Comparitive Analysis of Improvement in Power System Performance by Application of Shunt FACTS Device

IJSTE - International Journal of Science Technology & Engineering | Volume 3 | Issue 04 | October 2016 ISSN (online): 2349-784X

Comparative Analysis of Improvement in Power System Performance by Application of Shunt FACTS Device STATCOM & SVC Sapana A. Bhande Priyadarshini Bhagwati College of Engineering Nagpur

Nirmala A. Ramtekkar Priyadarshini Bhagwati College of Engineering Nagpur

Abstract In emerging electric power systems, increased transactions often lead to situations where system no longer remains in the secure operating region. The Flexible AC Transmission System (FACTS) controllers can play an important role in the power system security enhancement. This paper gives the comparative analysis of of Improvement in Power System Performance by Application of shunt FACTS device STATCOM & SVC. The methodology based on Reactive power sensitivity approach with respect to STATCOM & SVC control parameters. The effectiveness of the proposed algorithm is tested and illustrated on 5-bus system. The simulation is performed using Matpower 4.0 in MATLAB The effectiveness of the proposed algorithm is tested and illustrated on 5-bus system. The simulation is performed using Matpower 4.0 in MATLAB 7.1 environment.

Keywords: FACTS, Static Synchronous Compensator ________________________________________________________________________________________________________ I.

INTRODUCTION

A Power system consist of three main components i.e. generating units which supplies power to the system, loads which consumes power and transmission & distribution network which interconnects various buses in the system and carries power from the generating points to the load points[1] . In a competitive electricity market with the rapid development of society, the load demand has grown quickly. A s a result, transmission networks are becoming highly loaded which threatens the power system incurring greater losses, security and reliability[1],stability, ultimately make certain generation patterns economically undesirable. Though building new transmission lines can relive the severe situation, it is hard to implemented due to various limitations such as environmental, right-of-way and cost[1,2,6].

Flexible A.C. Transmission Line, which are power electronics based devices can change parameters like impedance, voltage and phase angle. FACTS devices also helps to reduce flows in heavily loaded lines, resulting in an increased loadability, low system loss, improved stability of the network, reduced cost of production and fulfilled contractual requirement by controlling the power flows in the network. They provide control facilities, both in steady state power flow control and dynamic stability control. The possibility of controlling power flow in an electrical power system without generation rescheduling or topological changes can improve the performance considerably [6].

FACTS devices can play a major role in congestion management, enhancement of security, transfer capability and reliability.

FACTS devices can be connected to a transmission line in various ways, such as in series, shunt or a combination of series and shunt. The static VAR compensator (SVC) and static synchronous compensator (STATCOM) are connected in shunt, static synchronous compensator (SSSC) and thyristor controlled series capacitor (TCSC) are connected in series. Thyristor controlled phase shifting transformer (TCPST) is connected in series and shunt combination. The reactive power support in the system plays a very important role in maintaining an acceptable system voltage profile and helping in improvement of security.

In this paper STATCOM & SVC are considered for improvement of power system performance and comparative results are obtained by using MATLAB programming with and without STATCOM & SVC. II. ABOUT STATCOM STATCOM is a self-commutated switching power converter supplied from an electric energy source. Operated to produce a set of adjustable multiphase voltage, which may be coupled to ac system for purpose of exchanging active and reactive power. Static based on solid state switching devices. Synchronous analogous to an ideal synchronous generator with 3 phase sine wave at fundamental frequency. Compensator provided with reactive power compensator.

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Comparative Analysis of Improvement in Power System Performance by Application of Shunt FACTS Device STATCOM & SVC (IJSTE/ Volume 3 / Issue 04 / 005)

Fig. 1: Functional Diagram Of STATCOM

III. ABOUT SVC An SVC is a shunt connected static var generator or absorber whose output is adjusted to exchange capacitive or inductive reactive current so as to maintain or control specific parameters of the power system i.e. typically bus voltages. The static var compensator is a parallel combination of capacitor and inductor; the latter is under phase angle control called as Thyristor Controlled Reactor (TCR). Fixed capacitor (FC) with TCR, shown in Fig. 1. This combination provides a fast variable source of reactive power.

