The Research on the Quick Discharge Circuit of Shunt Capacitor

Transcription

1 Journal of Power and Energy Engineering, 14,, Published Online April 14 in SiRes. hp:// hp://dx.doi.org/1.436/jpee The Researh on he Quik Disharge Cirui of Shun Capaior Shuheng Dan, Lei Ning Deparmen of Elerial Engineering, Shanghai niversiy of Eleri Power, Shanghai, China Reeived November 13 Absra Shun apaior is he main mehod o inensively ompensae reaive power in he power sysem. The exernal disharge irui, ommonly disharge oil whih is an induane oil wih low resisane, mus be alloaed o he large apaiy of apaior. This paper alulaes and ompares wo kinds of irui, apaior plaed wih a disharge oil or a resisane, o find he bes way o disharge he residual harge of apaior. Through he sudy, in he under damped ase, hese wo kinds of irui presen differen disharge properies. In over damped mode, heir disharge properies are similar. Keywords Disharge Coil; Disharge Propery; Capaior 1. Inroduion In he 66 kv and below power sysem, disharge oil shuned wih high-volage apaiors quikly release he residual harge of he apaior as i removed from he power sysem o ensure he seuriy of he apaior iself and oher devies when hey are pu ino use again [1]. The whole proess of disharge an be equaled wih irui in whih harged apaiane C inera wih induane L and resisor R []. The ombinaion of he hree parameers may resul in osillaion whih should be avoided in aual operaion [3]. In he proess of disharge, he irui wihou induane L an no only preven he phenomenon of osillaion, bu also reah he purpose of releasing energy. This paper ompared he disharge propery of he wo iruis by observing ime, during whih he volage of apaior deays o a urain value, and he variaion of he urren.. The Mahemaial Model The power indusry sandard DL/T653-9-HV shun apaior disharge oil ordering ehnology [4] makes a lear regulaion of he disharge propery of disharge oil. The volage of he apaior removed from he power sysem drops from n o 5 V in 5 s. Afer he equivalen irui swih losed, he whole proess is equal o zero inpu response of he seond-order irui. In order o make sure he hanging irumsane of he volage whih is beween he wo ends of he apaior, he seond order onsan oeffiien differenial equaion wih is iniial ondiions of How o ie his paper: Dan, S.H. and Ning, L. (14) The Researh on he Quik Disharge Cirui of Shun Capaior. Journal of Power and Energy Engineering,, hp://dx.doi.org/1.436/jpee

2 he equivalen irui depied in Figure 1 should be given based on he knowledge of irui, like in Equaion (1). LC + + = d d = d ( ) + = + = Due o he relaion beween he irui resisane R and he riial resisane Rr = LC, he siuaion of an be divided ino four kinds of irumsane, over damped non-osillaion, Criially damped non-osillaion, under damped osillaion and undamped osillaion. Beause he remaining energy anno be onsumed he undamped osillaion irui is no saisfied wih he demand of he sandard. The oher hree kinds of soluion are desribed in he following Equaions ()-(4). where, ( ) ( δ ) = + e δ () 1 se se s s s 1 s ( ) = ( 1 ) 1 ω δ ( ) = e sin ( ω+ β) (4) ω δ = R s 1, ω = ( L) = δ ± jω 1 ( LC) ( LC) ( R ( L) ) ω = 1 I is lear ha if he Equaion (4) wans o mee he need of he sandard, he oeffiien, whih is ω e δ ω, should deays o 5 V in ime. Equaion (5) is a simplified formula. ( ) L 1 = ln R 5 1 4L Figure shows a irui. Afer he swih losed, he apaior C ineras wih he resisane R. The whole proess is equal o zero inpu response of he firs-order irui. The firs order onsan oeffiien differenial equaion and he iniial ondiions of he equivalen irui are given in Equaion (6). (1) (3) (5) R C L Figure 1. equivalen irui. 58

3 C R And he soluion is Equaion (7) Figure. equivalen irui. d + = ( + ) = ( ) = e (7) Leing he righ side of Equaion (7) equals o 5, he ime in whih he volage of he apaior drops o 5 V an be go in Equaion (8). ln 5 3. The Analysis and Calulaion of he Mahemaial Model = (8) The ype of apaior is BW and is apaiane is.347µ F. The reduive reaane in irui is 1% of he apaiive reaane. Beause of he unerainy of he soluion of he seond order onsan oeffiien differenial equaion he omparison of he disharge propery of he wo kinds of irui mus be disussed separaely. The riial resisane R r equaled o LC in irui is deermined by apaiane C and induane L. Assuming ha he irui resisane R is a variable, he siuaion in irui an be analyzed in he siuaions of over damping, under damping and riial damping based on he relaion beween he irui resisane and he riial resisane. In irui, he size of resisane R an also be lassified aording o his sandard Criially Damped Case In his ase, he irui resisane of he and irui is boh equal o riial resisane. Equaions () and (7) are boh monoonous aenuaion funions. In order o ge heir disharge propery, he urves of he volage of he apaior an be drawn separaely in Figure 3. Figure 3 shows ha a he beginning he disharge rae of irui is higher han irui, neverheless he siuaion hen hanges as he volage deays o a erain value. Compared wih he irui, he volage of he irui uses less ime o reah he esablished value. 3.. nder Damped Case The resisane of he wo iruis here is smaller han riial resisane. Figure 4, in whih he resisane R is a variable, shows he urves of volage-deaying in under damped sae. Time whih sands for he duraion of volage-deaying in irui inreases as he resisane inreases. Bu for he irui, ime dereases a firs and hen inrease as he resisane inreases. Considering his mahemaial model, ime is signifianly greaer han he ime as he resisane hanges in he range of a few hundred ohms. Wih he value of resisane keeping inreasing and reahing.731r r (4647 Ω ) whih is he maximum of he range, ime is greaer han ime all he ime, bu he gap is onsanly narrowed. When he irui resisane (6) 581

