• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.2
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• pp.149-154
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• 2008

An air-gapped current transformer(CT) has been used to reduce a remanent flux in the core, particularly in the case of auto-reclosure. However, it causes larger transient, ratio and phase errors than the iron-cored CT because of the small magnetizing inductance. This paper proposes a compensation algorithm for the secondary current of the air-gapped CT during the fault conditions including auto-reclosure as well as in the steady-state. The core flux is calculated from the measured secondary current of the CT and inserted into the hysteresis loop to estimate the exciting current. Finally, the correct current is estimated by adding the measured secondary current to the estimated exciting current. Various test results clearly indicate that the proposed compensating algorithm can improve the accuracy of the air-gapped CT significantly and reduce the required core cross-section of the air-gapped CT significantly.

• Proceedings of the KIEE Conference
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• 2006.11a
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• pp.15-17
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• 2006

This paper proposes a compensation method for an air gapped current transformer (CT) in the steady state. An air gapped CT is used in order to reduce a remanent flux in the case of auto-reclosure. It causes larger ratio and angle errors than the closed core CT because the magnetizing inductance of an air-gapped CT is even smaller than the closed-core CT. The core flux is calculated and used to estimate the exciting current in accordance with the hysteresis curve of the air-gapped CT The correct current is obtained by adding the estimated exciting current to the measured secondary current. The performance of the method was investigated for the air gapped CTs with a gap of 0.083mm and 0.249mm for the 120%, 100% and 20% of the rated current. Various test results indicate that the proposed compensation algorithm can improves the accuracy significantly.