The impact of public lighting on voltage distortion in low voltage distribution systems

Harmonic distortion has become a main concern in electric distribution systems. Several public utilities are experiencing harmonic problems on their networks and some of them started to monitor the situation of the MV and LV distribution networks. The operation of the MV and LV networks of the AEM-Torino (the city utility) has been investigated with several on-site measurements. The survey led to the observation of a step increase in voltage distortion on LV feeder when the city street lighting is switched on and, vice versa, a sudden decrease when it is switched off. This phenomenon can be mainly traced back to the resonance, under certain conditions, between the capacitance of the capacitors for the improvement of the lamps power factor and the inductance of the MV/LV transformer. This work investigates the phenomenon both from a theoretical point and with laboratory and field tests. Some possible remedies and their practical implementation to reduce harmonic distortion are discussed.