he Use of ooing-factor urves for oordinating Fuses and Recosers arey J. ook Senior Member, IEEE S& Eectric ompany hicago, Iinois bstract his paper describes how to precisey coordinate distribution feeder automatic-circuit recosers using cooing-factor data that accounts for the heating and cooing of source-side or oadside fuses throughout the recoser s operating sequence. his method yieds resuts that are more accurate than other coordination methods commony empoyed. Different coordination methods are discussed in this paper and the resuts are compared. Keywords ooing factors, cooing factor curves, recoser-fuse coordination, fuse-recoser coordination I. INRODUION he appication of recosers on distribution systems wi require that they be coordinated with both source-side and oad-side fuses. In both cases, the faut current through the fuse wi be interrupted by the recoser and then restored as the recoser progresses through its operating sequence. Initiay, the temperature of the fusibe eement is determined by the pre-faut oad current and by the ambient temperature. When a faut occurs, the temperature of the fusibe eement increases toward its meting vaue. If the recoser opens before the fusibe eement reaches it s meting vaue, the fuse wi coo during the recosing-time interva contacts open). his current cycing wi continue unti the faut is ceared prior to the next recosing operation i.e., temporary faut), the fuse mets and cears the faut, or the recoser operates to ockout. Figure iustrates the heating and cooing of the fuse. HE OOL HE OOL HE David. Myers Member, IEEE S& Eectric ompany hicago, Iinois IEEE. Presented at the 004 IEEE Power Engineering Society Genera Meeting, June 7, 004, Denver, oorado, US, and pubished in the meeting s proceedings. eary, when coordinating recosers and fuses, the repeated heating and cooing of the fuse must be considered. o this end, adjustment factors are appied, not to the curves of the fuse, but to the curves of the recoser, to generate equivaent recoser curves as seen by the fuse. wo different techniques are often used to create equivaent recoser curves, each providing differing eves of accuracy. One method, caed the onservative Method, ignores fuse cooing entirey and considers ony the heating of the fuse. Resuts of this method are, as the name suggests, conservative. he ooing Factor Method precisey adjusts the recoser curves by refecting both the heating and the specific cooing characteristics of the fuse as a function of the duration of each recosing-time interva. Both methods are described in this paper, and the resuts are compared. third method, caed the K-Factor Method, uses predetermined scaing factors for certain common recoser sequences and fuse speeds. It yieds resuts somewhere between the onservative Method and the ooing Factor Method. It is not covered in this paper. he coordination methods discussed in this paper are aso appicabe when coordinating fuses with circuitbreakers equipped with recosing reays. s shown by Figure, cooing factors for fuses can vary substantiay. For exampe, after a recosing-time interva of seconds has eapsed, the sow speed fuse ink 0) has ost % of its heat input as compared to a very fast speed fuse ink 40N), which has ost 9% of its heat input. medium speed fuse ink 40 Std.) has ost 54% of its heat input after seconds. EMPERURE OF FUSIBLE ELEMEN URREN HROUGH FUSE IME LOD FUL RELOSING FUL RELOSING FUL INERVL INERVL Figure. Heating and cooing of a fuse in series with a recoser during the recoser s operating sequence. ime, Seconds Figure. ypica cooing factors versus time for severa fuse inks manufactured by the authors company. Page ooing Factor 0.9 0.8 0.7 0.6 0.5 0.4 0. 0. 0. 0 40N 40SD 0 0 4 6 8 0 4 6 8 0 4 6 8 0
00-76 II. SOURE-SIDE FUSE / LOD-SIDE RELOSER When a fuse is ocated on the source side of a recoser, the fuse must not met before the recoser operates to ockout. he maximum current vaue up to which the fuse and a recoser wi coordinate is determined by the ower of: a) the maximum interrupting rating of the recoser or the fuse, or b) the intersection of the minimum-meting curve of the fuse and maximum equivaent operating curve of the recoser i.e., the ockout curve). onservative Method he most conservative approach woud be to ignore the cooing of the fuse during the recosing-time interva, and simpy sum the heating effect of each recose operation. hat is, you woud create an equivaent recoser ockout curve by adding the proper number of fast and deayed operations. his method wi ensure coordination, but it may force the seection of a arger source-side fuse than is necessary. arger fuse, in turn, wi provide a reduced eve of equipment protection e.g., for a substation power transformer), and it may experience coordination probems with protective devices ocated even further upstream of the fuse. equivaent curves for the recoser are obtained by use of the foowing equation: Where: n j Rj P Point on the maximum equivaent ockout curve of the recoser, at seected current I). ) adjustment can be made to the recoser s fast ) and sow B,, etc.) curves by the appication of a factor "" to the cearing times. hese cooing factors ), for a specific recosing-time interva, or cooing time, refect the heat remaining in the fuse after preheating and cooing, in percent of preheating. See Figures and 4. equivaent ockout curves for the recoser, for various operating sequences, are obtained by use of the foowing equations: a. One operation of the recoser b. wo operations of the recoser R ) P) R + R P ) c. hree operations of the recoser ) + R + P ) R R 4) When the recosing times are the same, this simpifies to: d. Four operations of the recoser R + R + R 4a) P ) R + R + R + R4 5) P ) When the recosing times are the same, this simpifies to: P Reduction in meting time of the fuse due to preoading, expressed as a decima part of its tota meting time. Rj cearing time at current I) for the j th operation contacts cosed) of the recoser. Where: R + R + R + R 4 5a) P ) n Number of operations contacts cosed) of the recoser. ooing-factor Method In order to obtain precise coordination between a source-side fuse and a oad-side recoser, it is necessary to compensate for heat stored in the fuse when the recoser contacts are cosed, and heat ost when the contacts are open. t a seected current vaue, the heat stored in the fuse preheating), during the time the recoser contacts are cosed, is directy proportiona to the recoser s cearing time. herefore an Page Point on the maximum equivaent ockout curve of the recoser, at seected current I). P Reduction in meting time of the fuse due to preoading, expressed as a decima part of its tota meting time. Rj cearing time at current I) for the jth operation contacts cosed) of the recoser. k ooing factors from Figure or Figure 4 for the kth recosing-time interva contacts open) of the recoser.
