Electromagnetic Characteristics Analysis of Air-Core Transformer Used in Voltage Compensation Type Active SFCL

The three-phase voltage compensation type active superconducting fault current limiter (SFCL) is composed of three air-core superconducting transformers and a three-phase four-wire PWM converter. The primary winding of the air-core superconducting transformer is in series with AC main circuit, and the second winding is connected with the PWM converter. The electromagnetic condition in the transformer can be changed by the compensating current offered by the PWM converter. In this paper, the electromagnetic characteristics of the single phase air-core transformer are calculated by the circuit-field coupled time-stepping finite-element method. The magnitude of the magnetic field and current, phase difference between magnetic fields and current and loss characteristic under different compensating current are studied. The analysis results are very important for the establishment of the control strategy and the transformer's design in the engineering realization.