POWER SYSTEM TRANSIENT STABILITY IMPROVEMENT USING SERIES FACTS DEVICES

Transcription

1 U.P.B. Sci. Bull., Serie C, Vol. 77, I. 3, 2015 ISSN POWER SYSTEM TRANSIENT STABILITY IMPROVEMENT USING SERIES FACTS DEVICES Cotel CONSTANTIN 1, Mircea EREMIA 2, Contantin BULAC 3 The paper preent the impact of the thyritor controlled erie capacitor and the tatic ynchronou erie compenator over the power flow in a tranmiion network and the tranient tability limit of an electrical power ytem. Simulation are performed in the Eurotag oftware on a real databae of the Romanian tranmiion ytem. The analyi i focued on the outh-eat area of the country, where a large amount of power wa intalled in wind power plant, thi area becoming a trongly exce of power. Keyword: power ytem, tranient tability, thyritor controlled erie capacitor, tatic ynchronou erie compenator 1. Introduction Electric power ytem are now becoming increaingly treed and complex a a reult of evolving demand for efficiency and reliability [1]. The integration of the renewable energy ource leaded to the power tranfer increae and the power ytem become more inecure, more difficult to operate [2]. In addition, becaue of environmental and economic contraint, it i difficult to build new tranmiion line and conequently the power ytem i operated cloer to it capability limit. Secure and reliable operation i a fundamental requirement for an electric power ytem. Tranient tability analyi i one of the baic analye in the planning, deign and operation of the power ytem [3]. To analyze the tranient phenomena of the ytem, the time-domain imulation can be divided into three tage: pre-fault, fault-on and pot-fault. Before any fault occur, the pre-fault ytem i in normal teady tate condition. During the fault occurrence, the ytem i aid to be in the fault-on condition and it i cleared by the protective ytem operation. The tranient tability problem conit in the tudy of the tability of the pot-fault ytem after the opening of circuit breaker to iolate the fault. The 1 PhD tudent, Power Engineering Faculty, Univerity POLITEHNICA of Bucharet, C.N. Tranelectrica S.A., Bucharet, Romania 2 Prof., Power Engineering Faculty, Univerity POLITEHNICA of Bucharet, Romania, eremia1@yahoo.com 3 Prof., Power Engineering Faculty, Univerity POLITEHNICA of Bucharet, Romania

2 260 Cotel Contantin, Mircea Eremia, Contantin Bulac tranient analyi i required to enure that the power ytem will urvive large diturbance and move into an acceptable teady tate condition [4]. The Flexible AC Tranmiion Sytem (FACTS) offer many attractive advantage like voltage control and power flow control [5]. Once with the occurrence of the controlled thyritor device or voltage-ource converter baed on power electronic, new perpective were opened in term of power ytem tability improvement [6]. The paper aim i to underline the impact of the erie FACTS device, Thyritor Controlled Serie Capacitor () and Static Synchronou Serie Compenator (SSSC), over the power flow and the tranient tability limit in the outh-eat area of the Romanian power ytem. The imulation were made uing the Eurotag oftware [7]. 2. Thyritor Controlled Serie Capacitor The Thyritor Controlled Serie Capacitor i a FACTS device which conit of a erie capacitor bank connected in parallel with a thyritor-controlled reactor in order to provide a variable erie capacitive reactance and thu continuou control of the power flow on the tranmiion line [5]. The power flow model preented in thi ection i baed on the imple concept of a erie reactance that can be automatically varied o that to allow more or le power to flow acro the line, a required by the operating condition. The value of thi variable reactance i determined efficiently uing Newton-Raphon method. The reactance X, hown in Fig. 1, repreent the all element that are part of the, when operating in either the inductive or the capacitive region [8]. k m I k I m V k X Fig. 1. Thyritor controlled erie compenator equivalent circuit V m Applying the Kirchhoff theorem on the circuit, the nodal equation reult: 1 I k = ( V k V m ) jx 1 I m = ( V m V k ) jx Equation (1) can be written in matrix form: (1)

