An Efficient Load Shedding Scheme from Customer s Perspective

Transcription

1 Internatinal Jurnal f Advanced Research in Electrical, Electrnics and Instrumentatin Engineering (An ISO 3297: 2007 Certified Organizatin) Vl. 2, Issue 10, Octber 2013 An Efficient Lad Shedding Scheme frm Custmer s Perspective A.S.M. Abdullah 1, Md. Bayejed Bstami 2, Md. Tanvir Yeasin 3 & Md. Hasibur Rahman 4 Graduated, Dept. f EEE, Ahsanullah University f Science & Technlgy, Bangladesh 1,3 Graduated, Dept. f ECE, Khulna University, Bangladesh 2 Graduated, Dept. f EEE, Bangladesh University f Engineering & Technlgy, Bangladesh 4 ABSTRACT:The safe peratin f electrical pwer systems is an n-ging prblem. Despite the existing defence lines in the different electrical systems, they are nt immune t widespread incidents leading t tripping f mst custmers. In the defence plans against these majr incidents, selective lad shedding, even ptimized but brutal, is the last resrt befre ttal shutdwn. This paper addresses a new pwer system cntrl strategy frm custmer s perspective. Due t pwer deficit we ve t shed sme amunt f lads eventually. Nw the main challenge is t determine the minimum lad amunt fr shedding s that we can maximize the electricity supply t custmers. Using cntrl algrithm we ll find ut that minimum amunt f lad. Keywrds:Minimum Lad, Cntrl Algrithm, Pwer Deficit I. INTRODUCTION During pwer deficit, ne f the main peratr s tasks is t keep as many custmers n-line as pssible. The rise in need is very steep fr the reasns f rise in electrical utility appliances which is nw the rder f the day. S the develping cuntries where there is free market cannt ratin the usage f electrical appliances. This has steeply increased the necessity. The efficient lad shedding means t imprve pwer system stability, by prviding a real time adapted lad cntrl and lad shedding, in situatins where the pwer system therwise wuld g unstable. The main aspects are evaluating the right amunt and lcatin f pwer respnse fr a given disturbance and evaluating the right time respnse expected in rder t cmply with the acceptable stability recver. Blcking can be viewed as if the pwer exchanges were nt cntrlled. Sme lines lcated n particular paths may becme verlad and this phenmenn is called blcking. Blcking management can be defined as the quick peratins taken by the technical persns t relieve the prblem. One such apprach is efficient lad shedding. If excessive lad shedding in the system is dne, there will be sudden change in the system vltage prfile that causes transients in the system. II. FUNDAMENTALS OF LOAD SHEDDING The data s frm the substatin are taken and with these an idea fr ptimum lad shedding is arrived using different standard algrithm. The belw are the cnventinal lad shedding methdlgies fllwed by the utility prviders. 1. Breaker Interlck Lad Shedding This is the simplest methd f carrying ut lad shedding. Fr this scheme, the circuit breaker interdependencies are arranged t perate based n hard wired trip signals frm an intertie circuit breaker r a generatr trip. This methd is ften used when the speed f the lad shedding is critical. Even thugh its executin is fast but it has few drawbacks. 2. Under Frequency relay Lad Shedding Guidelines fr setting up a frequency lad shedding are cmmn t bth large and small systems. Upn reaching the frequency set pint and expiratin f pre-specified time delay, the frequency relay trips ne r mre lad breakers. This cycle is repeated until the system frequency is recvered. e.g., 10% lad reductin fr every 0.5% frequency reductin. 3. Prgramming based Lad Shedding With a prgrammable lgic cntrller scheme, lad shedding is initiated based n the ttal lad versus the number f generatrs nline r detectin f under-frequency cnditins. Each substatin PLC is prgrammed t initiate a trip Cpyright t IJAREEIE

