SVC_ STATCOM_ AND TRANSMISSION LINE

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					   INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING & –
    International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976
        6545(Print), ISSN 0976 –TECHNOLOGY (IJEET)January-June (2012), © IAEME
                                6553(Online) Volume 3, Issue 1,

ISSN 0976 – 6545(Print)
ISSN 0976 – 6553(Online)
Volume 3, Issue 1, January- June (2012), pp. 326-343
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        SVC, STATCOM, AND TRANSMISSION LINE RATING
    ENHANCMENTS ON INDUCTION GENERATOR DRIVEN BY WIND
                          TURBINE

                                      Youssef A. Mobarak
                   Electrical Engineering Department, Faculty of Engineering,
                       Rabigh, King Abdulaziz University, Saudi Arabia,
                                    y.a.mobarak@gmail.com

   ABSTRACT

   Multi-megawatt wind-turbine systems, often organized in a wind park, are the backbone of
   the power generation based on renewable-energy systems. This paper presents the effect of
   some system parameters like rating of capacitor bank, static var compensator SVC rating,
   static synchronous compensator STATCOM rating and transmission line length, on
   performance of induction generator driven by wind turbine. Also, the most-adopted wind-
   turbine systems, the adopted generators the topologies of the converters, the generator
   control and grid connection issues, as well as their arrangement in wind parks. This study
   is based on the SimPowerSystems for use with Matlab/Simulink.

   Keywords: Wind Turbine Induction Generator WTIG, SVC, STATCOM.

       1. INTRODUCTION

   Most of the electricity generated today uses non-renewable sources of fuel such as coal, oil
   and gas. These contribute to large quantities of CO2 to the atmosphere, and cause an
   enhanced green house effect, leading to the warming of the earth’s atmosphere. The
   increasing rate of depletion of conventional energy sources has increased emphasis on
   renewable energy sources to provide the growing demand. The adverse effects of
   conventional systems have given rise to a shift in focus towards renewable energy sources
   such as wind, solar, hydro, tidal wave, biomass, and so on. As already known, renewable
   energy sources have virtually no adverse effects on the environment. The Global Wind
   Energy Council GWEC [1] states that wind energy developments have occurred in more
   than 70 countries around the world.
   Induction machines are mostly used as generators in wind power based generations. Since
   induction machines have a performance problem as they draw very large reactive currents
   during fault condition, reactive power compensation can be provided to improve
   performance. This part presents general review and previous work of wind turbine and


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wind generators [2-4]. Also, it is intended to provide an overview of Static VAR
Compensator SVC and Static Synchronous Compensator STATCOM in order to provide
the merits and applications of Flexible AC Transmission System FACTS to the operations
of transmission and distribution systems [5-9]. In the present work, three applications of
SVC, and STATCOM, and transmission line length variations of rating are studied, on
performance of Induction Generator IG driven by wind turbine. The simulation study of
the wind turbine system connected to grid are performed using MATLAB/SIMULINK
SimPowerSystems toolbox.
   2. WIND-TURBINE SYSTEM OVERVIEW

The most-common wind-turbine systems and the control issues are reviewed here [10-13].
Wind-turbine systems directly coupled to the grid and/or without any power converter
directly or indirectly controlling the rotor speed will not be taken into consideration. The
electrical generators currently used for the implementation of multi-MW Wind-Energy
Conversion System WECSs are the doubly fed induction generator DFIG, the cage
induction generator IG, and the synchronous generator SG. The DFIG is widely used for
variable-speed generation and is one of the most important generators for wind-energy
applications [12-15]. Nowadays, this topology has a fraction of the wind-energy market,
which is close to 50%. For a typical DFIG, the power converters are connected to the rotor
and, for a restricted speed range, are rated at a fraction of the machine nominal power [14],
i.e., typically 30% of this value. The speed range is limited, and slip rings are required in
order to connect the machine-side converter to the rotor. For WECSs based on DFIGs,
gearboxes are still required because a multi-pole low-speed DFIG is not technically
feasible [12]. The WECS speed is regulated, adjusting the electrical torque via the rotor-
side converter. The speed regulation is mostly used to optimize the power extraction from
the wind. However, the possibility of controlling the active power and the reactive power
gives to this system the rolling capacity on the grid [16-17] because the active-power
injection is controlled not only with the pitch or active stall but also via the machine-side
pulse-width-modulation PWM converter.

The squirrel-cage induction generator SCIG is a very popular machine due to its
mechanical simplicity and robust construction [12]. The rotor is provided by metallic bars,
which are resistant to the effects of dirt and vibration. Unlike the DFIG, no brushes are
required for the operation of this machine, and little maintenance is necessary, mainly
bearing lubrication only. The SCIG was widely used in fixed-speed WECS, and it is still
used for variable-speed wind-energy generation [12]. The IG with a frequency converter is
completely decoupled from the grid, and as a consequence, this system has a complete
rolling capacity. The control system of a WECS based on a SCIG and on back-to-back
converters could be designed to avoid increasing the short-circuit power because the
control loops limit the fault current at the grid-side converter output. The main drawbacks
of the SCIG are in the fact that two full power converters are required for the operation of
this machine and that a multi-pole direct-drive operation is not technically feasible [12].
Therefore, SCIGs do not have the advantage of variable-speed operation using reduced-
size power converters, SCIGs can neither be used in direct-driven WECS.

