Voltage Sag Classification with Consideration of Phase Shift

Transcription

1 First IEEE International Conferene on Energy Internet Voltage Sag Classifiation with Consideration of Phase Shift Pengfei Wei, onghai Xu State Key Laoratory of Alternate Eletrial Power System with Renewale Energy Soures (CEP) Beijing, China Qiaoqian Lan Jiading Power Supply Company of State Grid Shanghai Muniipal Eletri Power Company Shanghai, China Astrat Voltage sag has eome one of the major power quality onerns in reent years. To aurately evaluate the voltage sag, it is neessary to otain its sag type. In this paper, a more generalized voltage sag lassifiation method with onsideration of phase shift is proposed ompared to the traditional lassifiation method. This new method an e used in the aurate disrimination of sag types. Moreover, the effets of transformers on phase shift are studied on the asis of the proposed lassifiation method. Keywords-voltage sag; phase shift; lassifiation; disrimination; transformer I. ITRODCTIO Energy Internet is the produt of the deep integration of energy and Internet, whih has een widely onerned y aademia and industry. With the inreasing numer of sensitive equipment and the strit requirement of industrial proess in the Energy Internet System, voltage sag has aught muh attention in power system. As a result, a etter lassifiation method of voltage sags is needed in order to evaluate sags aurately. Phase shift is defined as the sudden hange in the voltage phase angle during voltage sags []. In reent years, the influene of voltage sags with onsideration of phase shift on sensitive equipment has aused onern, moreover, phase shift has een disussed as one of the sag harateristis. There are two main methods in the lassifiation of voltage sags. One lassifiation method is ased on RMS values of phase voltages, and it was first introdued in [2]. With onsideration of phase shift, the voltage sags experiened y three-phase adjustale-speed drives were lassified into four types, whih are A, B, C and D. On the asis of this method, voltage sags were then lassified into seven types (e.g. [-5]). The other lassifiation method is ased on the theory of symmetrial omponents, and it was first introdued in [6]. In [6], two new sag harateristis were introdued and C and D were divided respetively into three types aording to the seletion of symmetrial phase. This method was then applied in [7-9]. Considering that the ourrene of voltage sag may e aompanied y phase shift [], the phase shift should e onsidered in the lassifiation of voltage sags. In this paper, first of all, the priniple of voltage sag lassifiation with onsideration of phase shift is proposed. Seondly, the proposed method is desried in detail, inluding the alulation of the phase shift and the disrimination of voltage sag types, through whih the type of eah voltage sag an e otained. Finally, ased on the short-iruit fault types and the proposed lassifiation method, the effets of different transformers on phase shift are studied. II. PRICIPLE OF VOLTAGE SAG CLASSIFICATIO WITH COSIDERATIO OF PHASE SHIFT Most voltage sags are assoiated with symmetrial or asymmetrial short-iruit faults in power system. Symmetrial faults inlude three-phase short-iruits, whereas asymmetrial faults inlude single-phase faults, phase-to-phase faults and two-phase-to-ground faults. Based on the existing sag lassifiation method, sags are divided into seven types with short-iruit types and onsideration of phase shift simultaneously in this paper. The features, vetor graphis, expressions and originations are shown in Appendix. C is taken as an example for etter understanding the harateristi and derivation proess of the proposed seven types of sags. C sags may originate in phaseto-phase faults, single-phase faults propagating via - transformer and phase-to-phase faults via -2 transformer. The voltage phase diagram of a phase-to-phase fault is shown as Figure, that is, the non-fault phase experienes no phase shift, whereas one fault phase has a phase lead of, and the other lag of. Following equation an e otained from Figure. Figure. Vetor graphi of phase to phase fault with phase shift a a ( j )(os jsin ) = ( + j )(os jsin ) 2 2 where is the sag magnitude with a range from.-.9. For a single-phase fault propagated via - transformer, the equation an e hanged into (2). () /7 $. 27 IEEE DOI.9/ICEI

