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
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
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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
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44-6 ©I EC – 3 –
CONTENTS
Page
FOREWORD 5
INTRODUCTION 7
Clause
1 Scope 9
2 Normative references
3 Definitions 9
rformance requirements 4 Ratings and pe
5 Methods of specification
6 Marking of rating plate
7 Tests
Annexes
35 A Basic theoretical equations for transient dimensioning
B Determination of core magnetization characteristic
C Direct tests 59
ormance criteria for current transformer for protection relaying
Guide to perf
D
E Determination of turns ratio error 85
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.
44-6©IEC – 7 –
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.
44-6 ©IEC - 9 -
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
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.
– 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
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
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
...
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