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WHAT IS CURRENT TRANSFORMER ACCURACY CLASS (IEC61869-2, IEC60044-1, IEEE/ANSI C57.13)?

The new standard IEC61869-2 and old Standard IEC60044-1 states that current transformers used at energy monitoring equipment and in energy usage monitoring systems in order to obtain higher accuracies that will soon be considered the new industry standard.

The old standard IEEE/ANSI C57.13, which outlines accuracy requirements for metering, is still used today for general instrument transformers. Now there is also “harmonized” worldwide standards that outlines more precise accuracy requirements for energy metering: IEC 61010-1 3rd edition and IEC 61869-2 & IEC 60044-1 should be referred to when designing current transformers.

Within IEC61869-2, the tables 201 and 202 & IEC60044-1, the tables 11 and 12 call out the overall product accuracy requirements for energy monitoring, metering for energy conservation and revenue purposes.
IEEE/ANSI C57.13 for instrument transformers shows accuracies, including phase requirements of 0.3, 0.6 or 1.2% accuracy from 10% to 100% of the instrument transformer.

The new current transformer and metering speci cations like the IEC61869-2 table above now require accuracies from 0.2%, 0.1% and up. Metering range for metering classes (IEEE/ANSI C57.13) cover 10% to 100% of the rated current.

It is not always satisfactory for revenue and precision metering. However, it is possible to extend the metering range i.e. from 1% to 150%. Note that the metering range must be speci ed separately. A better accuracy class 0.15 will sometimes be required.

Normally, the manufacturer will have no problem meeting the requirements. At lower rated currents there may be problems ful lling the accu- racy in the extended range.

Table 201 – Limits of ratio error and phase displacement for measuring current transformers (classes 0.1 to 1)

Accuracy Class ±Percentage current(ratio) error at percentage of rated current shown below ±Phase displacement at percentage
of rated current shown below
Minutes Centiradians
5 20 100 120 5 20 100 120 5 20 100 120
0.1 0.4 0.2 0.1 0.1 15 8 5 5 0.45 0.24 0.15 0.15
0.2 0.75 0.35 0.2 0.2 30 15 10 10 0.9 0.45 0.3 0.3
0.5 1.5 0.75 0.5 0.5 90 45 30 30 2.7 1.35 0.9 0.9
1.0 3.0 1.5 1.0 1.0 180 90 60 60 5.4 2.7 1.8 1.8

Table 202 – Limits of ratio error and phase displacement for measuring current transformers
(classes 0.2S to 0.5S)

Accuracy Class ±Percentage current(ratio) error at percentage of rated current shown below ±Phase displacement at percentage
of rated current shown below
Minutes Centiradians
1 5 20 100 120 1 5 20 100 120 1 5 20 100 120
0.2S 0.75 0.35 0.2 0.2 0.2 30 15 10 10 10 0.9 0.45 0.3 0.3 0.3
0.5S 1.5 0.75 0.5 0.5 0.5 90 45 30 30 30 2.7 1.35 0.9 0.9 0.9

IEC 60044-1, Table 11 – Limits of current error and phase displacement for measuring current transformers(classes from 0.1 to 1)

Accuracy Class ±Percentage current(ratio) error at percentage of rated current shown below ±Phase displacement at percentage
of rated current shown below
Minutes Centiradians
5 20 100 120 5 20 100 120 5 20 100 120
0.1 0.4 0.2 0.1 0.1 15 8 5 5 0.45 0.24 0.15 0.15
0.2 0.75 0.35 0.2 0.2 30 15 10 10 0.9 0.45 0.3 0.3
0.5 1.5 0.75 0.5 0.5 90 45 30 30 2.7 1.35 0.9 0.9
1.0 3.0 1.5 1.0 1.0 180 90 60 60 5.4 2.7 1.8 1.8

Table 202 – Limits of ratio error and phase displacement for measuring current transformers
(classes 0.2S to 0.5S)

Accuracy Class ±Percentage current(ratio) error at percentage of rated current shown below ±Phase displacement at percentage
of rated current shown below
Minutes Centiradians
1 5 20 100 120 1 5 20 100 120 1 5 20 100 120
0.2S 0.75 0.35 0.2 0.2 0.2 30 15 10 10 10 0.9 0.45 0.3 0.3 0.3
0.5S 1.5 0.75 0.5 0.5 0.5 90 45 30 30 30 2.7 1.35 0.9 0.9 0.9
Current Error (%)

Accuracy classes according to IEEE/ANSI C57.13

Class Error limits (the limits are valid for any of the standard burdens below)
Times rated
current
Power error
%
Designation Ohm PF Application
0.15 1.0 0.15 B-0.1
B-0.2
B-0.5
B-0.9
B-1.8
0.1
0.2
0.5
0.9
1.8
0.9 High-accuracy
metering
0.05 0.30
0.15S 1.0 0.15
0.15 0.15
0.3 1.0 0.3 Metering
0.1 0.6
0.6 1.0 0.6
0.1 1.2
1.2 1.0 1.2
0.1 2.5
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