2 (os sin ) a + j a j = T j = j 2 2 j j = ( os ) j( sin ) ( os + ) + j( + sin ) 2 2 For a phase-to-phase faults propagated via -2 transformer, the equation an e hanged into (). a a 2 = T2 2 ( j )(os jsin ) = ( + j )(os jsin ) 2 2 () 2 ( os + sin ) = + ( os + sin ) + j( sin os ) ( os + sin ) + j( sin + os ) From ()-(), one ommon feature an e found that one of the three phases does not have phase shift ut has opposite diretion to the vetor sum of the other two. In this paper, sags with suh harateristis are ategorized as C. Other sag types an also e ategorized ased on the same approah. Compared with the existing lassifiation method, a more generalized method with onsideration of phase shift is proposed in this paper. III. DISCRIMIATIO OF VOLTAGE SAG TPES Based on the voltage sag lassifiation disussed in setion II, a more generalized method is proposed with short-iruit types and onsideration of phase shift, whih is aimed to overome the defiieny of no onsideration of phase shift in the traditional lassifiation method. This new method will e desried in detail as follows. First of all, the voltage information inluding magnitude and phase otained y the original data of voltage an e got, then phase diagrams an e made. Seondly, the voltage sag information an e got through the information in the first step. The sag information inludes whether the voltage sags happen or not, the voltage sag magnitude, the phase value ϕ and the phase shift value β. The range of the voltage sag magnitude is etween and, whereas the phase value ϕ and the phase shift value β are etween -8 and 8. A, B, C, ϕa, ϕb, ϕc, β A, β B, β C are used to express the voltage information of eah phase. The alulation method of the phase shift in the seond step is shown as follows. Values of phase shift during sags an e otained y alulating the phase differene etween the last zero rossing point efore the sag ( ϕ a ) (2) and the first zero rossing point after the sag ours ( ϕ ). Here β is defined as the phase shift value, it an e alulated in (4). β= ϕ ϕa (4) Considering the influene of the distortion or the osillation during the voltage sags, the voltage waveform zero rossing phenomenon may appear frequently, it may ause that the maximum of the differene etween the adjaent zero rossings at the sag initiation eome less than 2% of a yle whih means.4 milliseond. As a result, it is neessary to disriminate it when alulating the phase shift, the speifi progress is shown in Figure 2. Start umer the zero rossings as k i Assume that i =, j = Calulate k2 k 4 Judge k2 k < 4 i = Calulate k i + 4 Judge k i k < + i 4 i = i+ Judge j = ki+ ki Calulate ϕ = 8. Calulate β = ϕ ϕa Figure 2. Calulation progress of phase shift End k i i= i+ j = Due to the results of sag judgement, phase shift values and voltage vetor expression in the seond step, seven types of sags aording to the new lassifiation method an e otained. The speifi steps are as follows. ) Input three-phase voltage sag information, inluding the magnitude, phase and phase shift values, whih are A, B, C, ϕa, ϕb, ϕc, β A, βb, β C. 2) Judge that whether the voltage is symmetrial or not: if A= B = C, ϕb ϕa= 2, ϕc ϕb = 2, the type is A, that is aused y three-phase short-iruits; if not, step to ). ) Judge that whether there is only one phase on sag or not: if only one of the following is true in. A.9,. B.9,. C.9, then the type is B, whih is aused y single-phase faults; if not, step to 4). 4) Judge that whether there is no shift in one of the three phases: if only one of the following is true in β A=, βb =, βc =, then step to 5); if not, step to 9). 5) Judge that whether the phase without shift is on sag or not: assuming that β A = is true in 4), then if. A.9, step to 6); if not, step to 7). 59 6