Fig. 2: Structure of SVC

IV. MODELLING OF STATCOM

Fig. 2: Equvalent Circuit Of STATCOM

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Comparative Analysis of Improvement in Power System Performance by Application of Shunt FACTS Device STATCOM & SVC (IJSTE/ Volume 3 / Issue 04 / 005)

A STATCOM consist of one VSC and its associated transformer. It is the static counterpart of rotating synchronous condenser but it generates or absorbs reactive power at a faster rate because no moving part is involved. In principle it performs the same voltage regulation function as the SVC but in a more robust manner. The Equvalent Circuit Of STATCOM is shown in Fig.2.In steady state fundamental frequency studies the STATCOM may be represented in the same way as asynchronous condenser, which in most cases is the model of synchronous generator with zero active power generation A more flexible model may be realized by representing STATCOM as a variable voltage source E vR, for which the magnitude and phase angle may be adjusted using a suitable iterative algorithm to satisfy a specified voltage magnitude at the point of connection with the AC network. The shunt voltage source of the three phase STATCOM may be represented by; 









E vR  V vR cos  vR  j sin  vR



(1) Where  indicate phase quintiles a, b, c. The voltage magnitude, V vR is given maximum & minimum limits, which are function of STATCOM capacitor rating. However  vR may take any value between 0 and 2πradian. With reference to the equivalent circuit assuming three phase parameters, the following transfer admittance equation can be written as:  Vk    E vR 

 I k   Y vR  

(2)

Where,



I k  I k  k



a

Vk  V 



a k

E vR  V vRk   vRk a

Y vR

a

I k  k

b

I k  k

a k

V 

b k

V 

b

b k

c

c k

V vRk   vRk

a Y vRk    0  0 

b

b

0 Y

b vRk

0

,

c t

a



c t k

V vRk   vRk c

c



t

0   0  c Y vRk 

V. MODELLING OF SVC A possible structure of the SVC is given in Fig. 1. It is a shunt-connected device composed of several modules built of a fixed capacitance in parallel with a thyristor controlled reactor. The equivalent susceptance Beq is determined by the firing angle α of the thyristors which is defined as the delay angle measured from the peak of the capacitor voltage to the firing instant. The fundamental frequency equivalent neglecting the harmonics of the current results in Beq= BL (α) +Bc Parallel equivalent susceptances of the modules, each controlled separately. Thus, the SVC can be modeled as a shuntconnected variable susceptance BSVC (Fig. 2) with a lower bound BSVC and an upper bound BSVC [7]. In the power flow equations this is accounted for by including the reactive power.

SVC can be modeled as shunt connected suseptance B SVC. In the power flow equations this is accounted for by including the reactive power. QSVC=-VK2 BSVC into the reactive power balance at bus k subject to: BSVCmin ≤ BSVC ≤ BSVCmax.

Fig. 2: SVC Model

VI. STATCOM POWER FLOW MODEL The power flow equation for the STATCOM are derived below the first principle and assuming the following voltage source representation:

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Comparative Analysis of Improvement in Power System Performance by Application of Shunt FACTS Device STATCOM & SVC (IJSTE/ Volume 3 / Issue 04 / 005) E vR  V vR cos ď ¤ vR  j sin ď ¤ vR



(3)

Based on the STATCOM equivalent circuit, the following may be written:



S vR  V vR I vR  V vR Y vR V vR  V k *

*

*

*



(4) After performing some complex operations, the following active and reactive power equations are obtained for the converter bus k , respectively PvR  V vR G vR  V vR V k ď ›G vR cos ď€¨ď ¤ vR  ď ą k   B vR sin ď€¨ď ¤ vR  ď ą k ď ?, 2

Q vR  V vR B vR  V vR V k ď ›G vR sin ď€¨ď ¤ vR  ď ą k   B vR cos ď€¨ď ¤ vR  ď ą k ď ?, 2

