Voltage Flicker Analysis and its Mitigation by STATCOM for Power Quality Improvement

Transcription

1 Voltage Fliker nalysis and its Mitigation y STTOM for Power Quality Improvement Mekathoti Ravi Kumar Dr. D. Ravi Kishore 2 PG Sholar(HVE),Department of EEE,Godavari Institute of Engineering and Tehnology, Rajahmundry. 2Professor & Head,Department of EEE,Godavari Institute of Engineering and Tehnology,Rajahmundry. STRT Voltage fliker is onsidered as one of the most severe power quality prolems (espeially in loads like eletrial ar furnaes) and muh attention has een paid to it lately. The reason for this disturane is mainly due to the large nonlinear loads suh as eletri ar furnaes. Due to the latest ahievements in the semiondutors industry and onsequently the emergene of the ompensators ased on voltage soure onverters, FTS devies have een gradually notied to e used for voltage fliker ompensation. This paper overs the ontrasting approahes; dealing with the voltage fliker mitigation in three stages and assessing the related results in details. Initially, the voltage fliker mitigation, using FTR (Fixed apaitor Thyristor ontrolled Reator), was simulated. Seondly, the ompensation for the Stati Synhronous ompensator (STTOM) has een performed. The voltage fliker ompensation y 8 pulse as well as 2 pulse stati synhronous ompensator (STTOM) has een performed. This paper deals with the voltage fliker mitigation and redution in total harmoni distortion (THD) and ompared the results in detail. The otained results show that STTOM is very effiient and effetive for the ompensation and mitigation of voltage fliker and harmonis all the simulation results have een performed on the MTL Software. KEYWORDS: Power Quality, Voltage Fliker, Mitigation, STTOM opyright 26 International Journal for Modern Trends in Siene and Tehnology ll rights reserved. I. INTRODUTION Some industry proesses suh as indution and ar furnaes, ar rushers, mine mahinery, and others present large flutuating loads to the supply. These flutuations ause small variations on the supply voltage at the point of ommon oupling to other users. While the voltage variation may not e large in magnitude it is suffiient to ause the output of eletrial lights to flutuate or fliker. This effet an ause signifiant annoyane to other users and must e kept elow the threshold of awareness []. The solution lies in the use of high speed IGT inverter ased shunt onneted voltage regulators. inverter ased ative VR soure is effetive in omating fliker eause it an modulate the urrent flowing in the supply very quikly at suffiient sale to reate a orretion voltage on the supply impedane [2]. The inverter will update the urrent flow many times per yle giving effetive ontrol. It an also manage the availale VRs to optimise the PST (rather than just the % variation) and to limit the impat on protetion systems fault urrents [3-6]. II. OJETIVE OF THE PPER The auses of power quality prolems are generally omplex and diffiult to detet. Tehnially speaking, the ideal line supply y the utility system should e a pure sine wave of fundamental frequeny (5/6Hz).Different power quality prolems, their haraterization methods and possile auses are disussed aove and whih are responsile for the lak of quality power whih affets the ustomer in many ways. We an therefore onlude that the lak of quality power an ause loss of prodution, damage of equipment or applianes or an even e detrimental to human health [7-8]. It is therefore imperative that a high standard of power quality is maintained. This projet demonstrates that the power eletroni 6 International Journal for Modern Trends in Siene and Tehnology

2 Voltage Fliker nalysis and its Mitigation y STTOM for Power Quality Improvement ased power onditioning using ustom power devies like DSTTOM an e effetively utilized to improve the quality of power supplied to the ustomers. The aim of the projet is to implement DSTTOM with different ontrol strategies in the MTL, simulink using Simpower systems tool ox and to verify and ompare the results through various ase studies applying different loads and study them in detail [9]. The term fliker is sometimes onsidered synonymous with voltage flutuations, voltage fliker, light fliker, or lamp fliker. The phenomena eing referred to an e defined as a flutuation in system voltage that an result in oservale hanges (flikering) in light output. eause voltage fliker is mostly a prolem when