Co-operating organizations
Foreword
Specification
1 General
1.1 Scope
1.2 Definitions
2 Requirements for all current transformers
2.1 Service conditions
2.2 Rating and performance requirements applicable
to all current transformers
2.3 General test requirements
2.4 Requirements for routine tests
2.5 Requirements for type tests
2.6 Commissioning tests on new current transformers
2.7 Marking
3 Additional requirements for measuring current
transformers
3.1 General
3.2 Accuracy requirements
3.3 Tests for accuracy
3.4 Marking
4 Additional requirements for protective current
transformers
4.1 General
4.2 Accuracy requirements
4.3 Special purpose current transformers
4.4 Tests
4.5 Marking
Appendices
A Service conditions
B Guidance in the application of current
transformers
C Short-time current rating of current
transformers
D Temperature measurements
E Maximum V A output of bar-primary and bushing
current transformers
F Information required by the manufacturer
G Use of current transformers for the dual purpose
of measurement and protection
H Current transformer test windings
J Composite error
K Distinction between low-reactance and high-
reactance current tranformers
L Determination of turns ratio
Tables
1 Limits of temperature rise of windings
2A Insulation test levels for rated highest
equipment voltages up to and including 72.5 kV
2B Insulation test levels for rated highest
equipment voltages of 100 kV and above
3 Permissible current densities
4 Power-frequency and d.c. test voltages on
primary windings (after erection on site)
5 Power-frequency voltage tests of durations
exceeding one minute (after erection on site)
6 Limits of error for accuracy Classes 0.1 to 1
7 Limits of error for accuracy Class 3 and Class 5
8 Limits of error for accuracy Class 5P and Class
10P
9 Selection of class of accuracy of measuring
current transformers
10A Maximum short-time factors obtainable
economically, corresponding to rated output,
accuracy class, accuracy limit factor and rated
time for wound-primary measuring current
transformers
10B Maximum short-time factors obtainable
economically, corresponding to rated output,
accuracy class, accuracy limit factor and rated
time for wound-primary protective current
transformers
11 Relationship between normal practical output and
rated primary current of bar-primary and bushing
current transformers
12 Maximum duration of current for transformer X
Figures
1 Single ratio transformer
2 Transformer with an intermediate tapping on
secondary winding
3 Transformer with primary winding in two sections
intended for connections either in series or in
parallel
4 Transformer with two secondary windings each
with its own magnetic core. (Two alternative
markings for the secondary terminals)
5 Transformer with an intermediate tapping on
secondary winding and incorporating test taps
6 - 10 Diagrams for determination of composite error
11 Equivalent circuit for the determination of
turns ratio (current transformers having fewer
than approximately 1000 turns)
12 Equivalent circuit for the determination of
turns ratio (current transformers having more
than approximately 1000 turns)