Application data explusion links

NOTE: Because Hubbell has a policy of continuous product improvement,we reserve the right to change design and specifications without notice.

© 2000 Hubbell • 210 N. Allen • Centralia, MO • (573) 682-5521 Printed in U.S.A.5M-RGS

Bulletin 10-7701Rev. 9/97

Applicationof

Primary Fuses

IntroductionThe wide variety of fuse links offered by the A.B.Chance Company is instrumental in reducing themany problems facing today’s coordination engineers.Besides the increasingly popular ANSI K and T fuselinks, there is available a series of precision engineeredfuse links designed especially for transformer protec-tion.

The up to date design and construction plus rigidquality control of Chance fuse links assures the co-ordination engineer of dependable electrical and me-chanical fuse link operation. In nearly all cases re-gardless of the application or coordination problemthere is a Chance fuse link to fill the need.

ScopeTo more clearly understand why Chance fuse linksare the answer to your every day fusing problems letus take a closer look at what is expected of a fuse linkas a protective device. The following discussion of fuselink application and coordination will be limited tofuse links only. However, in actual practice the utilityengineer must take into consideration substationbreakers and relay settings, reclosers, sectionalizers,

and power fuses. These devices are found on nearlyall systems and their coordination must be treated ina manner similar to that which will be discussed forfuse links.

The Fuse Link as a Protective DeviceThe fuse link may be considered as the electrical weakelement in the distribution system. This so-calledweak element is purposely introduced into the sys-tem to prevent any damage to the lines and equip-ment which make up the distribution network. When-ever an overload or fault current passes through asection of line or a piece of equipment the fuse linkwhich is the weakest element electrically must meltin time to open the circuit and prevent damage to theline or equipment. The relationship of the magnitudecurrent passing through the link to the time requiredfor the link to melt is referred to as the minimummelting time current characteristic of the fuse link,Figure 1. The relationship of the magnitude of thecurrent passing through the link to the time requiredfor the link to melt and the arc to be extinguished isreferred to as the total clearing time-current charac-teristics of the fuse link, Figure 1.

®®

POWER SYSTEMS, INC.

2

Transformer Overcurrent Protection

Consider first the fuse link as an overcurrent protec-tive device. In such an application, Figure 2, the ]inkserves to protect a piece of electrical equipment fromany damage resulting from an overcurrent. The se-lection of proper fuse links to protect equipment fromovercurrent is determined by the overcurrent capac-ity of the equipment involved. Fortunately theovercurrent capacity of electrical equipment is quiteoften expressed in a time and current relationship.The electrical equipment most commonly protectedagainst overcurrent is the distribution transformer.The time-current overcurrent capacity of distributiontransformers is given in ANSI/IEEE C 57.109 entitled“Guide For Transformer Through-Fault-Current Du-ration.” With the overcurrent time-current capacityof the equipment known, and by the use of time-cur-rent characteristic fuse link curves the proper fuselink can be chosen. The ideal fuse link should pro-vide 100% protection. In other words at any value ofovercurrent or secondary fault current up to the maxi-mum fault current available, the fuse link shouldoperate and clear the circuit before the equipment isdamaged. In actual practice however, some utilitiesmay select fuse links which permit loading of equip-ment in excess of their overcurrent capacity. Thispolicy reduces the amount of refusing necessary butalso subjects equipment to overcurrent which candamage it or shorten its life expectancy.

Short Circuit Protection

The ability to protect transformers and other electri-cal equipment from overcurrent is not all that is re-quired of a fuse link. A fuse link must act quickly toisolate equipment or lines when the equipment suf-fers internal or external failure or when the line issubjected to a fault. This requirement is necessary tolimit the outage to the smallest possible area. It isalso necessary in order to minimize damage to theequipment and lines. Limiting outages to the small-est area not only provides greater continuity of elec-trical service but also reduces the problem of locat-ing failed or damaged equipment.

Fuse links are not only applied at the transformerbut are also found in locations on the distributionsystem where only short circuit protection is required;such a situation is shown in Figure 2 where the fuselink is referred to as a sectionalizing or lateral fuse.The selection of the lateral fuse link is dictated by thefull load current and fault current at the point of itslocation and by the time-current characteristics ofthe largest fuse link in the lateral. The process ofmaking this selection is called coordination of fuselinks and will be discussed in detail under the head-ing of “Coordination of Sectionalizing Fuses.”

