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Instrument current transformers (CTs) can be heavily influenced by DC component in the measured current. 50 A DC current in 500 A CT may cause 40% error in the current and power measurement. For small power factors the situation can be even worse due to 20 deg phase error. We use digital feedback compensation of the DC flux to suppress the overall error to 0.15%.
This paper evaluates the effect of stray capacitances between primary and secondary windings on current transformers (CT) used in high voltage networks. Ground potential at all windings is the typical configuration during laboratory calibration. However, in service, the primary winding is at high voltage potential. The variation of current errors between both working conditions is evaluated for a...
Errors of instrument current transformers (ICT) are mostly determined using a comparative method. The difference between the secondary currents (magnitude and phase displacement) of a standard and of the ICT under test is evaluated by means of special systems which display the errors of the ICT calibrated in relation to the standard. These systems can evaluate errors in a certain range of measured...
This paper proposes a method for calibrating current transformers installed in power networks. The method compares primary to secondary currents in low voltage networks, and different secondary currents of the same transformer in high voltage networks. This last case is useful for transformers with multiple secondary windings, where only the metering winding is periodically calibrated, and relaying...
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