Pk  V k G vR  V k V vR ď ›G vR cos ď€¨ď ą k  ď ¤ vR   B vR sin ď€¨ď ą k  ď ¤ vR ď ?, 2

Q k  V k B vR  V k V vR ď ›G vR sin ď€¨ď ą k  ď ¤ vR   B vR cos ď€¨ď ą k  ď ¤ vR ď ?, 2

Using this power equations, the linearised STATCOM model is given below, where the voltage magnitude ď ¤ vR

V vR

and phase angle

are taken to be the state variables. ďƒŠ ď „ Pk ďƒš ďƒŞ ďƒş ďƒŞ ďƒş ď „ Q k ďƒş ďƒŞ ďƒŞ ďƒş ďƒŞ ďƒş ď „ PkR ďƒŞ ďƒş ďƒŞ ďƒş ďƒŞď „P ďƒş ďƒŤ kR ďƒť



ďƒŠ ď‚ś Pk ďƒŞ ď‚śď ą k ďƒŞ ďƒŞ ď‚śQk ďƒŞ ď‚śď ą k ďƒŞ ď‚śP ďƒŞ vR ďƒŞ ď‚śď ą k ďƒŞ ď‚ś Q vR ďƒŞ ďƒŤ ď‚śď ą k

ď‚ś Pk ď‚śVk ď‚śQk ď‚śVk ď‚ś PvR ď‚śVk ď‚ś Q vR ď‚śVk

Vk Vk Vk Vk

ď‚ś Pk ď‚ś ď ¤ vR ď‚śQk ď‚ś ď ¤ vR ď‚ś PvR ď‚ś ď ¤ vR ď‚ś Q vR ď‚ś ď ¤ vR

ď‚ś Pk

ďƒš V vR ďƒş ď‚ś V vR ďƒş ď‚śQk V vR ďƒş ďƒş ď‚ś V vR ďƒş ď‚ś PvR V vR ďƒş ď‚ś V vR ďƒş ďƒş ď‚ś Q vR V vR ďƒş ď‚ś V vR ďƒť

ďƒŠ ď „ď ą k ďƒŞ ďƒŞ ďƒŞ ď „ Vk ďƒŞ V k ďƒŞ ďƒŞ ďƒŞ ď „ ď ¤ vR ďƒŞ ďƒŞ ďƒŞ ď „ V vR ďƒŞ V ďƒŤ vR

ďƒš ďƒş ďƒş ďƒş ďƒş ďƒş ďƒş ďƒş ďƒş ďƒş ďƒş ďƒş ďƒť

VII. SVC POWER FLOW MODEL The SVC can be incorporated in N-R method using equation ISVC= jBSVC Vk (1) The reactive power drawn by the SVC, also the reactive power injected at bus k is QSVC = Qk =- V2k BSVC (2) The linearised equation is given by equation, where the equivalent susceptance đ??ľđ?‘†đ?‘‰đ??ś is taken to be the state variable (đ?‘–) ∆đ?œƒđ?‘˜ ∆đ?‘ƒđ?‘˜ (đ?‘–) 0 0 (đ?‘–) [ ] =[ ] [∆đ??ľđ?‘†đ?‘‰đ??ś ] (3) 0 đ?‘„đ?‘˜ ∆đ?‘„đ?‘˜ â „đ??ľ đ?‘†đ?‘‰đ??ś At the end of the iteration (i) the variable shunt susceptance BSVC is updated according to (4) The changing susceptance represents the total SVC susceptance necessary to maintain the nodal voltage magnitude at the specified value.