Figure 1

SUBSTATION

SECTIONALIZINGFUSE

TRANSFORMER

LOADOVERCURRENTFUSE

Figure 2

3

MECHANICAL APPLICATION OFFUSE LINKS IN CUTOUTSThe first step in the application of fuse links is todetermine the type of cutout in which the fuse link isto be used, and thereby establish the fuse link con-struction required. For example, most open type andenclosed type cutouts are designed to use the 20 inchminimum length “universal” type fuse links. Most 18and 23 kV cutouts and even some 15 kV cutouts re-quire fuse links longer than the 20 inch length. Openlink type cutouts require an open link type fuse linkspecifically designed for the purpose. Special cutoutsmay impose additional mechanical requirements onthe fuse links. Because of the adaptability of the fuselinks offered by the A. B. Chance Company these re-quirements can be met in nearly all cases regardlessof the cutout in use. Where problems exist on me-chanical applications not readily solved consult yourChance representative.

ELECTRICAL APPLICATION FUSE LINKSThe following factors are pertinent to the proper ap-plication of fuse links on a distribution system:

1. Safe loading characteristics of equipment to beprotected.

2. In the case of transformer fuses, the degree ofovercurrent protection to be provided.

3. Load current at the point of application.

4. The fault current available at various locationson the system.

5. Time current characteristics of fuse links to beused on the system.

6. The type of protection to be provided by the fuselink.

A typical lateral of a distribution system is shown inFigure 3. The information given in Figure 3 coversmost of the factors listed above. Providing that nosecondary fuses are used, the fuse links located atthe transformers ideally should provide overcurrentprotection, and should protect the sectionalizing fuselink. The sectionalizing fuse link will operate to iso-late the entire lateral and protect the remainder ofthe system from interruption when a primary faultoccurs between it and the transformer fuse links. Atthe cross marks on the line diagram of the lateral areindicated the fault current available at the variouslocations. The rated full load current of each singlephase transformer can be calculated by dividing theKVA of the transformer by its kV rating. If we assumeall transformers to be fully loaded the load current inthe sectionalizing fuse link will be approximately thesum of the individual transformer full load currents.

25 KVA 7.2 kVTRANSFORMER


6 AMP K OR0.7 AMP

SLOFAST

12 AMP K OR3.5 AMP

SLOFAST

2400AMPSS.C.

80 AMP KOR

40 AMP T

SECTIONALIZINGOR PROTECTED

FUSE

2000 AMPS S.C.

6 AMP K OR14 AMP

SLOFAST

10 AMP K OR2.1 AMP

SLOFAST



Figure 3

Transformer Fusing

Using the information given in Figure 3, let us deter-mine the fuse link required for each transformer. As-sume the utility has standardized on the ANSI type Kfuse links for reasons of economy and supply. The 5KVA 7.2 kV transformer has a full load current ratingof approximately 0.7 amperes. Any 1 ampere fuse linkwill carry the full load current of this transformerwithout melting. However, consideration must begiven to the time current characteristics of the 1 am-pere fuse link compared with the overload capacity ofthis transformer. The ANSI overcurrent curve for thisdistribution transformer is shown in Figure 4. Also

Figure 4

ANSI/IEEE OVERCURRENTCURVE FOR A 5 KVA 7.2 KVDISTRIBUTION TRANSFORMER

6AMP

K

1AMP

K

TIM

E IN

SE

CO

ND

S

CURRENT IN AMPERES

ASA CURVE AND K TOTAL CLEARING CURVES

4

pacity of the transformer but a large portion of thiscapacity is sacrificed. Also, protection is lost againstlow overcurrents of long duration.

It can be seen from the preceding discussion that theconventional type K fuse link leaves much to be de-sired in the way of transformer protection. Let us con-sider the steps possible to provide more ideal trans-former protection where such protection is consid-ered essential. There have been for many years fuselinks available with “dual” time current characteris-tics. These fuse links have characteristics which lendthemselves to better protection and utilization of theovercurrent capacity of distribution transformers.

