CreatingBenchmarks

Issued by : Switchgear Contracts Division LARSEN & TOUBRO LIMITED Powai Works, Mumbai 400 072

A new product or feature isconceptualised to meet dewhich cannot be taken carexisting product or featurenew product is manufacturinto operation, it caters of sthe expectations, but by thtechnological advances chsurrounding parameters. Sbecomes necessary to defparameters under which this expected to deliver its deperformance. And also it isto define what is meant byperformance.

Standards are defined to sstate these parameters. Stparaphrase conditions in wproduct is expected to perfthey also define what shoudesired performance. In acompetitive market, standabenchmarks which all simifunctioning products are exmeet or surpass. Thus, in

April - June 1996

eference line; theyor the game.

L&T PRODUCTS

L&T's Air Circuit Breakers typeC-Power have been successfullytested for various requirements of IS13947 (Part 2)-1993 and IEC 947-2(1989) at Central Power ResearchInstitute (CPRI), Electrical Research& Development Association (ERDA)and Association of Short CircuitTesting Authorities, U.K. (ASTA).

Prospect / Retrospectmandse of by

standards set rform the rules f. When thised and putome of

at time,angeo itine thee productsired essential desired

et andandardshich theorm andld be the

rds createlarpected to

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When technology all around isprogressing, the standards cannotremain rigid. They have to reflectreal life situations. They should alsoincorporate customer's higherexpectations. The benchmarks setonce need to be reviewed andupgraded whenever essential.

A proper co-ordination betweenadvancement in technology andrealistic stipulated conditions forperformance can result in an efficientproduct with optimum cost,benefiting both the customer and thesupplier.

In the last issue of L&T CurrentTrends, we highlighted majorrevision in LV Switchgear standardslaid down in Part I of IS 13947.This article will be concluded in thenext issue.

C-Power ACB

L&T switches, type FF and FFO andFuse combination units, type FN63,FN125 and FN200 comply with IS13947(Part 3)-1993.

In the previous issue, we discussedrevisions in general requirements forlow voltage switchgear andcontrolgear products covered by Part1 of IS 13947. In this issue, we shalldiscuss Part 2 and Part 3, productstandards pertaining to low voltagecircuit breakers, switches and fusecombination units respectively.

PART 2 : CIRCUIT BREAKERS :

This standard replaces IS 2516(Parts 1&2 / Sec. 1)-- 1985. The objective of this standard is tostate performance and constructionrequirements for circuit breakers andto lay down verifying tests. There aresignificant revisions in theserequirements. These are explained infollowing pages.

(I) CHARACTERISTICS :

(a) Utilization category :So far utilization categories weredefined only for contactors andswitches. In the new IS utilizationcategories have been specified forcircuit breakers also. These havebeen defined with reference toselectivity i.e. whether a circuitbreaker is intended for selectivity bymeans of an intentional time delayunder short circuit conditions.

Circuit breakers not specificallyintended for selectivity can beassigned utilization category A e.g.moulded case circuit breakers. Thesebreakers need not have short timewithstand rating (Icw).

Circuit breakers specifically meant forselectivity are assigned utilizationcategory B. Air circuit breakers withintentional time delay for tripping in

F E A T U R E

short circuit condition can beassigned utilization category B.These breakers will also be assignedshort time withstand rating (Icw).

(b) Short circuit ratings :Following two new short circuitratings have been introduced.

(i) Rated ultimate short circuitbreaking capacity (Icu):

Ultimate short circuit breakingcapacity is assigned by themanufacturer.

As the term indicates, continuedservice from the breaker is notexpected after the breaker hascleared a short circuit fault of suchmagnitude. Hence, the prescribedtest conditions do not includeverification of capability of breaker tocarry its rated current after shortcircuit test.

This rating is similar to P1 categoryrating defined in IS 2516.

(ii) Service short circuit breakingcapacity (Ics) :

Service short circuit breakingcapacity is also assigned by themanufacturer and can be expressedas percentage of ultimate short circuitbreaking capacity (Icu). The ratioshall be selected from standard ratiosindicated below.

Standard ratios between Ics and IcuUtilization UtilizationCategory A Category BIcs (as % of Icu) Ics (as % of Icu)

25 5050 7575 100100

Prescribed test conditions includeverification of capability of thebreaker to carry its rated current aftershort circuit test implying expectationof continued service (carrying ratedcurrent) till the breaker is replaced.

This rating is similar to ratingcorresponding to P2 categoryspecified in the earlier standard.

(II) PERFORMANCEREQUIREMENTS :

(a) Test sequences :

In order to evaluate performance of aproduct comprehensively, relevanttype tests are grouped into testsequences. All tests in a givensequence are carried out on thesame unit in prescribed order. Suchsequential testing represents actualservice conditions more closely.Details of test sequences applicableto circuit breakers are given in table 1.

(b) Operational performance capability :

This test, a part of test sequence 1, isto verify capability of breakers toperform minimum number ofmechanical (without current) andelectrical (with current) operations.Minimum number of operations forbreakers for ratings up to 100 A andabove 1250 A have been revised asshown in table 2.

(c) Number of units to be used :

Number of units to be tested for eachtest sequence is now laid down. Thisensures complete evaluation of theproduct performance.

Number of units to be tested is

Introduction to IS 13947 : A new Indian Standard on

Switchgear and Controlgear Products-II- H. T. Mistry, Senior Executive-Design, Switchgear Design and Product Development

based on whether

oduct is assigned morene operational voltage

als for line and loadctions are identified

borated in table 3.

uctors for shortit test :

t breakers of ratings up tonductors to be used foronnections in short circuit

and Icu) have now beenas given below.

of 75 cm in length having ation corresponding to thenal thermal current shall beas follows :

n supply siden load side

This requirement portrays actualapplication more realistically.

