5.6.203.2 Accuracy performance for current transformers with tapped secondary windings
For all accuracy classes, the accuracy requirements refer to the highest transformation ratio, unless specified otherwise.
When required by the purchaser, the manufacturer shall give information about the accuracy performance at lower ratios.
5.201 Standard values for rated primary current
The standard values for rated primary current are: 10 – 12,5 – 15 – 20 – 25 – 30 – 40 – 50 – 60 – 75 A, and their decimal multiples or fractions.
The preferred values are those underlined.
5.202 Standard values for rated secondary current
The standard values for rated secondary current are 1 A and 5 A.
For protective current transformers for transient performance, the standard value of the rated secondary current is 1 A.
5.203 Standard values for rated continuous thermal current
The standard value for rated continuous thermal current is the rated primary current.
When a rated continuous thermal current greater than the rated primary current is specified, the preferred values are 120 %, 150 % and 200 % of rated primary current.
5.204 Short-time current ratings
5.204.1 Rated short-time thermal current
A rated short-time thermal current shall be assigned to the transformer.
The standard value for the duration of the rated short-time thermal current is 1 s.
5.204.2 Rated dynamic current
The standard value of the rated dynamic current is 2,5 times the rated short-time thermal current.
6 Design and construction
6.4 Requirements for temperature rise of parts and components
6.4.1 General
This clause of IEC 61869-1:2007 is applicable with the addition of the following:
The temperature rise in a current transformer when carrying a primary current equal to the rated continuous thermal current, with a unity power-factor burden corresponding to the rated output, shall not exceed the appropriate value given in Table 5 of IEC 61869-1:2007. These values are based on the service conditions given in Clause 4.
6.13 Markings
6.13.201 Terminal markings
6.13.201.1 General rules
The terminal markings shall identify:
a) the primary and secondary windings;
b) the winding sections, if any;
c) the relative polarities of windings and winding sections;
d) the intermediate taps, if any.
6.13.201.2 Method of marking
The marking shall consist of letters followed, or preceded where necessary, by numbers. The letters shall be in block capitals.
6.13.201.3 Markings to be used
The markings of current transformer terminals shall be as indicated in Table 208.
6.13.201.4 Indication of relative polarities
All the terminals marked P1, S1 and C1 shall have the same polarity at the same instant.
6.13.202 Rating plate markings
6.13.202.1 General
In addition to those markings defined in IEC 61869-1:2007, Clause 6.13, all current transformers shall carry the general rating plate markings as defined in this clause. The markings related to the particular accuracy classes are given in Subclauses 6.13.202.2 to
6.13.202.6.
a) the rated primary and secondary current (e.g. 100/1 A);
b) the rated short-time thermal current (Ith), (e.g. Ith = 40 kA);
c) the rated dynamic current (Idyn) if it differs from 2,5 Ith (e.g. Idyn = 85 kA);
d) on current transformers with two or more secondary windings, the use of each winding and its corresponding terminals;
e) the rated continuous thermal current if different from the rated primary current.
A current transformer satisfying the requirements of several combinations of output and accuracy class may be marked according to all of them.