Once the level of compensation has been computed then the thyristor firing angle can be calculated. However the additional calculation requires an iterative solution because the SVC susceptance and thyristor firing angle are non-linearly related. The thyristor firing angle can be included using the following equations. The positive sequence susceptance of the SVC is given by (5) Where XL=ωL, XC= 1/ωc đ?‘„đ?‘˜ =

−đ?‘‰đ?‘˜2 đ?‘‹đ?‘? đ?‘‹đ??ż

{đ?‘‹đ??ż −

The linearised SVC equation can be given by đ?›Ľđ?‘ƒ (đ?‘–) đ??˝1 [ đ?‘˜] = [ đ?›Ľđ?‘„đ?‘˜ đ??˝3 Where J1=0, J2=0, J3=0 and

đ?‘‹đ?‘? đ?œ‹

[2(đ?œ‹ − đ?›źđ?‘†đ?‘‰đ??ś ) + đ?‘ đ?‘–đ?‘›(2đ?›źđ?‘†đ?‘‰đ??ś )]}

(đ?‘–) đ??˝2 (đ?‘–) đ?›Ľđ?›łđ?‘˜ ] [ ] đ??˝4 đ?›Ľđ?›źđ?‘†đ?‘‰đ??ś

J4 =

2đ?‘‰đ?‘˜2 đ?œ‹đ?‘‹đ??ż

(6)

(7)

[đ?‘?đ?‘œđ?‘ (2đ?›źđ?‘†đ?‘‰đ??ś ) − 1]

At the end of iteration (i), the variable firing angle Îąsvc is updated according to (đ?‘–) (đ?‘–−1) (đ?‘–) đ?›źđ?‘†đ?‘‰đ??ś = đ?›źđ?‘†đ?‘‰đ??ś + đ?›źđ?‘†đ?‘‰đ??ś (8) Susceptance value is determined effectively by Newton Raphson method. The linearised SVC power SVC Power flow equations with respect to firing angle are incorporated. Into an existing Newton-Raphson load flow algorithm. The SVC firing angle is combined with nodal voltage magnitudes and abgle inside the jacobian and mismatch equations leading to very robust iterative solution.

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Comparative Analysis of Improvement in Power System Performance by Application of Shunt FACTS Device STATCOM & SVC (IJSTE/ Volume 3 / Issue 04 / 005)

VIII. METHOD FOR OPTIMAL LOCATION OF STATCOM & SVC Sensitivity Approach A sensitivity approach is the Conventional approach which could be applied for finding the optimal location of shunt FACTS devices.

Reactive Transmission Congestion Distribution Factor (QTCDF) The real power flow & reactive power flow in a line k connected between bus i & bus j can be written as Pi j = Vi Vj Yij cos ( θij + δj - δi )-Vi2 Yij cos θij (1) Qi j= -Vi Vj Yij sin ( θij + δj - δi ) - Vi2 Yij sin θij-Vi2 Ysh/2 (2) Where Vi-magnitude of voltage at bus i Vj- magnitude of voltage at bus j δi-angle at bus i δj- angle at bus j Reactive transmission congestion distribution factor(QTCDF) are defined as the change in the reactive power flow (∆Q ij) in a transmission line k connected between bus i & bus j due to unit change in the reactive power injection(∆Q n) at bus-n & can be written as  Q ij (3) k QTCDF  n

Q n

Similarly, PTCDF for line K can be calculated as PTCDF

k n



 Pij

(4)

 Pn

Using Taylor series approximation Eq.3 & 4 can be written a  Pij   Q ij 

 Pij  i  Q ij  i

 i   i 

 Pij  i  Q ij  i

 j   j 

 Pij Vi  Q ij Vi

 Vi   Vi 

 Pij V j  Q ij V j

(5)

V j

(6)

V j

Eq.(5) &(6) can be written as  Pij  a ij   i  bij   j  c ij  V i  d ij  V j

(7)

 Q ij  a   i  b   j  c  V i  d  V j

(8)

