Improving Power System Transient Stability with Static Synchronous Series Compensator

Transcription

1 American Journal of Applied Science 8 (1): 77-81, 2011 ISSN Science Pulication Improving Power Sytem Tranient Staility with Static Synchronou Serie Compenator Prechanon Kumkratug Diviion of Electrical Engineering, Faculty of Engineering at Si Racha, Kaetart Univerity, 199 M.6, Tungukhla, Si Racha, Chonuri, 20230, Thailand Atract: Prolem tatement: Modern power ytem conit of the complicated network of tranmiion line and carrie heavy demand. Thu they caue in the taility prolem. One of the major interet of power utilitie i the improvement of power ytem tranient ehavior. Approach: Static Synchronou Serie Compenator (SSSC) i a power electronic aed device that ha the capaility of controlling the power flow through a line. Thi tudy applie the SSSC to improve tranient taility of power ytem. To verify the effect of the SSSC on tranient taility, the mathematical model and control trategy of a SSSC i preented. The SSSC i repreented y variale voltage injection with aociate tranformer leakage reactance and the voltage ource. The erie voltage injection model of SSSC i modeled into power flow equation and thu it i ued to determine it control trategy. Thi tudy ue machine peed deviation to control it. The wing curve of the three phae faulted power ytem without and with a SSSC i teted and compared in variou cae. Reult: The wing curve of ytem without a SSSC get increae monotonically and thu the ytem can e conidered a untale wherea the wing curve of ytem with a SSSC can e conidered a tale. Concluion: SSSSC can improve tranient taility of power ytem. Key word: Power ytem taility, tranient taility, FACTS device, tatic ynchronou erie compenator, generating tation, Static Synchronou Serie Compenator (SSSC), Single Machine Infinite Bu (SMIB), tranformer leakage, voltage injection, voltage ource INTRODUCTION From the energy utilization point of view, electricity i till eing regarded a mighty mean of energy carrier. Nowaday, the demand of electricity ha dramatically increaed and a modern power ytem ecome a complex network of tranmiion line interconnecting the generating tation to the major load point in the overall power ytem in order to upport the high demand of conumer. The complicated network caue the taility prolem. Tranient taility improvement i one of the important apect in modern power ytem (Al-Rawi et al., 2007; Baainejad and Keypour, 2010; Sahoo et al., 2010; Parry and Gangatharan, 2005). They have propoed many method to improve taility of power ytem uch a load hedding, High Voltage Direct Current (HVDC), Flexile AC Tranmiion ytem (FACTS), (Hannan and Chan, 2006; Chettih et al., 2008; Seyed et al., 2008a). A Static Synchronou Serie Compenator (SSSC) i a memer of the FACTS family that i connected in erie with power ytem. The SSSC conit of a olid tate voltage ource converter with GTO thyritor witche or other high performance of emi-conductor and tranformer. The SSSC can electrically mimic 77 reactor and capacitor y injecting a hunt current in quadrature with the line voltage. The reactive power (or current) of the SSSC can e adjuted y controlling the magnitude and phae angle of the output voltage of the hunt converter (Al-Huan, 2009; Seyed et al., 2008). Thi tudy preent the method of improving tranient taility of power ytem uing a SSSC. The mathematical model of power ytem equipped with a SSSC i ytematically derived. The preented mathematical model i applied to deign control trategy of a SSSC. The imulation reult are teted on a Single Machine Infinite u ytem. The effect of gain control of a SSSC on taility improvement i alo invetigated. MATERIALS AND METHODS Mathematical model: Figure 1a how the ingle line diagram of Single Machine Infinite Bu (SMIB) ytem without a SSSC and the correponding equivalent circuit i hown in Fig. 1. Here 1 i the equivalent reactance etween the machine internal u and the u m and 2 i the equivalent reactance etween u m and the infinite u. The generator i repreented y a contant voltage ource (E ) ehind tranient reactance ( d).

2 Here : E coδ θ tan Ein δ 1 V (2) The output electrical power of the ytem without a SSSC i given y: 0 EV Pe inδ (3) () Fig. 1: Single machine infinite u ytem chematic diagram () equivalent circuit Now, conider the ytem with a SSSC a hown in Fig. 2. The Fig. 2 repreent the equivalent circuit of Fig. 2a. The SSSC i repreented y a erie voltage injection (V ) and tranformer leakage reactance. From Fig. 2, the line current of the ytem with a SSSC i given y: E V V E V V I + (4) From the Eq. 1 and 4, the line current of the ytem with a SSSC i given y: I I0 + ΔI (5) Here ΔI V () Fig. 2: Single machine infinite u ytem with a SSSC chematic diagram () equivalent circuit of ytem with a SSSC repreented y a erie voltage injection Conider the ytem without a SSSC a hown in Fig. 1, the line current i given y: E V I0 (E coδ+ je in δ) (V ) E E V δ + δ+ ( in ) j( co ) (1) 78 From Eq. 1 and 4, ΔI i the additional component of the ytem of a SSSC. The output electrical power equation of generator can e expreed y: Pe Re[ E ( I) ] Re[ E ( I ) ] + Re[ E (Δ I)] 0 (6) The firt term of Eq. 6 repreent the ytem without a SSSC. The econd term i the additional component from the SSSC ( Δ ) rewritten y: P P +Δ P (7) e e e The ΔP e i written y: V V θ Δ Pe Re E Re E δ 2 EV in( δ θ ) P e (8)

