SIST IEC 60044-6:1995
(Main)Instrument transformers - Part 6: Requirements for protective current transformers for transient performance
Instrument transformers - Part 6: Requirements for protective current transformers for transient performance
Concerns requirements and tests, in addition to those given in chapter 1 of IEC 60185, that are necessary when inductive current transformers are used with electrical protective schemes in which the prime requirement is the maintenance of a defined performance up to several times the rated current when the current contains an exponentially decaying d.c. component of defined time constant.
Transformateurs de mesure - Partie 6: Prescriptions concernant les transformateurs de courant pour protection pour la réponse en régime transitoire
Décrit les prescriptions et les essais qui, en complément de ceux indiqués au chapitre 1 de la CEI 60185, s'appliquent aux transformateurs de courant inductifs destinés à être utilisés avec des systèmes de protection électrique pour lesquels il est primordial que les transformateurs de courant conservent une précision déterminée en présence d'un courant atteignant plusieurs fois le courant assigné et comportant une composante apériodique décroissante exponentiellement avec une constante de temps fixée.
Instrument transformers - Part 6: Requirements for protective current transformers for transient performance
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST IEC 60044-6:1995
01-oktober-1995
Instrument transformers - Part 6: Requirements for protective current transformers
for transient performance
Instrument transformers - Part 6: Requirements for protective current transformers for
transient performance
Transformateurs de mesure - Partie 6: Prescriptions concernant les transformateurs de
courant pour protection pour la réponse en régime transitoire
Ta slovenski standard je istoveten z: IEC 60044-6
ICS:
17.220.20 0HUMHQMHHOHNWULþQLKLQ Measurement of electrical
PDJQHWQLKYHOLþLQ and magnetic quantities
SIST IEC 60044-6:1995 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST IEC 60044-6:1995
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SIST IEC 60044-6:1995
CEI
NORME
IEC
INTERNATIONALE
44-6
INTERNATIONAL
Première édition
STANDARD First edition
1992-03
Transformateurs de mesure
Partie 6:
Prescriptions concernant les transformateurs
de courant pour protection pour la réponse
en régime transitoire
Instrument transformers
Part 6:
Requirements for protective current transformers
for transient performance
réservés — Copyright — all rights reserved
© CEI 1992 Droits de reproduction
rt of this publication may be reproduced or utilized in
Aucune partie de cette publication ne peut étre reproduite ni No pa
utilisée sous quelque forme que ce soit et par aucun pro- any form or by any means, electronic or mechanical,
ion
cédé, électronique ou mécanique, y compris la photocopie et including photocopying and microfilm, without permiss
les microfilms, sans l'accord écrit de l'éditeur. in writing from the publisher.
Suisse
Bureau Central de la Commission Electrotechnique Internationale 3, rue de Varembé Genève,
CODE PRIX
Commission Electrotechnique Internationale
PRICE CODE
(C` International Electrotechnical Commission
MemutyHapo tnaa 3netcrpoTexHHVecttaR
I HOMHCCHR
Pour prix, voir catalogue en vigueur •
For price, see current catalogue
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SIST IEC 60044-6:1995
44-6 ©I EC – 3 –
CONTENTS
Page
FOREWORD 5
INTRODUCTION 7
Clause
1 Scope 9
9
2 Normative references
3 Definitions 9
17
rformance requirements 4 Ratings and pe
21
5 Methods of specification
23
6 Marking of rating plate
27
7 Tests
Annexes
35 A Basic theoretical equations for transient dimensioning
37
B Determination of core magnetization characteristic
C Direct tests 59
73
ormance criteria for current transformer for protection relaying
Guide to perf
D
E Determination of turns ratio error 85
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SIST IEC 60044-6:1995
44-6 0O IEC – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
INSTRUMENT TRANSFORMERS
Part 6: Requirements for protective current transformers
for transient performance
FOREWORD
1)
The formal decisions or agreements of the IEC on technical matters, prepared by Technical Committees on
which all the National Committees having a special interest therein are represented, express, as nearly as
possible, an international consensus of opinion on the subjects dealt with.
