The 5th International Power Engineering and Optimization Conference (PEOCO2011), Shah Alam, Selangor, Malaysia : 6-7 June 2011

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1 The 5th International Power Engineering an Optimization onference (PEOO211), Shah Alam, Selangor, Malaysia : 6-7 June 211 Moeling an Simulation of Umlazi suburb of Durban Municipality Network (South Africa) G. P. Yuma, Member, SAIEE, an. usakana, Member, SAIEE Abstract--The main focus is to moel an simulate the portion locate in the ULMAZI suburb of the Durban municipality network incorporating FATS evices, in orer to improve the stability of the whole network. Instea of oing moeling an simulation for each generator while they all have the same characteristics, a simplifie ynamic moel of a power system is use in this stuy, name Single Machine Infinite Bus (SMIB) power system. This moel consists of a single synchronous generator connecte through a parallel transmission line to a very large network which is UMLAZI approximate by an infinite bus. For the esign purpose, the moel of example power system which is a SMIB power system installe with the evice an SSS connecte in series is evelope in MATLAB/Simulink. Simulation results in terms of power system responses prove the enhancement of power system performance an fast amping of power system oscillation. Inex Terms--Matlab/Simulink, Moeling an simulation, Single machine infinite bus, Synchronous series compensator, Thyristor controlle series compensator. I. INTRODUTION In practice, we classify the transmission network into the following subsystems: The transmission system interconnects all major generating stations an main loa centres in the system. The sub transmission system transmits power in smaller uantities from the transmission substations to the istribution substations. The istribution system represents the final stage in the transfer of power to the iniviual customers. The primary istribution voltage is typically between 3.3 kv an 33kV. The seconary istribution feeers supply resiential an commercial customers at 12/24 V. The electricity supply inustries of Southern Africa are ominate by the State owne utility of South Africa, ESOM. ESOM generates aroun two thirs of the electricity prouce in the whole of Africa an is extening its transmission gri north into neighbouring sub-sahara countries. Actually, moern society is very vulnerable in the case of power system blackout; so the conseuences of blackout are both social an economic. The conseuences of isturbances in office work will be loss of prouction an information. This paper is organize as follow. In section II, a single phase representation of UMLAZI power network is presente. The power system uner stuy, which is a SMIB power system with an SSS an a brief overview of the propose controllers are escribe in the same section. Simulation results are provie an iscusse in section III. onclusions are given in section IV. II. SINGLE PHASE REPRESENTATION OF UMLAZI NETWOR The primary network ivision of the Electricity epartment of the city of Durban operates an extensive network of 132 kv power substations as part of the electrical istribution network for the city of Durban. We consier a single phase representation of the UMLAZI network area, the moel of which is epicte in Fig. 1. There are 39 buses in the system, with a total of MW an 6 MVAr. The UMLAZI part of the power system is using synchronous generators, all of the same kin. Thanks to Mangosuthu University of Technology for proviing the financial support to make this stuy possible. G. P. Yuma is with the Department of Electrical Engineering, Mangosuthu University of Technology, Durban, 41 RSA ( gyuma@mut.ac.za).. usakana is with the Department of Electrical Engineering, entral University of Technology, Free State, RSA ( kuskybe@yahoo.fr). Fig. 1. Reuce UMLAZI network representation /11/$ /11/$ IEEE IEEE 335

2 The turbine governor ynamics is neglecte resulting in time being constant. Also the generators are represente by a flux-ecay moel by neglecting the subtransient reactance. The loas are assume to be constant impeance an converte to amittances. For simplicity spee-governor ynamics are not moele an the UMLAZI network is moele using Matlab/Simulink environment. The best location of FATS-base controller will be one by applying a three phase fault near a bus at the en of a line an the fault is cleare by tripping the line. This moel consists of a single synchronous generator connecte through a parallel transmission line to a very large network which is UMLAZI approximate by an infinite bus. A. SMIB with an S A Single machine Infinite-Bus (SMIB) power system installe with an SSS are investigate, as shown in Figs. 2 an 3. In Fig. 2, the moel of SMIB with controller is analyze for ifferent conitions of time constant using Matlab/Simulink. The synchronous generator is elivering power to the infinite-bus through a ouble circuit transmission line an a. Fig. 2. SMIB power system with The SMIB power system with SSS controller, as shown in Fig. 3, is consiere in this paper. The system comprises a generator connecte to an infinite-bus through a step-up transformer an a SSS followe by a ouble circuit transmission line. T 1 represents the transformer; V S an VR are the generator terminal an infinite-bus voltage respectively; V1 an V2 are the bus voltages; V an VNV are the voltage source an output voltage of the SSS converter respectively; I is the line current an PL is the real power flow in the transmission lines. Fig. 3. SMIB power system with SSS B. Generator The generator is represente by the thir-orer moel comprising of the electromechanical swing euation an the generator internal voltage euation. The swing euation is ivie into the following euations [1]: t t D ( t) ( ( t) ) ( Pe ( t) Pm ) 2H 2H Where Pm an 1 2 Pe are the input an output powers of the generator; H an D are the inertia constant an the amping coefficient, an are the rotor angle an spee respectively. The internal voltage 1 E ( t) ( E ( t) f T o E is: x x i E ( t)) 3 The output power of the generator can be expresse in terms of the -axis an -axis components of the armature current,i, an terminal voltage [13], v, as: P v i v i e 4 The SMIB system incluing SSS can be obtaine by linearizing the nonlinear ifferential euations aroun a nominal operating point [2]: f 1/ TA E f A TA V t E / V E V Where; V t m m E vv vmm 7 336