3 Power ytem tranient tability improvement uing erie FACTS device j I k X = I m 1 j X 1 j X V k 1 V j m jx (2) From the matrix equation (2), the nodal admittance matrix i obtained: jb jb Y = kk km nn (3) jb jb mk mm [ ] For inductive operation we have: B kk B km = B mm = B mk 1 = X 1 = X (4) wherea for capacitive operation the ign are revered. The active and reactive power equation at bu k are: P k = V k V m B km in( θk θm ) Q V 2 k = B kk V k V m B km co( θk θm ) k (5) 3. Static Synchronou Serie Compenator The Static Synchronou Serie Compenator ue a hunt capacitor which i connected to the tranmiion line via a voltage-ource converter and a erie tranformer in order to produce a controllable voltage, in quadrature with the line current. The teady-tate model of the SSSC device in erie with a tranmiion line i-j, can be repreented by a voltage ource which ha the voltage magnitude V SSSC and the voltage phae γ (Fig. 2) [9], [10].

4 262 Cotel Contantin, Mircea Eremia, Contantin Bulac P ij+jqij P ji+jq Z SSSC V SSSC ji V i V j Fig. 2. Repreentation of the SSSC device in erie with a tranmiion line The active and reactive power equation which flow between the node i and j are: P SSSC 2 ij = V i G SSSC V i V j [ G SSSC co( θi θ j ) + B SSSC in( θi θ j )] Q SSSC ij new Q i [ co( θ γ ) + in( θ γ )] V i V SSSC G SSSC i B SSSC i = V 2 i B SSSC V i V j G SSSC in( θi θ j ) B SSSC co( θi θ j ) = Q i + [ ] [ in( θ γ ) co( θ γ )] V i V SSSC G SSSC i B SSSC i where: G SSSC + jb SSSC = 1/ Z SSSC (6) Becaue the SSSC device can modify the power flow on the tranmiion line which connect the i node with j node, in the Newton-Raphon method the power value forced by the device will be added to the nodal power of thee two node: P new i = P i + P SSSC ij P SSSC ij (7) 4. Power ytem tranient tability Power ytem tranient tability i defined a an ability of an electric power ytem, for a given initial operating condition, to regain a tate of operating equilibrium after being ubject to phyical diturbance, with mot ytem variable bounded o that practically the entire ytem remain intact. The ytem repone to uch diturbance involve large excurion of generator rotor angle, power flow, bu voltage and other ytem variable. The mot practical available method of tranient tability analyi i time-domain imulation in which the nonlinear differential equation are olved by uing tep-by-tep numerical integration technique [11, 13]. The mathematic model which decribe the dynamic behavior of the power ytem i made up by [12]:

5 Power ytem tranient tability improvement uing erie FACTS device 263 a et of differential equation of the generator and the automatic ytem of them, aynchronou and ynchronou motor, FACTS device, etc. a et of algebraic equation compoed of the tator equation of the ynchronou generator, the power balance equation in the tranmiion network, etc. Thi hybrid model can be decribed through the following compact form:. x = f ( x, y, μ) (8, a) 0 = g( x, y, μ) (8, b) where: x i the dynamic variable vector; y - algebraic variable vector; µ - parameter vector; f,g - vector whoe component are nonlinear and derivable function. 4. Cae tudie and reult analyi Currently, the total capacity in the Romanian Power Sytem intalled in wind power plant i 1940 MW, of which 1870 MW are located in the Dobrogea region, in the outh-eat part of Romania (Fig. 3). Fig. 3. South-eat area of Romanian tranmiion ytem

