Optimization Possibilities for DC Current Transformer
Abstract— The paper analyzes the consumption performance of DC current transformers based on linear class B, and half bridge class D compensation amplifiers, as well as self-oscillating flux gate current transformers based on push-pull and source–sink output stages. Compensation amplifiers, push-pull and source-sink output stages are used to generate feedback current in order to compensate magnetic flux in the magnetic concentrator core, produced by electrical current flowing through a conductor under measurement. The focus of the analysis is the investigation of conditions for appearance of the bus-pumping effect to which all switching versions of DC current transformers are prone. All sufficient conditions for bus pumping effect appearance are explained for the most critical case of DC current measurement; the main issues are analyzed, giving better insight to power consumption, and possible hazards to DC current transformer circuitry. It is highlighted the existence of particular exploitation conditions that lead to the state where the class D based DC transformers are inferior to conventional class B based counterparts. Finally, when a linear compensating amplifier is replaced with a switching counterpart, it has been demonstrated that it is possible to expect a feasible improvement in energy consumption in the middle of the ideal half-class D class and classical B class realisations.
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