3 V mk I ts os I Sin ts 8 The signal m is the amplitue moulation ratio of the pulse, which is the input control signal to SSS, is the phase of the injecte voltages an k is the ratio between A an voltages an epens on the inverter structure, are linearization constants Overview of ontroller The configuration of consists of a thyristorcontrolle reactor (TR) in parallel with capacitor segments of series capacitor bank [3]. The basic structure an stability moel of the evice are shown in Figs. 4 an 5. Fig. 4. Structure of -base controller The input signal of the propose controller is the spee eviation ( ), an the output signal is the reactance offere by the,. The structure consists of a gain block with gain T, a signal washout block an two-stage phase compensation blocks [4]. The signal washout block serves as a high-pass filter, with the time constant T WT, high enough to allow signals associate with oscillations in input signal to pass unchange [5]. Fig. 5. Stability moel of -base controller The combination of TR an capacitor allow the capacitive reactance to be smoothly controlle over a wie range. is an effective an economical FATS controller in solving problems of ynamic stability in long transmission lines. The functioning of is one by analyzing the behaviour of a variable inuctor connecte in series with a fixe capacitor [6]. The reactance can be regulate by controlling the firing angle an its egree of compensation. It has been in use for many years to increase the line power transfer as well as to enhance system stability. It consists of three components: capacitor banks, bypass inuctor an biirectional thyristors [7]. The firing angles of the thyristors are controlle to ajust the reactance in accorance with a system control algorithm, normally in response to some system parameter variations. Accoring to the conuctance angle ( ) or the variation of the thyristor firing angle ( ), the controller can be moelle as a fast switch between corresponing reactance offere to the power system [8]. The reactance is given by the firing angle as: When: Sin 4os With: Min Max p Min Max /2 ktank /2 tan /2 2 k 1 p 9 1 An Min

4 D. Overview of ontroller The soli-state synchronous voltage source employing an appropriate to A inverter with gate turn-off thyristor can be use for series compensation of transmission lines. One of the euipment that can achieve this task is SSS. The PI of SSS base controller, to moulate the SSS injecte voltage V, is shown in Fig. 7. The integral an proportional parameters of the PI ontroller are respectively [12]. i an p The amping controller is esigne to improve the amping torue. The structure of SSS base amping controller is shown in Fig. 6 [9]. It consists of gain, signal washout an phase compensation blocks. Fig. 8. PI structure of SSS- base controller III. SIMULATION RESULTS AND DISUSSION Fig. 6. SSS- base amping controller The block of signal washout is a high pass filter that moifies the SSS input signal an prevents steay changes in active power. T W shoul have a large value to allow signals associate with active power oscillations pass unchange [1]. The SMIB power system installe with an SSS is investigate. an SSS are esigne to improve the power oscillations amping. To stuy the performance of the propose controllers, a simulation program is evelope. MATLAB/Simulink is use for all simulations. A small signal isturbance is impose on the loa active power for 2 sec. It can be seen from Figs that using the propose controllers, the angle of oscillations amping is improve. Also the coorinate esign approach provies the best amping characteristic an enhance greatly the first swing stability at loaing conition. In the Figs. to follow, the response without controller (no controller) is shown with otte line legen ; the response with controller only is shown with legen using thin soli line an the response with the simultaneously propose controllers is shown with thick soli line with legen -SSS. Fig. 7. Lea-lag structure of SSS- base controller The input signal of the propose controller is the spee eviation ( ), an the output signal is the injecte voltage V. The lea-lag of SSS ontroller consists of a gain block with gain S, a signal washout block an two-stage phase compensation blocks. The signal washout block serves as a high-pass filter, with the time constant T W, high enough to allow signals associate with oscillations in input signal to pass unchange [11]. 338

