ČSN EN 61869-2

5 Ratings
5.6 Rated accuracy class
5.6.201 Measuring current transformers
5.6.201.2 Standard accuracy classes
The standard accuracy classes for measuring current transformers are:
0,1 – 0,2 – 0,2S – 0,5 – 0,5S – 1 – 3 – 5

5 Ratings
5.6 Rated accuracy class
5.6.201 Measuring current transformers
5.6.201.6 Instrument security factor
An instrument security factor may be specified.
Standard values are: FS 5 and FS 10

5 Ratings
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 Ratings
5.6 Rated accuracy class
5.6.202 Protective current transformers
5.6.202.2.1 Standard accuracy limit factors (ALF)
The standard ALF values are:
5 – 10 – 15 – 20 – 30

5 Ratings
5.6 Rated accuracy class
5.6.202 Protective current transformers
5.6.202.2.3 Standard accuracy classes
The standard accuracy classes for protective current transformers are:
5P and 10P

5 Ratings
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 Ratings
5.204 Short-time current ratings
5.204.1 Rated short-time thermal current ($I_{th}$)
The standard value for the duration of the rated short-time thermal current is 1 s.

5 Ratings
5.204 Short-time current ratings
5.204.2 Rated dynamic current ($I_{dyn}$)
The standard value of the rated dynamic current ($I_{dyn}$) is 2,5 times the rated short-time thermal current ($I_{th}$).

6 Design and construction
6.13 Markings
6.13.201 Terminal markings
6.13.201.3 Markings to be used
The markings of current transformer terminals shall be as indicated in Table 208.

7 Tests
7.2 Type tests
7.2.201 Short-time current tests
The thermal test shall be made with the secondary winding(s) short-circuited, and at a current I’ for a time t’, so that
$I^{{}^{\prime }2}\times t^{{}^{\prime }}\ge I_{th}^2\times t$

7 Tests
7.2 Type tests
7.2.201 Short-time current tests
The dynamic test shall be made with the secondary winding(s) short-circuited, and with a primary current the peak value of which is not less than the rated dynamic current ($I_{dyn}$) for at least one peak.