the human eye oserves it, usually it is onsidered to e a prolem of pereption. There are, however, rare ases where voltage fliker an affet equipment operation suh as eletri drives and UPS systems. Voltage fliker an e separated into two types: yli and nonyli. yli fliker is a result of periodi voltage flutuations in the system voltage, with nonyli referring to oasional voltage flutuations. n example of sinusoidal-yli fliker is shown in Figure.s shown in Figure, fliker is simply amplitude modulation where the main signal (6Hz for North meria) is the arrier signal and fliker is the modulating signal. The usual method for expressing voltage fliker is similar to that of amplitude modulation. Voltage fliker is usually expressed as a perent of the total hange in voltage with respet to the average voltage (ΔV/V) over a speified time interval []. Fig : Example Graph of Voltage Fliker. Soures of Fliker Typially speaking, voltage fliker ours on relatively weak systems with a low short-iruit ratio. This, in omination with onsiderale variations in line urrent over a short period of time, results in voltage fliker. s the load inreases, the urrent in the line inreases, thus inreasing the voltage drop aross line. This phenomenon results in a sudden redution in us voltage. Depending upon the hange in magnitude of voltage and frequeny of ourrene, this ould result in oservale amounts of voltage fliker. If a lighting load were onneted to the system in relatively lose proximity to the flutuating load, oservers would see this as a dimming (or flikering) of the lights. ommon situation whih ould result in voltage fliker would e a large plant loated at the end of a weak distriution feeder. ommon load whih often auses voltage fliker would e an eletri ar furnae (EF) or welder. EFs are non-linear, time-varying loads, whih often ause large voltage flutuations and harmoni distortion. Large indution mahines undergoing startup or widely varying torque hanges are also known to produe voltage flutuations on systems. s shown in Figure 3, as an indution mahine is started up, most of the power drawn y the motor is reative. This results in a large voltage drop aross distriution lines. Figure 4 demonstrates the affet on voltage of indution motor starting and torque variations. lthough starting large indution mahines aross-the-line is not onsidered to e a reommended pratie, it does however oasionally our. Generally, motors are rought up to speed using redued voltage starters or variale speed drives.. Interharmonis In ertain irumstanes, superimposed interharmonis in the supply voltage an lead to osillating luminous flux and ause light fliker. Voltage interharmonis are omponents in the harmoni spetrum that are non-integer multiples of the fundamental frequeny. This phenomenon an e oserved with inandesent lamps as well as with fluoresent lamps. Soures of interharmonis inlude stati frequeny onverters, yloonverters, su - synhronous onverter asades, indution mahines and ar furnaes. Fig 2 : General Fliker urve 7 International Journal for Modern Trends in Siene and Tehnology

3 Fig 3 : Real and Reative Power During Indution Mahine Startup III. INTRODUTION TO POWER QULITY If there is any deviation of voltage, urrent and frequeny at the load side then it is said to e power quality prolem. Due to these power quality prolems the performane of various sensitive loads is very poor. If we said that the power quality is good the voltage should e within permissile limits. The shape of the wave form should e pure sinusoidal. In all the three phases voltage should e same. Power supply should e onsistent i.e. unremitting availaility without reak. ontemporary industrial mahines and usiness-related omputer networks are lying fae down to many diverse failure modes. When the ongregation line stops, or the omputer network rashes for no ovious reason, very frequently the eletri power quality is suspeted. Power quality prolems may e very diffiult to trouleshoot, and often the eletri power may not have any relation to the atual prolem. Fig 4: Power quality and reliaility oth the reliaility and quality of supply are equally important. For example, a onsumer that is onneted to the same us that supplies a large motor load may have to fae a severe dip in his supply voltage every time the motor load is swithed on. In some extreme ases even we have to ear the lak outs whih is not aeptale to the onsumers. There are also sensitive