6 264 Cotel Contantin, Mircea Eremia, Contantin Bulac Thi region encounter today a power urplu that i, ometime, very difficult to control by the ytem operator. A more power will be intalled in thi region in the next two year, an efficient olution hould be identified in order to manage the power tranfer. One olution for thi problem i to build new electric tranmiion line, but due to the complex legilation, he high cot of the land, and the duration of contruction, new olution hould be quickly identified. In order to identify the tranient tability limit the generated active power of the area ha been raied and were imulated three phae hort circuit on all the overhead line of the area. In Fig. 4 it can be oberved that for an exce of active power of the area of 4480 MW the tranient tability i lot at the occurrence of a three phae hort circuit on the OHL 400 kv Cernavoda-Pelicanu (red curve). For an exce of the active power of 4450 MW the tability limit i not lot and i obtained a limit tate (green curve) MW 175 deg [SPE00001@0594] POWER EXCESS 4450 MW [SPE00001@0609] POWER EXCESS 4480 MW [SPE00001@0594] MACHINE : G2 ANGULAR POSITION Unit : deg [SPE00001@0609] MACHINE : G2 ANGULAR POSITION Unit : deg a. b. Fig. 4. Power exce of the analyzed area (a) and angular poition for a generator (b) The impact of the and SSSC device on the power flow control and tranient tability ha been analyzed in thi paper. A. device in erie with the 400 kv OHL Bucureşti S.- G. Ialomiţei The purpoe i to increae the power flowing on the 400 kv OHL Bucureşti S. Gura Ialomiţei, and the device i et to operate in the capacitive domain. For a capacitive compenation of 30% of the inductive reactance of the line the active power will increae by 50 MW. In the cae of a diturbance that lead to a change in the power flow on the tudied line, the device will modify the compenation reactance in order to maintain the power at the deired value. Fig. 5 how that for a decreae in the power flow, will command the modification of the compenation reactance from -0,0045 p.u. to - 0,011 p.u. o that to force the power flow to reach the deired value.

7 Power ytem tranient tability improvement uing erie FACTS device 265 MW [var_-15%] ACTIVE POWER : LINE GIAL41-R-BUCU4-1 Unit : MW [var_-15%] MACHINE : -IN VARIABLE : XC Unit : p.u. a. b. Fig. 5. Active power flow on the OHL (a) and reactance (b) 5000 MW deg [SPE00001@0781] POWER EXCESS 4840 MW [SPE00001@0781] MACHINE : G2 ANGULAR POSITION Unit : deg [SPE00001@0766] POWER EXCESS 4810 MW [SPE00001@0766] MACHINE : G2 ANGULAR POSITION Unit : deg a. b. Fig. 6. Power exce of the analyzed area (a) and angular poition for a generator (b) The imulation for the determination of the tranient tability limit in the preence of the device ha leaded at a limit of the power exce of the area of 4810 MW for which the diturbance i producing a table regime (Fig. 6). In thi cae, other bigger value of the power exce lead to the intability of the generator group of the tudied area (red curve). B. SSSC device in erie with the 400 kv OHL Gutinaş-Smîrdan Aume that the reference value of the active power flow on the OHL Gutinaş - Smârdan i 620 MW, with 100 MW bigger that in the cae without the SSSC device. In order to maintain the power at the reference value, the phae hift between the voltage of the two ide of the SSSC i 4,48 degree. In the cae of a diturbance which lead to a decreae in the power flow on the analyzed line, SSSC will command the modification of the voltage angle at 5.68 degree (Fig. 7).

