An Approach to Quantify the Loss Reduction due to Distributed Generation

Transcription

1 nternatonal Journal of Computer Applcatons ( ) Volume 5 No.17, August 01 An Approach to Quantfy the Loss Reducton due to Dstrbuted eneraton S B Karajg Department of Electrcal Engneerng S.D.M. College of Engneerng and Technology, Dharwad,nda Udaykumar R. Department of Electrcal Engneerng Natonal nsttute of Technology Karnataka, Surathkal,nda ABSTRACT Lne Loss Reducton s one of the major benefts of Dstrbuted eneraton, amongst many others, when ncorporated n the Power Dstrbuton System. The quantum of the lne loss reducton should be exactly known to assess the effectveness of the dstrbuted generaton. n ths paper, the total loss of a practcal dstrbuton system s calculated wth and wthout dstrbuted generaton and an ndex, quantfyng the total lne loss reducton s proposed. Smulaton tests have been carred out on a practcal dstrbuton system and the proposed ndex s evaluated for varous ratngs, locatons of dstrbuted generaton. Keywords Dstrbuted eneraton, System Loss Reducton ndex. 1. NTRODUCTON The presence of Dstrbuted eneraton (D) has been shown to be benefcal n many respects lke voltage profle mprovement, lne loss reducton, mprovement n relablty etc. [1]-[5]. The evaluaton of these benefts s very crtcal n assessng the mert of D. The quantfcaton of the beneft of lne loss reducton was proposed n [6], whch evaluated the lne losses both wth and wthout D and the beneft ndex was defned as the rato of lne loss wth D and that wthout D. The subsequent researches [7]-[10], also defned the quantfcaton n a smlar way and the benefts of D were defned. These works, however, consdered only the losses n the lnes and the quantfcaton was defned for the lne losses only. These ndces, therefore, do not ndcate the loss reducton of the system tself. A practcal dstrbuton system conssts of several dstrbuton transformers, supplyng consumers at low voltage on the secondary sde. The losses occurrng n these transformers and the lne losses of the secondary low voltage dstrbuton system should also be consdered to arrve at the overall loss reducton of the system. n ths paper, a practcal dstrbuton system, supplyng a number of consumers at low voltage, s consdered. The losses occurrng n the transformers and the low voltage dstrbuton lnes have been consdered and the beneft of D n respect of total loss s evaluated.. DESCRPTON OF THE SSTEM A smple dstrbuton system shown n fg 1, s consdered for analyss. The system conssts a number of dentcal dstrbuton transformers, the secondary of whch supply power to the consumers at low voltage. The core loss 0f each transformer s represented by Pc. Subst aton Fg 1: The sngle lne dagram of a standard dstrbuton system. For smplcty, the followng assumptons are made. All loads are modeled as constant current loads, drawng the same current rrespectve of the respectve voltages. The core losses of the transformers reman constant at a value dependng on the ratng. All loads draw the power at a power factor of 0.8 laggng. D unt s capable of supplyng power at both leadng and laggng power factors. The copper losses of the dstrbuton transformer are of small value and are neglected 3. LOSS REDUCTON ANALSS The total loss of the dstrbuton system wthout D s gven by To loads 13

