testing of ct

7/24/2019 testing of CT

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PROCEDURE FOR CURRENT TRANSFORMER

(Factory and Site acceptance Tests)

1. PURPOSE:

To have a common practices to accept the manufacturing Quality of the product

and to ensure the Installation quality of the Current transformer.

. SCOPE:

Factory acceptance test & site acceptance test.

!. RESPONS"#"$"T%:

Factory acceptance test by manufacturer & witness by Greeno Central Quality

and Greeno !ite Q"#QC for siteacceptance test.

&. REFERENCE DOCUMENTS:

I! $%' ()art * to +,- "pproved GT) & "pproved rawings- I/C 0++1*.

'. PROCEDURE:

'.1. Factory acceptance test or crrent Transor*er:

"ll the factory acceptance test observations should be recorded on 2aterialQuality inspection report1 F1C31Q"01*.

'.1.1.For +enera, Crrent Transor*er:

!peci4cation limits should be as per IS 2705 (Part1):

'.1.1.1. Type test or +enera, Crrent Transor*er: (On,yre-ie o Test certi/cates issed 0y CPR" ERDA 2 3a,idity

period p to ' years on,y)

5elow type test certi4cate has to be submitted by vendor6

'.*.*.*.*. !hort1time current tests.'.*.*.*.$. Temperature1rise test.'.*.*.*.7. 8ightning impulse test for current transformer

for service in electrically e9posed installation.'.*.*.*.+. !witching impulse voltage tests for current

transformersof+$:and above.'.*.*.*.'. ;igh voltage power1frequency wet withstand

voltage tests on outdoor current transformers up to and

including $+'


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Note: *. The dielectric type tests in (7,. (+, "nd (', shall all be carried out

on the same transformer unless otherwise agreed.

$. "fter the current transformers have been sub=ected to the

dielectric type tests (7,- (+, and (', they shall be sub=ected to all the routine

tests.

7. Type tests may be omitted when the manufacturer holds a

certi4cate of type tests made on a similar transformer which is acceptable to us.

'.1.1.. Rotine Tests or +enera, Crrent Transor*er:'.1.1..1. 3eri/cation o ter*ina, *ar4in5 and

po,arity.

'.1.1..1.1. +enera,:The terminal maring shall identify6

'.*.*.$.*.*.*. the primary and secondary windings>'.*.*.$.*.*.$. the winding sections- if any>'.*.*.$.*.*.7. the relative polarities of windings and

winding sections> and'.*.*.$.*.*.+. the intermediate tapping- if any.

'.1.1..1.. Met6od o *ar4in5:'.*.*.$.*.$.*. The terminals shall be mared clearly and

indelibly either on their surface or in their

immediate vicinity.

'.*.*.$.*.$.$. The maring shall consist of lettersfollowed- or preceded- where necessary- by

numbers. The letters shall be in bloc capitals.

'.*.*.$.*.$.7. "ll the terminals mared )*- !* and C*shall have the same polarity at any instant.

'.*.*.$.*.$.+. The maring of current transformers shallbe as indicated in below 4gures.


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'.1.1... Po

er

re7ency

dry it6stand tests on pri*ary indin5s.

'.1.1...1. Re7ire*ent o E7ip*ent8s ortestin5:

;: Tester6 ( to $',


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$ The choice between 8ists * and $ should be made by considering the degree ofe9posure to lightning and switching over voltages- the type of system neutralearthing and the ind of the overvoltage protection. !ome guidance is given in I!$*0' ()art *,6 *?%%.

Ta0,e 1# Rated "ns,ation $e-e,s or 9i56est Syste* 3o,ta5es o 1! 43and A0o-eUp to and "nc,din5 &' 43

No*ina, Syste*

-o,ta5e

9i56est Syste*

3o,ta5e

Poer

Fre7ency

;it6stand

3o,ta5e

$i56tnin5

"*p,se

;it6stand

3o,ta5e


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%0' %0' * *7$* *+$'$+ *''

Met6od :

The current transformer shall be sub=ected to the appropriate speci4ed power1frequency pre stress voltage given in Table $5 for *o seconds. The voltage shallthen be reduced to the corresponding speci4ed partial discharge test voltagegiven in Table $5 without interruption and this voltage shall be maintained for *'minutes. The ma9imum permissible partial discharge magnitude measuredduring the last minute at the speci4ed partial discharge test voltage shall be *pC.