The A. B. Chance Company developed and markets acomplete line of dual characteristic fuse links. Thesefuse links have been so refined that their time cur-rent characteristic curves, to all practical purposes,coincide with the ANSI transformer overcurrent curve.In Figure 3, note that the alternate proper SloFastfuse links for the transformer installations are re-corded as well as the applicable type K fuse links.Figure 6 is a comparison of the total clearing timecurve of a 21 ampere SloFast fuse link with the ANSIovercurrent curve for a 15 KVA 7.2 kV transformer.The rather unusual current rating assigned to SloFastfuse links is an aid in their application since the cur-rent rating assigned is identical to the continuouscurrent rating of the transformer which they were spe-cifically designed to protect. It can be seen from Fig-ure 6 that the SloFast fuse link provides the high-est degree of transformer protection and yet allowsmaximum use of available transformer overcurrentcapacity.

Figure 5

shown is the total clearing time curve of the Chance1 ampere type K fuse link. Examination of Figure 4reveals that although protection is provided for thetransformer its full overcurrent capacity at the highvalues of current is not realized. The fusing of thistransformer with a 1 ampere type K fuse link will re-sult in the transformer being taken out of serviceunder many overcurrent conditions which would nothave damaged the transformer in any way. In orderto realize the full overcurrent capacity of the trans-former the 6 ampere type K fuse link in many in-stances would be chosen. The total clearing time curveof the 6 ampere type K fuse link is also shown inFigure 4. The application of the 6 ampere type K fuselink eliminates many unnecessary outages, but allovercurrent protection is lost. The only function thatthis fuse link can perform is to isolate the transformerfrom the system in case of faults. Many utilities jus-tify this over-fusing of transformers by the assump-tion that most secondary faults or overloads will clearthemselves before any damage to the transformer canoccur. The above assumption seems to hold truein some cases, but in others the record of burnedout transformers, does not justify this over-fus-ing practice.

The overcurrent curve of the 25 KVA transformer isshown in Figure 5. Since these larger transformersare more expensive some utilities feel that it is neces-sary to compromise between no transformer protec-tion and lOO% transformer protection. In such cases,the 12 ampere K fuse link might be selected for fus-ing the 25 KVA transformer. The use of this 12 am-pere K fuse link utilizes some of the overcurrent ca-

ANSI OVERCURRENT CURVEFOR A 25 KVA 7.2 KVTRANSFORMER

12AMP

K

20AMP

K

6AMP

K

Figure 6

ANSI OVERCURRENT CURVE FOR A15 KVA 7.2 KV TRANSFORMER

2.1 AMPSLOFAST

TIM

E IN

SE

CO

ND

S

CURRENT IN AMPERES

ANSI CURVE AND SLOFAST TOTAL CLEARING CURVE

TIM

E IN

SE

CO

ND

S

CURRENT IN AMPERES

ANSI CURVE AND K TOTAL CLEARING CURVES

5

The dual element SloFast Fuse Link has two distinctsections to assure overall protection.

Coordination of Sectionalizing Fuses

In selecting a fuse link for use at a sectionalizing point,we must give consideration to coordination, that isthe cooperation of one fuse link with another to limitoutages to the smallest possible section of the distri-bution system.

When coordination is being considered, thesectionalizing fuse link shown in Figure 3 is referredto as the “protected” fuse, whereas the fuse links lo-cated at the transformers are referred to as “protect-ing” fuses. These two terms, “protected” and “pro-tecting” are used to indicate that one fuse link, theprotecting, operates and clears the circuit before theother, the protected, is damaged. In order to providethe necessary coordination between these fuse linkswe must refer to the fuse link time current charac-teristic curves. Using these curves, we first determinethe maximum total time required by the protectingfuse link to clear the maximum short circuit faultcurrent which is available at the point of its applica-tion. The proper protected fuse must carry the fullload current and have a minimum melting time greaterthan the maximum total clearing time of the protect-ing fuse at the maximum fault current available atthe protecting fuse. To provide protection againstoperating variables, 75% of the minimum melting timeof the protected fuse link is often used. Naturally, indetermining the coordination of the sectionalizing fuselink with transformer fuse links the largest trans-former fuse link in the section should be consideredsince it will place the strictest coordination require-ments on the sectionalizing fuse link.