3 6) Judge that whether there is phase shift in the other two phases: if β B = or β C =, then the sag type is E, whih is aused y two-phase-to-ground faults; if not, the sag type is C, whih is aused y phase-to-phase faults and single-phase faults propagating via - transformer. 7) Judge that whether the phase shift values in the other two phases are equal or not: if βb = βc, then step to 8); if not, the sag type is C, whih is aused y phase-to-phase faults via -2 transformer. 8) Judge that whether the phase differene etween the other two phases is less than 2 or not: if ϕc ϕb< 2, the sag type is F, whih is aused y twophase-to-ground faults propagating via - transformer; if not, the sag type is G, whih is aused y two-phase-to-ground faults propagating via -2 transformer. 9) Judge that whether the vetor differene etween fault phases is parallel to the imaginary axis or not: assuming that Phase B and C are fault phases, if Bos( ϕb+ 8 ) = Cos(8 ϕc), the sag type is D, whih is aused y single-phase faults propagating via -2 transformer; if not, step to ). ) Judge that whether the phase differene etween two fault phases is less than 2 or not: if ϕc ϕb < 2, the sag type is F, whih is aused y two-phase-to-ground faults propagating via - transformer; if not, the sag type is G, whih is aused y two-phase-to-ground faults propagating via -2 transformer. Figure shows the disrimination of voltage sag types with onsideration of phase shift, from whih the type of eah voltage sag an e otained. Phase A voltage sag information A B D F Phase B voltage sag information Three phase symmetry One single phase on sag o shift in one of the phases Phase C voltage sag information Vetor differene etween fault phases parallel to imaginary axis Start Phase differene Between two fault phases less than 2 G End The phase without shift not on sags Phase shifts in the other two phases not equal Phase differene Between the two phases less than 2 F o shift in the other two phases Figure. Disrimination of voltage sag types with onsideration of phase shift In atual power system, power quality monitoring equipment is mainly installed at high-voltage side. There are often multiple voltage levels etween the voltage sag point and the load whih is affeted y the voltage sags. As a result, it is valuale to analyze and study the voltage sags with onsideration of phase shift. Compared with traditional lassifiation method, this new method an make whole response to the harateristis of voltage sags, and then the lassifiation and propagation property of voltage sags with phase shift an e more aurately. It E C plays a very important role in the evaluation of sensitive equipment on the load side and voltage sags. IV. IFLECE OF TRASFORMER O PHASE SHIFT Sag type will hange as it propagates via different types of transformers to lower voltage lass. Based on the transfer matrix and the voltage sag lassifiation disussed in Setion III, the sag type at seondary and primary side of transformers an e otained, as shown in Tale I. Tale I shows the propagation of voltage sags through a single transformer, among whih, A, B, C, and E are those types an e generated diretly y short-iruit faults without the propagation via transformers. A sag is not studied eause it will not hange via all kinds of transformers. It an e known that sags of D, F, and G ome from B, C and E via transformers propagation respetively from Tale I. Therefore, only researhes on B, C, and E are done here. - transformer refers to the transformers whih have the same per unit voltage values in the primary and seondary side. -2 transformer refers to the transformers without zero sequene voltage. - transformer refers to the transformers that the line voltage and phase voltage are exhanged. TABLE I. TRASFORMATIO OF SAG TPE TO LOWER VOLTAGE SAG CLASS WITH COSIDERATIO OF PHASE SHIFT Transformer 2 Voltage Sag at the Primary Side of Transformer A B C D E F G A B C D E F G A D C D G F G A C D C F G F A. -B Sag It is shown in Tale I that -B sag will hange into -D via -2 transformer, and into -C via - transformer. Assuming that the phase shift is and β at the primary and seondary side of transformer respetively. By using the sag type equation in Appendix and the orresponding transfer matrix, the values of and β an e got. Taken the asolute differene value of phase shifts as the vertial oordinates. In [], it is onluded that the phase shift has the high proaility to e within - 2 to 2, the phase shift propagation properties are drawn in Figure 4. It an e onluded from Figure 4 (a)-() that when -B sag hanges into -D via -2 transformer only Phase A of -B sag experienes phase shift, whereas three phases of -D sag all experiene phase shift. Furthermore, -2 transformer has an inhiitory effet on the phase shift of Phase A, and the lower the sag magnitude, the more ovious the inhiitory effet. However, -2 transformer an also intensify the phase shift of Phase B and Phase C, and the lower the magnitude, the more ovious the intensifiation. From Figure 4 (d)-(f), the following results aout the propagation properties of phase shift an e got when -B sag propagates via - transformer: - 6 6

4 transformer has an inhiitory effet on the phase shift of Phase A when the phase shift at the primary side is elow, otherwise, the transformer has intensifiation effet. And the inhiitory and intensifiation effets are not influened y sag magnitude. In addition, - transformer an intensify the phase shift of Phase B and Phase C, and the lower the magnitude, the more ovious the intensifiation (a) () 2 =.-.9 = () (d) 2 =.-.9 = = (e) (f) Figure 4. Phase shift propagation property of -B sag (a) -B via -2 transformer Phase A () -B via - transformer Phase A () -B via -2 transformer Phase B (d) -B via - transformer Phase B (e) -B via -2 transformer Phase C (f) -B via - transformer Phase C B. -C Sag As shown in Tale I, -C sag remains the same type after propagating via -2 transformer, and hanges into -D sag via - transformer. The omparison etween phase shifts at primary and seondary sides of the transformer is shown in Figure 5. Phase A of -C sag has no phase shift, and does not experiene phase shift after propagating via -2 and - transformer also. The results of Phase B are exatly the same as Phase C. It is shown from the (a)-(d) in Figure 4 and Figure 5 that the intensifiation effet of the transformer on phase shift weakens as sag magnitude rising when the sag magnitude is etween. and.7. C. -E sag As shown in Tale I, -E sag hanges into -G via -2 transformer, and into -F sag via - transformer. The omparison etween phase shifts at primary and seondary sides of the transformer is shown in Figure 6. It an e got from Figure 6 (a)-() that phase A of -E sag has no phase shift, ut phase shift ours after propagating via -2 transformer. -2 transformer an intensify the phase shift of Phase A. For Phase B and C, the intensifiation effet weakens as sag magnitude rising when the sag magnitude is etween. and.6. Aording to Figure 6 (d)-(f), -E sag hanges into -F after propagating via - transformer. The phase shift differene of Phase A is only related to the phase shift at the primary side and no orrelation with sag magnitude. For Phase B and C, the intensifiation effet weakens as sag magnitude rising when the sag magnitude is etween. and Figure 5. Phase shift propagation property of -C sag (a) -C via -2 transformer Phase B () -C via -2 transformer Phase C () -C via - transformer Phase B (d) -C via - transformer Phase C Figure 6. Phase shift propagation property of -E sag (a) -E via -2 transformer Phase A () -E via - transformer Phase A 6 62

