2017 IEEE 7th International Advance Computing Conference TRANSIENT STABILITY ANALYSIS OF A COMBINED CYCLE POWER PLANT USING ETAP SOFTWARE D. Sreenivasulu Reddy, Assistant Professor Electrical and Electronics Engineering Sree Vidyanikethan Engineering College Tirupathi, India seenu.d7@gmail.com Ch. Siva Kumari, PG Scholar Electrical and Electronics Engineering Sree Vidyanikethan Engineering College Tirupathi, India chsivakumari313@gmail.com Abstract Recently in the operation of power systems, transient stability analysis has become a major issue because of increasing stress on power system. The transient stability analysis for large power system network is very difficult and highly nonlinear problem. In this paper, different faults (like 3-phase faults, LG fault and sudden removal of generator) are considered at different bus levels in combined cycle power plant and the fault clearing times for stable operation of system (critical clearing time) are calculated by using the ETAP (Electrical Transient Analyzer Program) software. Index Terms Critical clearing time, ETAP, Transient stability analysis. I. INTRODUCTION Availability of various generation sources such as conventional and non-conventional sources. These sources can significantly impact the power flow and voltage profile as well as other parameters at customers and utility side. Electrical networks/installations are designed based on national and international standards depending on the type of the project and its requirements. In addition, some initial FEED (Front End Engineering Design) studies are taken before the system single line diagram is frozen. The power system Studies are essential to pre-confirm the parameters of various equipments/components of the planned electrical facility. In electrical power systems, most of the electrical parameters variation occurs dynamically due to sudden addition or sudden tripping of generators. The faulted / disturbance occurred part of the network is isolated by analyzing the electrical power system. Electrical power generation broadly classified into two types based on the utilization of power. The first one is captive power plants, it refers to power generated from the plant set up by an industry is used for its own exclusive consumption. Second one is utility power plants, it refers to the power generated from a power plant set up by an industry for sell or supply to various customers and not for its own exclusive consumption. The estimates for captive power generated in India given by the Central Electricity Authority s (CEA) are about 41542MW. Industrial sector is one of the largest consumers of electrical energy in India. The industries, mainly refinery based, are of very large scale production and even a minute of power failure can lead to major economic losses. Thus, these industries cannot rely on the power grid / State Electricity Boards for adequate, continuous, reliable and quality power supply. As such, a number of industries are now increasingly relying for power on their own in-house generation. At present, around 30% of the energy requirement of the industrial sector is met through in house captive power plants. The reasons for many industries setting up their own captive power plants are Non-availability of adequate and continuous grid supply, Poor quality and reliability of grid supply and High tariff as a result of heavy cross subsidization. Each captive power plant has to be tailor made to suit particular customer/ industry need. It includes setting up and commissioning of generators, hooking up with grid, catering to the power plant auxiliaries as well as customer s industrial loads to ensure availability of adequate reliable power supply to the industry. The combined cycle power plant