Abstract:

In an intelligent molded case circuit breaker (MCCB),the current transformer (CT) not only collects current signals but also supplies power to the electronic trip unit.If the design is inadequate, insufficient power can be provided at low current levels or when the load impedance is high,leading to core saturation,secondary-side current distortion,thereby causing measurement errors.To address these issues,a 63 A rated intelligent MCCB is selected as the research subject.The range of CT turns meeting the requirment of measurement and energy extractions is theoretically derived.Then, Ansys simulations are conducted to determine the optimal number of turns.Additionally, a MOSFET is introduced on the CT’s secondary side to control the load-side voltage by means of PWM.Simulation and experimental results show that the designed CT can maintain undistorted output waveforms with an equivalent load impedance of 1 kΩ in a current range of 0.4I_n to 10I_n.Across the entire current range, the solution ensures accurate measurement while meeting power supply requirements.

Key words: intelligent molded case circuit breaker (MCCB), energy extraction from current transformer, turns design, PWM control