The two subsystems, the electrical and mechanical ones that compose the WECS are
characterized by different control goals but interact in view of the main aim, the control of
the power injected into the grid. The electrical control system regulates the supply of the


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active/reactive power to the grid [16-17]. The electrical system also provides overload
protection. The mechanical subsystem is responsible of the power limitation, the maximum
energy capture, the speed limitation, and the reduction of the acoustical noise [18-19]. The
power has to react based on a set point given by the power-grid dispatch center or locally
with the goal to maximize the production based on the available wind power [19]. The
control of the WECS electrical subsystem can be divided into three different stages. The
first stage includes the basic functions that guarantee the proper operation of the power
converters, hence taking care of voltages and currents on the generator side, in the
intermediate direct-current dc link if present, and on the grid side [11]. The second stage
includes the WECS specific functions, hence the maximization and the limitation of the
power. The control of the WECS is organized such that below the maximum power
production, the wind turbine will typically vary the speed proportional to the wind speed
and keep the pitch angle fixed [18]. At very low wind, the speed of the turbine will be
fixed at the maximum allowable slip in order not to have overvoltage. A pitch-angle
controller will limit the power when the turbine reaches the nominal power. The third stage
includes extra functions that will become crucial in the future power system, characterized
by a significant inflow of the distributed power generation. The WECS is expected to
contribute and improve the power quality, to offer energy storage to buffer the energy
production, and to contribute to the grid stability with the inertia-emulation functionality.
In this sense, the transmission-system operator may also provide a supervisory command
to take advantage of these extra functions when required.

    3. SVC AND STATCOM OVERVIEW
Induction generator based wind parks usually draw a large amount of reactive power that
leads to problems of stability both in steady-state and during transients. In addition,
transmission system operators TSO nowadays put strict requirements on ride-though
capability. The wind parks themselves cannot fulfill these requirements without reactive
power support devices. Recent technology gives several solutions for this, of which
conventional switched capacitor CAP, static var compensator SVC, and static compensator
STATCOM are usually applied. Many studies on low voltage ride-through capability RTC
of wind parks with these support devices have been performed. For example, the influence
of STATCOM on the transient stability margin of squirrel-cage generator based wind parks
has been studied in [20]. Applying a STATCOM to an existing wind park with fixed-speed
induction generators to prevent voltage collapse caused by serious network disturbances
has been conducted in [21]. Reference [22] presents a method to compare the performances
of STATCOM and SVC on RTC. In earlier works, STATCOM has been identified as the
fastest responding device that can assist in improving power quality and fault ride through
of wind farms [23]. It has been also shown that it is technically practical to apply
electricity storage to wind generation that may be installed on the grid to improve
throughput of existing grid infrastructure, reduce system loss and improve power factor
[24]. Battery energy storage is an extremely well proven storage technology with low
losses [25].

Different solutions are found to support the transient behavior of cage induction generators
in case of changes in the grid voltage. Mechanically switched capacitors, SVC,
synchronous condensers and voltage source SVC such as the STATCOM can be used to
regulate voltage as shunt compensator to improve the grid interface of directly connected

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asynchronous wind generators. Thyristor-controlled SVCs have been reported in [26-27]
for voltage support of critical loads, transient stability improvement and power oscillation
damping in electric power transmission systems. The STATCOM has the same
capabilities, as reported in [28-29], but with a higher control bandwidth and the additional
capability of providing higher currents at low voltage levels. Studies of transient stability
of induction generators related to the use of a STATCOM have been reported in [30-31],
and a general analysis of the ride through capability of fixed-speed wind farms with a
STATCOM is provided in [32-33]. Both the STATCOM and the SVC are analyzed from
the point of view of their potential for increasing the transient margin as reported in [34-
35] to indicate their capability as candidate solutions for providing LVRT to wind farms
with induction generators directly connected to the electric grid.

   4. STUDIED SYSTEM AND MODELING

The mathematical models of wind turbine, and wind generators are presented in this
section. The general concepts of FACTS controllers modeling are explained in steady-
state. The wind farm using Induction Generators IG driven by variable-pitch wind turbines
test system is utilized.

4.1 Wind Turbine Model
The wind turbine model employed in the present study is based on the steady-state power
characteristics of the turbine. The stiffness of the drive train is infinite and the friction
factor and the inertia of the turbine are combined with those of the generator coupled to the
turbine. The wind turbine mechanical power output is a function of rotor speed as well as
the wind speed and is expressed as:
                          ρA 3
        Pm = C P (λ , β )     Vwind                                              (1)
                           2
Normalizing (1) in the per unit system as:
                             3
        Pm− pu = k PCP− puVWind − pu                                             (2)
A generic equation is used to model CP(λ,β). This equation, based on the modeling turbine
characteristics is:
                                                      − C5
                              C2                       λi
        C P (λ , β ) = C1 (        − C3 β − C 4 ) e          + C6 λ                (3)
                              λi
        1        1       0.035
With:       =          − 3                                                  (4)
       λi λ + 0.08β β + 1
The coefficients C1 to C6 are constants: C1=0.5176, C2=116, C3=0.4, C4=5, C5=21, and
C6=0.0068.

In this studied a constant pitch angle β is used and its value is assigned as zero, the based
speed is selected at 9m/s. The turbine power characteristics of the model in Fig. (1), and
shows how PWT varies with rotor speed for different wind speeds. The optimum tip speed
ratio curve gives the highest efficiency points for PWT. As seen from figure, rated power
3MW (1pu) occurs at rated wind speed of 9m/s. In dynamic simulations, the electricity-
producing wind turbine is treated as a complex electromechanical system consisting of the
IG, the drive train system and the rotating wind turbine. Its modular diagram is given in
Fig. (2).