2) They have the form of recommendations for international use and they are accepted by the National
Committees in that sense.
3)
In order to promote international unification, the IEC expresses the wish that all National Committees
should adopt the text of the IEC recommendation for their national rules in so far as national conditions will
permit. Any divergence between the IEC recommendation and the corresponding national rules should, as
far as possible, be clearly indicated in the latter.
This part of International Standard IEC 44 has been prepared by IEC Technical Committee
No. 38: Instrument transformers.
The text of this part is based on the following documents:
Six Months' Rule Repo rts on Voting Two Months' Procedure Report on Voting
38(CO)78 38(00)81 & 81A 38(CO)83 38(00)86
Full information on the voting for the approval of this part can be found in the Voting
Reports indicated in the above table.
This part of IEC 44 is to be read in conjunction with IEC 185 and its Amendment No. 1.
Annexes A, B, C, D and E form an integral pa rt of this part.
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SIST IEC 60044-6:1995
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INTRODUCTION
Performance criteria for class P current transformers included in Chapter III of IEC 185
relate to a steady state a.c. symmetrical primary energizing current which allows the
limiting secondary e.m.f. to be as defined in 34.5 of IEC 185. In this part of IEC 44,
requirements for protective current transformers as classified by 3.5 take account of the
additional flux linking the secondary winding due to the d.c. component of energizing
current. Strictly, the limiting condition is defined by the integral of the voltage which is
induced in the secondary winding of the current transformer in order to drive current in the
secondary loop, inclusive of winding and secondary resistance, for the specified energiz-
ing conditions. For mathematical convenience, an equivalent sinusoidal e.m.f. is used to
define the limiting condition. Refer also to annex B.
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SIST IEC 60044-6:1995
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INSTRUMENT TRANSFORMERS
Part 6: Requirements for protective current transformers
for transient performance
1 Scope
This part of IEC 44 covers the requirements and tests, in addition to those in Chapter I of
IEC 185, that are necessary for inductive current transformers for use with electrical
protective schemes in which the prime requirement for the current transformers is the
ormance up to several times the rated current when the
maintenance of a defined pe rf
current contains an exponentially decaying d.c. component of defined time constant.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute
provisions of this part of IEC 44. At the time of publication, the editions indicated were
valid. All standards are subject to revision, and parties to agreements based on this part
of IEC 44 are encouraged to investigate the possibility of applying the most recent editions
of the standards indicated below. Members of IEC and ISO maintain registers of currently
valid International Standards.
High-voltage alternating-current circuit-breakers.
IEC 56: 1987,
Current transformers.
IEC 185: 1987,
3 Definitions
of IEC 44, the following definitions apply.
For the purpose of this pa rt
R.M.S. value of primary symmetrical
(Ipso):
3.1 rated primary short-circuit current
ormance of the current transformer is
short-circuit current on which the rated accuracy pe rf
based.
): Difference between the instantaneous values of
(iE
3.2 instantaneous error current
) and the primary
) multiplied by the rated transformation ratio (K m
the secondary current (is
current (in):
iE = Kn is - ip
When both alternating current and direct current components are present, the constituent
components are separately identified as follows:
i
i i i
+ cdc - (K nsac - ^pac)+ (K i nsdc - pdc)
c— cac
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SIST IEC 60044-6:1995
44-6 © I EC - 11 -
Maximum instantaneous error current, for the
3.3 peak instantaneous (total) error (é):
specified duty cycle, expressed as a percentage of the peak instantaneous value of the
rated primary short-circuit current:
i'." = 100 ï / (4-2-/
) (%)
psc
(Eac): Maximum instanta-
3.4 peak instantaneous alternating current component error
neous error of the alternating current component expressed as a percentage of the peak
instantaneous value of the rated primary short-circuit current:
= AI 2
100 / (
(%)
/psc)
Éac sac
Current transformers for protection are
protective current transformer classes:
3.5
classified according to functional performance as follows:
c ) with steady state symmetrical Accuracy limit defined by composite error (£
class P:
primary current. No limit for remanent flux.
class TPS: Low leakage flux current transformer for which performance is defined by the
secondary excitation characteristics and turns ratio error limits. No limit for
remanent flux.
class TPX: Accuracy limit defined by peak instantaneous error (É) during specified
transient duty cycle. No limit for remanent flux.