8 266 Cotel Contantin, Mircea Eremia, Contantin Bulac MW deg [var_-15%] ACTIVE POWER : LINE SMIR4S -GUTI4-1 Unit : MW [var_-15%] VOLTAGE ANGLE AT NODE : SMIR41 Unit : deg [var_-15%] VOLTAGE ANGLE AT NODE : SMIR4S Unit : deg a. b. Fig. 7. Active power flow on the OHL (a) and SSSC phae hift (b). Regarding the tranient tability, SSSC doe not lead to a ignificant improvement of the tability limit. In Fig. 8 it can be oberved that for a power exce of the area of 4500 MW the tranient tability i lot at the occurrence of a three phae hort circuit on the OHL 400 kv Cernavoda-Pelicanu (red curve) MW deg [SPE00001@0594] POWER EXCESS 4500 MW [SPE00001@0578] POWER EXCESS 4470 MW [SPE00001@0594] MACHINE : G2 ANGULAR POSITION Unit : deg [SPE00001@0578] MACHINE : G2 ANGULAR POSITION Unit : deg a. b. Fig. 8. Power exce of the analyzed area (a) and angular poition for a generator (b) 6. Concluion The imulation have hown that the and SSSC device repreent effective olution for active power flow control and may cope the problem about the power tranfer from the Dobrogea region under the increaing intalled power in wind power plant. The device i a good olution for increae the tranient tability limit, in our cae the limit increae with 360 MW while the

9 Power ytem tranient tability improvement uing erie FACTS device 267 SSSC device caue an increae of only 20 MW. However, the optimal place hould be performed in order to determine the mot effective olution. Acknowledgement The work ha been funded by the Sectoral Operational Programme Human Reource Development of the Romanian Minitry of Labour, Family and Social Protection through the Financial Agreement POSDRU/107/1.5/S/76903 and C.N.T.E.E. Tranelectrica S.A. REFERENCES [1]. X. Du, D. Ernt, P. Croley, A model Predictive baed Emergency Control Scheme uing to Improve Power Sytem Tranient Stability, Power and Energy Society, General Meeting, San Diego, USA, July 2012; [2]. C. Contantin, M. Eremia, I.C. Contantin, L. Toma, Improving Network Controllability for a Secure Operation of the Interconnection, 7th International Conference on Deregulated Electricity Market Iue in South-Eatern Europe, Bucharet, Romania, September 2012; [3] L. Wang, Technique for High Performance Analyi of Tranient Stability, Power and Energy Society, General Meeting, San Diego, USA, July 2012; [4] N. Hahim, N.R. Hamzah, P. Mohd Arad, R. Baharom, N.F. Nik Imail, N. Aminudin, D. Johari, A.A. Sallehhudin, Modeling of Power Sytem Dynamic Device Incorporated in Dynamic Computation for Power ytem (DCPS) for Tranient Stability Analyi, International Electric Machine & Drive Conference, Niagara Fall, Canada, May 2011; [5] G. Hingorani, L. Gyugyi, Undertanding FACTS-Concept and Technology of Flexible AC Tranmiion Sytem, IEEE Pre, New York, 2000; [6] F.E. Ciauiu, M. Eremia, Improvement of Power Sytem Security Margin by Uing FACTS Device, IEEE Trondheim PowerTech Conference, June 2011; [7] *** Tractebel Engineering- GDF SUEZ, Eurotag Uer Manual, 2010; [8] E. Acha, H. Ambriz-Perez, C. Angle-Camacho, C.R. Fuerte-Equivel, FACTS: Modelling and imulation in power network, John Wiley & Son, 2004; [9] L. Yao, P. Cartwright, L. Schmitt, X.P. Zhang, Congetion Management of Tranmiion Sytem Uing FACTS, IEEE/PES Tranmiion and Ditribution Conference and Exhibition: Aia and Pacific, Augut 2005; [10] S. Kamel, M. Abdel-Akher, M.K. El-Nemr, Implementation of SSSC model in the Newton- Raphon power flow formulation uing current injection, 2010 Univeritie Power Engineering Conference, Cardiff, 2010; [11] P. Kundur, Power Sytem Stability and Control, New York: McGraw-Hill, 1994.

10 268 Cotel Contantin, Mircea Eremia, Contantin Bulac [12] C. Bulac, M. Eremia, Dinamica itemelor electroenergetice (in Romanian), (Power ytem dynamic), Editura PRINTECH, 2006; [13] M. Eremia, M. Shahidehpour, Handbook of Electrical Power Sytem Dynamic: Modeling, Stability, and Control, Wiley-IEEE Pre, 2013.