2 nternatonal Journal of Computer Applcatons ( ) Volume 5 No.17, August 01 N 1 N 1 Loss Syst w/o D = rl PC PLV 1 (1) 1 Where s the current flowng through th segment,l s the length of th segment, r s the resstance of lne n ohms per unt length., s the core loss of th transformer, s the Losses on the low voltage sde of the th transformer and N s the number of busses n the system. n order to determne the losses of the system, the core loss of each transformer and the LV sde losses on each transformer must be known. t s evdent from the above equaton that the total losses can be reduced only by reducng the frst term of equaton (4.1) whch represents the feeder lne losses, snce the other term representng the core loss and the LV sde loss of each transformer reman same ndependent of the presence of D. Wth the ncluson of D, the currents n the feeder segments wll be redstrbuted. f a D unt s nserted at K th bus, the feeder segments up to bus K wll carry the dfference of the ntal current and the njected current by the D unt. The segments beyond K wll contnue to carry the same currents. The total loss of the feeder wth D s the gven by Loss Feed w D = K 1 N 1 ) rl 1 K ( rl () Where s the current njected by the D unt and remans the same at earler value. The total loss of the dstrbuton system wth D s now Loss SystwD = K 1 1 N 1 K N 1 PC PLV ( ) rl rl (3) 1 A factor, System Loss Reducton ndex (SLR), whch quantfes the loss reducton wth the nserton of D s defned as SLR = Loss n the system wth D Loss n the system wthout D = K 1 1 ( ) rl N 1 K rl N 1 PC PLV 1 K 1 N 1 ) rl 1 K ( rl (4) The dstrbuton system loss can be rewrtten as Loss SyswD = K 1 N 1 N 1 rl rl PC PLV 1 K 1 K 1 N1 N1 = ( ) rl rl PC PLV (5) Substtutng equaton () n equaton (5) we get Loss SystwD = Loss Systw/o D + ( ) (6) On smplfcaton, followng equaton s obtaned K 1 1 Loss Syst w D = Loss Syst w/o D + = Loss Syst w/o D + K loss (7) Where K loss s the loss factor gven by K 1 1 K loss = rl rl (8) The SLR s now obtaned as SLR = = Loss Syst w/o D + K loss (9) Loss Syst w/o D f SLR < 1, the D has reduced the losses and s benefcal = 1the D has not made any changes n the system. 1, the D has ntroduced more losses n the system. t s clear from equaton (9) that the loss factor K loss must be negatve f D s expected to reduce the losses n the system. Snce the loss factor depends on the summaton of the dfference between the njected D current and twce the feeder segment current, t attans maxmum negatve value when t s nstalled at the remote end N. 14

3 nternatonal Journal of Computer Applcatons ( ) Volume 5 No.17, August 01 The Loss factor and thus the SLR are greatly nfluenced by the power factors of the D unt. n case the unt s operatng at unty power factor, all the reactve power requred by the load s suppled by the source and hence the there may not be any apprecable decrease of lne current suppled by the source leadng to hgher losses and thus low SLR. 4. SMULATON TESTS A practcal 36 bus, 11 KV dstrbuton feeder shown n fg, s consdered. The system conssts of 35 dstrbuton transformers wth varous ratngs. The detals of the dstrbuton transformers are gven n table 1. The base MVA used n the study s 5 MVA. The conductor used s Rabbt wth resstance of pu/km and reactance of pu/km. The lengths of the feeder segments are gven n table. The total connected load on the system s 300 KVA and the peak demand for the year s 000 KVA at a pf of 0.8 lag. The connected loads on the transformers are lsted n table 3. The system conssts of two D unts descrbed below. 1. D1, of ratng 70 KW, connected at No 6, shown wth arrow mark n the fg... D, of ratng 800 KW connected at No 41, shown wth arrow mark n fg. Table 1. Detals of transformers n the system Fg : Sngle lne Dagram of the dstrbuton system 11 KV MUSS Table. Dstrbuton System Lne Data from To Ratng (KVA) Number No Load Losses (Watts) % mpedance Length (mtrs) From To Length (mtrs) From To Length (mtrs)

4 nternatonal Journal of Computer Applcatons ( ) Volume 5 No.17, August 01 Table 3. Detals of the connected loads. Transformer Load n Transformer Load No KVA No KVA n Specfc cases consdered for study: The mpact of D n respect of Lne Loss mprovement s studed wth and wthout D n the system. The operatng power factor of D1 s kept constant at unty and that of D s vared from 0.8 lag, 0.9 lag, unty, 0.9 lead and 0.8 lead. Whle carryng out the tests, the followng assumptons are made METHOD OF STUD Followng steps are followed to evaluate the mpacts of D on the system loss reducton and also to quantfy the proposed ndex. All the loads draw power at 0.8 laggng. The loads on the low voltage sde are dstrbuted over lne of length 300 mtrs. The core losses of the transformers reman constant at ther rated value. 6. RESULTS The smulaton results are gven n fgure 3. These results reveal that the ncluson of D reduce the lne losses as expected. t can be shown from the graphs that, SLR decreases margnally, snce the core losses of the transformers and the LV sde losses reman constant beng ndependent of the presence of D. Ths s an mprovement over the ndex derved n [6], whch consdered only the feeder lne losses. t can also be seen that wth the ncrease n the D output, SLR, decrease but agan show an ncreasng trend after a threshold value e.g. as the power output s ncreased the SLR starts ncreasng as shown n fg.4. Ths s because the system receves more power from D than requred and hence the lne loss ncrease apprecably. Ths should be consdered before fxng up the value of D output. Under such a case, one D unt can be swtched off so that the advantage of lower SLR can be enjoyed. The power outputs of both D1 and D are fxed. The detals of the dstrbuton system are collected and the system s smulated usng CMEDST computer smulaton program and the D unts are ncorporated n the smulated system. Load flow studes are conducted for all the specfed cases and the results are obtaned. The results are analyzed and the mpacts of D on the loss reducton are evaluated. The operatng power factor of D also nfluences the SLR. t s very clear from the fg 5 that SLR has lower values wth D operatng at laggng power factor and ncrease under leadng power factor. Ths s because the D unt absorbs reactve power from the lnes under leadng power factor. Further, t can be seen that the ndex may exceed unty, ndcatng that the presence of D has ncreased the lne losses than decreasng t. Ths factor should be consdered whle fxng the operatng power factor of D. The varaton of loss factor s shown n fg. 6. t s clear from the fgure the Loss Factor remans farly constant and hence 16

