CT accuracy at low current
CT accuracy at low current
(OP)
I'm planning on using a digital metering system (Allen Bradley PowerMonitor 1000), and I require fairly accurate readings below 5% of the CT rating. IEEE C57.13 defines CT accuracy from 5% to 100% of the CT rating, but not below 5%.
What kind of accuracy can I expect in the 1% to 5% current range with a standard CT? Are there CT's available with published accuracies in this range?
What kind of accuracy can I expect in the 1% to 5% current range with a standard CT? Are there CT's available with published accuracies in this range?






RE: CT accuracy at low current
Look at the CT saturation curves. If your CTs don't have saturation curves available, get different CTs. You can get an approximation of the error based on the amount of excitation current required for a given operating quantity. You need to know the CT, wiring and meter impedance. Use that to calculate the secondary voltage of the CT then look at the ratio of excitation current to nominal secondary current. The actual current you see will be roughly the nominal value (based on the CT ratio) minus the excitation current.
One thing you can do to increase low load accuracy is to use smaller CTs with a higher thermal rating. Just make sure your meter and everything else in the circuit can take the extra current too.
RE: CT accuracy at low current
RE: CT accuracy at low current