is one of the types of captive power plants and it is considered as the coupling of a gas turbine and a steam turbine through a heat recovery steam generator (HRSG). In this gas based plant, the heat in the exhaust gases of the gas turbine is utilized for generating steam with the help of Heat Recovery Steam Generator (HRSG). The steam generated is in turn utilized for running a steam turbine generator for further generation of power. A. Designing Objectives While designing a captive power plant and offerings as a business solution, following are the major objectives to be met: Ensuring optimization in equipment selection. Identifying and rectifying deficiencies in the system at the design stage itself before it goes into operation. Analysing different power plant operating scenarios for economic operation. Establishing system performance and guarantees. Ensuring safe and reliable operation. 978-1-5090-1560-3/17 $31.00 2017 IEEE 511 510 DOI 10.1109/IACC.2017.103
Establishing the provisions of the system s future expansion plans. In the past, Electrical networks designed by considering various cushions for absorbing various sudden changes in the energy parameters like fault currents, voltage variations, frequency variations. But now we can analyze the planned electrical network with the help of soft wares like ETAP and visualize the response of the network to the sudden and dynamic changes of the power parameters. Hence no need to invest more on providing cushion in the network design. With the impending deregulated environment, electric utilities are seeking new technologies to provide acceptable power quality and reliability to their customers. Small nonconventional generation option is rapidly becoming attractive to many utilities across the world because these technologies produce energy with less environmental impact, easy to site and are highly efficient. In this multi-dimensional source of energies it is very much required to study the planned network through simulation with the help of some simulating tools like ETAP. II. SINGLE LINE DIAGRAM USING ETAP Figure 1 shows the combined cycle power plant consisting of two steam turbine generators (STG) with a capacity of 36MW each, two gas turbine generators (GTG) with a capacity of 34.5MW each and it is connected to grid [1]. Different loads are connected at different bus levels (33KV, 6.6KV, 415V). Different types of loads are lump loads, HT motors and LT motors. Lump loads are the combination of 70% motor load and 30% non-motor load operating with a power factor of 0.88 lag. IEC standard ETAP software library data [2] is considered as default data for impedances of the system components. GRID I/C-1 15242 MVAsc STG 1 36 MW STG 2 36 MW GTG 1 34.5 MW GTG 2 34.5 MW CB1 CB3 CB5 CB9 CB11 GRID TRAFO-1 220/33 kv 15 %Z CB15 GEN TRAFO-1 15.62 %Z GEN TRAFO-2 15.49 %Z GEN TRAFO-4 15.53 %Z GEN TRAFO-5 15.47 %Z 33 KV BUS-A 33 kv CB2 33KV BUS-B 33 kv CB4 CB6 CB10 CB12 SAT-1 12.13 %Z CB19 CB20 CB21 SAT-3 12.01 %Z 100 MVA Lump1 CB129 60 MVA Lump16 CB22 SAT-2 12.13 %Z CB23 CB29 SAT-4 12.33 %Z 6.6KV BUS A (BOARD 1) CB30 CB31 CB32 CB33 CB34 CB24 CB35 CB36 CB25 CB37 6.6KV BUS B (BOARD 1) CB38 CB39 CB40 CB26 CB41 CB42 CB43 CB44 CB45 CB27 CB46 CB47 6.6KV BUS A(BOARD 2) CB48 CB49 CB50 CB51 CB52 CB53 CB28 6.6KV BUS B(BOARD 2) CB55 CB57 CB54 CB56 CB58 CB60 CB59 CB61 CB62 CB63 S/S-1-I/C1 BFP-1(S/B) 3125 kva 850 kw CC-1 CWP-1 CAP-1 650 kw 1250 kw UAT-1 10.53 %Z UAT-3 10.57 %Z UAT-4 10.48 %Z UAT-2 10.35 %Z S/S-1-I/C2 3125 kva BFP-2 CC-2 CC-3(S/B) CWP-2(S/B) CAP-2 850 kw 650 kw 650 kw 1250 kw ACW-1 360 kw UAT-5 10.54 %Z CAP-3 UAT-7 CTP-1 GBC-1 BFP-UB-1(S/B) BFP-HRSG-1 315 kw 750 kw 1750 kw 910 kw FD FAN-UB-1 1200 kw 10.55 %Z CB97 BFP-HRSG-2 BFP-HRSG-3(S/B) CTP-2(S/B) 910 kw 910 kw 315 kw UAT-8 10.4 %Z CAP-4 GBC-2(S/B) BFP-UB-3 750 kw ACW-2(S/B) FD FAN-UB-2 1750 kw 360 kw 1200 kw UAT-6 10.28 %Z BUS-A(BOARD1) CB65 CB64 CB66 BUS-B(BOARD1) BUS-A(BOARD 3) CB99 CB98 BUS-B(BOARD 3) BUS-A(BOARD 2) CB67 CB68 CB69 CB70 CB71 CB72 CB124 CB126 CB125 HRSG-2. LCO-2 AUG. AF-2(S/B) HRSG-2 800 kva LCO-1 AUG. AF-1 75 kw 55 kw 800 kva 75 kw 55 kw BUS 57 BUS 58 Lump2 Lump3 160 kva 160 kva CB75 CB74 CB73 BUS-B(BOARD 2) CB92 UPS1 CB91 CB93 CB94 CB95 CB96 CB100 CB101 CB103 CB102 CB104 BOIL-1. 