Public lighting network three-phase balanced variable supply - has injection transformers with secondary windings connected between tap-off points of respective auto-transformers and supply

摘要

In the variable level balanced three phase lighting supply for a public lighting network, in order to achieve minimum running cost, the lighting levels are reduced during part of the day. The supply accommodates both high pressure mercury and sodium lamps and can be varied from 50% to maximum output. Each phase (P1, P2, P3) is supplied via an injection transformer one winding of which is in series with the supply, the secondary winding being connected between the tap-off point (C1, C2, C3) of an autotransformer (AT1, AT2, AT3) and the supply. Lamps L2, L"2) can be connected across any pair of the three phases.