Analysis of Contingencies Leading to Transients and Transient Stability Assessment in Power System Network

Supriya BimalKumar Rakshit1,Prakash Makhijani2 and Falguni Bhavsar3

1PG Student, Department of Electrical Engineering, Parul Institute of Engineering and Technology, Limda 2Director, OHMENCON Pvt. Ltd, Makarpura 3Professor, Department of Electrical Engineering, Parul Institute of Engineering and Technology, Limda [email protected] [email protected] [email protected]

Abstract - Recently, the security and stability of loss of synchronism, or falling "out of power system are the concerned issues, especially the transient stability. In this paper large power step." Transient stability is the ability of the system network is modeled in detail in order to power system to maintain synchronism assess the transient stability. Transient stability is when subjected to a severe transient important because the severity of fault can be determined which otherwise would lead to severe disturbance. Power system stability loss or damage to the equipment. Further, the problems are classified into three basic computation of critical clearing time (CCT) in types i.e. steady state, dynamic and different scenarios is proposed and simulation is also done to analyze the different characteristic. The transient [2]. result of CCTs in different scenarios can evaluate the impact of transient stability. • Steady state stability – A Power system is said to be steady state stable for a Keywords - Critical clearing time, ETAP, transient stability. specific steady state operating condition following a disturbance. Such disturbances are generally small in nature. 1. I. INTRODUCTION • Transient stability – Larger disturbances Electrical power systems are highly may change the operating state complex and dynamic in nature: circuit significantly, but still into an acceptable breakers are closing and opening, faults steady state. Such a state is called are being cleared, generation is varying transient state. in response to load demand, and the • Dynamic stability – It is generally power systems are subjected to associated with excitation system atmospheric disturbances, that is, response and supplementary control lightning [1]. Assuming a given steady signals involving excitation system. state, the system must settle to a new acceptable steady state in a short 2. II. CLASSIFICATION OF TRANSIENTS duration. Power-system stability is a term Transient are studied in two categories, applied to alternating current electric based upon on their origin: [3] power systems, denoting a condition in which the various synchronous machines • Of atmospheric origin, that is lightning of the system remain in synchronism, or • Of switching origin, that is, all switching "in step," with each other. Conversely, operations, load rejection and faults. instability denotes a condition involving Page 1 Another classification can be done based estimated because of dc component upon mode of generation of transients: present. • Electromagnetic transients - Generated predominantly by the interaction between the electrical fields of capacitance and magnetic fields of inductances in the power systems. The electromagnetic phenomena may appear as traveling waves on transmission lines, cables, bus sections, and oscillations between inductance and Fig.1 One Line Diagram capacitance Different contingencies which lead to • Electromechanical transients - transient conditions are: Interaction between the electrical energy Case 1: Fault on bus at different locations. stored in the system and the mechanical Case 2: Fault in transmission line. energy stored in the inertia of the rotating Case 3: Fault at lumped load. machines, that is, generators and motors. Buses 33 Branches 32 III. ORIGIN OF TRANSIENTS Transients are disturbances that occur for Generators 23 a very short duration and the electrical Loads 31 circuit is quickly restored to original 4053.0 operation. For transients to occur there Load-MW 52 must be some of the more common 2986.2 causes of transients [4]. Load-Mvar 5 • Atmospheric phenomena Generation- • Switching loads on or off MW 849 • Interruption of fault currents Generation- 526.16 • Switching of power lines Mvar 5 • Switching of capacitor banks Loss-MW 9.829 480.48 3. IV. ANALYSIS OF CONTIGENCIES Loss-Mvar 5 LEADING TO TRANSIENTS Table.1 General Information Transient stability of the generator is dependent on the following: [1] • How heavily generator is overloaded Lump 100000 6810 4221 420 • Generator output during fault. 1 kVA 9 0 2 • Fault clearing time Lump 30000 2573 1594 158 • Post fault transmission system reactance 2 kVA 1 6 1 • Generator reactance Lump 400000 3415 2116 175 • Generator inertia 3 kVA 31 61 3 • Infinite bus voltage magnitude Lump 50000 4250 2634 262 • Generator internal voltage magnitude. 4 kVA 2 0 4 Single line diagram of power system Lump 400000 3387 2099 174 scheme is shown below. Transient 5 kVA 11 13 6 stability is important since system is Lump 150000 1022 6334 630 interconnected and if the fault persists for 6 kVA 19 9 5 the longer period of time it can lead to Lump 75000 5097 3159 314 system instability and voltage collapse of 7 kVA 7 2 8 the system. Depending on critical clearing Lump 400000 3391 2102 174 angle the time required should be 8 kVA 80 04 7

