Testing of CT

 

PROCEDURE FOR CURRENT TRANSFORMER (Factory and Site acceptance Tests) 1. PUR PURPOSE: OSE:

 T  To o have a common practices to a accept ccept the manufacturing Quality of the product and to ensure the Installation quality of the Current transformer. . SCOPE:

Factory acceptance test & site acceptance test. !. RESPO RESPONS" NS"#"$ #"$"T% "T%::

Factory acceptance test by manufacturer & witness by Greeno Central Quality and Greeno !ite Q"#QC for site  acceptance test. &. REFERE REFERENCE NCE DOCUM DOCUMENT ENTS: S:

I! $%' ()art * to +,- "pproved GT) & "pproved rawings- I/C 0++1*. '. PROC PROCED EDUR URE: E: '.1. '.1.

Facto actory ry acce accept ptan ance ce test test or crr crren entt Trans ranso or* r*er er::

"ll the factory acceptance test observations should be recor recorded ded on 2aterial Quality inspection report1 F1C31Q"01*. '.1.1.For +enera, Crrent Transor*er:

!peci4cation limits should be as per

IS 2705 (Part 1):

'.1.1.1. Type test or +enera, Crrent Transor*er: (On,y re-ie o Test certi/cates issed 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. Temperature ure1rise test.

'.*. '.*.*. *.*. *.7. 7. service 8i 8igh ghtn tnin ing g im impu puls lse ee9posed ttes estt fo forr c cur urrren entt ttra rans nsfo forrme merr for in electrically installation. '.*. '.*.*. *.*. *.+. +. !w !wit itch chin ing g iimp mpul ulse se vo volt ltag age e ttes ests ts for for c cur urrren entt transformersof+$:and above. '.*. '.*.*. *.*. *.'. '. ;i ;igh gh vo volt ltag age ep pow ower er1f 1frreq eque uenc ncy yw wet et wi with thst stan and d voltage tests on outdoor current transformers transformers up to and including $+' '.*. '.*.*. *.$. $.*. *.*. *.7. 7. the the relati lativ ve pola polarritie itiess of win indi ding ngss and winding sections> and '.*.*.$.*.*.+. the intermediate tapping- if any. '. '.1. 1.1. 1.. .1. 1.. .

Met6 et6od o *a *ar4in r4in5: 5:

'.*. '.*.*. *.$. $.*. *.$. $.*. *. Th The e tter ermi mina nals ls surface sha halll b be eor m mar ar ed c cle lear arly ly an and d indelibly either on their in their immediate vicinity. '.*.*.$.*.$.$. The m ma aring ssh hall c co onsist o off lle etters followed- or preceded- where necessary- by numbers. The letters shall be in bloc capitals. '.*. '.*.*. *.$. $.*. *.$. $.7. 7. "ll "ll th the e ter termin inal alss mar ar ed )*- !* and C* shall have the same polarity at any instant. '.*. '.*.*. *.$. $.*. *.$. $.+. +. Th The em mar ari in ng o off c cur urrrent tran transsfor formers ers ssha hall ll be as indicated in below 4gures.

 

PROCEDURE FOR CURRENT TRANSFORMER (Factory and Site acceptance Tests)

'.1.1... Po er re7ency dry it6stand tests on pri*ary indin5s. '.1.1...1. Re7ire*ent testin5:

o

E7ip*ent8s

or

;: Tester6 ( to $', t trn rn te test st..

'.1.1..&.1. Re7ire*ent testin5:

o

E7ip*ent8s

or

;: Tester6 ( to ', T6is test is app,ica0,e on,y or crrent transor*ers it6 so,id ins,ation or 6i56est syste* -o,ta5es . 43 and a0o-e and crrent transor*s it6 ,i7id i**ersed ins,ation or 6i56est syste* -o,ta5es o .' 43 and a0o-e. '.1.1..'.1. Re7ire*ent testin5:

 

o

E7ip*ent8s

or

)artial ischarge Tester '.1. '.1.1. 1.. .'. '.. .

Meas easri rin5 n5 "ns "nstr tr*ents ents::

 The measuring instrument instrument used shall comply with 7.+ of I!6 0$?1 *?$.  The instrument used will depen depend d on the quality to be be measur measured ed and the quality preferred 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 * ; oers certain advantages especially where test ob=ects with distributed capacity and inductance are concerned. Dormally- however however-- a narrow band measurement measurem ent of partial discharges is suJcient for instrument transform transformersersparticularly if there is a possibility of choosing between measuring frequencies frequencies in the range @*' 2; to $ 2; )referr )referred ed values are .' 2; and * 2;- but- if feasible- the measurement should be performed at the frequenc frequency y which gives the highest sensitivity.   '. '.1 1.1..'.!.