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           Fig. (1) Power as a function of rotor speed for different wind speeds




Fig. (2) Grid-connected model stall-controlled WT equipped with an IG

4.2 IG Model:
                                                          second-order state-space model and
The electrical part of the machine is represented by a second                  space
                                second-order
the mechanical part by a second order system. All electrical variables and parameters are
                                                                             two
referred to the stator. All stator and rotor quantities are in the arbitrary two-axis reference
                                 axis     q-axis
frame (d-q frame). The d-axis and q axis block diagram of the electrical system is show
Fig. (3), and the electrical equations are given by:
                         d
        Vqs = RS iqs + ϕ qs + ωϕ ds                                                    (5)
                        dt
                         d
        Vds = RS ids + ϕ ds − ωϕ qs                                              (6)
                        dt
                         d
           ′                  ′
        Vqr = Rr′iqr + ϕ qr + (ω − ω r )ϕ dr′                                      (7)
                        dt
                         d
           ′                  ′
        Vdr = Rr′idr + ϕ dr − (ω − ωr )ϕ qr ′                                        (8)
                        dt
        Te = 1.5 p (ϕ ds iqs − ϕ qs ids )                                         (9)
                                                  ′                               ′     ′′
Where: ϕ qs = Ls iqs + Lmiqr , ϕ ds = Ls ids + Lmidr , ϕ qr = Lr iqr + Lm iqs , ϕ dr = Lr idr + Lmids
                          ′                              ′     ′′
                           ′     ′
With: LS = Lls + Lm and Lr = Llr + Lm
The mechanical equations are given by:
       d        1
         ωm =      (Te − Fω m − Tm )                                                              (10)
      dt       2H



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        d
           θ m = ωm                                                         (11)
        dt




                     Fig. (3) Induction machine equivalent circuits
                   axis
             (a) d-axis equivalent circuit        q axis
                                              (b) q-axis equivalent circuit

4.3 WTIG:
The block diagram of WTIG is shown in Fig. (4), and the stator winding is connected
directly to the 60Hz grid and the rotor is driven by a variable pitch wind turbine. The
                                                                                    inducti
power captured by the wind turbine is converted into electrical power by the induction
generator and is transmitted to the grid by the stator winding. The pitch angle is controlled
in order to limit the generator output power to its nominal value for high wind speeds. In
                                                                          hronous
order to generate power the IG speed must be slightly above the synchronous speed. The
pitch angle controller regulates the WT blade pitch angle β, according to the wind speed
                                                              ,
variations. Hence, the power output of WTIG depends on the characteristics of the pitch
                                                     characteristics. This control guarantees
controller in addition to the turbine and generator characte
that, irrespective of the voltage, the power output of the WTIG for any wind speed will be
equal to the designed value for that speed.




                        lock
         Fig. (4) WTIG block diagram                            itch
                                                      Fig. (5) Pitch angle control

The pitch angle β is controlled in order to limit the generator output power at its nominal
value for winds exceeding the nominal speed. β is controlled by a Proportional
                                                                    Proportional-Integral PI
                                                                         mec
controller in order to limit the electric output power to the nominal mechanical power.
When the measured electric output power is under its nominal value, β is kept constant at
zero degree. When it increases above its nominal value the PI controller increases β to
                                                                    angle
bring back the measured power to its nominal value. The pitch angle control system is
shown in Fig. (5).




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4.5 SVC Modeling
The primary task of an SVC is to maintain the voltage at a particular bus by means of
reactive power compensation. SVC is basically a shunt connected Static Var Generator
SVG whose output is adjusted to exchange capacitive or inductive current so as to maintain
                                                                   single-line
or control specific power system variables. Figure (6) shows the single line diagram of a
                                                               typically,
SVC and a simplified block diagram of its control system. A typically, the power system
control variable controlled by SVC is the terminal bus voltage, and total susceptance of
SVC can be controlled by firing thyristors. Consequently, it represents the controller with
variable impedance that is changed with the firing angle of TCR. The terminal or V-I
characteristics of SVC is illustrated in Fig. (7).




                      oltage
        Fig. (6) SVC voltage control system                        I
                                                    Fig. (7) SVC V-I characteristics

As long as the SVC susceptance B stays within the maximum and minimum susceptance
                                                                    (B
values imposed by the total reactive power of capacitor banks ( Cmax) and reactor banks
(Blmax), the voltage is regulated at the reference voltage Vref. However, the V-I characteristic
                                                                              V
is described by the following three equations.
SVC is in regulation range (− BC max < B < Bl max )
         V = Vref + IX S                                                      (12)
SVC is fully capacitive (B = BC max )
                I
        V=                                                                        (13)
            BC max
SVC is fully inductive (B = Bl max )
               I
        V =                                                                       (14)
             Bl max
Where V is Positive sequence voltage pu, I is reactive current pu/Pbase, XS is Slope or
droop reactance pu/Pbase, BCmax is maximum capacitive susceptance pu/Pbase with all TSCs
                                         aximum
in service, no TSR or TCR , Blmax is maximum inductive susceptance pu/Pbase with all
                                                                    phase
TSRs in service or TCRs at full conduction, no TSC , Pbase is three-phase base power