' ij

' ij

' ij

' ij

The coefficient appearing in above eq. Can be obtained using partial derivative of real &reactive power flow with respect to variable δ and V as aij = Vi Vj Yij sin ( θij + δj -δi ) bij =- Vi Vj Yij sin ( θij + δj -δi ) cij = Vj Yij cos( θij + δj -δi ) - 2Vi Yij cos θij dij = Vj Yij cos( θij + δj -δi ) '

a ij = Vi Vj Yij cos ( θij + δj -δi ) '

b ij = -Vi Vj Yij cos ( θij + δj -δi ) '

c ij = -Vj Yij sin ( θij + δj - δi ) +2 Vi Yij cos θij-Vi Ysh '

d ij = - Vi Yij sin( θij + δj -δi ) For determining of congetion distribution factor following jacobian relation has been used: (9) Neglecting P-V & Q-V above eq. Can be simplified as ∆P = [J11][∆δ] ∆Q = [J22][∆V] Therefore ∆ δ = [J11]-1[∆P]=[M] [∆P] ∆V = [J22]-1[∆Q]=[N][ ∆Q] Above eq. Can be written as

(10) (11)

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27

Comparative Analysis of Improvement in Power System Performance by Application of Shunt FACTS Device STATCOM & SVC (IJSTE/ Volume 3 / Issue 04 / 005)

It is assumed that change in the bus voltage on real power flow & bus angle on active power flow is negligible therefore above eq. Becomes  Pij  a ij   i  b ij   j  Q ij  a ij  V i  b ij  V j '

'

Substituting the values of Δδi & ΔVi in above both eq. & expanded as + (aijmin+ bij mjn) ∆Pn  Pij = (aijmi1 + bij mj1) ∆P1 + (aijmi2 + bij mj2) ∆P2 +-------- Q ij =

' ij

' ij

' ij

' ij

' ij

(12)

' ij

( a ni1 + b nj1) ∆Q1 + ( a ni2 + b nj2) ∆Q2 + ---------- + ( a nin+ b njn) ∆Qn

(13)

Eq. Can be written as  Pij = PTCDF  Q ij =

k 1

QTCDF

∆P1 + PTCDF k 1

k 2

∆P2 +---------

∆Q1+ QTCDF

k 2

+ PTCDF

∆Q2 +-------+ QTCDF

k n

k n

∆Pn

∆Qn

Where k n

PTCDF QTCDF

k n

= (aijmin + bij mjn) '

'

= ( a ij nin + b ij njn)

These are real & Reactive transmission congestion distribution factor corresponding to the bus n & line K connected between bus i & j.

The optimal location of STATCOM can be considered at a bus having most negative QTCDF. IX. 5-BUS SYSTEM

Fig. 3: 5 Bus Test System

Bus No 1 2 3 4 5

Bus Voltage Magnitude (p.u.) Phase angle Degree 1.06 0.00 1.01 0.00 1.0 0.00 1.0 0.00 1.0 0.00

Line No.

From Bus

To Bus

1 2 3 4 5 6 7

1 1 2 2 2 3 4

2 3 3 4 5 4 5

Table - 1 Bus Data (100 MVA BASE) Generation Real Power (p.u.) Reactive Power (p.u) 0.2

Table – 2 Line data (100 MVA BASE) Line Impedance Resistance (p.u.) Reactance (p.u.)

0.02 0.06 0.08 0.24 0.06 0.18 0.02 0.18 0.04 0.12 0.01 0.03 0.08 0.24

Real Power (p.u.)

Load Reactive Power (p.u)

0.00 0.45 0.4 0.6

0.1 0.15 0.05 0.1

Half Line Charging Admittance (p.u.)

0.030 0.025 0.020 0.020 0.015 0.010 0.035

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Comparative Analysis of Improvement in Power System Performance by Application of Shunt FACTS Device STATCOM & SVC (IJSTE/ Volume 3 / Issue 04 / 005)

Table – 3 Line Flow Limit for 5-Bus System From Bus-To Bus Line Flow Limit(pu) 1-2 1.20 1-3 0.55 2-3 0.55 2-4 0.55 2-5 0.55 3-4 0.55 4-5 0.55 Table - 4 Sensitivity Approach Results of 5 Bus System Bus Number QTCDF 3 -0.761141 4 -0.481845 5 -0.436032

The optimal placement of shunt fact device has been considered at a bus having most negative transmission congestion distribution factor (QTCDF) i.e. at Bus no. 3.