ooing Factor 0.9 0.8 0.7 0.6 0.5 0.4 5K 0K, 0K, 0K, 40K, 80K 8K, 5K, 50K, 65K K,00K 6K 40K a. onservative Method Since the fuse must aow the recoser to operate to ockout without meting, the recoser s maximum equivaent ockout curve is cacuated by adding up the individua operating times of the two fast ) curves and two sow B) curves at the specified faut-current eve. Note that recoser fast ) curves, as pubished, are expressed as maximum cearing times. Pubished sow B) curves are expressed as average cearing times, and must be adjusted by a 0% positive toerance. See Figure 5. 0. 0. 0. 0 00K 0 4 6 8 0 000 00 urve: earing ime, Variations Negative B urve: verage earing ime, Variations ±0% ime seconds) Figure. ooing factor vs. time for K-Speed fuse inks manufactured by the authors company. ime, Seconds 0 urve 5 oi B urve 00 0.9 40 0.8 0.7 6, 8, 50, 0, 40, 65, 80, 00 0. ooing Factor 0.6 0.5 0.4 0. 0. 0, 5, 0, 5 0.0 0 00 000 0000 urrent, mperes Figure 5. fast) and B sow) curves for a ype 4H recoser with a 5-ampere trip coi. 0. 0 0 4 6 8 0 ime seconds) Figure 4. ooing factor vs. time for -Speed fuse inks manufactured by the authors company. Exampe Determine if a ype 4H oi-circuit recoser, with a 5 trip coi, wi coordinate with a source-side 65K fuse ink. he recoser is set for two fast ) and two sow B) operations i.e., /B), with a fixed.5-second recosing-time interva between each operation. s noted before, the fuse must not met before the recoser operates to ockout. he avaiabe faut current is 600 amperes. It is assumed that the fuse is preoaded to 70% of its ampere rating. Page he recoser s maximum equivaent ockout curve can then be cacuated by using Equation : +. B ) P Where and B are points from the pubished recoser and B curves, respectivey, at the seected current I. t 600 amperes: 0.07 second, and B 0.6 second both from Figure 5). For 70% preoad: P 0.0 see Figure 6) 0.07 +. 0.6) 0.66s 0.0
urrent haracteristic urve Meting ime in Percent of ime Shown on ime- 00 80 60 40 0 0 Figure 6. Fuse ink preoading adjustment factors. eary, the fuse ink must take onger than 0.66s to met at 600 amperes to achieve coordination. 65K fuse ink mets in 0.57 second, so fu coordination is not achieved. n 80K fuse ink, which takes 0.49 second to met at 600 amperes, woud be required for coordination. See Figure 7. 00 "K" Ratings through 00 0 0 40 60 80 00 0 40 60 80 00 Load urrent in Percent of Fuse Link mpere Rating "" vaiabe urrent 600) + +. B +. P ) Where and B are points from the pubished recoser and B curves, respectivey, at the seected current I. t 600 amperes: 0.07 second and B 0.6 second both from Figure 5). For 70% preoad: P 0.0 see Figure 6). For a.5 second recosing-time interva: 0.55 for a 65K fuse ink from Figure ) 0.07 0.55 + 0.07 0.55 +. 0.6 0.55 +. 0.6 0.9s 0.0 0.55 ) 65K fuse ink mets in 0.57 second, so fu coordination is achieved. See Figure 8. 00 0 B vaiab Faut urrent 600) 0 65K Minimum Met urve ime, Minimum Met urve 65K 80K Equivaent Recoser Lockout urve ime, Equivaent Recoser Lockout urve 0. Recoser urve B urve 0. 0.0 Recose B urve 0 00 000 Figure 7. Source-side fuse / oad-side recoser coordination using the onservative Method. b. ooing-factor Method urrent, mperes 0.0 Figure 8. Source-side fuse / oad-side recoser coordination using the ooing Factor Method. omments 0 00 000 urrent, mperes he above exampe iustrates that incuding the cooing of the fuse ink during the recosing-time intervas aows for the seection of a smaer source-side fuse. s in the previous exampe, the fuse must aow the recoser to operate to ock-out, and the recosing-time interva is fixed at.5 seconds. he maximum equivaent ockout curve of the recoser is cacuated using Equation 5a: Page 4
III. SOURE-SIDE RELOSER / LOD-SIDE FUSE When a fuse is ocated on the oad-side of a recoser, the fuse shoud not met whie the recoser operates through its fast operations, but it must operate during the deayed operations to avoid recoser ockout. his is commony referred to as a fuse saving scheme. he maximum current vaue up to which a fuse and recoser wi coordinate is determined by the ower of: a) the maximum interrupting rating of the recoser or the fuse, or b) the intersection of the minimum-meting curve of the fuse with the maximum equivaent curve for just the fast operations of the recoser. Note: his is not the ockout curve. he equations given in Section II are used to cacuate the maximum