(É) during specified
class TPY: Accuracy limit defined by peak instantaneous error
transient duty cycle. Remanent flux not to exceed 10 % of the saturation flux.
class TPZ: Accuracy limit defined by peak instantaneous alternating current component
d during single energization with maximum d.c. offset at specified
error (ga
secondary loop time constant. No requirements for d.c. component error limit.
Remanent flux to be practically negligible.
(T ): That specified value of the time constant of
3.6 specified primary time constant
which the pe rformance of the current trans-
the d.c. component of the primary current on
former is based. This value may also be a rated value for class TPX, TPY and TPZ current
transformers and then will be marked on the rating plate.
): Time during which the specified accuracy
permissible time to accuracy limit (tat
3.7
is maintained during any specified energization period of a given duty cycle.
NOTE - This time will usually be defined by the critical measuring time of the associated protection
scheme. When stable operation of the protection scheme is a limiting requirement, it may also be
necessary to consider the time taken by the circuit breaker to interrupt the current.
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SIST IEC 60044-6:1995
– 13 –
44-6 © IEC
Elapsed time during a prescribed energization period
time to maximum flux
3.8
(tmax):
at which the transient flux in a current transformer core achieves maximum value, it being
assumed that saturation of the core does not occur.
): Time interval between interruption and
3.9 dead time (during auto -reclosing) (tfr
re-application of the primary short-circuit current during a circuit breaker auto-reclosing
duty cycle (refer also to IEC 56).
Duty cycle in which, during each
3.10 specified duty cycle (C-0 and/or C-0-C-0):
specified energization, the primary energizing current is assumed to be "fully offset" (see
) and be of rated amplitude (/psc).
p
note below), with the specified decay time constant (T
Duty cycles are as follows:
Single energization: C - t'- 0
Double energization: C - t'- 0 - - C - t"- 0
th.
(both energizations in the same polarity of flux)
where:
t' is the duration of first current flow: specified accuracy being maintained during time t'ai
t" is the duration of second current flow: specified accuracy being maintained during time t al.
NOTE - Specification of partial offset would reduce the required transient factor by an amount approxi-
mately proportional to the reduction. For this reason specification of full offset parameters is recommended.
(R b): Rated value of the secondary connected resistive
3.11 rated resistive burden
burden in ohms.
ct): Secondary winding d.c. resistance in ohms,
3.12 secondary winding resistance (R
corrected to 75 °C or such other temperature as may be specified.
Total resistance of the secondary circuit,
3.13 secondary loop resistance (Rs):
inclusive of the secondary winding resistance corrected to 75 °C, unless otherwise
specified, and inclusive of all external burden connected.
(Ts): Value of the time constant of the
3.14 rated secondary loop time constant
secondary loop of the current transformer obtained from the sum of the magnetizing and
) and the secondary loop resistance (Rs):
the leakage inductances (L s
s=Ls/Rs
ssc): The ratio:
short-circuit current factor (K
3.15 rated symmetrical
Kssc – /psc / /pn
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SIST IEC 60044-6:1995
44-6 ©I EC - 15 -
Ratio of the theoretical total secondary linked flux to the
3.16 transient factor (Kif):
peak instantaneous value of the a.c. component of that flux, when a current transformer is
s) is
subjected to a specified single energization and the secondary loop time constant (T
assumed to have retained a constant value throughout the energization period.
