within a DR zone16 Isolate DR for Upstream Fault

Issue17 Close-in fault Causes Voltage Dip Trips DR18 Switchgear Ratings19 Self Excited Induction Generator20 Long Feeder Steady State Stability21 Stability During Faults22 Loss of Exciters Causes Low Voltage23 Inrush of Induction Machines Can Cause Voltage Dips24 Voltage Cancelled by Forced Commutated Inverters25 Capacitor Switching Causes Inverter Trip26 Flicker from Windmill Blades27 Upstream Single Phase Fault Causes Fuse Blowing28 Under frequency Relaying29 Distribution Automation Studies

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THE ROAD MAP FOR ACHIEVING FULLEST CUSTOMER SATISFACTIONTHE ROLE OF REGULATORY AND STANDARDS AGENCIESTHE ROLE OFMANUFACTURERSTHE ROLE OF CUSTOMERSTHE ROLE OF UTILITIES1234*

*REFERENCE

E.Acha, V.G.Agelidis, O.Anaya-Lara, T.J.E.Miller, Power Electronic Control in Electrical Systems, Elsevier, 2002

2. D.P.Kothari, I.J.Nagrath, Modern Power System Analysis, McGrawHill, 2011

3. K.R.Padiyar, FACTS controllers in Power Transmission and Distribution, New Age International Publishers, 2007.

4. www.abb.com

5. www.areva.com

6. www.epri.com

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**KSR-FDP***************Congestion:Doesnt occur at all hours and on all daysOccurs at electrical rush hoursLots of room at non-rush hours usuallyMust be careful with usage data:-Averaging use will show little congestion - i.e. like averaging use on highways-Netting - I.e. algebraic sum of traffic in both directions if heavy in both directions will show near zero use.This would be like commuters from Salem to Portland switching jobs with commuters from Portland to Salem. Full Plane analogy:Firm seats on the plane versus going standby for parts of the tripAuctioning tickets to replace other passengers on the full planePrice of the ticket if plane usually flew half fullNew generators would like firm reservations on the delivery system so they can assure financing.***********Active power, measured in kilowatt (kW), is the real power (shaft power, true power) used by a load to perform a certain task. However, there are certain loads like motors, which require another form of power called reactive power (kVAR) to establish the magnetic field. Although reactive power is virtual, it actually determines the load (demand) on an electrical system. The utility has to pay for total power (or demand) The vector sum of the active power and reactive power is the total (or apparent) power, measured in kVA (kilo Volts-Amperes). This is the power sent by the power company to customers. Here the different powers are represented of a power triangle where the vector sum of the active power and reactive power make up the total power used. This is the power sent by the power utility companies for the user to perform a given amount of work. Total power, also known as apparent power is measured in kilo Volts-Amperes. You can see from the figure that the active power, and the reactive power required are 90 degrees apart vectorically in a pure inductive circuit. In other words reactive power kVAr lagging the active kW. The apparent power, kVA, is the vector sum of active and reactive power. Mathematically it may be represented with the following formula (Click once): kVA = (KW)2 + (KVAR)2**The power factor is the ratio between active power (kW) and total power (kVA), or the cosine of the angle between active and total power. A high reactive power, will increase this angle and as a result the power factor will be lower The power factor is always less than or equal to one. Theoretically, if all loads of the power supplied by electricity companies have a power factor of one, the maximum power transferred equals the distribution system capacity. However, as the loads are inductive and if power factors range from 0.2 to 0.3, the electrical distribution networks capacity is stressed. Hence, the reactive power (kVAR) should be as low as possible for the same kW output in order to minimize the total power (kVA) demand. **********EPRI understands that these critical issues cannot be resolved in the policy or market arenas alone. Technology also has a vital role to play in moving us toward economic and environmental sustainability. To re-establish the commitment to strategic R&D, we have spearheaded an effort called The Electricity Technology Roadmap, which is currently engaging over 150 leaders across organizations in government, R&D, high-tech, environment, and academia. The Roadmap offers a unique perspective by setting forth a series of ambitious, but doable goals or destinations, that address these fundamental issues through accelerated breakthrough technology development and implementation over the next 25 years and beyond. They include:

Strengthening our power delivery infrastructure Enabling customer-managed service networks Boosting economic productivity and prosperity Resolving the energy/carbon conflict Managing the global sustainability challenge

Let me take a few minutes to run through these destinations, focusing primarily on the first and last.

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