GUIDING PRINCIPLES FOR THE SELECTION OF REFERENCE VALUES FOR ELECTRICAL STANDARDS
|Publication Date:||1 December 1962|
Test results and general performance of electric apparatus, conductors and materials frequently are influenced by conditions such as Temperature, Pressure, Altitude, Density and Humidity of the surrounding air or other medium. For comparative results, it is necessary to standardize the conditions under which tests are made or to which test results are corrected. Other conditions which may affect tests or operating performance for particular apparatus are Contamination, Surges, Vibration, Shock or Radiation. Since these are not of general application, standardization should be left to the apparatus groups concerned.
This pamphlet serves as a guide in the preparation or revision of standards for testing or performance* of apparatus or materials of specific types or fields of use. If a particular existing standard calls for other provisions, the existing standard should be followed. The values given are not mandatory, but are recommended for use in preference to other values unless there are good technical or economic reasons for using others. The values recommended have in general been selected to agree with wellestablished practices particularly in the power and industry fields.
Provisions are made for a great variety of conditions and for widely different apparatus and materials, some of which may be of practical importance only under unusual circumstances. In an individual standard, only those quantities of real practical importance in the particular case should be used. When ranges are suggested, it is generally with the thought that acceptance tests may be made within that range. Tests may be made outside the range, if acceptable, and agreed-upon correction factors are available.
For various good reasons different reference values have become firmly established sometimes in the same field for the same type of tests. Dielectric tests on insulation are an example. Flashover tests in International usage are referred to 20C and 11 grams per cubic meter absolute humidity (65 percent relative humidity). In the U.S.A. the references for flashover tests are 25 C and 0.6085 inch of mercury vapor pressure (65 percent relative humidity). For a standard laboratory atmosphere and for conditioning and weathering insulating materials, 23C and 50 percent relative humidity have been selected. Although a single set of references might be considered desirable, the effects on such considerations as laboratory practices, catalog data and insulation levels would seem to preclude changes.