Inrush current and ferroresonance in low-voltage networks - An integral approach

The work suggests a synchronous instigation of two transients: inrush current and ferroresonance. These could occur in actual low-voltage networks at the switching moment of different devices with iron-cores (e.g. light loaded transformers). Correspondingly, a time-domain investigation is carried-out by adopting a circuit-model for the transformer and by solving the corresponding differential equations, which describe the inrush current and ferroresonance transient and stationary phenomena. The core magnetic properties of the transformer are adequately modelled by a descriptive relation that properly covers the device saturation area. Thus, the time evolution of the circuit is predicted instantly after the energizing process and the major features of these power quality issues are critically examined. Supplementary, some mitigation technique of both phenomena detrimental consequences on the network are also proposed. The entire analysis is illustrated on toroidal transformer with a rated power of 500 VA often encountered in low-voltage installations.