In Figure 3 it is necessary to determine thesectionalizing fuse link required to coordinate withthe largest fuse link in the branch which in this caseis the 3.5 ampere SloFast fuse link used to protectthe 25 KVA transformer. The total clearing time curveof the 3.5 ampere SloFast fuse link indicates that themaximum time required by this fuse link to clear a2400 ampere fault is .0134 seconds. The propersectionalizing fuse link, therefore, must be capableof carrying 2400 amperes for .0134 seconds withoutbeing damaged. The ANSI type T fuse links have beenselected for our sectionalizing fuse because of theirslow time current characteristics. The minimum melt-ing time curves of the type T fuse links indicate thatthe minimum melting time of a 40 ampere T link at2400 amperes is .0185 Sec. As previously stated, toallow for operating variables, 75% of this minimummelting time is used, or .0139 seconds. The 40 am-

SUBSTATION

14 AMPSLOFAST

100 KVA 7.2 KVTRANSFORMER

40 AMP TPROTECTING

FUSE

2400 AMPS. S.C

3.5 AMPSLOFAST

25 KVA 7.2 KVTRANSFORMER

80 AMP TPROTECTED

FUSE

Figure 7

pere T fuse link will, therefore, meet the necessarycoordination requirements.

Where two sectionalizing fuses are in series the onefarthest from the power source becomes the protect-ing link and the one nearest the power source be-comes the protected link. In this application the properprotected link has to be selected in the same manneras in the application where a transformer fuse pro-tects a sectionalizing fuse. As an example, there aretwo sectionalizing fuses shown in series in Figure 7.In the consideration to select the proper fuse link forthe point nearest the power source this fuse link be-comes the protected link. It has already been deter-mined that a 40 ampere type T link is required forwhat has now become the protecting link. By refer-ence to the time current characteristic curves andthe use of the 75% operating variable factor it can bedetermined that the protected link should be an 80ampere type T.

Use of Time Current Characteristic Curves

and Coordination Tables

Since time current characteristic curves are usuallyprinted on transparent paper, it is possible to overlaythe total clearing time characteristic curve with theminimum melting time characteristic curve or viceversa. The minimum melting curve can be shifteddownward by 25% with respect to the total clearingtime curve. This shift, since the curves are printed onlog-log paper, automatically provides for 75% of the

Heat absorberHeater coil Fuse wire

Strain wire

Solder junction

Insulated strain pinFast

sectionSlow section

6

minimum melting time to be used in coordination.With the time current characteristic curves so ar-ranged we can readily determine the values of cur-rent at which any two fuse links will coordinate.

To simplify the process of coordination the A. B.Chance Company also provides coordination chartsfor all fuse links which they manufacture. In the caseof the SloFast fuse links, coordination charts are pro-vided with the SloFast link as the protecting fuse linkand all other Chance fuse links as the protected fuselinks. These charts are used to determine the properprotected fuse link when the short circuit currentavailable and the size of the protecting fuse link areknown.

The use of coordination charts can be illustrated inFigure 7 by determining the proper fuse link to belocated nearest the substation. In order to use thecharts, we must first determine which fuse link isthe protecting fuse link and which fuse link is theprotected fuse link. The protected fuse link is alwaysthe fuse link which is located nearest the power sourceand the protecting fuse link is that fuse link locatedadjacent to the protected fuse link and nearest theload. Refer to the coordination chart of the type Tfuse link. If a 40 ampere Type T fuse link is the pro-tecting fuse link and the available short circuit cur-rent is 2400 amperes, this chart indicates that theprotected link must be an 80 ampere T. The 80 am-pere T link will coordinate with a 40 ampere T link atshort circuit currents up to 3700 amperes.

“Rule of Thumb” Method for Coordination

of ANSI Type K or Type T Fuse Links

Another method of coordinating fuse links is possiblewhen the ANSI K or T fuse links are used. This isreferred to as the “Rule of Thumb” method. The “Ruleof Thumb” method is stated as follows:

Satisfactory coordination between adjacentratings of preferred or adjacent ratings ofnon-preferred fuse links is provided up tocurrent values of 13 times the smaller orprotecting fuse link rating for Type K fuselinks and 24 times the smaller or protect-ing fuse link rating for Type T fuse links.

