54　A Theoretical Review of Existing Measurement Methods for Insulation Resistance of PV Module String against the Earth

Abstract

Nowadays in Japan we have several methods to measure insulation resistance of a photovoltaic module string against the earth, i.e., “Short-circuit” method, “Open-circuit” method and “Self-Bias” method. These methods are commonly used but theoretical differences among them are not understood well so far. Therefore, in this report, the methods are reviewed from a theoretical viewpoint by using a simple equivalent circuit model and compared based on outdoor experiment. In, addition, the author introduces estimation equations which enable to obtain the insulation resistance from two different value measured by the “Open-circuit” method.