Testin5 Pr Pro ocedre:

 The partial discharge discharge test shall be c carried arried out af after ter all dielectr dielectric ic tests ar are e completed. The applied voltage shaI* be raised to the pre stress voltage (values given in Table *, before reducing it to the partial discharge measuring voltage also given in below Table 7. Ta0,e ! Per*issi0,e -a,es o partia, disc6ar5e ,e-e,s

 T  Type ype of /arthing ( !ee note *,

 T  Type ype of Instrument transforme r

)re1 !tress voltage ( see note $,

2easuring :oltage ( see note $,

 T  Type ype of Insulation

Detwors with an

Current  T  Transforme ransforme

*.7 Am

*.* Am ( !ee note

8iquid Immersed

7, *.* Am

!olid 8iquid

isolated or resonant

r and )hase to

)ermissible partial ischarge 8evel charge * pC $' pC * pC

 

PROCEDURE FOR CURRENT TRANSFORMER (Factory and Site acceptance Tests) star point

earth voltage  T  Transforme ransforme r )hase to )hase voltage transforme

K7

*.7 Am

*.* Am

Immersed !olid 8iquid Immersed !olid

' pC * pC ' pC

rCurrent . E *.7 *.*Am 8iquid * pC   K7 Immersed transforme Am r and !olid ' pC phase to earth voltage transforme r *.7 Am *.*Am 8iquid * pC )hase to phase Immersed voltage !olid ' pC transforme r Dote *6 If there is no clear distinction to be made for which ind of networ (star point either isolated or eectively earthed, the instrument is meant- the levels for the isolated star point shall be taen.

Detwors with an eectively earthed star point

Dote $6 here the rated voltage of a voltage transforme transformerr is considerably lower than its declared highest system voltage Am- then- sub=ect to agreement between manufacturer and customer- lower pre1str p re1stress ess 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 performed while decreasing the voltage after the power frequency withstand voltage. If the measured partial discharge values e9ceed the permitted limits of Table 7- a separate test as speci4ed above may be carried out. '.1. '.1.1. 1.. .'. '.&. &.

Per* Per*is issi si0, 0,e e part partia ia,, disc disc6a 6ar5 r5e e ,e-e ,e-e,s ,s::

)referred values for the permissible levels of partial discharges are given in Table 7. These values are found by e9perience to guarantee reasonably reliable products at reasonable cost. henever it is possible to clearly distinguish between higher bacground disturbances and the partial discharges arising from the test ob=ect- these higher disturbances may be permissible if agreed by manufacturer and the customer.   '. '.1 1.1..'.'.

Res,ts to 0e 0e o0 o0tained:

"ll the partial discharges should be within limits that mentioned in Table 7. '.1. '.1.1. 1.. .. .

Dete Deter* r*in inat atio ion no o err error ors s or or ot6 ot6er er

c6aracteristics c6aracteristic s accordin5 to t6e re7ire*ents o

 

PROCEDURE FOR CURRENT TRANSFORMER (Factory and Site acceptance Tests) t6e appropriate desi5nation or accracy c,ass (see indi-ida, parts o t6is procedre).

Dote6 *.The determination of errors errors of other characteristics in (', shall be carried out after the tests ($,- (7, and (+,. The order or possible combination of other tests is not standardied.  

$. Lepeat Lepeated ed power freque frequency ncy tests on the primary windings shall be

performed performe d at  percent of the speci4ed test voltage. '.1.1. '.1 .1.!. !. Option Optiona, a, Test Tests: s:

 The following tests tests where applicable- shall be car carried ried out by mutua mutuall agreeme agreement nt between the purchaser and the manufacturer6 '. '.1. 1.1. 1.!. !.1. 1. C6op C6oppe ped d ,i5 ,i56t 6tni nin5 n5 i*p i*p,s ,se e tes testt as as a ty type pe test. '. '.1. 1.1. 1.!. !.. . Meas Measr re* e*en entt o di die, e,ec ectr tric ic diss dissip ipat atio ion n actor or oi, i**ersed crrent transor*ers o .' 43 and a0o-e.

 The measurem measurement ent of dielectric dissipation factor (tan 0, shall be made after the power frequency test on the primary windings. The ambient temperature and the temperature temperatur e of the equipment under test shall be between *MC and +MC. The measurement measurem ent of tan shall be made by means of a !chering 5ridge or other equivalent method.  The test voltagevoltage- which shall be a agreed greed betw between een the manu manufacturer facturer and the purchaser but in no case e9ceeding the highest system voltage divided by 4shall be applied to the primary terminals connected together together.. The secondary terminals- any screen screen and isolated metal casing shall be connected to the measuring bridge. If the transform transformer er has a special device (terminal, suitable for the measurementmeasurement- the other terminals shall be short1circuited and connected to the earthed or the screen screened ed metal casing.. '. '.1. 1.1. 1.!. !.. .1. 1.