5 () -E via -2 transformer Phase B (d) -E via - transformer Phase B (e) -E via -2 transformer Phase C (f) -E via - transformer Phase C V. COCLSIO Based on the short-iruit fault types and traditional lassifiation method, a more generalized voltage sag lassifiation method with onsideration of phase shift is proposed in this paper. Firstly, onsidering the phase shift, voltage sags are lassified into seven types. The feature, vetor graphi, expression and origination of eah sag type are given. Seondly, the speifi alulation progress is given, inluding the alulation method of phase shift and the disrimination of voltage sag types. Finally, the effets of different types of transformers on the propagation property of phase shift are studied on the asis of the proposed method. As the ourrene of voltage sag may often e aompanied y phase shift, the proposed method an e used in the aurate disrimination of sag types. With the rapid development of Energy Internet, it may help the deep researh on the assessment of voltage sags and its influene on sensitive equipment as well as the development of effetive mitigation measures in the atual power system. ACKOWLEDGMET This work was supported y the ational atural Siene Foundation of China (o ). REFERECES [] S. Ž. Djoki, J. V. Milanovi. Advaned voltage sag haratierisation. Part I: Phase shift, IEE Pro.-Gener. Transm. Distri., 26, 5(4), pp [2] M. H. J. Bollen. Charaterisation of voltage sags experiened y three-phase adjustale-speed drives[j]. IEEE Trans. Power Deliv., 997, 2(4), pp [] M. Bollen. nderstanding power quality prolems: Voltage sags and interruptions[m]. IEEE Press, 2. [4] M. H. J. Bollen, P. Goossens, A. Roert. Assessment of voltage dips in HV-network: dedution of omplex voltages from the measured RMS voltages[j]. IEEE Trans. Power Deliv., 24, 9(2), pp [5] P. Thakur, A.K. Singh, R.C. Bansal. ovel way for lassifiation and type detetion of voltage sag[j]. IET Generation, Transmission & Distriution, 2, 7(4), pp [6] J. Arrillaga, M. H. J. Bollen,. R. Watson. Power quality following deregulation[j]. Proeedings of the IEEE, 2, 88(2), pp [7] M. H. J. Bollen. Algorithm for haraterizing measured three phase unalaned voltage dips[j]. IEEE Trans. Power Deliv., 2, 8(), pp [8] S. Lotfifard, M. Kezunovi, M. J. Mousavi. Voltage sag data utilization for distriution fault loation[j]. IEEE Trans. Power Deliv., 2, 26(2), pp [9] P. Thakur, A. K. Singh, R. C. Bansal. A novel way to distinguish single phase dips through potential gradient method[j]. Eletr. Power Compon. Syst., 22, 4(), pp APPEDIX CLASSIFICATIO OF VOLTAGE SAGS WITH COSIDERATIO OF PHASE SHIFT of Sag Features Vetor Graphis Expression Origination Three-phase symmetry, A with equal sag magnitude a a Three-phase shortiruit = ( j ) 2 2 ( + j ) 2 2 B Voltage sags in one phase, with phase shift a (os sin ) a + j = j j 2 2 Single-phase shortiruit C One phase has no phase shift; the vetor sum of the other two phases has the opposite diretion to this phase a a = ( j )(os + jsin ) 2 2 ( + j )(os jsin ) 2 2 a = ( sin ) + j( os ) 2 2 ( sin ) + j( os + ) 2 2 Two phase shortiruit, or our after -B sags propagate via - transformer, or -C sags propagate via -2 transformer 62 6

6 2 ( os + sin ) a = + ( os + sin ) + j( sin os ) ( os + sin ) + j( sin + os ) D The vetor differene of two phases is parallel to the imaginary axis a 2 2 ( os ) j sin + + a = ( os ) + j( sin ) 6 2 ( os ) + j( sin ) 6 2 a (sin + os ) = ( sin os ) j( os sin ) ( sin + os ) + j( os sin + ) Our after -B sags propagate via -2 transformer, or -C sags propagate via - transformer E Two vetors have the same sag magnitude and phase shift value a a ( j )(os jsin ) = ( + j )(os + jsin ) 2 2 Two-phase-toground fault F The vetor different of the two phases is V(os jsin ) a 2 + (os + j sin ) a = + ( os + sin ) + j( sin os ) ( os sin ) + j( sin + os ) Our after -E sags propagate - 2 transformer G The vetor sum of the two phases is V(os + jsin ) a a (os + j sin ) = ( os sin ) j( os sin ) ( os sin ) + j( + os sin ) Our after -E sags propagate via - transformer 6 64