Reference Values for Temperature, Pressure, and Humidity

Abstract
Reference values in present use are partly a product of history and were partly selected as a result of analysis. In some cases they represent average conditions and sometimes they do not. For certain applications different standardizing groups use different values and co-operative activities are thereby hindered. An attempt has been made here to show the relation of reference values to variations found in practice. In most cases correction factors are available to correct measured values to standard conditions. The importance of correction factors is shown by figure 8 which gives the correction factor for humidity for the 60-cycle flashover voltage of suspension insulators. This indicates a correction of 16.5 per cent for tests made at 0.1 inch vapor pressure, a common condition in the winter months. Hence, from this point of view the selection of reference levels to minimize correction factors is to be recommended. Attention is called to existing conditions, particularly where they are not conducive to easy comparisons of testing data and to simple testing procedures. It is hoped to stimulate the study of the problems involved and to assist present and future standardizing bodies in avoiding the confusion of the past and in organizing further work on a rational basis. At best all reference values and specified testing ranges must be a compromise for broader variations encountered by equipment under service conditions. Therefore, it seems reasonable to minimize the number and the ranges of the reference conditions.

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