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 | ||||
|---|---|---|---|---|---|
| 5 % | 20 % | 50 % | 100 % | 120 % |
0,5 | 1,5 % | 0,75 % | - | 0,5 % | 0,5 % |
1 | 3,0 % | 1,5 % | - | 1,0 % | 1,0 % |
3 | - | - | 3 % | - | 3 % |
Class accuracy | Phase shift/error angle (±) at % of rated current | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
Angular minutes [ ´ ] | Radians [rad] | |||||||||
| 5 % | 20 % | 50 % | 100 % | 120 % | 5 % | 20 % | 50 % | 100 % | 120 % |
0,5 | 90‘ | 45‘ | - | 30‘ | 30‘ | 2,7 rad | 1,35 rad | - | 0,9 rad | 0,9 rad |
1 | 180‘ | 90‘ | - | 60‘ | 60‘ | 5,4 rad | 2,7 rad | - | 1,8 rad | 1,8 rad |
3 | - | - | - | - | - | - | - | - | - | - |
 | Adjusting the transducer rating In order to use the optimum accuracy of the transducer, you must ensure a suitable transducer rating 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 terminal to each other. |