144 kva CB344 CB345 CB107 CB109 CB286 CB105 CB108 ASB (CUS) 110V UPS-1 LUBE-1 STG-1 LUBE-1 STG-2 CB106 LUBE-2 STG-2 BSCWP-1 BUS-A(BOARD 4) BUS 76 90 kw BUS-B(BOARD 4) 90 kw 90 kw 90 kw LUBE-2 STG-1 BOIL -1. ACELDB 110 UPS-2 144 kva 90 kw 144 kva ASB(CUS) 110V UPS-3 ACELDB. 144 kva BUS-A(BOARD 5) BUS-B(BOARD 5) Lump6 Lump7 85 kva 85 kva Lump8 460 kva Lump9 Lump10 185 kva 185 kva CB112 CB111 BUS-A(BOARD 6) CB110 BUS-B(BOARD 6) CB81 CB77 CB76 CB78 CB79 CB80 CB88 BUS 66 LT HEAT-1 MHU-1 RCC CTID-1 RCC CTID-2 RCC CTID-3 55 kw CB90 CB82 CB83 CB84 CB85 CB86 CB87 CB89 BUS 67 MHU-2 LT HEAT-2 RCC CTID-4 Mtr1 55 kw 75 kw RCC CTID-6 CB115 CB113 CB114 CB120 CB121 BOIL-2 LUBE-3 90 kw CB116 CB119 BOARD 8 CB118 CB117 BOIL-3 BOIL-2. 220V DC-2 BOIL-3. LUBE-4 220V DC-1 CB122 90 kw Lump4 235 kva Lump5 235 kva Lump11 BUS-A(BOARD 7) 542 kva BUS-B(BOARD 7) Lump12 125 kva CB123 Lump13 125 kva Fig. 1. Single line diagram 512 511
III. SHORT CIRCUIT ANALYSIS AND ITS RESULTS Fault level (short circuit) analysis are used to determine both maximum and minimum three phase faults and earth fault level at all switch boards under fault make and fault break conditions including the dc component [3]. Types of short circuit faults are line to ground (LG) fault, line to line (LL) fault, double line to ground (LLG) fault, three phase (LLL) fault and three phase to ground (LLLG) fault. IEC standards use the following definitions, which are relevant in the calculations and outputs of ETAP for Short circuit analysis. Initial Symmetrical Short Circuit Current (I K): This is the RMS value of the AC symmetrical component of an available short circuit current applicable at the instant of short circuit if the impedance remains at zero time value. Peak Short Circuit Current (I p): This is the maximum possible instantaneous value of the available short circuit current. Symmetrical Short Circuit Breaking Current (I b): This is the RMS value of an integral cycle of the symmetrical AC component of the available short circuit current at the instant of contact separation of the first pole of a switching device. Steady-State Short Circuit Current (I k): This is the RMS value of the short circuit current, which remains after the decay of the transient phenomena. Voltage Factor (c): This is the factor used to adjust the value of the equivalent voltage source for minimum and maximum current calculations. A. CALCULATION METHODS Initial Symmetrical Short Circuit Current Calculation: Initial symmetrical short-circuit current (I k ) is calculated using the following formula: I cu '' n k = (1) 3Z k Where, Z k is the equivalent impedance at the fault location. Peak Short Circuit Current Calculation: Peak shortcircuits current (i p) is calculated using the following formula: i = (2) p '' 2kI k Where, k is a function of the system R/X ratio at the fault location. In this paper, we considered three faults i.e., LG, LLG and three phase faults at randomly considered buses. The following table I gives the short circuit fault current at different buses. TABLE I. Fault currents at different buses considering LG Fault FAULTED BUS VOLTAGE (KV) FAULT CURRENT (KA) 33KV BUS-A 19.76 32.07 6.6KV BUS-A (BOARD 1) 6.55 0.63 415V BUS-A (BOARD 1) 0.26 41.09 415V BUS-B (BOARD 3) 0.25 37.97 415V