): That theoretical value representative of
3.17 rated transient dimensioning factor (Kid
the transient dimensioning necessary to satisfy the specified duty cycle.
are given in annex A.
p, s , Kif and Ktd
Mathematical relationships between T
Current transformer for which a knowledge
3.18 low leakage flux current transformer:
of the secondary excitation characteristic and secondary winding resistance is sufficient
for an assessment of its transient performance for any combination of burden and duty
cycle at rated or lower value of primary symmetrical short-circuit current up to the theo-
retical limit of the current transformer capability determined from the secondary excitation
characteristic.
Current transformer which does not
3.19 high leakage flux current transformer:
satisfy the requirements of 3.18 and for which an additional allowance is made by the
manufacturer to take account of influencing effects which result in additional leakage flux.
Such a current transformer is expected to satisfy a specified duty cycle.
td ) is satisfied for a C-0-C-0 duty
NOTE - In general, if the theoretical transient dimensioning factor (K
cycle, then the accuracy is maintained during a C-0 duty cycle at least up to the time at which the rated
al ), defined in 3.20, is reached.
equivalent limiting secondary e.m.f. (E
(Eat): That r.m.s. value of the
3.20 rated equivalent limiting secondary e.m.f.
equivalent secondary circuit e.m.f. of rated frequency necessary to satisfy the specified
duty cycle and derived from the following:
Rb) Isn V, r.m.s.)
(
ct + Eal = Kssc Ktd (R
(Uai): That r.m.s. value of
rated equivalent excitation limiting secondary voltage
3.21
sinusoidal voltage of rated frequency necessary to ensure that the rated equivalent limiting
secondary e.m.f. will be attained after due account is taken of the current transformer
construction and which, when applied to the transformer secondary winding, would result
in a magnetizing current not exceeding the maximum permissible error current appropriate
to the current transformer class.
( V, r.m.s.)
Ual = Eal F
is the factor of construction defined in 3.29.
where Fc
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SIST IEC 60044-6:1995
44-6 ©I EC – 17 –
(Ealc): That equivalent r.m.s.
3.22 equivalent secondary accuracy limiting e.m.f.
e.m.f. of rated frequency determined during a direct test when the observed error current
corresponds to the appropriate limit for the class.
NOTE - The error current is an absolute value based on the specified primary current value and is thus
not affected by any parametric changes which may have been necessary to attain the secondary error
limiting condition.
(Ualc): That r.m.s. value of
3.23 equivalent secondary accuracy limiting voltage
sinusoidal voltage of rated frequency which, if applied to the secondary winding of a
current transformer, would result in an exciting current corresponding to the maximum
permissible error current appropriate to the current transformer class.
): That peak value of the flux which would exist in a core in the
3.24 saturation flux (T s
transition from the non-saturated to the fully saturated condition and deemed to be that
point on the B-H characteristic for the core concerned at which a 10 % increase in B
causes H to be increased by 50 %.
): That value of flux which would remain in the core three
3.25 remanent flux (T r
minutes after the interruption of an exciting current of sufficient magnitude as to induce
the saturation flux (`P S) defined in 3.24 above.
remanence factor (Kr): The ratio
3.26
Kr = r / ^s
): That peak value of the secondary linked flux correspond-
3.27 accuracy limit flux (cDal
ing to E
al :
Eal / (2icf)
(Dal =
When is given in volts, r.m.s., is expressed in weber.
Eai (Dal
d: Peak value of the exciting
accuracy limiting secondary exciting current (la
3.28
(error) current appropriate to the current transformer class.
): Factor declared by the manufacturer for the design.
3.29 factor of construction (F0
The factor of construction is determined from the ratio:
Fc = Ualc / Eaic
4 Ratings and performance requirements
Standard values for rated symmetrical short-circuit current factor (Kssc)
4.1
rformance are:
Standard values of for protective current transformers for transient pe
K0
3-5-7,5-10-12,5-15-17,5-20-25-30-40-50
The preferred values are underlined.