loads suh as hospitals (life support, operation theatre, patient dataase system), proessing plants, air traffi ontrol, finanial institutions and numerous other data proessing and servie providers that require lean and uninterrupted power. In proessing plants, a ath of produt an e ruined y voltage dip of very short duration. Suh ustomers are very wary of suh dips sine eah dip an ost them a sustantial amount of money. Even short dips are suffiient to ause ontators on motor drives to drop out. Stoppage in a portion of proess an destroy the onditions for quality ontrol of produt and require restarting of prodution. Thus in this senario in whih onsumers inreasingly demand the quality power, the term power quality (PQ) attains inreased signifiane [3]. Transmission lines are exposed to the fores of nature. Furthermore, eah transmission line has its load aility limit that is often determined y either staility onstraints or y thermal limits or y the dieletri limits. Even though the power quality prolem is distriution side prolem, transmission lines are often having an impat on the quality of the power supplied. It is however to e noted that while most prolems assoiated with the transmission systems arise due to the fores of nature or due to the interonnetion of power systems, individual ustomers are responsile for more sustantial fration of the prolems of power distriution systems. IV. INTRODUTION TO FTS DEVIES Flexile Transmission Systems, alled FTS, whih are power eletronis devies. These devies have high ontrollaility in power system. There are several FTS devies whih are used to ontrol the power system. For the most part of the appliations the ontrollaility is used to avoid ost intensive [4]. FTS-devies provide a etter edition to hanging funtioning onditions and improve the usage of ative installations. The asi appliations of FTS devies are: Voltage fliker ompensation To ontrol Power flow, Inrease of transmission apaility, To Voltage ontrol, To ompensate the Reative power, To improve the Staility, For improvement of Power quality, For Power onditioning, Interonnetion of renewale and distriuted generation and storages. ording to IEEE FTS an e defined as Transmission Systems inorporating power eletroni devies other ontrollers (stati ontrollers) to improve the tive Power Transfer apaility and ontrollaility. Due to the inrease in industries day y day there is a hane to 8 International Journal for Modern Trends in Siene and Tehnology

4 Voltage Fliker nalysis and its Mitigation y STTOM for Power Quality Improvement inrease in power demand. This leads to inrease power system stailizers. Due to rapid growth of power system stailizers there are some disadvantages. Power outages and power interruptions are some of the prolems whih affet the ustomer as well as eonomy of any ountry. The aove onstraints affet the power quality. These prolems an e overome y improving the power system ontrol. FTS devies are one of the power system ontrollers to ompensate the power quality prolems. Figure 5 shows a numer of asi devies separated into the onventional ones and the FTS-devies [5]. Fig 5: Overview of FTS devies V. VOLTGE FLIKER Voltage fliker does not atually exist, though this term is often heard. When lamps produe flutuating light levels, and this is reognized y someone, we all this, light fliker, or simply, fliker. Fliker an e produed either y a prolem in the light soure or a flutuation in the soure voltage. If someone omplains of fliker, and it is aused y voltage flutuation, then its ause needs to e found. Sometimes fliker is aused y load flutuations in the ustomer s equipment near the flikering lamp. Suh prolems an often e easily solved. If not, investigation must e taken eyond the meter into the utility system. This usually ditates that the fliker must e ojetively measured. 