Reduction of Neutral Current in Airport Lighting System

Airport electrical distribution network has a number of non-linear and single-phase loads that cause imbalances, resulting in significant amount of current flow in the neutral conductor, even under normal operating conditions. The power quality of the airport distribution system is adversely affected by its lighting load controlled by a constant current controller. This paper addresses the related issues of unbalances, harmonics and neutral current in a typical airport power distribution network. Efforts have been made to estimate the required size of the neutral conductor given the ratings of various loads in the distribution system. The lighting load has been modeled (i) as an incandescent lamp controlled by a power electronic controller (ii) as a fluorescent lamp having an electronic ballast as the starter and being controlled by an AC voltage controller. It is found that the neutral current flow is about 300% of the full-load current rating when the lighting system is being controlled by a constant current controller. The paper explores two solution methodologies namely, application of zigzag transformer and application of star delta transformer along with a single phase active filter, for reducing the neutral current. The relative merits and demerits of these proposed solutions have been brought out.