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SIST IEC 60044-6:1995
44-6 ©IEC - 19 -
4.2 Standard values for symmetrical short-circuit current
4.2.1 Rated short-time thermal current
(lth)
Standard r.m.s. values, expressed in kiloamperes, are:
6,3-8-10-12,5-16-20-25-31,5-40-50-63-80-100
4.2.2 Rated primary short-circuit current
(ipsc)
selected from the values
Preferred values are derived from the product of and K
/n sc
of IEC 44 respectively. The product need not
rt
given in 4.1 of IEC 185 and 4.1 of this pa
be exactly equal to
/th.
Standard values for rated primary time constant (Tp)
4.3
Standard values, expressed in milliseconds, are:
40-60-80-100-120
NOTE - For some applications, higher values of rated primary time constant may be required. Example:
large turbo -generator circuits.
4.4 Standard values for rated transient dimensioning factor
(Ktd)
At present there are no standard values for the rated transient dimensioning factor
because the values of this factor depend upon the application.
(Rb)
4.5 Standard values of rated resistive burden
Standard values of rated resistive burden in ohms for class TP current transformers,
based on a rated secondary current of 1 A are:
2,5-5-7,5-10-15
The preferred values are underlined. For current transformers having a rated secondary
current other than 1 A, the above values should be adjusted in inverse ratio to the square
of the current.
4.6 Error limits for TPS current transformers
. The error
The turns ratio of a TPS current transformer shall be numerically equal to 1/Kn
in this turns ratio shall not exceed ±0,25 %.
The accuracy limiting conditions are defined by the magnetization characteristic and the
shall not be less than the specified value. The
excitation limiting secondary voltage (Jai
value shall be such that an increase of 10 % in magnitude does not result in an increase in
the corresponding peak instantaneous exciting current exceeding 100 %.
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SIST IEC 60044-6:1995
44-6©IEC –21 –
When specified by the purchaser, the measured value of the peak exciting current at the
excitation limiting secondary voltage shall not exceed the specified value. If no limit is set,
the exciting current shall, in any case, not exceed that value corresponding to 10 % of
'th
referred to the secondary side (see TPX CTs, table 1).
The excitation limiting secondary voltage defined by the purchaser is generally expressed
as follows:
KKsc (Rct+
Ua^>_
/sn
R b)
ct is defined by
in which is a dimensioning parameter assigned by the purchaser. R
K
the manufacturer's design except that for some applications limits may need to be set
by the purchaser to enable co-ordination with other equipment.
Error limits for TPX, TPY and TPZ current transformers
4.7
Rs = Rct + Rb , the errors shall
With the secondary loop resistance adjusted to the value
not exceed the values given in table 1.
Table 1 - Limits of error
At rated primary current At accuracy limit condition
Phase displacement
Class Maximum peak
Ratio
instantaneous error
error
ok
Min Centirad
±30 ±0,9 É = 10
TPX ±0,5
±1,0 ±60 ±1,8 e = 10
TPY
180 ± 18 5,3 ± 0,6
TPZ ±1,0
Sac = 10
NOTE - For some applications, deviation from the above values may be necessary (refer also to
annex D.3). Similarly, the absolute value of the phase displacement may in some cases be of less
importance than achieving minimal deviation from the average value of a given production series.
5 Methods of specification
The methods of specification for the different CT classes are illustrated in table 2.
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SIST IEC 60044-6:1995
23 -
44-6© I EC -
Table 2 - Methods of specification
TPZ
TPS TPX TPY
CT class
x x
x x
Rated primary current
x x
Rated secondary current x x
x
x x x
Rated frequency
Highest voltage for equipment
x x x
and rated insulation level x
X
X X X
' th
X X X
X
'dyn
x x
Ratio to which specification applies x x
x
x x
K x
sso
x
– x x
T
P
– – –
Ts –
see note
Duty cycle
x –
Single: t', t'a , – x
double: t', t' t
a1 , tfr' t", al
X
Rb X X X
x – – –
K
x – – –
Maximum at Uai
/al
x – – –
Rif
x applicable – not applicable
NOTE - When the purchaser wishes to obtain compatibility between existing equipment and new units, an alignment
specification may define limiting values for certain parameters, for example s or Rif . It will be necessary, however,
to recognize possible differences between designs. Issue of the principal objectives for the intended application and
best available (name-plate) data for the existing current transformers will usually achieve acceptable results.