5 2 1 -SSS.1. -SSS Fig. 9. Variation of spee eviation (p.u) with k 2 -SSS Fig. 1. Response of power angle (p.u) with time Fig. 12. Variation of electrical power P e (p.u) IV. OLUSION In this paper, power system stability enhancement by an SSS amping controllers is presente. Simulation results are use to emonstrate the impact an effectiveness of esigne controllers in improving angle oscillations amping. The propose controllers have been applie an teste on power system uner loaing conition. The effectiveness of the both the propose -SSS base amping controllers, for power system stability improvement, are emonstrate by a weakly connecte example power system subjecte to isturbance. The simulation results presente show that both -SSS improve the system stability. The propose controllers provie a better effectiveness on amping power system oscillation. It is also clear that the coorinate esign of an SSS base controller provie great amping characteristic an enhance significantly the system stability SSS Fig. 11. Variation of terminal voltage V t (p.u) 339

6 V. APPENDI All ata are in p.u unless specifie otherwise ontroller: T 2ms, 15,.5623, k 2, T W 1s, MA. 9 L, MIN Generator: H , D, x , x , x. 5647, T , T. 51, R, P. 68, Q. 23, a e e Transmission line: R, o.1467,. 1236, G, B T SSS: TH L o, S nom 15MVA, V nom 45kV, f 6Hz, V max. 3, Max rate of charge of V ref 3/ s, R. 615, L. 2, V 3kV, nv nv 45e F, p _ IVR. 267 I _ IVR e e 6 p _ VR 2, _ 1 3 p VR [7]. A. anizares an Z.T. Faur, Analysis of SV an ontrollers in Voltage ollapse, IEEE Transactions on Power Systems, Vol.14, February [8]. A. anizares, Power flow an transient stability moels of FATS ontrollers for voltage an angle stability stuies, IEEE/PES WM on Moeling, Simulation an Applications of FATS ontrollers in Angle an Voltage Stability Stuies, Singapore, January 2. [9] B. H. Li, Q. H. Wu, D. R. Turner, p. Y. Wang an.. Zhou, Moeling of ynamics for control an analysis of power system stability, Electric Power an Energy Systems, Vol. 22, 2. [1]. R. hen, N.. Pahalawaththa, U. D. Annakkage,. S. umble, Design of Decentralise Output Feeback Damping ontrollers. [11] M.S. astro, H. M. Ayres, V. F. a osta an L.. P. a Silva, Impacts of the SSS control moes on small signal transient stability of a power system, Electric Power Systems Research, vol. 77, 27. [12] F. A. R. Al Jower, Influence of Moe of Operation of the SSS on the Small Disturbance an Transient Stability of a Raial Power System, IEEE Transactions on Power Systems, vol. 2, May 25 Books: [13]. R. Paiyar, Power System Dynamic Stability an ontrol, BS Publications, 2 n Eition, Hyeraba, Inia, 22. VIII. BIOGRAPHIES Galu Papy Yuma was born in isangani, Democratic Republic of ongo, on July 15, He has obtaine his BSc egree from the University of Lubumbahi, Democratic Republic of ongo, in 26, an M Tech from the Tshwane University of Technology, Republic of South Africa, in 29. He has 4 years of teaching experience. He is presently working as Lecturer in the Department of Electrical Engineering, Mangosuthu University of Technology, Republic of South Africa. His special fiels of interest are mainly Power System Stability, Transmission an Distribution Network an FATS. VI. ANOWLEDGMENT The authors gratefully acknowlege the contribution of A. Lonappan for his work on the original version of this ocument. VII. REFEREES Perioicals: [1] H. F. Wang, F. J Swift, A Unifie Moel for the Analysis of FATS Devices in Damping Power System Oscillations. I. Single Machine Infinite Bus Power Systems, Power Delivery, IEEE Transactions on, Volume: 12, Issue: 2, April [2] N. G. Hingorani an L. Gyugyi, Unerstaning FATS, IEEE Press, [3] Y. H. Song an A. T. Johns, Flexible A Transmission Systems (FATS), IEE Power an Energy Series 3, [4] S. N. Singh an A.. Davi, A new approach for placement of FATS evices in open power markets, IEEE Power Enginnering Review, September 21. [5] igre 95 TP 18, FATS Overview, IEEE Power Engineering Society, [6] Y. iao, Y. H. Song,.. Liu, an Y. Z. Sun, Available transfer capability enhancement using FATS evices, IEEE Transactions on Power System, Vol.8, February