coordination current, but for the source-side recoser / oad-side fuse and case, ony the fast operations of the recoser are considered. he minimum current vaue down to which the fuse and the recoser wi coordinate is determined by the intersection of the tota-cearing curve of the fuse and the minimum equivaent ockout curve of the recoser. Note that the fina operation incudes ony reay time when the recosing device is a reay-actuated circuit breaker. onservative Method o determine the maximum coordination current use Equation, incuding ony the recoser fast operations in the cacuation. For the minimum coordination current, consider the intersection of the tota-cearing curve of the fuse with the minimum equivaent ockout curve for the recoser, obtained by use of the foowing equation: Where: R 6) Point on the minimum equivaent ockout curve of the recoser, at seected current I). R Minimum cearing time at current I) for the deayed operation contacts cosed) of the recoser. ooing-factor Method o determine the maximum coordination current use Equations through 5a, incuding ony the recoser fast operations in the cacuation. For the minimum coordination current, consider the intersection of the tota-cearing curve of the fuse with the minimum equivaent ockout curve for the recoser, obtained by use of the foowing equations: a. One operation of the recoser R 7) P) b. wo operations of the recoser R + R 8) P ) c. hree operations of the recoser R + R + R 9) P ) When recosing times are the same, this simpifies to: d. Four operations of the recoser + R + P ) R R 9a) R + R + R + R4 0) P ) When recosing times are the same, this simpifies to: Where: + R + P ) + R R R4 0a) Point on the minimum equivaent ockout curve of the recoser, at seected current I). P Reduction in the meting time of fuse due to preoading, expressed as a decima part of its tota meting time. Rj Minimum cearing time at current I) for j th operation contacts cosed) of the recoser. k ooing factors from Figure or Figure 4 for the k th recosing-time interva contacts open) of the recoser. Exampe Determine the coordination range for a ype R Recoser with a 00 trip coi with a oad-side 65 fuse ink. he recoser is set for two fast ) and two sow ) operations i.e., /), with a fixed -second recosing-time interva between each operation. he fuse must not met during the recoser fast operations, but the fuse must met and cear the Page 5
faut before the recoser operates to ockout. It is assumed that the fuse is preoaded to 70% of its ampere rating. 00 a. onservative Method Since the fuse must withstand the two recoser fast operations without meting, the maximum equivaent recoser fast curve is cacuated by summing the two fast ) curves. s noted previousy, pubished curves are expressed as maximum cearing times. he maximum equivaent recoser curve for the two fast operations can be cacuated by using Equation : f P Where is the point from the pubished recoser fast ) curve for the seected current I. For 70% preoad: P 0.09 from Figure 6) ime, Seconds 0 Equivaent Recoser Fast urve 0 65 Minimum Equivaent Recoser Lockout urve f 0.09 0. Recoser urve his equation is appied at severa current eves. he intersection of the maximum equivaent recoser curve for the two fast operations with the minimum-meting curve of the fuse is the maximum coordination current. s shown in Figure 9, the maximum coordination current is 700. he fuse must operate to cear the faut after the recoser s fast operations, but before the recoser operates to a the way ockout. he minimum equivaent recoser ockout curve can be cacuated by using Equation 6: 0. 9 Where is the point from the pubished recoser curve at the seected current I. he 0.9 factor represents the negative toerance from the pubished average curve. he intersection of the minimum equivaent recoser ockout curve with the tota cearing curve of the fuse is the minimum coordination current. From Figure 9, the minimum coordination current is 0. 0.0 Figure 9. Source-side recoser / oad-side fuse coordination using the onservative Method. b. ooing-factor Method s before, the fuse shoud withstand the two recoser fast operations without meting, with the recosing-time interva fixed at seconds. he maximum equivaent recoser fast curve is cacuated using Equation : f urrent, mperes + P) 700 0 00 000 Where is the point from the pubished recoser curve at the seected current I. For 70% preoad: P 0.09 from Figure 6). For a.0 second recosing-time interva: 0.8 for a 65 fuse ink from Figure 4) f 0.8 + 0.09 0.8) Page 6 his equation is appied at severa current eves. he intersection of the maximum equivaent recoser fast curve with the minimum-meting curve of the fuse is the maximum coordination current. s shown in Figure 0, the maximum coordination current is 05. he fuse must cear after the recoser fast operations but before the recoser operates to ockout. he minimum equiva-