4.. Fliker Meter Fliker produed y flutuating soure voltage is measured indiretly y a fliker meter. The modern fliker meter measures voltage flutuation and infers light fliker y taking into aount the following: how often the voltage flutuation ours, how aruptly the voltage flutuates, the kind of lamp, the sensitivity of the eye to light, and the rain s pereption. ll of these fators are modeled in a modern IEEE 453 ompliant fliker meter (this measurement is more omplex than simply measuring voltage flutuation and frequeny). Fig 6: Voltage Fliker output voltage waveform Fortunately, despite its internal omplexity, an IEEE fliker meter s output is simple: if the output is greater than., the fliker is generally irritale to humans; if less than., it is not. These results have een suessfully validated with many years of real-world testing in several ountries. The fliker meter s main output is in a unit alled Pst, meaning, Pereption of light fliker in the short term. Planned load harateristis should e otained diretly from the ustomer or equipment manufaturer. Gathering data for existing flutuations requires the use of a reording voltmeter having a time resolution smaller than the ourrene of the fliker. Many reording voltmeters do not have suffiient resolution to perform this task. VI. VOLTGE FLIKER OMPENSTION Voltage osillation was produed y a 3-phase fliker soure. The Studied power system with omplete STTOM ontrol and fliker soure sheme is shown in figure. STTOM is used to regulate voltage on a 69KV transmission Network. 44V load onneted to a us through a 69KV/44V transformer represents a plant asoring ontinuously harging urrents similar to an ar furnae, thus produing voltage fliker. The STTOM regulates the us 3 voltage through the leakage reatane of the 3-phase two winding transformers y generating a seondary voltage. Fig.7 Voltage Fliker ompensation urrent wave form 9 International Journal for Modern Trends in Siene and Tehnology

5 urrent in P.U Volatge In P.U a. ontrolling System The onept of instantaneous reative power is used for the ontrolling system. Following this, the 3-phase voltage upon the use of the park presented y kagi has een transformed to the synhronous referene frame (Park or dq transformation). This transformation leads to the appearanes of three instantaneous spae vetors: Vd on the d-axis (real or diret axis), Vq t h e q-axis (imaginary or quadrature axis) and V, from the 3-phase voltage of Va, V and V. The related equations of this transformation, expressed in the MTL software, are as follows: new tehnique ased on a novel ontrol algorithm, whih extrats the voltage disturane to suppress the voltage fliker, is presented in this thesis. The onept of instantaneous reative power is used for the ontrolling system. Following this 3Ø fliker voltage has een transformed to synhronous referene frame y the use of a to dqo transformation (Park s transformation). To implement the synhronous referene frame some kind of synhronizing system (phased looked loop) should e used. 3Ø system load voltage is the input to the phase loked loop (PLL), this PLL an e used to synhronize on a set of variale frequeny, and 3Ø sinusoidal signals.3ø PLL lok provides three outputs. Soure [Vaload] From7 VII. SIMULTION RESULTS Disrete, s = e-5 s powergui Va Ia a V-I Measurement a V-I Measurement Transformer (Two Windings) Fig.9.Simulink diagram of 2-pulse voltage soure onverter STTOM Va(pu) onn onn2 onn3 Susystem Vafl From6 Freq wt Sin_os Disrete 3-phase PLL 3 Out3 PI Setion Line a sin_os dq a_to_dq Transformation onstant Sope Out 2 Out2 Transformer (Two Windings) Sope dd Step Fig. ontrol iruit for 2-pulse voltage soure onverter STTOM PI Disrete PI ontroller Vafl From8 -T- -K- Gain N Programmale Voltage Soure alpha_deg Freq lok PY PD a Disrete Synhronized 2-Pulse Generator a Va Ia a V-I Measurement2 Vafl From5 V-I Measurement3 Sope4 Sope3 Goto Parallel RL Load Series RL ranh [s] Goto [s2] Goto2 [s3] Goto3 [s4] Goto4 [s5] Goto5 [s6] Goto6 [s2] Goto7 [s22] Goto8 [s23] Goto9 [s24] Goto [s25] Goto [s26] Goto Time(mes) Time(mses) Fig.8 lok diagram of the investigated power system The word data is plural, not singular. The susript for the permeaility of vauum µ is zero, not a lowerase letter o. The term for residual magnetization is remanene ; the adjetive is remanent ; do not write remnane or remnant. Use the word mirometer instead of miron. graph within a graph is an inset, not an insert. The word alternatively is preferred to the word alternately (unless you really mean something that alternates). Use the word whereas instead of while (unless you are referring to simultaneous events). Do not use the word essentially to mean Fig.. Output Voltage and urrent of FTR. ompensation y Four Leg Inverter The three-phase 8 pulse VS ased STTOM is shown in figure5 and figure6. There are swithes in the onverter eah onverter is made up of Thyristor/ MOSFET with a diode onneted in anti-parallel. In this type of STTOM, eah with is triggered and turn off one time per line voltage yle. In this ase, eah swith in a single ranh is onduted during a half-yle (8 degree) of the fundamental period. The omined pulses of eah leg have a 2 degrees phasedifferene to produe a alaned set of International Journal for Modern Trends in Siene and Tehnology