6 Marking of rating plate
The rating plate shall carry the appropriate information given in accordance with clause 23
of IEC 185. Table 3 identifies additional information to be included.
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SIST IEC 60044-6:1995
- 25 -
44-6 © I EC
Table 3 - Information to be included in the rating plate
References
TPZ to to Notes
CT class TPS TPX TPY
IEC 185 IEC 44-6
3.6 1
x X X X -
p n
x 3.7 - 1
x x
/
snn
3
x x x 3.25 -
x
/th
3
/ x X x 3.26 -
X
dYn
- 3.1
x - 3.15
x x x
K
ssc
- 4.2
3.11
x x x -
Rb x
3.12
x x x -
Rot (at . °C) x
Kid — x x x — 3.17
4.6
x - -
K
3.21
—
X —
ai
3.28
— —
— -
X
l
a
x x x - 3.29 2
F -
c
x x - 3.6 5
TP - x
x - - 3.14 4,5
T - -
s
Duty cycle
3.9
- x x - -
single: t', t'ai
3.10
— 5
double: (, t'ai, tir, t", r
ai
x applicable - not applicable
NOTES
and K will usually be the highest values applicable
1 For multiratio protective current transformers, / ID.
to the range of ratios.
2 Data to be given if Fr,> 1,1.
may exceed 2,5 /iii depending on the values of and /PSC.
3 Values for ion
P
4 When s is greater than 10 s, it will usually be adequate to mark on the rating plate 5 > 10 s.
5 T , s and the duty cycles are interrelated and their indication on the rating plate could be omitted for1
low leakage flux CTs.
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SIST IEC 60044-6:1995
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44-6 ©I EC
7 Tests
7.1 To prove compliance of the current transformer with the requirements of this standard
the following tests shall be performed as required by the test schedule - table 4.
Table 4 - Test schedule
References
CT class
Test
Clause or
Note
TPS TPX TPY TPZ
subclause
— — 7.2.1 1
Turns ratio error x —
Steady state ratio error
x 7.2.2 1
— x x
and phase displacement
7.2.3 1
x x x x
Rct
x 7.2.4 1
x x x
Excitation characteristic
K — — x — 7.2.5 1
•
r
— — x 7.2.6 1
x
T
s
x 7.3 2
— x x
Errors at limiting conditions
x 7.3.1 2
— x x
F
c
Verification of low leakage
— 7.4 3
(F < 1,1) x — —
flux design
x applicable — not applicable
NOTES
1 Type and routine tests.
2 Type tests.
Special tests performed only on agreement between manufacturer and purchaser.
3
7.2 Type and routine tests
7.2.1 Turns ratio error
The turns ratio error shall be determined by an appropriate method. Refer to annex E.
7.2.2 Steady state ratio error and phase displacement
(Rs = Rct + Rb) ratio error and
With the secondary loop resistance adjusted to rated value
phase displacement shall be measured at rated current (Ipn).
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7.2.3 Determination of secondary winding resistance (Red
The secondary winding resistance shall be measured and an appropriate correction
applied if the measurement is made at a temperature which differs from 75 °C or such
other temperature as may have been specified. The value so adjusted is the rated value
for Rct.
7.2.4 Determination of secondary excitation characteristic
For type tests, an excitation curve is required up to not less than 1,1 times saturation flux.
The manufacturer may choose the test method. Some test methods are given in annex B.
For routine tests on TPX and TPY current transformers, the peak value of the exciting
current at (Jai is to be measured.
For routine tests on TPZ current transformers, the peak value of the exciting secondary
current 1 shall not exceed the value obtained from the expression given below:
a1
/c0 7-5] +0,1 {
fa,
NOTE - For TPZ current transformers the accuracy is specified only for the a.c. component while, in the
during indirect tests, it is necessary to take into account also
determination of the permissible value of
ial
the d.c. component of the exciting current. In the above equation, the d.c. component is represented by
(Ktd – 1) and the permissible error in the a.c. component by 0,1.