The above coordination factors are made possible bythe standardization of maximum allowable arcing timeapplied to the fuse links. The 75% of minimum melt-ing time factor is also taken into consideration by thisrule of thumb method. Obviously, when ANSI fuselinks are used, the rule of thumb method simplifiesthe process of coordination in some instances.

Referring again to Figure 7, this method can be usedin checking the fuse link required adjacent to thesubstation . In using the rule of thumb method, wemust again use the terms “protected” and “protect-ing” fuse links. The method states that satisfactory

coordination between adjacent preferred or adjacentnon-preferred ratings of type “T” fuse links is pos-sible if the short circuit current does not exceedtwenty-four times the rating of the protecting fuselink, or in this case our 40 ampere “T” fuse link. It isevident that if the short circuit current does not ex-ceed 960 amperes (24 x 40 + 960) we could use a 65ampere T fuse link at the substation. However, theactual current is 2400 amperes and the rule of thumbmethod only establishes that a “T” fuse link largerthan the 65 ampere rating is required. Either of thetwo previous described methods (time current curvesor coordination charts) can be used to determine thislarger required “T” fuse link.

MECHANICAL INTERCHANGEABILITYIn addition to electrical characteristics, a fuse linkmust have certain physical and mechanical featuresin order for it to be interchangeable. Mechanical in-terchangeability is equally as important as electricalinterchangeability. Besides the standard universalfuse link for open and enclosed type cutouts, thereare a few special fuse links for use in what might becalled non-conventional or non-universal type cut-outs.

7

TABLE 1COORDINATION CHART

forCHANCE TYPE “K” (FAST) ANSI FUSE LINKS

6

14510060

8

220185150

10

295295295

170

12

370370370

320190

15

490490490

490400250

20

620620620

620620480

310

25

840840840

840840840

700440

30

100010001000

100010001000

1000750480

40

130013001300

130013001300

130013001000

600

50

160016001600

160016001600

160016001600

1175740

65

225022502250

225022502250

225022502250

225018401150

80

265026502650

265026502650

265026502650

265026501950

1250

100

345034503450

345034503450

345034503450

345034503450

26501500

140

580058005800

580058005800

580058005800

580058005800

580058004800

3000

200

940094009400

940094009400

940094009400

940094009400

940094009400

94004500

Maximum Currents (R.M.S. Amperes) For Safe Co-ordination

Protected Type “K” Fuse Link Ampere Rating


forCHANCE TYPE “T” (SLOW) ANSI FUSE LINKS

Above Coordination Chart based on maximum total clearing time of the protecting link and the minimum melting time of the protectedlink.