5 SLR SLR Loss factor SLR SLR nternatonal Journal of Computer Applcatons ( ) Volume 5 No.17, August 01 the loss reducton depends manly on the current njected by the D unt. When s more than L, loss factor becomes postve and the total losses n the system ncrease, leadng SLR to acqure a value greater than one. The locaton of D s also very crtcal n decdng the loss reducton. t s evdent from fgure 7, that SLR show a decreasng trend when D s located away from the substaton. Ths ssue should be consdered before nstallng D n the system D Output (pu) 0.95 Fg 5: Varaton of SLR wth hgh penetraton of D D Output (pu) -0. Fg 3: Varaton of SLR wth D Output D Output (pu) 1.05 Fg 6: Varaton of Loss Factor wth D output D connected at 6 D connected at Lag 0.9 Lag UPF 0.9 Lead 0.8 Lead Operatng power factor of D D Out put (pu) Fg 4: Varaton of SLR wth operatng power factor of D Fg 7: Varaton of SLR wth the same D connected at two dfferent locatons. 17

6 nternatonal Journal of Computer Applcatons ( ) Volume 5 No.17, August CONCLUSON The smulaton results show that the ncluson of D, margnally reduce the losses n a dstrbuton system. Ths s because; the lne losses form only a mnor part of the dstrbuton system losses and the D can reduce only the lne losses. The other losses vz. the transformer losses and the LV sde dstrbuton losses reman unaltered. Hence ths fact should be consdered before nstallng a D nto a system. 8. REFERENCES [1] T. Ackermann,. Andersson, and L. Soder, Dstrbuted generaton: A defnton, Elect. Power Syst. Res., vol. 57, pp , 001. [] N. Hadjsad, J. Canard, and F. Dumas, Dspersed generaton mpact on dstrbuton networks, EEE Comput. Appl. Power, vol. 1, no., pp. 8, Apr [3] Peter. Daly, Understandng the potental Benefts of D on Power Delvery System, a paper presented at Rural Electrc Power conference 001, Lttle Rock, Arkansas, 001. [4] Ahmed Azmy, mpact of D on the Stablty of Electrcal Power Systems,, EEE Trans. On Power Delvery, 005, pp 1 8 [5] E. Vdyasagar, P.V.N.Prasad, mpact of D on Radal Dstrbuton System Relablty, n 15th Natonal Power System Conference Conference (NPSC), T Bombay 008, pp [6] P. Chradeja, Beneft of dstrbuted generaton: A lne loss reducton analyss, n Proc. EEE-Power Eng. Soc. Transmsson and Dstrbuton Conf. Exhb.: Asa and Pacfc, Dalan, Chna, Aug , 005. [7] Chradeja, Ramkumar, An Approach to quantfy the Benefts of Dstrrbuted eneraton Systems, EEE trans. On Energy Converson, Vol. 19, Dec 004, pp [8] M.A.Kashem, M.Negnevtsky,.Ledwch, " Dstrbuted eneraton for mnmzaton of power losses n dstrbuton systems ", EEE conference 006 [9] Hugo A. l, eza Joos, Models for Quantfyng the Economc Benefts of Dstrbuted eneraton, EEE TRANSACTONS ON POWER SSTEMS, VOL. 3, NO., MA 008,pp [10] A.Kazem, and M.Sadegh, Sttng and Szng of Dstrbuted eneraton for Loss Reducton, Proc. Of Power and Energy Engneerng Conference, APPEEC, 009, Asa-Pacfc, pp