Notes On Class Accuracy Sct Transformers; Fig. 9 Characteristic Curves Accuracy Classes/Primary Current - Beckhoff SCT Series Documentation

2.3

Notes on class accuracy SCT transformers

Current transformers are divided into classes according to their accuracy. The Beckhoff SCT current
transformers are available in the standard accuracy classes 0.5; 1 and 3, depending on the product
category. The class designation corresponds to an error curve with regard to current amplitude and angular
error. Beckhoff SCT current transformers conform to the IEC 61869 standard.
The accuracy classes of current transformers are related to the rated current. If current transformers are
operated with a current that is low in relation to the rated current, the measuring accuracy decreases. The
following tables show the fault limit values taking into account the rated current values:
Class accuracy Current error (±) in % at % of rated current
0,5
1
3
Class accuracy Phase shift/error angle (±) at % of rated current
5 %
0,5 90'
1 180'
3 -
Fig. 9: Characteristic curves accuracy classes/primary current
SCTxxxx
5 % 20 %
1,5 % 0,75 %
3,0 % 1,5 %
- -
Angular minutes [ ´ ]
20 % 50 % 100 %
45' - 30'
90' - 60'
- -
Version: 1.1
50 %
-
-
3 %
120 % 5 %
30' 2,7 rad
60' 5,4 rad
- - -
Product overview
100 % 120 %
0,5 % 0,5 %
1,0 % 1,0 %
-
Radians [rad]
20 % 50 % 100 %
1,35 rad - 0,9 rad
2,7 rad - 1,8 rad
- - -
3 %
120 %
0,9 rad
1,8 rad
-
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