PART 3 : SWITCHES,DISCONNECTORS, SWITCHDISCONNECTORS AND FUSECOMBINATION UNITS

This part pertains to low voltageswitches, disconnectors, switchdisconnectors and fuse combinationunits and replaces both parts of IS4064 - 1978.

Following changes have beenincorporated in the new IS.

(I) CHARACTERISTICS :

(a) Rated short time withstandcurrent (Icw) :

This characteristics has been revised.As per IS 4064, minimum short timewithstand current was 20 times themaximum rated operational currentfor a duration of 1 second. This hasbeen changed to 12 times themaximum rated operational current.

(b) Utilization category :

Designation of utilization category

6.Verification of overload releases

Combined testsequence

Circuit breakers ofutilization category Bi) when Icw=Ics(Replaces Seq II & IV)ii) when Icw=Ics=Icu(Replaces Seq II,III&

1.Verification of overload releases2.Rated short time withstand current3.Rated service s.c. breaking capacity4.Verification of dielectric withstand5.Verification of temperature rise

TABLE 2 : CIRCCOMPARISION OF MINIM

IS 13947-2MINIMUM OP.CYCRATED CURRENT

WITHOUTCURRENT

WITHCURRENT

In < = 100 A 8500 1500

630 < In < = 1250 2500 500

1250 < In < = 250 2500 500

2500 < = In 1500 500

TABLE 3 : CIRCUIT BREAKERS - NUM

NO. OF MARKEDOPERATIONAL VOLTAG

TEST SEQUENCE

1 2 MULTIPI X X X

XX

X

II (Ics)AND

COMBINEDX

XX

X

III (Icu)

XIV (Icw) AS PER TES

Example : For sequence II and combined test assigned one operational voltage a identified than three breakers needIV) 6.Verification of overload releases

UIT BREAKERSUM OPERATING CYCLES

IS 2516LES MINIMUM OP.CYCLES

TOTAL WITHOUTCURRENT

WITHCURRENT

TOTAL

10000 4000 4000 8000

3000 2500 500 3000

3000 900 100 1000

2000 Subject to agreement

BER OF UNITS FOR TEST SEQUENCES

EWHETHER TERMINALSMARKED LINE / LOAD

LE YES NO

NO. OF SAMPLESFOR TEST

X X 1X 2

X 3X X 3X X 4X 2

X 3X X 3X X 4

T SEQUENCE III

sequence, if the breaker is and line/load terminals are notarrived at

- the prthan o

- terminconne

This is ela

(d) Cond circu

For circui630 A, coterminal ctests (Icsspecified

"A cable cross secconventioincluded

- 50 cm o- 25 cm o

TABLE 1 : CIRCUIT BREAKERS -- TEST SEQUENCES

TESTSEQUENCE

APPLICABLE TO TESTS

IGeneral performa

characteristics

All circuit breakers 1. Tripping limits and characteristics2. Dielectric properties3. Operational performance

capability4. Overload performance5. Verification of dielectric withstand6. Verification of temperature rise7. Verification of overload releases

IIRated service s.c.breaking capacity

(Ics)

All circuit breakers 1. Rated service s.c. breakingcapacity

2. Verification of dielectric withstand3. Verification of temperature rise4. Verification of overload releases

IIIRated ultimate s.c.breaking capacity

(Icu)

All circuit breakers 1.Verification of overload releases2.Rated ultimate s.c. breaking capacity3.Verification of dielectric withstand4.Verification of overload releases

IVRated short timewithstand current

(Icw)

Circuit breaker ofutilization category B

1.Verification of overload releases2.Rated short time withstand current3.Verification of temperature rise4.S.c. breaking capacity at maximum

short time withstand current5.Verification of dielectric withstandhas been changed. In the new IS, to be tested.

The designation is completed bysuffix A or B according to whether theintended applications requirefrequent or infrequent operations.

Utilization categories with suffix B areappropriate for devices which, due todesign or application, are onlyintended for infrequent operations.

Typical applications covered byvarious utilization categories,however, have remainedunchanged.

Category AC 23A includesoccasional switching of individualmotors. Utilization categories

applicable to equipment normallyused to start, accelerate and / or stopindividual motors (e.g. AC 2, AC 3/4)are covered in appendix A. Thesewere hitherto covered by part 2 ofIS 4064.

(II) PERFORMANCEREQUIREMENTS :

(a) Test sequences :

All relevant type tests are groupedinto four test sequences. These aregiven in table 4.

(b) Making and breaking capacity :

Test parameters for this test havebeen significantly modified. Theseare summarized below :

(i) This test can be carried out in two parts viz. test for making

capacity followed by test forbreaking capacity. However,unlike IS 4064, make operationsare followed by make-breakoperations instead of only breakoperations.

(ii) Test voltage is 1.05 times ratedoperational voltage instead of1.1 times.

(iii) Test currents for AC 23A havebeen revised upwards asindicated in table 5.

TABLE 4 : SWITCHES, DISCONNECTORS, FUSE COMBINATION UNITSTEST SEQUENCES

TEST SEQUENCE TESTI

General performancecharacteristics

(1) Temperature rise(2) Dielectric properties(3) Making and breaking capacities(4) Dielectric verification

Oc

Sc

C

1236

8

# Un op$ Un@ F fo

Table 5 : SWITCHES, DISCONNECTORS, FUSE COMBINATION UNITSCOMPARISION TEST PARAMETERS FOR AC 23A CATEGORY

IS 13947-3 IS 4064MAKE MAKE/BREAK MAKE BREAKRATING, A

I/ie U/Ue p.f. Ir/Ie Ur/Ue p.f. I/Ie U/Ue p.f. I/Ie U/Ue p.f.

Ie