Dote6 The method $ may be preceded by lightning impulse test in order tocomplete the di electric routine tests of the primary windings.

Ta0,e # Rated "ns,ation $e-e,s or 9i56est Syste* 3o,ta5es o &< 43

and A0o-e:

9i56est Syste*

3o,ta5e

Poer Fre7ency Pre

stress 3o,ta5e

Partia, Disc6ar5e test

3o,ta5e


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;: Tester6 ( to ',


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'.1.1..&.!. Res,ts to 0e o0tained:

The applied voltage shall be withstood satisfactorily for one minute.

'.1.1..'. Partia, disc6ar5e tests in accordance it6

"S 11!: 1?@'.NOTE >T6is test is app,ica0,e on,y

or crrent transor*ers it6 so,id ins,ation or

6i56est syste* -o,ta5es . 43 and a0o-e and

crrent transor*s it6 ,i7id i**ersed

ins,ation or 6i56est syste* -o,ta5es o .' 43

and a0o-e.

'.1.1..'.1. Re7ire*ent o E7ip*ent8s ortestin5:

)artial ischarge Tester'.1.1..'.. Measrin5 "nstr*ents:

The measuring instrument used shall comply with 7.+ of I!6 0$?1 *?$.

The instrument used will depend on the quality to be measured and the qualitypreferred in this standard is the apparent charge q e9pressed in )ico coulombs(pC,.

D3T/ 1 ideband measurement of partial discharges with a bandwidth of at least

* ; oers certain advantages especially where test ob=ects with distributedcapacity and inductance are concerned. Dormally- however- a narrow bandmeasurement of partial discharges is suJcient for instrument transformers-particularly if there is a possibility of choosing between measuring frequencies inthe range @*' 2; to $ 2; )referred values are .' 2; and * 2;- but- iffeasible- the measurement should be performed at the frequency which gives thehighest sensitivity.

'.1.1..'.!. Testin5 Procedre:

The partial discharge test shall be carried out after all dielectric tests are

completed. The applied voltage shaI* be raised to the pre stress voltage (valuesgiven in Table *, before reducing it to the partial discharge measuring voltagealso given in below Table 7.

Ta0,e ! Per*issi0,e -a,es o partia, disc6ar5e ,e-e,sType of/arthing( !ee note*,

Type ofInstrumenttransformer

)re1 !tressvoltage( see note$,

2easuring:oltage( see note$,

Type ofInsulation

)ermissiblepartialischarge8evelcharge

Detworswith an

isolated orresonant

CurrentTransforme

r and)hase to

*.7 Am *.* Am( !ee note

7,

8iquidImmersed

* pC

!olid $' pC*.*Am 8iquid * pC


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star point earthvoltage

Transformer

K7 Immersed!olid ' pC

)hase to

)hasevoltagetransformer

*.7 Am *.* Am 8iquid

Immersed

* pC

!olid ' pC

Detworswith aneectivelyearthedstar point

Currenttransformer andphase toearthvoltagetransformer

. E *.7Am

*.*Am K7

8iquidImmersed

* pC

!olid ' pC

)hase tophasevoltagetransformer

*.7 Am *.*Am 8iquidImmersed

* pC

!olid ' pC

Dote *6 If there is no clear distinction to be made for which ind of networ (star

point either isolated or eectively earthed, the instrument is meant- the levels

for the isolated star point shall be taen.

Dote $6 here the rated voltage of a voltage transformer is considerably lower

than its declared highest system voltage Am- then- sub=ect to agreement

between manufacturer and customer- lower pre1stress voltages may be chosen.

Dote 76 these values apply only if agreed between manufacturer and customer.

D3T/ + 1 "lternatively- the partial discharge test may be performed whiledecreasing the voltage after the power frequency withstand voltage. If themeasured partial discharge values e9ceed the permitted limits of Table 7- aseparate test as speci4ed above may be carried out.

'.1.1..'.&. Per*issi0,e partia, disc6ar5e ,e-e,s:

)referred values for the permissible levels of partial discharges are given in Table7. These values are found by e9perience to guarantee reasonably reliableproducts at reasonable cost. henever it is possible to clearly distinguishbetween higher bacground disturbances and the partial discharges arising fromthe test ob=ect- these higher disturbances may be permissible if agreed bymanufacturer and the customer.