6

280280280

8

390390390

10

510510510

340

12

690690690

690400

15

920920920

920850480

20

115011501150

11501150990

550

25

150015001500

150015001500

1190670

30

190019001900

190019001900

19001500890

40

249024902490

249024902490

249024902000

1100

50

300030003000

300030003000

300030003000

22501250

65

390039003900

390039003900

390039003900

390030001700

80

480048004800

480048004800

480048004800

480048003700

2100

100

620062006200

620062006200

620062006200

620062006200

50002700

140

950095009500

950095009500

950095009500

950095009500

950095006600

3900

200

150001500015000

150001500015000

150001500015000

150001500015000

150001500015000

150005200


Protected Type “T” Fuse Link Ampere Rating


Protecting Type“K” Fuse LinkAmpere Rating

123

68

10

121520

253040

506580

100140200

Protecting Type“T” Fuse LinkAmpere Rating

123

68

10

121520

253040

506580

100140200

8


forCHANCE “MS” FUSE LINKS


Protected Type “MS” Fuse Link Ampere Rating


forCHANCE TYPE SLOFAST FUSE LINKS


5 7

640

10

980980

15

13001300850

20

163016301600

780

25

210021002100

16501000

30

260026002600

260019001200

40

325032503250

325032502250

1400

50

420042004200

420042004000

30002150

65

530053005300

530053005300

530039002800

80

620062006200

620062006200

620062004900

3200

100

840084008400

840084008400

840084008400

62001400

125

100001000010000

100001000010000

100001000010000

1000073001700

150

100001000010000

100001000010000

100001000010000

10000100009700

6700

200

100001000010000

100001000010000

100001000010000

100001000010000

10000100008200

3Protecting Type“MS” Fuse LinkAmpere Rating

357

101520

253040

506580

100125150

200



Protected Type SloFast Fuse Link Ampere Rating

.2 .3

35

.4

52

.6

62

.7

65

1.0

1128775

6760

1.3

135112100

9590

1.4

143120110

104100

1.6

175160150

14514090

2.1

230225215

211208168

145130

3.1

325325325

325325295

275265230

3.5

340340340

340340315

300285250

4.2

440440440

440440440

415405380

310

5.2

530530530

530530530

530530500

445330300

6.3

620620620

620620620

620620620

570450430

300

7.0

660660660

660660660

660660660

610510480

350

7.8

820820820

820820820

820820820

820740700

610480

10.4

106010601060

106010601060

106010601060

106010501025

940820690

650

Protecting TypeSloFast Fuse Link

Ampere Rating

.2

.3

.4

.6

.71.0

1.31.41.6

2.13.13.5

4.25.26.3

7.07.8

10.4

9


forCHANCE TYPE SLOFAST AND TYPE “K” (FAST) ANSI FUSE LINKS


forCHANCE TYPE SLOFAST AND TYPE “T” (SLOW) ANSI FUSE LINKS



Protected Type “K” Ampere Rating

6

165140125

8

220210195

190190

10

295295295

285285240

12

370370370

370370350

320320

15

490490490

490490490

490490440

20

620620620

620620620

620620620

550

25

840840840

840840840

840840840

840700700

30

100010001000

100010001000

100010001000

1000950950

820

40

130013001300

130013001300

130013001300

130013001300

12301100

50

160016001600

160016001600

160016001600

160016001600

160015501400

1400

65

225022502250

225022502250

225022502250

225022502250

225022502250

225020001700

80

265026502650

265026502650

265026502650

265026502650

265026502650

265025502300

100

345034503450

345034503450

345034503450

345034503450

345034503450

345034503250

140

580058005800

580058005800

580058005800

580058005800

580058005800

580058005800

200

940094009400

940094009400

940094009400

940094009400

940094009400

940094009400


Ampere Rating

.2

.3

.4

.6

.71.0

1.31.41.6

2.13.13.5

4.25.26.3

7.07.8

10.4



Protected Type “T” Fuse Link Ampere Rating

6

285285285

275275

8

385385385

385385370

10

510510510

510510510

510510

12

690690690

690690690

690690690

15

920920920

920920920

920920920

920

20

115011501150

115011501150

115011501150

115011501150

25

150015001500

150015001500

150015001500

150015001500

1500

30

190019001900

190019001900

190019001900

190019001900

190019001800

1800

40

249024902490

249024902490

249024902490

249024902490

249024902490

24902300

50

300030003000

300030003000

300030003000

300030003000

300030003000

300030002800

65

390039003900

390039003900

390039003900

390039003900

390039003900

390039003900

80

480048004800

480048004800

480048004800

480048004800

480048004800

480048004800

100

620062006200

620062006200

620062006200

620062006200

620062006200

620062006200

140

950095009500

950095009500

950095009500

950095009500

950095009500

950095009500

200

150001500015000

150001500015000

150001500015000

150001500015000

150001500015000

150001500015000

3

83

3

78


Ampere Rating

.2

.3

.4

.6

.71.0

1.31.41.6

2.13.13.5

4.25.26.3

7.07.8

10.4

10

TABLE 8ELECTRICAL AND MECHANICAL INTERCHANGEABILITY TABLE

forEQUIVALENT FUSE LINKS


forCHANCE TYPE SLOFAST AND TYPE “MS” FUSE LINKS

Catalog Number

M3MSAM5MSAM7MSAM10MSAM15MSA

M20MSAM25MSAM30MSAM40MSAM50MSA

M65MSAM80MSAM100MSAM125MSAM150MSAM200MSA

