For a Perfect CT, difference in phase between the primary and secondary currents, the positive direction of the primary and secondary currents, will be zero. However, in Practice its not possible, hence, Allowed phase displacement at various % of rated currents are defined in IEC 61869-2.
Phase displacement or Phase sift is immaterial for Current measurement, however its very important factor for Power, Energy, Power Factor and Power Quality Measurements.
| Accuracy Class | Allowed Phase Displacement at 1 % of Rated Current | Allowed Phase Displacement at 5 % of Rated Current | Allowed Phase Displacement at 20 % of Rated Current | Allowed Phase Displacement at 100 % of Rated Current | Allowed Phase Displacement at 120 % of Rated Current |
|---|---|---|---|---|---|
| Class 1 | Minutes — 180 CentiRadian — 5.4 | Minutes — 90 CentiRadian — 2.7 | Minutes — 60 CentiRadian — 1.8 | Minutes — 60 CentiRadian — 1.8 | |
| Class 0.5 | Minutes — 90 CentiRadian — 2.7 | Minutes — 45 CentiRadian — 1.35 | Minutes — 30 CentiRadian — 0.9 | Minutes — 30 CentiRadian — 0.9 | |
| Class 0.5s | Minutes — 90 CentiRadian — 2.7 | Minutes — 45 CentiRadian — 1.35 | Minutes — 30 CentiRadian — 0.9 | Minutes — 30 CentiRadian — 0.9 | Minutes — 30 CentiRadian — 0.9 |
| Class 0.2 | Minutes — 30 CentiRadian — 0.9 | Minutes — 15 CentiRadian — 0.45 | Minutes — 10 CentiRadian — 0.3 | Minutes — 10 CentiRadian — 0.3 | |
| Class 0.2s | Minutes — 30 CentiRadian — 0.9 | Minutes — 15 CentiRadian — 0.45 | Minutes — 10 CentiRadian — 0.3 | Minutes — 10 CentiRadian — 0.3 | Minutes — 10 CentiRadian — 0.3 |
| Class 0.1 | Minutes — 15 CentiRadian — 0.45 | Minutes — 8 CentiRadian — 0.24 | Minutes — 5 CentiRadian — 0.15 | Minutes — 5 CentiRadian — 0.15 |