THE FUNDAMENTALS OF CURRENT SENSE TRANSFORMER DESIGN
The following paper will first review the basic principles of operation of a Current Sense Transformer and then follow a simplified design procedure. The design procedure will take into account the effects of temperature and frequency and how they relate to the choice of a magnetic core.
Current sense trans formers (CTs) are used in a variety of applications ranging from power management to precise current measurement in the automotive telecommunications, computer, industrial, consumer and medical industries.A current sense transformer is essentially a standard transformer whose primary is placed in series with a conductor carrying AC current. The secondary is usually terminated in a resistance and the voltage on the secondary is more or less proportional to the current in the primary. Some CTs are designed to produce a voltage output which accurately tracks the AC component of the current in the primary; a linear design. Others may be designed to merely produce a change in output for a significant change in input current so that a logic device or fault circuit may be triggered. This type would not be linear. Basic Principles of Operation This standard design uses an accurate and specific resistive termination on the secondary.By transformer action, the loading effect of this resistance is transferred to the primary and appears as a shunt resistance across the primary. The parallel combination of this shunt resistance and the impedance of the primary winding form the impedance through which the current flow
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