The influence of climatic conditions on the diagnostic results of return voltage measurements

The return voltage method is easy to use and widely accepted method to monitor the condition of paper-oil insulated cables or transformers. The data acquisition is not very sensitive to external disturbances, but the results of the measurements may be influenced by the climatic conditions. Hence for the comparison of results of measurements performed in different seasons-e.g. in winter or in summer-this influence has to be taken into account. The paper presents experimental results from the field and discusses them in detail on the basis of the underlying physical mechanism. Based on this concept a new parameter is introduced, that allows the better characterisation of the ageing status of paper-oil-insulations.