Chance Type MSA Fuse Links

Catalog Number

21003 & 21003-U21005 & 21005-U21007 & 21007-U21010 & 21010-U21015 & 21015-U

21020 & 21020-U21025 & 21025-U21030 & 21030-U21040 & 21040-U21050 & 21050-U

21065 & 21065-U21080 & 21080-U21100 & 21100-U21125 & 21125-U21150 & 21150-U21200 & 21200-U

Ampere Rating

357

1015

2025304050

6580

100125150200

Kearney Type KS and KS-U Fuse Links

Ampere Rating

357

1015

2025304050

6580

100125150200


Protected Type “MS” Fuse Link Ampere Rating

5

410410410

410410400

7

650650650

650650650

650650650

10

980980980

980980980

980980980

980

15

130013001300

130013001300

130013001300

130013001300

20

163016301630

163016301630

163016301630

163016301630

16301500

25

210021002100

210021002100

210021002100

210021002100

21002100

30

260026002600

260026002600

260026002600

260026002600

260026002600

2600

40

325032503250

325032503250

325032503250

325032503250

325032503250

325032503000

50

420042004200

420042004200

420042004200

420042004200

420042004200

420042004200

65

530053005300

530053005300

530053005300

530053005300

530053005300

530053005300

80

620062006200

620062006200

620062006200

620062006200

620062006200

620062006200

100

840084008400

840084008400

840084008400

840084008400

840084008400

840084008400

125

100001000010000

100001000010000

100001000010000

100001000010000

100001000010000

100001000010000

150

100001000010000

100001000010000

100001000010000

100001000010000

100001000010000

100001000010000

200

100001000010000

100001000010000

100001000010000

100001000010000

100001000010000

100001000010000

3

300300300

300300

Above Coordination Chart based on maximum total clearing time of the protecting link and the minimum melting time ofthe protected link.


Ampere Rating

.2

.3

.4

.6

.71.0

1.31.41.6

2.13.13.5

4.25.26.3

7.07.8

10.4

11

CONVERSION TO ANSI FUSE LINKS

buttonhead, removable buttonhead and/or open link styles— that you would use on your system.

Construction details such as construction of the fuse ele-ment, auxiliary tubes and fuse link cable size and coatingshould also be considered along with the quality and per-formance of the fuse links produced.

In Chance type “K” fuse links, elements are made of silvercopper or silver alloy and Type “T” fuse links are made witha tin fuse element.

The purpose of the auxiliary tube is to assist the cutout inthe clearing of low fault currents and to protect the fuseelement from physical damage.

Converting to EEE-NEMA LinksAfter the type of link, “K” or “T” is selected, the followingsteps are suggested as a guide to implementing a conver-sion program.

1. Select the supplier — Considerations in determiningwhich manufacturer or manufacturers from whom youwould purchase fuse links include availability of stocks,reputation of company service rendered by salesman, and,of course, the quality and consistency of performance ofthe fuse links produced.

Samples of links should be obtained from all potential sup-pliers and should include all physical types — solid

Advantages of ConversionThrough the joint efforts of users and manufacturers, the ANSI Standards for Distribution Fuse Links were established toprovide the levels of performance and utility necessary to meet modern protective practices and operating conditions.They serve the two-fold purpose of providing guidance to the manufacturer and assurance to the user that specificelectrical requirements are met.

These joint standards, along with existing ANSI standards, set forth characteristics that will allow and provide for theelectrical, as well as mechanical, interchangeability of fuse links. Conversion to ANSI standard fuse links therefore per-mits multiple sources of supply for fuse links.

The ANSI standards are prepared so as to still permit the utility engineer to select fuse links using his individual judgmentbased on the details of manufacture, use with related equipment and other application factors.

Two Speed Ratios AvailableThe joint ANSI standards have established two types of fuse links, designated Type “K” and Type “T”. The Type “K” linkcommonly called “fast” has speed ratios of the melting time-current characteristics varying from 6 for the 6-ampere ratingto 8.1 for the 200 ampere rating. Type “T” (slow) fuse links have speed ratios of the melting time-current characteristicvarying from 10 for the 6-ampere rating to 13 for the 200 ampere rating.

The type of link selected, “K” or “T”, is based largely on the time-current characteristics of the fuse link presently used, ifsuch characteristics meet present day coordination requirements. The more closely the time-current characteristics meetthose of the present fuse links, the easier the conversion.

TIM

E IN

SE

CO

ND

S

“Representative” minimum and maximum curvesfor ANSI Type “T” (slow) fuse links.

“Representative” minimum and maximum timecurrent characteristic curves for ANSI Type “K”(fast) fuse links.

