Appendix C Partial discharges. 1. Relationship Between Measured and Actual Discharge Quantities

Transcription

1 Appendi Prtil dishrges. Reltionship Between Mesured nd Atul Dishrge Quntities A dishrging smple my e simply represented y the euilent iruit in Figure. The pplied lternting oltge V is inresed until the oltge ross the ity () produes dishrge, with suseuent pulse ross the smple of Δ V. Δ ΔV () where nd Δ V Δ V instntneous pplied oltge V ELE97: Appendi PD lirtion p. /0 The sudden hnge Δ V will produe oltge pulse t the smple terminls: Δ V V Δ () nd the pprent hnge in hrge ross the smple on rekdown of is: Δ Δ V ΔV. ΔV. (3) [Note: will lso inlude ny eternl pitne tht is in prllel with test ojet, ]. If (this is usully the se ut not lwys, e.g. for point-plne system) then, efore rekdown of the oid, eution () eomes: Δ ( ). ΔV (4) nd if [ ssumed to e muh thinner nd sme ross setion s ] eution (3) eomes: Δ ( ). ΔV (5) ( ). V Δ [from e.]. Δ V (6) s mesurle t terminls. Note tht nd known indiidully. ELE97: Appendi PD lirtion p. /0 Δ V re rrely Now from (4) nd (6): Δ prtil dishrge dissipted in oid Δ pprent prtil dishrge t terminl or: Δ Δ (7) Δ if i.e. the mesured PD is muh smller thn the tul PD dishrged in n elementry ity for the simple se onsidered.

2 . Derition of Reltionships for Indiret nd Diret lirtors A. Indiret lirtors An indiret lirtor is used with the HV test oltge pplied. The euilent iruit is shown in Figure 3. The lirtor internl impedne is ssumed zero. See lso Figure. Figure : () Representtion of oid in solid, () the euilent iruit, nd () possile oltge weforms. Figure 3: Euilent iruit for derition of reltionships for indiret lirtors. Figure : Bsi iruit for PD mesurements. The lirtor step oltge is e nd pitor. For e 0 nd pulse ross smple of Δ V. Δ Δ V Δ V (8) ELE97: Appendi PD lirtion p. 3/0 ELE97: Appendi PD lirtion p. 4/0

3 nd oltge t the deteting impedne is ELE97: Appendi PD lirtion p. 5/0 s / s Δ V Δ V nd is: ( ) / Δ ΔVs Δ Vs Δ V For e e Δ // s s ΔV Δ V e ( ) e (9) (0) If oltges due to the lirtor nd the dishrge re mde eul, this is euilent to: Δ V Δ V / s s // then y euting (9) nd (0): ( ) Δ e or Δ e Note tht if the pprent hnge in hrge is: () Δ e () B. Diret lirtion Referring to Figure 4, nd ssuming the internl lirtor remins in iruit. Figure 4: Euilent iruit for derition of reltionships for diret lirtors For ey 0 nd e 0, y is lirtor pitor. Δ Δ V ( y) y Δ V nd oltge t deteting impedne is: Δ Δ Δ Vs Vs3 V Δ ( ) y ELE97: Appendi PD lirtion p. 6/0 (3)

4 Δ. For ey ey nd e 0: y y Δ Vs Δ Vs4 ey ( y ) e y y y (4) Euting Δ V s 3 nd Δ V s 4, whih ssumes the y is in the iruit during the HV test. Δ e y y or: eyy Δ (5) for y in iruit. From eution () oe nd for e e : y ( y ) Δ e e y e if (6) Thus for the ondition tht y, y my e remoed during the HV test nd the diret lirtion is pproimtely lid. In prtie, omprison is mde etween the defletions produed on the detetor y the two lirtion oltges e nd e y. 3. PD Energy Mesured t Terminls Let: W nd ssume omplete dishrge of the ity, the energy is: W Δ Δ V Δ Δ V s Δ Also: ΔV Δ (en.7) V where V instntneous lue of pplied oltge. Hene: W Δ V Δ V W i.e. the totl energy nd the ity energy re eul ssuming idel onditions of omplete dishrge. The omple phenomen sed on pitne only re shown in Figure () for V V. i ELE97: Appendi PD lirtion p. 7/0 ELE97: Appendi PD lirtion p. 8/0

5 Mesurement of the pprent hrge is speified in the IE Stndrd. Its mgnitude is tht ssoited with the lrgest repetedly ourring pulse whih n e mesured y suitle nlogue pek olt-meter. This speifition is not preise s the pproprite time onstnt of the meter is not gien. Typil ommeril nlog PD detetors he pek detetor dey time of seond. For digitl PD detetors, the following integrted untities re used insted of : Pek dishrge mgnitude m - this is defined s the mgnitude of the lrgest pprent hrge, epressed in ouloms m m [,,, n] Aerge dishrge mgnitude : n n i i Note tht in the IE-6070 Stndrd, it is proposed tht the dey time onstnt for the nlogue meter to e no greter thn 0.44s. To mke the digitl PD detetor gie similr reding to this reommendtion, modified weighted men hs een suggested to reple : n Rr s i 00 n i where the weighting ftor R r ries with the repetition rte r, otined from look-up tle. Bsilly, the weighting gies smller s (ompred to ) for low pulse rte, e.g. R r 8 for r5pps, nd lrger lue t high pulse rte. s is eul to when the pulse rte is 00pps. The integrted (or dedued) untities re prmeters deried from the si untities to hrterise the generl trend of the dishrge tiity oer gien period of mny yles. The integrted untities speified in IE-6070 re: Dishrge urrent I - this is the erge of the solute lues of the pprent hrges, epressed in mperes or ouloms/seond n i T i I Qudrti rte D - this is the erge of the sures of the pprent hrges, epressed in ouloms/seond D n i T i Dishrge power P - this is the erge power loss due to PDs s seen etween the two min terminls of the test ojet, epressed in wtts n i i T i P Repetition rte r - this is the erge numer of PD pulses per seond: n r T Here, n is totl numer of dishrges ourred within time interl T, i s re pprent hrges nd i s re instntneous test oltge lues t instnt of dishrges. The integrtion period T is not speified in the Stndrd. One suggestion is tht T should e no less thn thousnd yles, i.e. 0s for the 50Hz se. ELE97: Appendi PD lirtion p. 9/0 ELE97: Appendi PD lirtion p. 0/0