Amplitude & Phase Error for Miniature Current Transformer
Amplitude & Phase Error for Miniature Current Transformer
Amplitude error (current error or ratio error) and phase angle error (phase shift) are two important parameters for a miniature current transformer. From the manufacturer’s view, the amplitude error is usually caused by wrong turns number in coil winding station.
Limitation
According to the Chinese National Standard, the limitation of the amplitude 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 angle error will be out of spec, if the enamel wire for winding coil is too thin, or the soft magnetic core inside has bad quality of magnetic properties. For different kind of accuracy class, the maximum phase error allowed is as below.
| 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 |
Normal CT
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.
High-precision CT
For close loop miniature current transformer, the most common is 0.1 class. But we can also provide high-precision current transformers with accuracy class 0.05 and 0.02.
Typical Curve
The typical curve of amplitude error and phase angle error is as below.