4.6 STATCOM Modeling

                                             STATCOM.
There are two techniques for controlling the STATCOM. The first technique, referred to as
phase control, is to control the phase shift β to control the STATCOM output voltage
magnitude. The other technique referred to as PWM on the other hand allow for
independent control of output voltage magnitude and phase shift, in this case, the dc

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                                                          voltage.
voltage is controlled separately from the ac output voltage. The basic structure of a
                          based
STATCOM with PWM-based voltage controls is depicted in Fig. (9). Eliminating the dc
voltage control loop on this figure would yield the basic block diagram of a controller with
a typical phase angle control strategy. In PWM controls, switching losses associated with
the relatively fast switching of the electronic devices and their snubbers play an important
role in the simulation, as these have a direct effect on the charging and discharging of the
                       should
capacitor, and hence shoul be considered in the modeling. By varying the amplitude of
output voltage can control the reactive power exchange between the inverter and the ac
system. If the amplitude of the output voltage is increased above that of ac system voltage,
                nerates
the inverter generates reactive power for the ac system. If the amplitude of the output
voltage is decreased below that of the ac system, the inverter absorbs the reactive power. If
                                                                                        zero
the output voltage is equal to the ac system voltage, the reactive power exchange is zero.
Conversely, the inverter absorbs real power from the ac system, if the inverter output
voltage is made to lag the ac system voltage. The V-I characteristic of STATCOM
                                                                                    induct
controller is shown in Fig. (10), the controller can provide both capacitive and inductive
compensation and is able to control output current over the rated maximum capacitive or
inductive range independent of the ac system voltage. It can provide full capacitive output
current at any practical system voltage.




    Fig. (9) STATCOM with PWM                                     I
                                            Fig. (10) STATCOM V-I characteristics
This is in contrast to the SVC which can supply only a diminishing output current with
decreasing system voltage as determined by the designed maximum equivalent capacitive
admittance. The active and reactive power exchange between the VSC and the system are a
function of the converter output voltage denoted as Vout, i.e.
            V V
        P = out sin α conv                                                    (15)
              X
              2
            Vout − VoutV cos α conv
       Q=                                                                          (16)
                       X
Where αconv is the angle between the ac system voltage V and Vout, and X denotes the
reactance of the coupling transformer. Two control strategies may be used for a
                                                    control.
STATCOM, namely, phase control and PWM control. With phase control, the dc bus
voltage Vdc is regulated by changing αconv, i.e. charging and discharging the dc capacitor,
which ultimately controls Vout, as this voltage is proportional to Vdc.



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4.7 Studied System
The one line diagram of the test system employed in this study is shown in Fig. (11). The
network consists of a 120kV, 60Hz, sub-transmission system with short circuit level of
2500MVA, feeds a 25kV distribution system through 120/25kV step down transformers. A
wind farm consisting of 1.5MW wind turbines and driven squirrel-cage induction generator
is connected to the 25kV distribution system, exports power to the 120kV grid through a
25km, and 25kV feeder.

                                                          3        25Kv/575V
                                                                     4MVA
                                                              T.L 1Km



                                                                        400kvar         WTIG #1
                 Network                                                                2×1.5MW
                 120/25KV                                          25Kv/575V
                1 47MVA 2                                            4MVA
                                            T.L 25Km
                                                              T.L 1Km



                                                                        400kvar        WTIG #2
                                                                                       2×1.5MW
                                                                   25Kv/575V
                                                                     4MVA

                                                               T.L 1Km

                MW flow
                                             Coupling                   400kvar         WTIG #3
                                            transformer                                 2×1.5MW
                               STATCOM   Voltage
                                 3MVA    Source                 SVC               Wind farm
                                                                3MV



                                        Vdcc
       Fig. (11) Distribution system embedded with WTIG and FACTS devices

Part of the reactive power consumed by the IG is locally supplied by fixed capacitors of
400Kvar each, installed at the terminals of the machines. Dynamic reactive power
compensation is provided by a 3MVA STATCOM and 3MVA SVC. In order to limit the
generator output power at its nominal value, the pitch angle is controlled for winds
exceeding the nominal speed of 9m/s. To inject active power to the distribution network,
the IG speed must be slightly above the synchronous speed. Each wind turbine has a
protection system, monitoring voltage, current and machine speed. The amount of active
power injected by WTIGs to the distribution system is limited by transient stability issues.
It is intended to improve the performance of WTIG by changing some system parameters,
such as capacitor bank connected parallel with WTIG, FATCS rating and change in feeder
length used to connect WTIG with network. Also SVC and STATCOM ratings varied to
depict the WTIG and feeder bus performances are discussed.




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               5. RESULTS AND DISCUSSIONS

5.1 Effect of Change Capacitor Bank Rated:
Figure (12) illustrates active power from WTIG, reactive power to WTIG, and turbine
speed responses without FC or with FC of 200kvar rating. It's noted that three WTIG are
tripped at t=5sec, so generated active power and absorbed reactive power become zero. By
the increase of FC rating to reach 400kvar, three WTIG are still working so each WTIG
generates 2.9MW. Total active power injected to the network, total reactive power
absorbed from the network and voltage at feeder bus responses are shown in Fig. (13) due
to the change of FC rating. It's noted that the total active power injected to the network is
zero without FC or with FC of 200kvar rating but, it becomes 8.7MW with FC of 400kvar
and the voltage at feeder bus is improved to reach 0.945pu.


