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IEC 61869-2 Edition 1.0 2012-09 INTERNATIONAL STANDARD NORME INTERNATIONALE Ins

IEC 61869-2 Edition 1.0 2012-09 INTERNATIONAL STANDARD NORME INTERNATIONALE Instrument transformers – Part 2: Additional requirements for current transformers Transformateurs de mesure – Partie 2: Exigences supplémentaires concernant les transformateurs de courant INTERNATIONAL ELECTROTECHNICAL COMMISSION COMMISSION ELECTROTECHNIQUE INTERNATIONALE XB ICS 17.220.20 PRICE CODE CODE PRIX ISBN 978-2-83220-293-7 ® Registered trademark of the International Electrotechnical Commission Marque déposée de la Commission Electrotechnique Internationale ® Warning! Make sure that you obtained this publication from an authorized distributor. Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé. This is a preview - click here to buy the full publication IEC 61869-2:2012/ISH1:2022 – 1 – © IEC 2022 ICS 17.220.20 INTERNATIONAL ELECTROTECHNICAL COMMISSION ____________ IEC 61869-2 Edition 1.0 2012-09 INSTRUMENT TRANSFORMERS – Part 2: Additional requirements for current transformers I N T E R P R E T A T I O N S H E E T 1 This interpretation sheet has been prepared by IEC Technical Committee 38: Instrument transformers. The text of this interpretation sheet is based on the following documents: DISH Report on voting 38/687/DISH 38/692/RVDISH Full information on the voting for the approval of this interpretation sheet can be found in the report on voting indicated in the above table. ___________ 5.6.201.3 Limits of ratio error (ε) and phase displacement for measuring current transformers BACKGROUND: Subclause 5.6.201.3 states the following: ...For all classes, the burden shall have a power-factor of 0,8 lagging except that, when the burden is less than 5 VA, a power-factor of 1,0 shall be used, with a minimum value of 1 VA. QUESTION: How shall this sentence be interpreted when the rated output is above 5 VA, but the test burden for the test at 25 % of the rated output is below 5 VA? For example, when testing a current transformer with a rated output of 10 VA, the test burden at 25 % of the rated output is 2,5 VA. Shall this test burden be at power factor 1,0 or 0,8? IEC 61869-2:2012-09/ISH1:2022-01(en) This is a preview - click here to buy the full publication – 2 – IEC 61869-2:2012/ISH1:2022 © IEC 2022 INTERPRETATION: The "burden" mentioned in the above-stated sentence of 5.6.201.3 is to be understood as the "test burden" and therefore in the proposed example the test at 2,5 VA has to be carried out at power factor 1,0. Rationale: The sentence under discussion is about the burden connected to the current transformer during the accuracy test. This is the understanding of manufacturers, metrological institutes and test laboratories. This is also reflected in the commercially available test burdens used for accuracy testing of current transformers. These burdens have the possibility to choose values of 5 VA and above with a power factor of 0,8 and values below 5 VA with a power factor of 1,0. The minimum test burden is 1 VA. For the above-mentioned reasons, it is logical to conclude that: • the power factor value is 0,8 for test burdens of 5 VA and above, • the power factor value is 1,0 for test burdens of less than 5 VA, • 1 VA is the minimum value for the rated output, as well as for the test burden. Some users need to compare accuracy measurements at 25 % and 100 % of the rated output with the same power factor of 0,8. The best way of doing this is a measurement. If this is not possible, the following method shows a possibility to calculate the ratio error and phase displacement at power factor 0,8 based on a measurement performed with power factor 1,0 for a given test burden [1]1 [2]. This interpretation sheet does not make a statement about the inaccuracies of this method. ( ) ( ) ( ) ( ) ( ) 0 0,8 0 1 1 0,6 Δ 1 0,8 0,8 0,6 Δ B φ ε ε R B / R B R B ε B φ / R B R B     = − + + + + + − +     + (1) ( ) ( ) ( ) ( ) ( ) 0 0,8 0 1 1 0,6 Δ Δ 1 0,8 0,8 Δ 0,6 Bε φ φ R B / R B R B φ Bε / R B R B     = − + + − + + + +     + (2) where ε0,8 calculated ratio error (in percent) at test burden with power factor 0,8; Δφ0,8 calculated phase displacement (in centiradians) at test burden with power factor 0,8; ε0 extrapolated ratio error (in percent) at zero total burden; Δφ0 extrapolated phase displacement (in centiradians) at zero total burden; ε1 measured ratio error (in percent) at test burden with power factor 1,0; Δφ1 measured phase displacement (in centiradians) at test burden with power factor 1,0; R secondary winding resistance (in ohms) at ambient temperature; B test burden (in ohms) with power factor 1,0. _____________ 1 Numbers in square brackets refer to the Bibliography. This is a preview - click here to buy the full publication IEC 61869-2:2012/ISH1:2022 – 3 – © IEC 2022 In order to estimate the ratio error and phase displacement at zero total burden, two measurements must be made at two different test burdens, both with power factor 1,0, followed by a linear extrapolation to zero total burden. Note that the total burden is equal to the external burden (B) plus the internal burden (R). Where it is known that the current transformer is manufactured without any turns compensation, the errors at zero total burden may be assumed to be zero and the Formulas (1) and (2) may be simplified to the following: ( ) ( ) 0,8 1 1 0,8 0,6 Δ ε R B ε B φ / R B   = + − +   (3) ( ) ( ) 0,8 1 1 Δ 0,8 Δ 0,6 φ R B φ Bε / R B   = + + +   (4) NOTE 1 The secondary winding resistance may be taken as the value measured in DC. NOTE 2 For the calculation according to the above formula, all phase displacements are in centiradians. Phase displacements in minutes require a conversion to centiradians (1 minute = 0,029 1 centiradian). Bibliography [1] POKORNY, P. Conversion of current transformer errors at unity power factor burden, to 0,8 power factor-equivalent, MAPAN – Journal of Metrology Society of India, Vol. 24, No. 1, 2009, pp 3-8 [2] Australian Standard AS 60044-1:2007, Instrument transformers – Part 1: Current transformers ___________ This is a preview - click here to buy the full publication – 2 – 61869-2 © IEC:2012 CONTENTS FOREWORD ........................................................................................................................... 