7.2.5 Determination of remanence factor (Kr)
The remanence factor (Kr) shall be determined to prove compliance with the appropriate
class limits. Refer to annex B.
Calculation of secondary loop time constant (Ts)
7.2.6
) shall be determined and shall not differ from the
The secondary loop time constant (Ts
declared or the rated value by more than ±30 % for class TPY and ±10 % for class TPZ
current transformers. Refer to annex B.
7.3 Type tests
7.3.1 General
Direct tests intended to be made at the specified limiting parameters and duty cycle are
type tests. Their purpose is:
- to measure the peak instantaneous error current of the CT, when subjected to the
specified duty cycle, according to 3.3 (classes TPX and TPY) and 3.4 (class TPZ);
e) (see 3.29).
- to determine the factor of construction (F
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The tests can be performed on a full scale model of the active part of the current trans-
former assembly inclusive of all metal housings but with reduced insulation.
Direct tests may be replaced by the secondary exciting test, if either of the following is
satisfied:
the current transformer is of the low leakage flux type.
a)
To satisfy this requirement, it shall be shown by a drawing that the current transformer
has substantially continuous ring core with air gaps uniformly distributed, uniformly
distributed secondary winding, a primary conductor symmetrical with respect to rotation
and the influences of conductors of the adjacent phase outside of the CT housing and
of the neighbouring phases are negligible.
a type test report of a current transformer having substantially the same cons-
b)
truction and rated primary short-circuit current is available.
NOTE - If, despite the information given above, direct tests are required by the purchaser, it will be stated
in the order.
7.3.2 Measurement of peak instantaneous error current
Methods for direct measurement of the peak instantaneous error current at accuracy
limiting conditions are given in annex C.
Records shall be taken of the instantaneous values of primary, secondary and error
currents in addition to the integral with time of the voltage across the secondary terminals
from which record the equivalent secondary e.m.f. can be derived at limiting conditions
(Ea, and
Ealc).
rt :
The following data shall be included in the type test repo
type designation;
a)
b) year of manufacture/serial number;
rating plate markings;
c)
d) results of secondary exciting test (see annex B);
results of direct tests including test parameters, test circuit diagram, photo(s) of test
e)
arrangement, records and evolution of results;
declaration of the manufacturer concerning the validity to the ordered CT of the type
f)
test made on CT having other technical data.
Correlation between direct and indirect (secondary excitation characteristic measurement)
tests may be selected from either of the following but may not be necessary if certificates
are available for a previously type-tested unit of substantially the same construction and
performance requirements.
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SIST IEC 60044-6:1995
— 33 —
44-6 ©IEC
(Fe)
7.3.3 Determination of factor of construction
The method for the determination of the factor of construction is given in annex D.
is valid for the current trans-
The factor of construction, obtained from the ratio
Ualc/Ealc,
former performance at rated conditions and at the highest theoretical value of the transient
td). That is, if both C-0 and C-0-C-0 duty cycles are specified,
dimensioning factor (K
Ktd
will be determined from whichever duty cycle yields the higher value.
When the factor of construction does not exceed 1,1, the design may or may not satisfy
the criteria for a low leakage flux design.
Strictly, the factor of construction relates the secondary excitation characteristics to the
current transformer performance under specified conditions only.
7.4 Special tests to verify a low leakage flux design
Direct tests to verify that a current transformer will satisfy the basic requirements of a low
shall be made at a sufficiently large number of energizing
leakage flux design (see 3.18)
current, duty cycle and burden combinations as can reasonably establish that the devia-
tion between the theoretical equivalent secondary e.m.f. and the measured value does not
exceed 10 %.
NOTES
Available test experience does not permit precise specification of parametric relationships and limits
1
for all classes at this time.
Indirect tests to verify that the design is of the low leakage flux type may be made in addition to direct
2
tests at specified limits.
is determined from the secondary excitation characteristics at a value su
...
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