                                          4                                                                              10


                                                                                                                         8
                                          3
                       Active pow [M ]
                                 er W




                                                                                                   Active pow [M ]
                                                                                                             er W
                                                                                                                         6
                                          2
                                                                                                                         4

                                          1                               without FC                                                                 without FC
                                                                                                                         2
                                   each (200Kvar)
             (a) Active power from with FC WTIG
                                   with FC (400Kvar)
                                                                                                                                                     to network
                                                                                                                         (a) Active power injected (200Kvar)
                                                                                                                                             with FC
                                                                                                                                             with FC (400Kvar)
                                          40                                                                             12
                                                                                                                          0
                                               0         5           10         15
                                                                          without FC       20                                 0         5       10   without FC
                                                                                                                                                           15        20
                                                                 Time [sec]                                              10                 Time [sec]
                                                                                                                                                     with FC (200Kvar)
                                                                          with FC (200Kvar)
                                                                                                               er var]
                           er var]




                                          3                               with FC (400Kvar)                                                          with FC (400Kvar)
                                                                                                                          8
                                                                                                    eactive pow [M
                eactive pow [M




                                                                                                                          6
                                          2
                                                                                                                          4

                                                                                                                          2
                                          1
                                                                                                   R
               R




                                                                                                                          0

                                          0                                                                              -2
                                              0          5           10           15         20                               0         5       10         15             20
                                                                 Time [sec]                                                                 Time [sec]

                (b) Reactive power to each WTIG (b) Reactive power absorbed from network
                                          1.1                                                                            1.1
                                                                              without FC
                                                                              with FC(200Kvar)
                                         1.08                                                                                 1
                                                                              with FC(400Kvar)
  T rb e sp e [p ]
           ed u




                                                                                                               ltag u]




                                         1.06                                                                            0.9
                                                                                                             Vo e [p




                                         1.04                                                                            0.8
   u in




                                                                                                                         0.7                          without FC
                                         1.02
                                                                                                                                                      with FC (200Kvar)
                                                                                                                                                      with FC (400Kvar)
                                               1
                                                   0         5        10           15        20                                   0     5        10        15         20
                                                                  Time [sec]                                                                 Time [sec]



                                                       (c) Wind Turbine speed                                                     (c) Voltage at feeder bus

  Fig. (12) Effect of the FC rating on                                                                                   Fig. (13) Effect of the FC rating
          WTIG performance                                                                                                 on feeder bus performance
5.2 Effect of Change SVC Rated:
When the IG operates at normal steady state by nominal wind speed 9m|s, the generated
active power from each WTIG is 2.9MW, absorbed reactive power is 1.41Mvar and


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turbine speed reaches to 1.0047pu. The active power generated from each WTIG, the
reactive power absorbed with each WTIG and the turbine speed responses without SVC
and with the presence of SVC of 1MVA, and 3MVA rating are depicted in Fig. (14). It's
noted that without SVC or with the presence of SVC of 1MVA rating three WTIG are
tripped at t=5sec, so generated active power and absorbed reactive power become zero. By
increasing SVC to reaches 3MVA three WTIG are still working, so each WTIG generated
active power is 2.9MW, absorbed reactive power is 1.41Mvar and turbine speed is
1.0047pu. Figure (15), illustrates total active power injected to the network, total reactive
power absorbed from the network and voltage at feeder bus #3 responses without SVC and
with the presence of SVC of 1MVA, and 3MVA rating, it's noted that total active power
injected to the network is zero without SVC and with the presence of SVC of 1MVA. The
total active power injected to the network becomes 8.7MW, total absorbed reactive power
from the network is decreased to reach 2.39Mvar and improve voltage at feeder bus, with
the presence of SVC of 3MVA rating.
                                                   4                                                                                             10


                                                                                                                                                 8
                                                   3
                           Active power [MW]




                                                                                                                        Active power [MW]
                                                                                                                                                 6
                                                   2
                                                                                                                                                 4

                                                   1                             without SVC                                                                                       without SVC
                                                                                                                                                 2
                                                                                 with SVC (1Mvar)                                                                                  with SVC(1Mvar)
                                                                                 with SVC (3Mvar)                                                                                  with SVC(3Mvar)
                                                   0                                                                                             0
                                                       0        5         10             15         20                                                0          5        10              15         20
                                                                      Time [sec]                                                                                      Time [sec]
               (a) Active power from each WTIG                                                                                                       (a) Active power injected to network


                                   4                                                                                                        12
                                                                             without SVC                                                                                          without SVC
                                                                             with SVC (1Mvar)                                               10                                    with SVC (1Mvar)
                                                                                                                     er var]
  Reactive power [Mvar]




                                   3                                         with SVC (3Mvar)                                                                                     with SVC (3Mvar)
                                                                                                         reactive pow [M




                                                                                                                                                 8


                                   2                                                                                                             6

                                                                                                                                                 4
                                   1
                                                                                                                                                 2

                                   0                                                                                                             0
                                               0            5           10          15         20                                                    0          5        10            15           20
                                                                    Time [sec]                                                                                       Time [sec]
                   (b) Reactive power to each WTIG (b) Reactive power absorbed from network
                                               1.1                                                                                               1.1
                                                                                 without SVC
                                                                                 with SVC (1Mvar)
                                      1.08                                                                                                           1
                                                                                 with SVC (3Mvar)
      Turbine speed [pu]