Page 2 Lump 150000 1014 6289 628 Gen 398.9 307.9 264 88.7 9 kVA 91 8 3 1 97 58 54 Lump 30000 2571 1593 158 Gen 411.9 323.6 274 91.5 10 kVA 4 6 1 2 4 06 95 Lump 400000 3432 2127 175 Gen 392.5 287.3 255 87.2 11 kVA 72 40 8 3 92 79 36 Lump 25000 2144 1329 131 Gen 361.0 264.1 234 80.2 12 kVA 7 1 8 4 29 96 81 Lump 400000 3393 2103 174 Gen 404.5 319.4 270 89.9 13 kVA 90 34 8 5 41 55 55 Lump 150000 1024 6347 631 Gen 400.7 313.3 267 89.1 14 kVA 14 0 1 6 85 68 03 Lump 400000 3405 2110 175 Gen 417.0 322.6 276 92.7 15 kVA 09 28 1 7 2 27 74 Lump 150000 1027 6367 632 Gen 417.1 321.4 276 92.7 16 kVA 39 1 1 8 48 96 43 Lump 50000 3386 2098 209 Gen 27.88 277 45 90 17 kVA 2 5 5 9 9 6 Lump 400000 3389 2100 174 Gen 27.88 276 45 90 18 kVA 66 72 7 10 9 6 Lump 100000 6846 4243 421 Gen 27.88 277 45 90 19 kVA 5 0 3 11 9 8 Lump 100000 6760 4189 418 Gen 27.88 277 45 90 20 kVA 3 6 7 12 9 6 Lump 400000 3392 2102 174 Gen 27.88 277 45 90 21 kVA 00 17 8 13 9 9 Lump 100000 6764 4192 418 Gen 55.77 557 90 90 22 kVA 9 5 8 14 7 1 Lump 150000 1015 6293 628 Gen 27.88 276 45 90 23 kVA 43 0 4 15 9 6 Lump 50000 4250 2633 262 Gen 52.05 516 84 84 24 kVA 0 9 4 16 9 2 Lump 50000 4250 2633 262 Gen 27.88 277 45 90 25 kVA 0 9 4 17 9 3 Lump 50000 4250 2633 262 Gen 27.88 276 45 90 26 kVA 0 9 4 18 9 9 Lump 50000 4250 2633 262 Gen 55.77 556 90 90 27 kVA 0 9 4 19 7 9 Lump 50000 4250 2633 262 Gen 27.88 276 45 90 28 kVA 0 9 4 20 9 9 Lump 50000 4250 2633 262 Gen 27.88 278 45 90 29 kVA 0 9 4 21 9 7 Lump 50000 4250 2633 262 Gen 27.88 278 45 90 30 kVA 0 9 4 22 9 6 Lump 50000 4250 2633 262 Gen 55.77 557 90 90 31 kVA 0 9 4 23 7 0 Table.2 Load Data Table.3 Generation Data

% 4. V. TRANSIENT STABILITY ID MW Mvar Amp Gen. ASSESSMENT

Page 3 Case 1: Fault on bus at different location a. Fault at bus no. 24 – The bus 24 is located at the lower level towards the load side so the fault at this particular bus will have critical clearing time of 1sec and beyond this limit the system will undergo transient condition. As it is located far away from the grid the critical clearing time is more and therefore severity of fault at this location is less.

Fig.3 Generator Absolute Power Angle

Fig.1 Generator Electrical Power

Fig.4 Generator Reactive Power The entire above graph presented in section a indicates that as the fault is located on the bottom end at it does not result in the total failure of the system. Also it indicates that as the fault does not affect the generator located on the grid side but it would definitely affect the generators located at Industrial Power Plant (IPP).

Fig.2 Generator Exciter Voltage b. Fault at bus no. 16 – Bus 16 is located on the grid side. Fault at this location may lead generator to go out of step. Therefore in such case it is necessary to have less critical clearing time. Critical clearing time for such case is found to be 0.8secs. If the fault continues more than determined time it can lead to the severe damage.

Page 4 Fig.5 Generator Absolute Power Angle Fig.8Generator Exciter Voltage The entire above graph presented in section b indicates that as the fault is located on the grid side it result in the total failure of the system starting from top to bottom i.e. from grid towards distribution end. Also it indicates that as the fault moves away from the location the effect gets minimized due to presence of reactor in the line, so the generator 1 is having less effect then generator 8 and also due to lower inertia of the generator at lower end Industrial Power Plant (IPP) it also gets affected. Fig.6 Generator Reactive Power Case 2: Fault in transmission line Fault in transmission line1 causes the transient condition in the power system network. If the fault persists for longer period of time then circuit breaker CB1 is opened. The critical clearing time for such case is found to be 0.6secs.

Fig.7 Generator Electrical Power

Fig.9 Generator Absolute Power Angle

Page 5 less effect then generator 8 and also due to lower inertia of the generator at lower end i.e. Industrial Power Plant (IPP) it also gets affected.

Case 3: Fault at lumped load. Fault at lumped load also result in transients. Lumped load consist of static as well as motor load. Whenever a large amount of load is removed from the system it would result in the instability of the system.

Fig.10 Generator Electrical Power

Fig.13 Generator Absolute Power Angle Fig.11 Generator Reactive Power

Fig.14Generator Reactive Power Fig.12 Generator Exciter Voltage The entire above graphs presented in section indicates that as the fault occurs on transmission line result in the total failure of the system starting from top to bottom i.e. from grid towards distribution end. Also it indicates that as the fault moves away from the location the effect gets minimized due to presence of reactor in the line, so the generator 1 is having

Page 6 located in grid side but it would definitely affect the generators which are having less inertia and located at IPP i.e. industrial power plant

VI. CONCLUSION Transient stability is the ability of the power system to maintain synchronism after subjected to severe disturbance. The synchronism is assessed with relative rotor angle violations among the different machines. Accurate analysis of the transient stability requires the detailed Fig.15Generator Electrical Power modeling of generating units and other equipment. Transient stability is critical even small disturbance can make the generator to go out of step. This analysis allows to assess that the system is stable, unstable and also allows to determine the critical clearing time of power system with three-phase faults.

REFERENCES 1. Power system stability and control, P. Kundur, McGraw-Hill International Editions, 1994. 2. Modern Power system analysis, I. J. Nagrath and D. P. Kothari, Tata McGraw-Hill, 2003. 3. Transients in electrical systems analysis, recognition and Fig.16 Generator Exciter Voltage mitigation, J. C. Das, McGraw-Hill Companies, 2010. The entire above graphs presented in 4. Power quality, C. Sankaran, CRC Press LLC, 2002. section indicates that as the fault occurs at load it does not affect the generators

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