X. RESULTS With & Without STATCOM With STATCOM & SVC placed at bus-3 again the load flow of 5 bus system is obtained. Table 5 to 8 shows the comparison of results with and without STATCOM & SVC

Bus No. 1 2 3 4 5

Table – 5 Voltage Magnitude(P.U.) Line With SVC Without SVC 1 0.058+j0.0429 0.0581+j0.0431 2 0.0416+j0.0155 0.0455+j0.029 3 0.0238-j0.0085 0.0241-j0.0065 4 0.0244-j0.0063 0.0256-j0.0014 5 0.0263+j0.0197 0.0267+j0.0212 6 0.0126-j0.002 0.0103-j0.0062 7 0.0246-j0.0226 0.0234-j0.0218 Total Losses 0.02113+j0.0387 0.02137+j0.0574 Table – 6 Voltage Phase Angle (Degree) Bus Number 1 2 3 4 5 With STATCOM 1.06 1.01 1 0.986 0.9809 Without STATCOM 1.06 1.01 0.97430 0.96531 0.97396 With SVC 1.06 1 1 0.984 0.9737 Without SVC 1.06 1 0.9668 0.9574 0.9648 Table - 7 Bus power(p+jq) p.u.

Without STATCOM With STATCOM With SVC Without SVC 1.3357 + 0.8615i 1.3382+ 0.75i 1.3415+0.9239i 1.3359+1.0683i 0.4433 - 0.0456i 0.4557- 0.3638i 0.4501-0.6475i 0.4341-0.2421i -0.4297 - 0.1300i -0.4342+0.2858i -0.4336+0.4082i -0.4273-0.13i -0.3612 - 0.4585i -0.3694-0.464i -0.3685-0.462i -0.3578-0.4535i -0.5777 - 0.0877i -0.5832-0.0862i -0.5782-0.0841i -0.5711-0.0853i Table – 8 Transmission Line Losses(I2Z) p.u.

Line 1 2 3 4 5 6 7

Without STATCOM P loss Q loss 0.0538 0.0295 0.0443 0.0248 0.0247 -0.0062 0.0263 -0.0011 0.0271 0.0213 0.0104 -0.0066 0.0238 -0.0221

With STATCOM P loss Q loss 0.0537 0.0293 0.0414 0.015 0.0239 -0.0095 0.0249 -0.006 0.0267 0.0198 0.012 -0.0037 0.0246 -0.0231

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Comparative Analysis of Improvement in Power System Performance by Application of Shunt FACTS Device STATCOM & SVC (IJSTE/ Volume 3 / Issue 04 / 005)

Total Losses

0.2103

0.0397

0.2072

0.0218

XI. CONCLUSION FACTS devices are a powerful tool to improve the voltage profile of the system. In this paper STATCOM & SVC is simulated using Matpower 4.0 in MATLAB 7.1 environment. Finally, comparative results are obtained which compares the following parameter with STATCOM & SVC.  Improvements of the voltage profile  Active and reactive power losses are reduced.

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S. Gerbex, R. Cherkaoui, and A. J. Germond, Member, IEEE,” Optimal Location of FACTS Devices to Enhance Power System Security”, 2003 IEEE Bologna PowerTech Conference, June 23-26, Bologna, Italy, B. Kalyan Kumar, S.N. Singh and S.C. Srivastava, “Placement of FACTS controllers using modal controllability indices to damp out power system oscillations”, The Institution of Engineering and Technology 2007, IET Gener. Transm. Distrib., 2007, 1, (2), pp. 209–217.

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Text Books Enrique Acha,Claudio R.Fuerte-Esuivel,Hugo Ambriz-Perez,Cesar Angeles-Camacho,”FACTS Modelling and Simulation in Power Networks”,John Wiley & Sons Ltd. D.P. Kothari,I.J.Nagrath,”Modern Power System Analysis”, Third Edition,Tata McGraw Hill Education Private Limited,Pg No. 510-524

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