 

Re7 Re7ir ire* e*en entt o E7 E7ip ip*e *ent nt8s 8s or or tes testi tin5 n5::

!chering 5ridge. '.1. '.1.1. 1.!. !.. .. .

Testi estin5 n5 proc proced edr re: e:

!chering 5ridge6

 

PROCEDURE FOR CURRENT TRANSFORMER (Factory and Site acceptance Tests)

 The test ob=ect and the rreferenc eference e capacitance is set on high voltage- the balancing elements lay on low voltage and with the null indicator the bridge is balanced (Fig. *,.  The balancing condition is ful4lled ful4lled in the case of same elec electric tric potential on both ends of the null indicator respectively no current Now through the null indicator.  The accuracy of measurem measurement ent depends es essentially sentially on the sensitivity of tthe he null indicator.. The balancing condition can be described with following formula6 indicator   H9 # H7 O HD # H+   TanPO  TanPO CRLR  O C+L+ '.1. '.1.1. 1.!. !.. .!. !.

Res Res,t ,ts s to 0e o0tai 0taine ned: d:

 The issipation factor factor value measur measured ed shall not e9 e9ceed ceed the v value alue agreed between the manufacturer and the purchaser.

  '.1. '.1.1. 1.!. !.!. !. Co** Co**is issi sion onin in5 5 test tests s on ne ne cr crre rent nt transor*ers p to and inc,din5 ! 43. '.1. '.1.1. 1.!. !.!. !.1. 1. Poe Poer> r>F Fre7 re7en ency cy Test est on Pri* Pri*ar ary y ;indin5s: (T (Test est procedre sa*e as '.1.1.. '.1.1. . c,ase o t6is procedre)

 

PROCEDURE FOR CURRENT TRANSFORMER (Factory and Site acceptance Tests) 5y agreement between the manufacturer and the purchaser- separate source power frequency frequency tests on the primary winding insulation may be made after erection on site provided that the transformer is in a satisfactory conditions for testing and has not been in service. The transformers shall be temporarily disconnected from any other apparatus to which it may be connected. The one minute test voltage shall !3 percent of speci4ed power freque frequency ncy test voltage. If for any special reasons the duration of the test e9ceeds one minute- the relationship between duration of the test and the percentage of the one minute test voltage shall be as given in Table +. D3T/1Commissioning test on curr current ent transformers for highest system voltage over 70 : are deprecated. Ta0,e & App,ied Poer>Fre7ency 9i56 3o,ta5e Tests or Dration EBceedin5 One Minte (Ater Erection on Site) Dration o test in *intes

Percenta5e o One Minte Test 3o,ta5e

$ 7 + ' * *'

7.' %'. %. 00.0 0. '%.%

'.1..For Measrin5 Crrent Transor*er:

!peci4cation limits should be as per

IS 2705 (Part 2):

e have to do all type test & routine test required for general current transformer transform er & we have to do below mentioned test also as additional. '.1..1. Type Test: Test: (On,y re-ie o Test Test certi/cates issed issed 0y CPR" ERDA 2 3a,idity period p to ' years on,y)

'.*.$.*.*.

"ccuracy test.

'.1.. '.1 ... . Rotin Rotine e Test Test::

'.*.$.$.*.

"ccuracy test.

 The accuracy class shall be designated by the highest permissible percenta percentage ge current error at rated current for that accuracy class . '. '.1. 1.. .. .1. 1.1. 1. Acc Accra rac cy C,a C,ass sses es:: '.1. '.1.. .. .1. 1.1. 1.1. 1. Stan Standa dard rd Acc Accra racy cy C,a ,ass sses es

  The  standard accuracy classes for measuring current transformers shall be6  

.*- .$- .'- *- 7 and '.

 

PROCEDURE FOR CURRENT TRANSFORMER (Factory and Site acceptance Tests) '. '.1. 1.. .. .1. 1.1. 1.. . Spec Specia ia,, App, App,ic icat atio ion n Acc Accra racy cy C,asses

For the special application in connection only with special electricity meters which measure accurately at a current between ' m" and 0 " (that is- between * percent and *$ percent of the rated curr current ent of' ",- the special application accuracy classes shall be .$ ! and .' !. These classes shall apply only for the rated secondary current of ' " and for the ratios $'#'- '#' and *#' and their current decimal multiples. '. '.1. 1.. .. .1. 1.. . $i*i $i*its ts o Crre Crrent nt Erro Error r and and P6as P6ase e Disp,ace*ent: '.1. '.1.. .. .1. 1.. .1. 1. For t6e t6e Sta Stand ndar ard d Acc Accr rac acy y C,a C,ass sses es