2 Internatinal Jurnal f Advanced Research in Electrical, Electrnics and Instrumentatin Engineering (An ISO 3297: 2007 Certified Organizatin) Vl. 2, Issue 10, Octber 2013 signal t the apprpriate feeder breakers t shed a preset sequence f lads. This static sequence is cntinued until the frequency returns t a nrmal, stable level. III. PROPOSED METHODOLOGY Till nw there is n standard lad shedding methds implemented in Bangladeshi pwer grid peratins. Decisin fr lad shedding will be taken using cnventinal pwer flw calculatins at centralized lad centres and it will be cmmunicated t lcal r sub lad centres where it will be implemented. The lad shedding scheme mainly has included the measurements f imprtant parameters fr estimating the magnitude f disturbance. The initial estimatin f the disturbance is based n the rate f change f frequency. The lcatin f lad t be shed and the amunt t be shed frm each bus is calculated by the empirical frmula. Here we ll use Fuzzy Lgic as cntrl algrithm t find ut the minimum lad amunt t be shed. IV. PROCEDURES FOR LOAD SHEDDING The data s which are respnsible fr system transients are cllected firstly. Fr ur cnsideratin, the data s frm Rampura substatin is cllected and used fr lad shedding. The ranges f vltage, frequency, pwer is taken here. After the data s are cllected it is cnverted t per unit basis, if it nt s. Create a table and enter the values f vltage, frequency, pwer. The value f reactive pwer is cnsidered here. Nw change in vltage and frequency with respect t time is calculated fr calculatin purpse. The amunt f lad shedding is calculated by using the frmula, S= ((dv/dq) / ( dv/dq)) pdiff. Where, S= lad t be shed. dv = change in vltage w.r.t time. dq = change in pwer w.r.t time. Pdiff= pwer difference. T calculate the pdiff value, Pdiff= (2H/f) (df/dt). Where, H= inertia cnstant (5sec). f= nminal frequency After calculatin the amunt f lad t be shed is knwn. Nw a new clumn in which lad t be shed and in anther the pdiff values are entered. Frm the table the minimum and maximum ranges f values f each variable is calculated t create the membership functin. Nw membership functin is created fr vltage, frequency, pdiff, reactive pwer by dividing the ranges int 3 categries, fr simple calculatin. Membership functin fr this cnsideratin is LOW, MEDIUM, HIGH. Find the crrespnding values in table. Create rules based n membership functin. (if-then rule) Create a fuzzy linguistic cntrl table. Apply the values in fuzzy MATLAB sftware and create the rules frm the table. It must be nted that the rules which we create must radis must satisfy all the values within given range Fr ur given value the amunt f lad shed is displayed Nw if we cmpare the utput with the cnventinal methds f lad shedding it will be minimum nly. Cpyright t IJAREEIE

3 Internatinal Jurnal f Advanced Research in Electrical, Electrnics and Instrumentatin Engineering (An ISO 3297: 2007 Certified Organizatin) Vl. 2, Issue 10, Octber 2013 V. FLOW CHART FOR LOAD SHEDDING VI. MEMBERSHIP FUNCTION CREATION Let each variable and the lad shedding amunt, s, be distinguished by three linguistic terms: LOW (L), MEDIUM (M), HIGH (H). After analysis and frm bservatin, the fllwing linguistic rules describing the lad-shedding amunt at substatin can be frmed. The membership functin is created by cnsidering the min and max ranges f the variables and dividing each int 3 equal values and classifying each by the name lw, medium, high as we mentined earlier. Table 1: Lad s Data S.N. Vltage Reactive pwer Frequency Cpyright t IJAREEIE

4 Internatinal Jurnal f Advanced Research in Electrical, Electrnics and Instrumentatin Engineering (An ISO 3297: 2007 Certified Organizatin) Vl. 2, Issue 10, Octber Table 2: Rate f Change S.N. dv/dt dq/dt df/dt Cpyright t IJAREEIE

5 Internatinal Jurnal f Advanced Research in Electrical, Electrnics and Instrumentatin Engineering (An ISO 3297: 2007 Certified Organizatin) Vl. 2, Issue 10, Octber dv/dt=0.441 dq/dt=19.63 Table 3: Lads t be shed S.N Pdiff Lad t be shed Cpyright t IJAREEIE