5 1 Scope ............................................................................................................................... 8 2 Normative references ....................................................................................................... 8 3 Terms and definitions ....................................................................................................... 8 3.1 General definitions .................................................................................................. 8 3.3 Definitions related to current ratings ........................................................................ 9 3.4 Definitions related to accuracy .............................................................................. 10 3.7 Index of abbreviations ........................................................................................... 18 5 Ratings ........................................................................................................................... 20 5.3 Rated insulation levels ........................................................................................ 20 5.3.2 Rated primary terminal insulation level ............................................. 20 5.3.5 Insulation requirements for secondary terminals ............................... 20 5.3.201 Inter-turn insulation requirements ..................................................... 20 5.5 Rated output ....................................................................................................... 20 5.5.201 Rated output values ......................................................................... 20 5.5.202 Rated resistive burden values .......................................................... 20 5.6 Rated accuracy class .......................................................................................... 21 5.6.201 Measuring current transformers ........................................................ 21 5.6.202 Protective current transformers ........................................................ 22 5.6.203 Class assignments for selectable-ratio current transformers ............. 26 5.201 Standard values for rated primary current ........................................................... 26 5.202 Standard values for rated secondary current ....................................................... 27 5.203 Standard values for rated continuous thermal current ......................................... 27 5.204 Short-time current ratings ................................................................................... 27 5.204.1 Rated short-time thermal current (Ith) ............................................... 27 5.204.2 Rated dynamic current (Idyn) ............................................................ 27 6 Design and construction ................................................................................................. 27 6.4 Requirements for temperature rise of parts and components .............................. 27 6.4.1 General ............................................................................................ 27 6.13 Markings ............................................................................................................. 27 6.13.201 Terminal markings ............................................................................ 27 6.13.202 Rating plate markings ....................................................................... 28 7 Tests .............................................................................................................................. 30 7.1 General .............................................................................................................. 30 7.1.2 Lists of tests ..................................................................................... 30 7.2 Type tests ........................................................................................................... 31 7.2.2 Temperature-rise test ....................................................................... 31 7.2.3 Impulse voltage withstand test on primary terminals ......................... 33 7.2.6 Tests for accuracy ............................................................................ 33 7.2.201 Short-time current tests .................................................................... 35 7.3 Routine tests ...................................................................................................... 36 7.3.1 Power-frequency voltage withstand tests on primary terminals ......... 36 7.3.5 Tests for accuracy ............................................................................ 36 7.3.201 Determination of the secondary winding resistance (Rct) ................... 38 7.3.202 Determination of the secondary loop time constant (Ts) .................... 38 This is a preview - click here to buy the full publication 61869-2 © IEC:2012 – 3 – 7.3.203 Test for rated knee point e.m.f. (Ek) and exciting current at Ek .......... 39 7.3.204 Inter-turn overvoltage test ................................................................ 39 7.4 Special tests ....................................................................................................... 40 7.4.3 Measurement of capacitance and dielectric dissipation factor ........... 40 7.4.6 Internal arc fault test ........................................................................ 40 7.5 Sample tests ....................................................................................................... 41 7.5.1 Determination of the remanence factor ............................................. 41 7.5.2 Determination of the instrument security factor (FS) of measuring current transformers uploads/s3/info-iec61869-2-ed1-0-b.pdf