'.1.1..'.'. Res,ts to 0e o0tained:"ll the partial discharges should be within limits that mentioned in Table 7.

'.1.1... Deter*ination o errors or ot6er

c6aracteristics accordin5 to t6e re7ire*ents o


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t6e appropriate desi5nation or accracy c,ass

(see indi-ida, parts o t6is procedre).

Dote6 *.The determination of errors of other characteristics in (', shall be carried

out after the tests ($,- (7, and (+,. The order or possible combination of other

tests is not standardied.

$. Lepeated power frequency tests on the primary windings shall be

performed at percent of the speci4ed test voltage.

'.1.1.!. Optiona, Tests:

The following tests where applicable- shall be carried out by mutual agreement

between the purchaser and the manufacturer6

'.1.1.!.1. C6opped ,i56tnin5 i*p,se test as a type

test.'.1.1.!.. Measre*ent o die,ectric dissipation

actor or oi, i**ersed crrent transor*ers o

.' 43 and a0o-e.

Themeasurement of dielectric dissipation factor (tan 0, shall be made after thepower frequency test on the primary windings. The ambient temperature and thetemperature of the equipment under test shall be between *MC and +MC. Themeasurement of tan shall be made by means of a !chering 5ridge or otherequivalent method.

The test voltage- which shall be agreed between the manufacturer and the

purchaser but in no case e9ceeding the highest system voltage divided by 4-shall be applied to the primary terminals connected together. The secondaryterminals- any screen and isolated metal casing shall be connected to themeasuring bridge. If the transformer has a special device (terminal, suitable forthe measurement- the other terminals shall be short1circuited and connected tothe earthed or the screened metal casing..

'.1.1.!..1. Re7ire*ent o E7ip*ent8s or testin5: !chering 5ridge.

'.1.1.!... Testin5 procedre:

!chering 5ridge6


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The test ob=ect and the reference capacitance is set on high voltage- thebalancingelements lay on low voltage and with the null indicator the bridge is balanced

(Fig. *,.

The balancing condition is ful4lled in the case of same electric potential on bothends of the null indicator respectively no current Now through the null indicator.

The accuracy of measurement depends essentially on the sensitivity of the nullindicator. The balancing condition can be described with following formula6

H9 #H7 O HD # H+

TanPO CRLR O C+L+

'.1.1.!..!. Res,ts to 0e o0tained:

The issipation factor value measured shall not e9ceed the value agreed

between the manufacturer and the purchaser.

'.1.1.!.!. Co**issionin5 tests on ne crrent

transor*ers p to and inc,din5 ! 43.'.1.1.!.!.1. Poer>Fre7ency Test on Pri*ary

;indin5s: (Test procedre sa*e as '.1.1..

c,ase o t6is procedre)


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5y agreement between the manufacturer and the purchaser- separate sourcepower frequency tests on the primary winding insulation may be made aftererection on site provided that the transformer is in a satisfactory conditions fortesting and has not been in service. The transformers shall be temporarilydisconnected from any other apparatus to which it may be connected. The one

minute test voltage shall !3 percent of speci4ed power frequency test voltage.If for any special reasons the duration of the test e9ceeds one minute- therelationship betweenduration of the test and the percentage of the one minute test voltage shall beas given in Table +.

D3T/1Commissioning test on current transformers for highest system voltageover 70 : are deprecated.

Ta0,e & App,ied Poer>Fre7ency 9i56 3o,ta5e Tests or DrationEBceedin5 One Minte (Ater Erection on Site)

Dration o test in *intes Percenta5e o One Minte Test3o,ta5e

$ 7.'7 %'.+ %.' 00.0* 0.*' '%.%

'.1..For Measrin5 Crrent Transor*er:


e have to do all type test & routine test required for general current

transformer & we have to do below mentioned test also as additional.

'.1..1. Type Test: (On,y re-ie o Test certi/cates issed 0y

CPR" ERDA 2 3a,idity period p to ' years on,y)'.*.$.*.*. "ccuracy test.

'.1... Rotine Test:

'.*.$.$.*. "ccuracy test.

The accuracy class shall be designated by the highest permissible percentagecurrent error at rated current for that accuracy class .

'.1...1.1. Accracy C,asses:'.1...1.1.1. Standard Accracy C,asses

Thestandard accuracy classes for measuringcurrent transformers shall be6

.*- .$- .'- *- 7 and '.