6 Internatinal Jurnal f Advanced Research in Electrical, Electrnics and Instrumentatin Engineering (An ISO 3297: 2007 Certified Organizatin) Vl. 2, Issue 10, Octber The range f vltage value is selected and the membership functin is created within that range by dividing the difference value f max and min value by 3. Nw the value is added with the least (min) value t find the first membership functin. With the first membership value the divided value is again added t frm the secnd membership functin and s n. Nw the lgic table cnsidering range in the table fr abve data. Input1 Vltage Input2 r.pwer Fuzzy Lgic Table Input3 freq Input4 pdiff utput lad shed medium( ) medium( ) high( ) lw(0-0.12) lw(0-0.68) lw( ) medium( ) high( ) lw(0-0.12) lw(0-0.68) high( ) high( ) medium( ) lw(0-0.12) medium( ) high( ) lw( ) medium( ) medium( ) medium( ) lw( ) medium( ) lw( ) high( ) high( ) Generatin Data S.N Vltage r.pwer frequency Rate f Change S.N dv/dt dq/dt Cpyright t IJAREEIE

7 Internatinal Jurnal f Advanced Research in Electrical, Electrnics and Instrumentatin Engineering (An ISO 3297: 2007 Certified Organizatin) Vl. 2, Issue 10, Octber 2013 Lads t be shed S.N Pdiff Lad t be shed Lgic table cnsidering range in the table fr abve data. Input1 Vltage Fuzzy Lgic Table Input2 freq Input3 pdiff utput lad shed lw( ) lw( ) lw( ) lw( ) lw( ) lw( ) high( ) medium( ) medium( ) medium( ) medium( ) lw( ) high( ) high( ) medium( ) lw( ) high( ) lw( ) high( ) high( ) lw( ) high( ) lw( ) lw( ) Simulatin Result Cpyright t IJAREEIE

8 Internatinal Jurnal f Advanced Research in Electrical, Electrnics and Instrumentatin Engineering (An ISO 3297: 2007 Certified Organizatin) Vl. 2, Issue 10, Octber 2013 Transfrmer Data Transfrmer Specificatin Tap Setting Per Unit VII. COMPARATIVE RESULT S.N. Vltage Frequency Lad t be shed (Cnventinal) Lad t be shed(fuzzy) VIII. CONCLUSION Frm the cmparisn it is clear that fuzzy scaling f critical parameters and writing the fuzzy linguistic rules prperly, has clearly given fd results. The amunt f lad t be shed is minimized. This methd has been develped frm the data s btained frm the substatin and the discussins with the field engineers. It is a lgical thught by sme ways and means the lad shedding has t be minimized. Even thugh lad shedding is the last resrt and practically fllwed methd t relieve blcking, there is a cnstant urge bth frm field engineers and academic circle t analyze and find sme ways t minimize the lad shedding. In that regard this wrk can be respected. By building rbust electrnics in such a Way that the fuzzy utputs are tuned t an fuzzy cntrller which is again gverned by anther cntrl device with feedback system and data acquisitin system t mnitr the bus parameters, when this frms a rbust lp, this idea can be tested and if the results are satisfactry this can be implemented in distributin substatins. REFERENCES 1. Micrsft StreamInsight. [Online]. Available: 2. Rss, T. J., Fuzzy Lgic with Engineering Applicatins, secnd editin, Jhn Wiley and Sns, Ltd, West Sussex, England, Thmpsn J. G., and B. Fx, "Adaptive Iad shedding fr islated pwer sfiem.3," 1EEPrc.-Gener. T r a m. Distrib.,VI. 141, N. 5, pp , Sep Vladimir V. Terzija," Adaptive Under- frequency Lad Shedding Based n the Magnitude f the Disturbance Estimatin", IEEE TRANS. ON POWER SYS., VOL. 21, NO. 3, AUG Yng Zheng and N. Chwdhury, Expansin f Transmissin systemsin a deregulated envirnment, IEEE Canadian Cnference n Electrical and Cmputer Engineering, Vl.4, May 2-5, 2004, pp Yng Zheng and N. Chwdhury, Expansin f Transmissin systems in a deregulated envirnment, IEEE Canadian Cnference n Electrical and Cmputer Engineering, Vl.4, May 2-5,2004, pp Cpyright t IJAREEIE