3 When V i poitive, the SSSC upplie the reactive power to the ytem, it i called capacitive mode and then the erie voltage angle θ i in lagging with the line current a hown in Fig. 3 wherea V i negative, the SSSC aor the reactive power to the ytem, it i called reactive mode and then the erie voltage angle θ i in leading with the line current a hown in Fig. 3c. With the capacitive mode the Eq. 8 i given y: EV Δ Pe co( δ θ ) (9) From the Eq. 2, it can e written y: E in δin θ V coθ E coδcoθ (10) With ome mathematical manipulation of Eq. 10, it can e written y: V co( δ θ ) co( θ) E (11) From the phaor diagram a hown in Fig. 3, it indicate that the SSSC doen t change the line current angle. However, the SSSC affect on the line current magnitude. When V lag line current 90, the line current magnitude i increaed and when V lead line current 90, the line current magnitude i decreaed a can e een in Fig. 3. From the Fig. 3, the coine of the line current angle i given y: Ein( δ) co( θ ) xy Ein( δ) (E ) + (V ) 2E V co( δ) (12) From Eq. 9 and 12, the additional component of output electrical power i: VEV Δ P inδ (E) + (V ) 2EV coδ e (13) From Eq. 7 and 13, the output electrical power of ytem with a SSSC i given y: () P P + VP e e e (E ) + (V ) 2E V coδ (14) It can e een from Eq. 14 that the output electrical power flow can e controlled y a SSSC. With poitive value of V, the output electrical power i increaed wherea with negative value of V, the output electrical power i reduced. (c) Fig. 3: Phaor diagram without a SSSC () with a SSSC operating in capacitive mode (c) with a SSSC operating in reactive mode 79 Tranient taility control: The tranient taility of power ytem a hown in Fig. 2a can e expreed y following equation: δ ω (15) 1 ω [P m P e ] (16) M

4 Here, δ, ω and P m are the rotor angle, peed deviation, mechanical input power and moment of inertia, repectively of machine. The taility of the ytem can e improved y increaing the electrical output power when it peed deviation i poitive and decreaing the power when peed deviation i negative. Thu the control trategy of SSSC i given y: V kω (17) Here, k i contant gain control RESULTS The propoed model of power ytem equipped with a SSSC of Fig. 2a i invetigated in thi ection. The ytem parameter are: M5.6, t 0.1, d 3, L1 0.4, L2 0.4, L3 0.9, L4 0.4, P m 0.9 It i conidered that a 3-phae fault appear on line L 1 and it i cleared y opening the faulted line. Figure 4 how the wing curve of the ytem without (K 0) and with variou gain (K) OF a SSSC. Tale 1 ummarize the maximum and minimum wing curve of Fig. 4. DISCUSSION It can e oerved from the imulation reult that with t cl 120 mec and without a SSSC (K 0), the ytem i conidered a untale. However, with a SSSC, the ytem i conidered a tale. With K 10, the maximum and minimum machine angle are and 10.55, repectively. The tranient taility get increae a the K i increaed. With K 50, the maximum and minimum machine angle are improved to and 39.36, repectively. CONCLUSION Thi tudy preent the method of improving tranient taility of power ytem uing a SSSC. The mathematical model of power ytem equipped with a SSSC i ytematically derived. It wa found that the power flow of the ytem can e control a erie injected voltage of a SSSC. The taility of the power ytem can e controlled y a SSSC. Thi tudy ue machine peed deviation to control parameter of a SSSC. The imulation reult are teted on a Single Machine Infinite u ytem. The effect of gain control of a SSSC on taility improvement i alo invetigated. From the imulation reult, it indicate that a SSSC can improve tranient taility of the ytem and the taility of ytem get increae when the gain control i increaed. Fig. 4: Swing curve of the ytem without and with variou gain of a SSSC Tale 1: Maximum and minimum machine angle with variou cae gain of SSSC K δ max (degree) δ min (degree) REFERENCES Al-Huan, A.N., An eigentructure aignment for a tatic ynchronou compenator. Am. J. Eng. Applied Sci., 2: DOI: /ajeap Al-Rawi, N.M., A. Anwar and A.M. Adul-Majeed, Computer aided tranient taility analyi. J. Comput. Sci., 3: DOI: /jcp Baainejad, S. and R. Keypour, Analyi of tranient voltage taility of a variale peed wind turine with douly fed induction generator affected y different electrical parameter of induction generator. Trend Applied Sci. Re., 5: Chettih, S., M. Khiat and A. Chaker, Optimal ditriution of the reactive power and voltage control in Algerian network uing the genetic algorithm method. Inform. Technol. J., 7: DOI: /itj Hannan, M.A. and K.W. Chan, Tranient analyi of FACTS and cutom power device uing phaor dynamic. J. Applied Sci., 6: DOI: /ja

5 Parry, M. and N. Gangatharan, Adaptive data tranmiion in multimedia network. Am. J. Applied Sci., 2: DOI: /ajap Sahoo, A.K., S.S. Dah and T. Thyagarajan, Power flow tudy including FACTS device. J. Applied Sci., 10: DOI: /ja Seyed, A.T, H. Reza and N. Majid, 2008a. Comparion of different control trategie in GA-aed optimized UPFC controller in electric power ytem. Am. J. Eng. Applied Sci., 1: DOI: /ajeap Seyed, A.T, H. Reza and N. Majid, Decentralized controller deign for tatic ynchronou compenator uing rout quantitative feedack theory method. Am. J. Eng. Applied Sci., 1: DOI: /ajeap