ent recoser ockout curve can then be cacuated by using Equation 0a: 0.8 + 0.8 + 0.9 P ) + 0.9 Where and are the points from the pubished recoser and curves, respectivey, at the seected current I. For 70% preoad: P 0.09 From Figure 6). For a.0 second recosing-time interva: 0.8 for a 65 fuse ink see Figure 4) 0.8 0.8 + 0.8 0.8 + 0.9 0.09 0.8 ) 0.8 + 0.9 he intersection of the minimum equivaent recoser ockout curve with the tota-cearing curve of the fuse is the minimum coordination current. From Figure 0, the fuse and the recoser coordinate for a currents ess than 05, since the minimum recoser ockout curve and the fuse tota-cearing curve do not intersect. ime, Seconds 000 00 0 0. 0.0 65 Equivaent Recoser Fast urve Recoser urve Minimum Equivaent Recoser Lockout urve Recose r 05 0 00 000 0000 urrent, mperes Figure 0. Source-side recoser / oad-side fuse coordination using the ooing Factor Method. omments In this exampe each method resuted in a different coordination range. See abe. he onservative Method resuted in a substantiay smaer coordination range than the ooing Factor Method. In this exampe, if the avaiabe faut current is 000, the ony method that indicates that compete coordination exists between the source-side recoser and the oadside fuse ink is the ooing Factor Method. BLE Load-Side Fuse / Source-Side Recoser oordination Exampe oordination Range Method Minimum urrent ) urrent ) onservative 0 700 ooing Factor 05 IV. ONLUSIONS When coordinating recosers and fuses, the repeated heating and cooing of the fuse shoud be considered. his paper has shown that the proper use of specific cooing factors, to account for the therma response of the fuse during mutipe recosing operations, resuts in more precise coordination of recosers and fuses, and the seection of smaer fuse ampere ratings for better equipment protection. V. BIBLIOGRPHY ime-current characteristic curves, preoad- and ambienttemperature adjustment curves, and cooing-factor curves, for fuses and fuse inks manufactured by the authors company are avaiabe for downoading from the company s website www.sandc.com). ime current characteristic curves for recosers can be obtained from the recoser manufacturer. so avaiabe on the author s company s website is a protective device coordination program oordinaide M ) that can be used to evauate specific source-side fuse / oad-side recoser and source-side recoser / oad-side fuse coordination probems. arey J. ook SM 9) Mr. ook received a BSEE from ri-state University, ngoa, Indiana in 977, and a Masters of Engineering Management from Northwestern University, Evanston, Iinois in 000. He joined S& Eectric ompany in 977, and is now Manager Business Deveopment, Fuse Products Division. Mr. ook has extensive expertise in the seection and appication of a types of medium- and highvotage power fuses. He has authored a number of fuse seection guides, appication guides, and technica papers covering a aspects of overcurrent protection and coordination. Page 7 Mr. ook is active in IEEE, and is currenty hairman of the Power System Protection ommittee, of the Industry ppications Society.
David. Myers M 89). Mr. Myers received his BSEE and MSEE degrees from the University of Iinois, Urbana, IL, in 99 and 997, respectivey. He joined S& Eectric ompany in 99 and has hed various engineering positions in R&D and Engineering Services. He is currenty Manager Fied Service, Power Systems Services Division. Mr. Myers has had extensive invovement in turnkey engineering, procurement, construction, and instaation projects. He has aso been invoved in distribution automation, power quaity, and system studies incuding protective device coordination, short-circuit anaysis, oad-fow anaysis, transient anaysis, and product certification. He has authored a number of papers on various distribution system topics and has deveoped and presented technica seminars in the area of distribution system overcurrent and protection. Page 8