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'.1...1.1.. Specia, App,ication AccracyC,asses

For the special application in connection only with special electricity meterswhich measure accurately at a current between ' m" and 0 " (that is- between* percent and *$ percent of the rated current of' ",- the special applicationaccuracy classes shall be .$ ! and .' !. These classes shall apply only for therated secondary current of ' " and for the ratios $'#'- '#' and *#' and theirdecimal multiples.

'.1...1.. $i*its o Crrent Error and P6aseDisp,ace*ent:

'.1...1..1. For t6e Standard Accracy C,asses


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The secondary burden used for test purposes shall have a power factor of .lagging e9cept thatwhen the burden is less than ' :"- a power factor of * may be used. In no caseshall the test burden be less than * :".

Ta0,e 'C:Accracy

c,ass

Percenta5e crrent( ratio)error at percenta5e o rated

crrent

P6asor disp,ace*ent in*intes at percenta5e o

rated crrent* ' $ * *$ * ' $ * *$

.$! .%'

.7' .$ .$ .$ 7 *' * * *

.'! *.' .%' .' .' .' ? +' 7 7 7

'.1...1.!. Re7ire*ent o E7ip*ent8s or testin5:

Current in=ection


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The accuracy class shall be designated by the highest permissible percentagecomposite error at the rated accuracy limit primary current prescribed for theaccuracy class concerned- followed by the letter S) (meaning protection,.

'.1.!..1.1.1. Standard Accracy C,asses:

The standard accuracy classes for protective current transformers shall be ')-*3) and *').

Dote U )rotective current transformers are designated by accuracy class followedby the accuracy limit factor (for e9ample ')*).

'.1.!..1.. $i*it o Errors:

The current error- composite error and the phase displacement at .the ratedfrequency and with rated burden connected- shall not e9ceed the values given in

Table 0.Ta0,e :AccracyC,ass

Crrent Errorat RatedPri*ary Crrent( percent )

P6asedisp,ace*entat RatedPri*ary Crrent( *intes)

Co*posite errorat Ratedaccracy ,i*itpri*ary crrent( percent)

') V * V 0 '

*) V 7 111111111 **') V ' 111111111 *'

'.1.!..1.!. Re7ire*ent o E7ip*ent8s or

testin5: Current in=ection


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Test rig for measurement of composite error.

'.1.!.... Testin5 Procedre:'.1.!....1. Direct test:

Compliance with the limit of composite error given in table 0 shall be

demonstrated by a direct testin which a substantially sinusoidal current equal tothe rated accuracy limit primary current is passed through the primary winding-with the secondary winding connected to the rated burden. The composite errormay be determined as given below.

#asic Circit or

Direct

Measre*ent oCo*posite Error

Current transformer having aturn@s ratio *6* is shown inFig. +. It is connected to asource of primary (sinusoidal,current- a secondary burdenwith linear characteristics-

and to an ammeter in such a manner that both the primary and the secondarycurrent pass through the ammeter- but in oppositedirections. In this manner the resultant current through the ammeter will beequal to the e9citingcurrent under the prevailing conditions of sinusoidal primary current and the rmsvalue of that current- related to the rms value of the primary current- is thecomposite error according to the de4nition.

'.1.!...!. Res,ts to 0e o0tained:

3btained composite error should within the limits mentioned in Table 0.

'.1.&.For Protecti-e Crrent transor*er or specia, prpose

App,ications:


)rotective current transformers for special purpose applications shall bedesignated WClass )!@.

'.1.&.1. Type Test: (On,y re-ie o Test certi/cates issed 0yCPR" ERDA 2 3a,idity period p to ' years on,y)


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'.*.+.*.*.


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Incoming Inspection shall be done as per the Incoming material site

Inspection report F1C31Q"01$ & observation shall be recorded on it.

'.!. Site acceptance test o Crrent transor*er:

!ite acceptance testas per :endor or Greeno1 Inspection and test plan andobservation will be recorded on Chec list for erection of Current transformer1 F1

C31Q"1*%1*.

. RECORDS:

0.*.2aterial Quality Inspection report 1 F1C31Q"01*.0.$.Incoming Inspection report 1 F1C31Q"01$.

0.7./rection Checlist of Current transformer 1 F1C31Q"1*%1*.

testing of ct

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