Current error (amplitude error or ratio error) and phase angle error (phase shift) are two important parameters for a mini current transformer. From the manufacturer’s view, the current error is usually caused by wrong turns number in coil winding process. According to the Chinese National Standard, the limitation of the current error is stipulated as below table, where In means the rated current.
| Accuracy Class | 0.01In | ≥0.05In |
|---|---|---|
| 0.05 | 0.1 | 0.05 |
| 0.1 | 0.2 | 0.1 |
| 0.2 | 0.4 | 0.2 |
| 0.5 | 1.0 | 0.5 |
The phase error will be out of spec, if the enamel wire for winding coil is too thin, or the nanocrystalline / amorphous cores (or other soft magnetic cores) inside has bad quality of magnetic properties. For different kind of accuracy class, the maximum phase error allowed is as below. For mass production, we’ll test each piece of our miniature current transformers and the test point are usually placed at the point of 0.05In. At that point, the required phase angle error should be less than 8′ for 0.1 class current transformers.
| Accuracy Class | 0.01Inn | 0.05In | 0.2In | In | 2In | 3In | Imax |
|---|---|---|---|---|---|---|---|
| 0.05 | 8 | 4 | 2 | 2 | 2 | 2 | 2 |
| 0.1 | 15 | 8 | 5 | 5 | 5 | 5 | 5 |
| 0.2 | 30 | 15 | 10 | 10 | 10 | 10 | 10 |
| 0.5 | 90 | 45 | 33 | 30 | 30 | 30 | 30 |
For close loop miniature current transformer, the most common is 0.1 class. But we can also provide high accuracy current transformers with accuracy class 0.05 and 0.02.