BUS-B (BOARD 6) 0.25 38.32 TABLE II. Fault currents at different bus considering LLG Fault FAULTED BUS VOLTAGE (KV) FAULT CURRENT (KA) 33KV BUS-A 19.67 31.9 6.6KV BUS-A (BOARD 1) 5.64 0.311 415V BUS-A (BOARD 1) 0.26 37.26 415V BUS-B (BOARD 3) 0.25 35.93 415V BUS-B (BOARD 6) 0.26 36.1 TABLE III. Fault currents at different bus considering LLL Fault FAULTED BUS FAULT CURRENT (KA) 33KV BUS-A 33.1 6.6KV BUS-A (BOARD 1) 25.9 415V BUS-A (BOARD 1) 46.1 415V BUS-B (BOARD 3) 40.5 415V BUS-B (BOARD 6) 41.1 IV. TRANSIENT STABILITY ANALYSIS When subjected to a disturbance, the ability of a system to return back to its steady state without losing synchronism is known as system stability [4]. Power system stability is classified as follows: The steady state stability of a power system is defined as the ability of the system to bring itself back to its stable configuration following a small disturbance in the network [7]. 513 512
Dynamic stability is defined as the ability of a power system to maintain stability under continuous small disturbances. It is also known as small signal stability. Fig. 4. Speed Fig. 2. Power system stability classification Transient stability is defined as the ability of the system to reach a stable condition following a large disturbance in the network condition. The large disturbances are sudden removal or addition of load or generator, line losses and short circuit faults [8]. V. SIMULATION RESULTS Transient stability analysis is analyzing whether the system is stable under severe disturbances or it loses synchronism or not during the different fault conditions [5]. In this paper we considered three different cases which are three phase fault at 33 KV bus board, single line to ground fault at 6.6 KV bus board and sudden removal of a generator. First we are applying a three phase fault at 33 KV bus board at 0.5 sec and the fault is clearing at 5 sec. This process will continuous till it becomes stable. And we will get the critical clearing time [6] as 240 msec. The simulation results for this condition are shown in fig. 3 to fig 5. Fig. 5. Real power Now we are applying a single line to ground fault at 6.6 KV bus board at 0.5 sec and the fault is clearing at 5 sec. This process will continuous till it becomes stable. And we will get the critical clearing time as 2 sec. The simulation results for this condition are shown in fig. 6 to fig 8. F Fig. 6. Power angle Fig. 3. Power angle 514 513
F Fig. 7. Exciter current Fig. 10. Voltage angle Fig. 8. Real power Now we are removing a generator (GTG1) at 1 sec and the load is removing by opening a circuit breaker at 5 sec. This process will continuous till it becomes stable. And we will get the critical clearing time as 1 sec. The simulation results for this condition are shown in fig. 9 to fig 11. Fig. 11. Frequency VI. CONCLUSION Thus, in this paper, we have modeled the combined cycle power plant in the ETAP software. ETAP is very helpful to reduce the malfunctioning of network and to increase the efficiency of the system by operating proper relay coordination within less time. The transient stability studies are used to determine system electrical frequency, speed deviations, real and reactive power flows of the machines, the machine power angles as well as the voltage levels of the buses and power flows of lines and transformers in the system. Transient stability analysis has been performed on ETAP software. The maximum allowable value of the clearing time for which the system remains to be stable i.e., Critical Clearing Time (CCT) is calculated for a given fault. System frequency and voltage is analyzed for different loading conditions and faults on busses. Fig. 9. Real power loading 515 514
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