                                                                                                                                  Voltage [pu]




                                      1.06                                                                                                       0.9


                                      1.04                                                                                                       0.8

                                      1.02                                                                                                       0.7                          without SVC
                                                                                                                                                                              with SVC (1Mvar)
                                                   1                                                                                                                          with SVC (3Mvar)
                                                       0        5         10          15        20                                                       0       5       10          15        20
                                                                      Time [sec]                                                                                     Time [sec]

                                                           (c) Wind Turbine speed                                                                            (c) Voltage at feeder bus

                                 Fig. (14) Effect of the rating of                                                                               Fig. (15) Effect of the rating of
                                  SVC on WTIG performance                                                                                        SVC at feeder bus performance
                                                                                                         336
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5.3 Effect of Change STATCOM Rated:
Figure (16) illustrates active power generated from each WTIG, reactive power absorbed
with each WTIG and turbine speed responses without STATCOM and with presence of
STATCOM of 1MVA, and 3MVA rating. Without STATCOM or with the presence of
STATCOM of 1MVA rating, three WTIG are tripped at t=5sec, so generated active power
and absorbed reactive power become zero. By the increase of STATCOM rating to reach
3MVA, three WTIG are still working so each WTIG generated active power is 2.9MW,
absorbed reactive power is 1.41Mvar and turbine speed is 1.0047pu. Total active power
injected to the network, total reactive power absorbed from the network and the voltage at
feeder bus #3 responses without STATCOM and with the presence of STATCOM of
1MVA, and 3MVA rating are shown in Fig. (17). It is noted that the total active power
injected to the network is zero without STATCOM and with the presence of STATCOM of
1MVA. With the presence of STATCOM of 3MVA rating, the total active power injected
to the network becomes 8.7MW, total absorbed reactive power from the network decreases
to reach 2.39Mvar and the voltage at feeder bus #3 is improved.
                                                                                                                      10


                                                                                                                      8


                                                                                           Active power [MW]          6


                                                                                                                      4

                                                                                                                                                 without STATCOM
                                                                                                                      2
                                                                                                                                                 with STATCOM (1Mvar)
                                                                                                                                                 with STATCOM (3Mvar)
                                                                                                                      0
                                                                                                                           0          5           10         15        20
                                                                                                                                              Time [sec]

   (a) Active power from each WTIG                                                                                     (a) Active power injected to network
                                      4
                                                                 without STATCOM                                      12
                                                                                                                                                  without STATCOM
                                                                 with STATCOM (1Mvar)
                                                                                                                      10                          with STATCOM (1Mvar)
              Reactive power [Mvar]




                                      3                          with STATCOM (3Mvar)
                                                                                              Reactive power [Mvar]




                                                                                                                                                  with STATCOM (3Mvar)
                                                                                                                       8

                                      2
                                                                                                                       6

                                                                                                                       4
                                      1

                                                                                                                       2

                                      0
                                          0           5           10        15       20                                0
                                                                                                                           0           5          10         15         20
                                                              Time [sec]
                                                                                                                                              Time [sec]

   (b) Reactive power to each WTIG (b) Reactive power absorbed from network
                                       1.1                                                                            1.1
                                                                  without STATCOM
                                                                  with STATCOM (1Mvar)
                                      1.08                                                                                 1
                                                                  with STATCOM (3Mvar)
      Turbine speed [pu]




                                                                                             Voltage [pu]




                                      1.06                                                                            0.9


                                      1.04                                                                            0.8

                                      1.02                                                                            0.7                           without STATCOM
                                                                                                                                                    with STATCOM (1Mvar)
                                          1                                                                                                         with STATCOM (3Mvar)
                                              0           5        10       15       20                                        0          5         10            15         20
                                                               Time [sec]                                                                       Time [sec]
                                                  (c) Wind Turbine speed                                                           (c) Voltage at feeder bus
  Fig. (16) Effect of the rating of                                                          Fig. (17) Effect of the rating of
STATCOM on WTIG performance                                                               STATCOM on feeder bus performance
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International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –
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5.4 Effect of Change TL Length with SVC Rated:
It is intended to improve the performance of WTIG by changing TL length. These are
studied with the presence of SVC of 3MVA rating connected at feeder bus #3 and with the
presence of STATCOM of 3MVA connected at feeder bus #3. Figure (18) illustrates active
power from each WTIG, reactive power absorbed from each WTIG and turbine speed
responses due to the change in TL length with the presence of SVC of 3MVA rating. The
three WTIG are tripped at t=5sec at TL length 30km so the active power generated from
the WTIG is zero. By decreasing TL length to reach 15km or 25km, three WTIG are still
working and generated active power from WTIG is 2.9MW. Total active power injected to
the network, total reactive power absorbed from the network and bus voltage responses are
depicted in Fig. (19) due to change in the TL length. At TL length is 30km, the active
power injection to the network is zero, but by decreasing TL length to reach 15km or
25km, the active power injection to the network is 8.7MW.
                                                              4                                                                           10


                                                              3                                                                           8
                                        Active pow [M ]
                                                  er W




                                                                                                                    Active power [MW]
                                                                                                                                          6
                                                              2