4 Figure 3. Volage-deaying in riially damped ase. hanges in he range (.731 R, R ) Figure 4. Time for volage-deaying o 5V in under damped ase. r r, ime is smaller han ime. In addiion, hese wo urves have a endeny o inerse a he riial resisane Over Damped Case The resisane of he wo kinds of irui is larger han riial resisane. Equaion (3) esablished he volagedeaying of he irui in over damped non-osillaion. Given by he equaion, is a superposiion of wo iems of exponenial deay and he apaior is disharging all he ime. Figure 5 is he urves of Equaions (3) and (8) and he relaion beween he volage-deaying ime and he variable R. From his figure, he ime inreases as he irui resisane inreases and he wo lines are less disin. The soluions of Equaions (1) and (6) an be alulaed by MATLAB. Adjusing he size of he resisane in he iruis he series of volage-deaying ime an be obained in Table 1. And he firs olumn is he raio of irui resisane and riial resisane. In Table 1, in irui ime dereases a firs and hen inreases as he irui resisane inreases onsisenly. However, ime in irui is inreases all hrough. Compared wih he wo olumns of Table 1, ime is similar when he irui resisane is above R r. Take 5R r as an example depied in Figure 6. 58

5 Figure 5. Time for volage-deaying o 5V in over damped ase. Figure 6. Volage-deaying in 5 R r. Table 1. Time for volage-deaying o 5 V wih variable irui resisane. Raio R / R r Time for volage deaying o 5 V /ms irui irui

6 3.4. The Change of Cirui Curren Figure 7 is a variaion of irui urren when he irui resisane equals o.731r r. The ampliude of he urren in irui is higher, whih is abou 1.6 imes of irui s value, meanwhile he duraion of volage-deaying o 5 V of boh iruis is same. I is a ommon sense ha exess urren may influenes he normal operaion, or even desroys devies. Figure 8, in whih x-oordinae is he raio of irui resisane and riial resisane, shows he relaion beween he urren peak and irui resisane. The ampliude of boh iruis is dereases as he irui resisane inreases. And he peak value of is smaller han s. 4. Conlusions This paper analyzes he propery of a apaior assembled wih a disharge oil and a resisane. And some general onlusions an be obained based on hese resuls. 1) In under damped ase, in irui he volage-deaying ime dereases a firs and hen inreases as he irui resisane inreases; in irui he ime inreases onsisenly. In over damped ase, he rend of he volage-deaying in wo iruis is similar. ) The ampliude of he urren in boh iruis goes down as he resisane inreases, and he peak value of urren in irui is smaller han s all he ime. Figure 7. Curren in wo iruis wih R equaled o.731 R r. Figure 8. The urren peak wih he variable raio R/ R r. 584

7 3) Considering of aual operaion, disharge irui should limi he size of disharge ime and he urren peak well. On his oasion defined by minimum disharge ime and smaller urren peak, he propery of disharge oil is beer han resisane. Aknowledgemens I owe appreiaion o he fund of naional naure siene and he Shanghai Muniipal Eduaion Commission. This paper is finanially suppored by he Fund of Naional Naure Siene, proje number is And suppored by Leading Aademi Disipline Proje of Shanghai Muniipal Eduaion Commission, proje number is J5133. Referenes [1] Zhang, H.L., Huang, X.M. and Wu, Y.M. (1) Seleion of Disharge Coil for High Volage Shun Capaior Bank. Power Capaior and Reaive Power Compensaion, 31, 6-9. [] Zhou, G.L. () Tes and Researh on Charaerisis of Disharge Coils for High Volage Shun Capaiors. Zhejiang Eleri Power, 5, 7-1. [3] Wu, B. and Wang, X.J. (6) Researh on he Parameers of Disharge Coil of Shun Capaior Bank. Tianjin Eleri Power Tehnology, 4, [4] The Naional Energy Adminisraion of China (9) DL/T653-9 HV Shun Capaior Disharge Coil Ordering Tehnology. China Eleri Power Express, Beijing. 585