Notes On Class Accuracy Sct Transformers - Beckhoff SCT6 Series Manual

2.4

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. 14: Characteristic curves accuracy classes/primary current
Adjusting the transducer rating
In order to use the optimum accuracy of the transducer, you must ensure a suitable transducer rat-
ing in your application through the wiring between the transducer and the measuring terminal. This
is done by using 0.25 to 1.0 times the rated power of the transducer.
Additional resistors in the secondary path can be used to match the transducer and measuring ter-
minal to each other.
SCT6xxx
5 % 20 %
1,5 % 0,75 %
3,0 % 1,5 %
- -
Angular minutes [ ´ ]
20 % 50 % 100 %
45' - 30'
90' - 60'
- -
Version: 1.3
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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