6 Mag (% of Fundamental) urrent in P.U Volatge in P.U Mag (% of Fundamental) urrent in P.U Voltage In Pu Voltage Fliker nalysis and its Mitigation y STTOM for Power Quality Improvement voltages. y ontrolling the triggering angle of the thyristor we an ontrol the generated voltage of the STTOM and also the asored/injeted power of the STTOM Time(mses) Fig 2.Output Voltage and urrent of Four Leg Inverter Time(mses) Frequeny (Hz) Fig.3 Output Voltage and urrent of Four Leg Inverter in THD. ompensation 2 Pulse VS-STTOM Fundamental (6Hz) =.44, THD= 2.77% Time(mses) Time(mses) Fig.4 Output Voltage and urrent of 2-Pluse Inverter.5..5 Fundamental (6Hz) =.9999, THD=.5% Frequeny (Hz) Fig 6. Output Voltage and urrent of 2-Pluse Inverter in THD VIII. ONLUSION In this paper, the appliation of three phase inverter tehnology ased on voltage-soure onverters for voltage fliker mitigation has een investigated and simulation results emphasized its signifiant effet. 6 pulse STTOM is dereasing the voltage fliker y 5 %. However, there is injetion of the harmoni from 6-pulse inverter into the system whih an e improved with the inrease of the voltage soure onverters of STTOM using a 2-pulse STTOM equipped with a harmoni filter. The otained results learly demonstrate that 2-pulse STTOM equipped with a harmoni filter an redue the voltage fliker ompletely and the output is otained with minimum THD value REFERENES [] J. Sun, D. zarkowski, Z. Zaar, Voltage Fliker Mitigation Using PWM-ased Distriution STTOM, IEEE Power Engineering Soiety Summer Meeting, Vol., (2-25 July 22), pp [2] N. G. Hingorani, L.Gyugyi, "Understanding FTS", IEEE Press. [3] Rozmyslaw, Miensik, Ryszard.pawelk, ppliation of STTOM ontrollers for powr quality improvement-modelling and simulation. IEEE Trans. (22), [4] L. Tang, S. Kolluri, M.F. MGranaghan, "Voltage Fliker Predition for Two Simultaneously Operated r Furnaes" IEEE Trans. on Power Delivery; Vol.2, No.2, (997), pp [5] M. Zouiti, S. Saadate, X. Lomard,. Poumarede,. Levillain Eletroni ased Equipment for Fliker Mitigation, Proeedings of International onferene on Harmonis nd Quality of Power, Vol.2, (998), pp [6] T. Larsson,. Poumarede, STTOM, an effiient means for fliker mitigation IEEE Power Engineering Soiety Winter Meeting, Vol.2, (Jan- 4Fe 999), pp [7]. S. hen, H. J. huang,. T. Hsu, S. M. Tsng, Stohasti Voltage Fliker nalysis and Its Mitigation for Steel Industrial Power Systems, IEEE Power Teh Proeedings, Vol., (-3 Sept. 2). [8] Z. Zhang, N. R. Fahmi, W. T. Norris, Fliker nalysis and Methods for Eletri r Furnae Fliker (EF) Mitigation ( Survey), IEEE Power Teh Proeedings, Vol., (-3 Sept. 2). [9] J. R. louston, J. H. Gurney, Field Demonstration of a Distriution Stati ompensator Used to Mitigate Voltage Fliker,IEEE Power Engineering Soiety Winter Meeting, Vol.2, (3 Jan-4 Fe 999), pp []. Elnady, W. El-khattam, M.. Salama, Mitigation of r Furnae Voltage Fliker Using the Unified Power Quality onditioner, IEEE Power Engineering Soiety Winter Meeting, Vol.2, (27-3 Jan. 22), pp [] S. Suzuki, Y. Hara, E. Masada, M. Miyatake, K. Shutoh, ppliation of Unified Flow ontroller for Power Quality ontrol at Demand Side, The Third International Power Eletronis and Motion ontrol onferene Proeedings (PIEM 2), Vol.3 (5-8ug 2), pp [2] Y. Hara, E. Masada, M. Miyatake, K. Shutoh, ppliation of Unified Flow ontroller for Improvement of Power Quality IEEE Power International Journal for Modern Trends in Siene and Tehnology

7 Engineering Soiety Winter Meeting, Vol.4, (23-27 Jan. 2), pp [3] T. Vijay Muni, K. Venkata Kishore, Experimental Setup of Solar-Wind Hyrid Power System Interfae to Grid System. International Journal for Modern Trends in Siene and Tehnology, Vol 2, Issue, January 26 [4] Vijayraj Patel, Mr mit grawal, and Dharmendra Kumar Singh. "n Improved UPQ ontroller to Provide Grid-Voltage Regulation.", International Journal for Modern Trends in Siene and Tehnology, Vol 2, no.5, pp.3-37, May 26. [5] L.V Narasimha. "Power Quality Improvement in a Grid onneted PV ell using UPQ with Fuzzy Logi ontroller.", International Journal for Modern Trends in Siene and Tehnology, Vol 2, no.2, pp.3-37, Fe International Journal for Modern Trends in Siene and Tehnology