Experimental verification of 2.4 kVAr and 12 kVAr prototype variable inductors controlled by virtual air gaps with magnetic orthogonality

This paper describes experimental verification of single-phase variable inductor prototypes rated at 2.4 kVAr (75 mH, 10 A, 230 V, 24 kg) and 12 kVAr (43 mH, 30 A, 400 V, 78 kg). Results for much smaller devices rated at 1-10 Var are also shown. The variability of inductance of the main AC winding was achieved by adding a DC winding, wound through the apertures placed symmetrically in the core such that both windings were magnetically orthogonal. Local saturation caused by the magnetic field due to DC winding creates virtual air gaps. This method is capable of lowering the main inductance by over 90% if no real air gap is present, but for industrial applications the range of variability is likely to be closer to 20-30% range, depending on the size of the real air gap in the magnetic circuit. The amount of variation/control can be improved by using more than one control winding. Very good repeatability of performance was observed, with relatively small total harmonic distortion introduced due to control. The experimental findings agree with a generalised analytical model.