                                                                                                                                          4
                                                              1                                    T.L=15Km
                                                                                                                                                                          T.L=15Km
                                                                                                   T.L=25Km                               2
                                                                                                                                                                          T.L=25Km
                                                                                                   T.L=30Km
                                                              0                                                                                                           T.L=30Km
                                                                  0          5         10      15             20                          0
                                                                                                                                               0        5       10        15         20
(a) Active power fromTime [sec]
                       each WTIG                                                                                    (a) Active power injected to network
                                                                                                                                   Time [sec]


                                                5                                                                                         12
                                                                                              T.L=15Km                                                                         T.L=15Km
                                                                                              T.L=25Km                                                                         T.L=25Km
                                                4                                                                                         10
                              er var]




                                                                                              T.L=30Km
                                                                                                                                er var]




                                                                                                                                                                               T.L=30Km
                   eactive pow [M




                                                                                                                     eactive pow [M




                                                                                                                                           8
                                                3

                                                                                                                                           6
                                                2
                                                                                                                                           4
                  R




                                                1
                                                                                                                    R




                                                                                                                                           2

                                                0
                                                          0              5           10       15         20                                0
                                                                                                                                               0        5        10        15         20
                                                                                 Time [sec]
                                                                                                                                                             Time [sec]
(b) Reactive power to each WTIG (b) Reactive power absorbed from network
                                               1.1
                                                                                              T.L=15Km                                    1.1
                                                                                              T.L=25Km
                                        1.08
                                                                                              T.L=30Km                                     1
    Turbine speed [pu]




                                        1.06
                                                                                                                     Voltage [pu]




                                                                                                                                          0.9

                                        1.04
                                                                                                                                          0.8

                                        1.02                                                                                                                                   T.L=15Km
                                                                                                                                          0.7
                                                                                                                                                                               T.L=25Km
                                                          1                                                                                                                    T.L=30Km
                                                              0              5       10       15         20
                                                                                                                                                0        5       10        15             20
                                                                      (c) WindTime [sec] speed
                                                                               Turbine                                                              (c) Voltage at feeder bus
                                                                                                                                                              Time [sec]


           Fig. (18) Effect of TL length on                                                                                 Fig. (19) Effect of TL length on
           WTIG performance with SVC                                                                                      feeder bus performance with SVC
5.5 Effect of Change TL Length with STATCOM Rated:
The active power from each WTIG, reactive power absorbed from each WTIG and the
turbine speed responses are shown in Fig. (20) due to change in TL length, it's noted that


                                                                                                                   338
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –
    6545(Print), ISSN 0976 – 6553(Online) Volume 3, Issue 1, January-June (2012), © IAEME

the three WTIG are tripped at t=5sec at TL length 35km, so active power generated from
WTIG is zero. By decreasing TL length to reach 15km or 25km, the three WTIG are still
working and generated active power from WTIG is 2.9MW. Also, Fig. (21) depicts total
active power injected to the network, total reactive power absorbed from the network and
bus voltage responses due to change in TL length, At TL length of 35km, the active power
injection to the network is zero, but by the decrease of TL length to reach 15km or 25km,
the active power injection to the network will be 8.7MW.
                                                        4                                                                             10


                                                                                                                                                      8
                                                        3
                                      ]




                                                                                                                        ]
                        Active pow [MW




                                                                                                        Active power [MW
                                                                                                                                                      6
                                  er




                                                        2
                                                                                                                                                      4

                                                        1                             T.L=15Km                                                                                              T.L=15Km
                                                                                                                                                      2
                                                                                      T.L=25Km                                                                                              T.L=25Km
                                                                                      T.L=35Km                                                                                              T.L=35Km
                                                        0                                                                                             0
                                                            0       5       10       15          20                                                       0            5         10         15         20
                                                                        Time [sec]
       (a) Active power from each WTIG                                                                                                           Time injected to network
                                                                                                                                    (a) Active power [sec]
                                                        5                                                                                                 12
                                                                                      T.L=15Km                                                                                                   T.L=15Km
                                                                                      T.L=25Km                                                            10                                     T.L=25Km
                                                        4
                                reactive power [Mvar]




                                                                                                                              Reactive power [Mvar]
                                                                                      T.L=35Km                                                                                                   T.L=35Km
                                                                                                                                                              8
                                                        3

                                                                                                                                                              6
                                                        2
                                                                                                                                                              4
                                                        1
                                                                                                                                                              2

                                                        0
                                                            0       5       10       15          20                                                           0
                                                                                                                                                                  0        5          10     15         20
                                                                        Time [sec]
                                                             from
(b) Reactive power to each WTIG (b) Reactive power absorbed [sec] network
                                                        Time


                                   1.1                                                                                                          1.1
                                                                                     T.L=15Km
                                                                                     T.L=25Km
                        1.08                                                                                                                              1
                                                                                     T.L=35Km
   Turbine speed [pu]




                                                                                                               Voltage [pu]




                        1.06                                                                                                                    0.9


                        1.04                                                                                                                    0.8

                                                                                                                                                                                                 T.L=15Km
                        1.02                                                                                                                    0.7
                                                                                                                                                                                                 T.L=25Km
                                                                                                                                                                                                 T.L=35Km
                                                        1                                                                                                     0            5       10            15         20
                                                            0      5        10       15         20
                                                                                                                                                                               Time [sec]
                                                                        Time [sec]
                                                                (c) Wind Turbine speed                                                                            (c) Voltage at feeder bus
Fig. (20) Effect of TL length on WTIG                                                                       Fig. (21) Effect of TL length on feeder
    performance with STATCOM                                                                                 bus performance with STATCOM

