Current Transformer Accuracy Classes
Current Transformer Accuracy classes according to IEC 61689-2
Class | For burdens | Limits of errors | Application | ||
at % rated current | Ratio error % | Phase displacement Minutes | |||
0.1 | 25-100% of rated burden | 5 | 0.4 | 15 | Laboratory |
20 | 0.20 | 8 | |||
100 | 0.1 | 5 | |||
120 | 0.1 | 5 | |||
0.2 | 25-100% of rated burden <15 VA 1 VA-100% | 5 | 0.75 | 30 | Precision revenue metering |
20 | 0.35 | 15 | |||
100 | 0.2 | 10 | |||
120 | 0.2 | 10 | |||
0.2S | 25-100% of rated burden <15 VA 1 VA-100% | 1 | 0.75 | 30 | Precision revenue metering |
5 | 0.35 | 15 | |||
20 | 0.2 | 10 | |||
100 | 0.2 | 10 | |||
120 | 0.2 | 10 | |||
0.5 |
25-100% of
| 5 | 1.5 | 90 | Standard commercial metering |
20 | 0.75 | 45 | |||
100 | 0.5 | 30 | |||
120 |
| 30 | |||
0.5S | 25-100% of rated burden | 1 | 1.5 | 90 | Precision revenue metering |
5 | 0.75 | 45 | |||
20 | 0.5 | 30 | |||
100 | 0.5 | 30 | |||
120 | 0.5 | 30 | |||
1.0 | 25-100% of rated burden | 5 | 3.0 | 180 | Industrial grade meters |
20 | 1.5 | 90 | |||
100 | 1.0 | 60 | |||
120 | 1.0 | 60 | |||
3.0 | 50-100% | 50 | 3.0 | - | Instruments |
120 | 3.0 | - | |||
5.0 | 50-100% | 50 | 5.0 | - | Instruments |
120 | 5.0 | - | |||
5P and 5PR | 100% | 100 | 1.0 | 60 | Protection |
ALF x In | 5 | - | |||
10P and 10PR | 100% | 100 | 3.0 | - | Protection |
ALF x In | 10 | - | |||
PX | Ek, Ie, Rct | - | - | - | Protection |
1) PF of secondary burden 0.8 (for 5 VA burden and lower PF = 1.0)
2) Composite error
3) Remanence factor (Kr) shall not exceed 10% after 3 minutes
4) Rated knee point e.m.f. (Ek). The minimum sinusoidal e.m.f. (r.m.s.) at rated power frequency when applied to the secondary terminals of the transformer, all other terminals being open-circuited, which when increased by 10% causes the r.m.s. excitation current to increase by no more than 50%.
Note! The actual knee point e.m.f. will be the rated knee point e.m.f.
5) Rct = CTs secondary resistance at 75 ℃.
Current Transformer
Accuracy classes according to IEEE C57.13
Class | Error limits (the limits are valid for any of the standard burdens below) | |||||
Times rated current | Power error % | Designation | Ohm | PF | Application | |
0.15 | 1.0 | 0.15 | B-0.1
B-0.2
B-0.5
B-0.9
B-1.8 | 0.1
0.2
0.5
0.9
1.8 | 0.9 | High-accuracy metering |
0.05 | 0.30 | |||||
0.15S | 1.0 | 0.15 | ||||
0.05 | 0.15 | |||||
0.3 | 1.0 | 0.3 | Metering | |||
0.1 | 0.6 | |||||
0.6 | 1.0 | 0.6 | ||||
0.1 | 1.2 | |||||
1.2 | 1.0 | 1.2 | ||||
0.1 | 2.5 | |||||
Class | Times rated current | Ratio error % | Secondary terminal voltage | Designation | PF | Application | |
Rated current | Low rated current | ||||||
C100 T100 | 20 | 3 | 10 | 100 | B-1.0 | 0.5 | Protection |
C200 T200 | 20 | 3 | 10 | 200 |
B-2.0 | ||
C400 T400 | 20 | 3 | 10 | 400 |
B-4.0 | ||
C800 T800 | 20 | 3 | 10 | 800 | B-8.0 | ||
X | - | 1 | - | Es, Ie, Rct | |||
1) Class C is used for cores with evenly distributed winding, i.e. when the leakage flux is negligible.
Class T is valid for CTs in which the leakage flux in the core of the transformer has an appreciable effect on the ratio.
2) Rated knee point voltage Es; specified in IEEE C57.13 -2008 6.10.2