ransformer insulation diagnosis: recovery voltage measurement and DC absorption test

Abstract

The primary motivation in insulation diagnostic study is to understand the exact state of insulation. Traditional methods using insulation resistance measurements, polarization index measurements and capacitance, tan delta measurements serve as good quality assurance criterion of acceptable values. However, for obtaining a more clear and focussed information on insulation health, newer testing and analytical techniques have to be adapted. This paper discusses two such methodologies. Recovery voltage measurement (RVM) is a technique based on measurement of increase of voltage across the transformer insulation after a charge-discharge cycle. This method yields key insulation parameters like moisture content and temperature withstand capability. A full cycle of recovery voltage measurement often requires a large amount of time. The DC absorption test aims at finding similar information as in the case of RVM with simple instrumentation and in a lesser amount of time. This paper describes the technique of RVM and later explores the possibility of using the DC absorption test for determination of health of transformer insulation. Experimental results to support the contention have also been included.