5.6 Effect of TL length on SVC and STATCOM Rating:
Figure (22) illustrates the effect of TL length on SVC rating, it's noted that by the increase
of the TL length to reach 26km, the SVC susceptance increases to reach the maximum
value of 0.866pu, while by increasing TL length above 26km the three WTIGs are tripped
because of insufficiency of SVC to supply necessary reactive power and it's tripped. Also,
the effect of TL length on STATCOM rating is depicted in Fig. (23), by the increase of the
TL length to reach 32km, the generated reactive power increases to reach maximum value
of 2.46Mvar, but by the increase of TL length above 32km, three WTIGs are tripped


                                                                                                      339
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –
    6545(Print), ISSN 0976 – 6553(Online) Volume 3, Issue 1, January-June (2012), © IAEME

because of the insufficiency of STATCOM to supply the necessary reactive power and it's
tripped
                                1                                                                                  3




                                                                                  enerated reactive pow [Mvar]
      Susceptance Bsvc [pu]   0.8                                                                                2.5




                                                                                                       er
                                                                                                                   2
                              0.6
                                                                                                                 1.5
                              0.4
                                                                                                                   1
                              0.2
                                                                                                                 0.5
                                0
                                                                                                                   0




                                                                                 G
                              -0.2
                                     0   5   10       15    20    25   30   35                                   -0.5
                                                                                                                        0   5   10       15    20    25   30   35
                                                  T.L length [Km]
                                                                                                                                     T.L length [Km]
                              Fig. (22) Effect of TL length on                                                      Fig. (23) Effect of TL length on
                                         SVC rating                                                                        STATCOM rating

      6. CONCLUSIONS

Three applications of FC, SVC, and STATCOM to wind farm are studied to improving the
performance of WTIG. In both cases the system behavior was analyzed and is discussed
using steady state phasor simulation and results are confirmed. The performance study
considered active power from each WTIG, and active power injected to the network. Also,
reactive power to each WTIG, and reactive power absorbed from network, reactive power
compensation, Wind Turbine speed, and Voltage at feeder bus. This paper presents the
choice of the best parameters to improve the performance of WTIG, these parameters such
as FC rating, SVC rating, STATCOM rating and TL length. The simulation shows that the
FC, SVC, and STATCOM can be used to the three WTIG are still working so each WTIG
generated active power, absorbed reactive power, and improving turbine speed. The SVC
susceptance, and STATCOM reactive power rating are increasing to reach the maximum
value when the TL length up to 26km for SVC, and 32km for STATCOM discussed.

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APPENDICES

Wind Turbine Induction Generator WTIG Parameters
Turbine: 3MW, base wind speed =9m/s, β controller Kp=5, Ki=25, βmax=45°
Generator: P=3.33MVA, V=575V, f=60Hz, Rs=0.004843, Ls=0.1248, Rr’=0.004377,
Lr’=0.1791, Lm=6.7, H=5.04s, F=0.01, p=3.
Transformer parameters: 47MVA, 120/25kV, R2=0.0026, L2=0.08, Rm=500 , Xm=500 .
WTIG to distribution network: 4MVA, 25kV/575V, R2=0.0008, L2=0.025, Rm=500 , Xm=
inf.
Transmission line parameters per km: R1=0.1153 , R0=0.413 , L1=1.05mH, L0=3.32mH,
C1=11.33nF, C0=5.01nF.
STATCOM parameters: 25kV, 3MVA, R=0.071, L=0.22, Vdc=4kV, Cdc=0.0011F,
Regulator gains: Vac-Kp=5, Ki=1000, Vdc-Kp=0.0001, Ki=0.02, Kp=0.3, Ki=10, Kf=0.22,
Droop=0.03.
SVC parameters: Vrms=25kV, Fn=60Hz, Pbase=3MVA, Qc=3Mvar, Ql=-3Mvar, Td=4msec,
Vref=1.0pu, Xs=0.03pu, Kp=0, Ki=300.
Inductive load: First load: 3MW+J1Mvar, Second load:5MW+J2Mvar
Plant: 2MVA, V=2.3kV, RL=200KW, P.F=0.93 Lag., Qc=800Kvar


                                           342
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –
    6545(Print), ISSN 0976 – 6553(Online) Volume 3, Issue 1, January-June (2012), © IAEME

Induction Motor: P=1.86MVA, V=2300V, f= 60Hz, Rs=0.0092, Ls=0.0717, Rr’=0.007,
Lr’=0.0717, Lm=4.14, H=0.5s, F=0, p=2.

Biographies

                   Youssef A. Mobarak was born in Egypt. He received his B.Sc. and
                   M.Sc. degrees in Electrical Engineering from South Valley University,
                   Aswan, Egypt, in 1997 and 2001 respectively and Ph.D. from Cairo
                   University, Egypt, in 2005. He joined Electrical Engineering
                   Department, High Institute of Energy, South Valley University as a
Demonstrator, as an Assistant Lecturer, and as an Assistant Professor during the periods of
1998–2001, 2001–2005, and 2005–2009 respectively. He joined Artificial Complex
Systems, Hiroshima University, Japan as a Researcher 2007–2008. Also, he joined King
Abdulaziz University, Rabigh, Saudi Arabia, Faculty of Engineering 2010 to present. His
research interests are power system planning, operation, and optimization techniques
applied to power systems, Nanotechnology materials via addition nano-scale particles and
additives for usage in industrial field.




                                           343

				
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