Experimental study and circuit analysis model of lightning isolation transformer for railway signal system

Japanese railway systems run throughout Japan and are the main means of transportation for many people. In recent years, with the development of energy-saving techniques in these railway systems, they are recognized as an ecologically friendly means of transportation with low CO2 emissions. In particular, signal facilities used in the railway systems have been progressively computerized, and the railway systems have had weak resistance to an overvoltage caused by lightning. Thus, for insulating AC power sources, railway companies use devices such as insulation transformers or lightening isolation transformers, which can withstand high voltages. This document presents results obtained by examining surge characteristics of the insulation transformer and the lightning isolation transformer which are used in one of methods of taking countermeasures against lightning damage. To recognize the lightning isolation transformer's response to lightning-caused overvoltage, frequency characteristics among terminals were determined using an impedance analyzer to construct an accurate circuit analysis model.