CURRENT IN AMPERES CURRENT IN AMPERES

TIM

E IN

SE

CO

ND

S

12

Type K Fuse Link

For OverloadProtection of

Transformers*

Ampere Rating

“K” or “T”

368

1015202530

40506580

100

100 or 140140

140 or 200

“K”

101220

25 or 3040506580

80 or 100100 or 140

140140 or 200140 or 200

200——

“T”

68

10 or 12

1520 or 2525 or 3030 or 40

40

5065 or 8080 or 100

100100 or 140

140200—

For Short CircuitProtection**

Ampere Rating

Figure 6

TABULATION OFMINIMUM MELTING CURRENT VALUES

TYPE K 10 AMP FUSE LINKManufacturer

Time Periodin Seconds

300100101.1

CHANCE

19.520.025.042.5

129.0

A

19.520.023.043.0

130.0

C

20.021.026.045.0

130.0

B

19.520.024.543.0

129.0

Current in Amperes

TABULATION OFMINIMUM CLEARING VALUES

TYPE K 10 AMP FUSE LINK

Time Periodin Seconds

300100101.1

CHANCE

23.524.029.552.0

167.0

A

23.023.527.049.0

170.0

C

23.025.031.054.0

180.0

B

23.024.029.054.0

170.0

Manufacturer

Current in Amperes

CHANCE TYPE MS ANDMSA FUSE LINKS

Ampere Rating

357

1015202530

40506580

100

125150200

RECOMMENDED CHANCE ANSIFUSE LINK

3. Make-up cross reference charts — Using either thecomposite curves or the tabulations used to develop thesecomposite curves, a cross reference chart like the one shownbelow should be made comparing the ANSI link and thelink now in use. (See Fig. 8 for typical example.)

4. Check coordination with other overcurrent protec-tion equipment — In some instances it may be necessaryto check the coordination of the ANSI link with otherovercurrent protection devices, but this should not be aserious problem unless the time-current characteristics ofthe selected ANSI link has a considerably different speedratio than the fuse link now in use.

5. Change records and drawings — With the cross refer-ence charts you can change over all records and drawingsto specify the proper size ANSI links.

You are now ready to put these new links on your system.There are several methods by which this has been done.One of the following examples may be found to have par-ticular advantages to your company.

Convert one division at a time, using salvaged links inun-converted districts.

Convert all but one division, using all the salvagedfuse links in one un-converted division until they aredown to a disposable level.

Convert all divisions simultaneously, scrapped all non-ANSI links in stock.

Many factors will affect the conversion finally adopted. Thesefactors can best be evaluated by the utility involved.

The weather resistance of these auxiliary tubes should beevaluated since any fuse link may be in service many yearsbefore it operates.

The type of coating used on the fuse link cable should pre-vent excessive corrosion which could result in cable break-age. Chance engineers have found that lead coating givesexcellent resistance to corrosion.

It is imperative that every link used on your system consis-tently match the published time-current characteristiccurves so as to properly coordinate the protective equip-ment.

2. Make-up composite time current characteristicscurves — In order to meet specified electrical interchange-ability requirements, all manufacturers’ fuse links are re-quired to meet minimum and maximum melting currentvalue at three time points (a) 300 seconds for fuse linksrated 100 amps and below and 600 seconds for fuse linksrated 140 and 200 amps, (b) 10 seconds and (c) 0.1 sec-onds. These standards for minimum, and maximum melt-ing time result in a band curve for each rating of each type(see Fig. 1 and 2 on page 2).

Because these ANSI standards allow a band width for theminimum and maximum melting time curves and a vari-ance in factors applied for arcing time by different manu-facturers, each manufacturer’s curve varies slightly al-though still within the limits of the standards. It is there-fore recommended that on each size of link a compositeminimum melting curve and a composite total clearing timecurve be constructed from the individual curves on eachmake of link to be used. This can be done by preparing achart for each size link as shown below.

To actually prepare the composite curve for each size link,the minimum figure at each current rating should be se-lected and plotted for the minimum melting composite curve.

When plotting the total clearing time curve, the maximumfigure should be selected at each current rating.

The composite curves thus obtained will provide a bandwithin which the fuse links of all the selected suppliers willoperate.

Type T Fuse Link

Art & Photos

Application data explusion links