IEEE/AIEE 62-1956

The following general methods of test are either discussed or referred to in this publication: Low-frequency, low- and high-voltage losscharacteristic measurements. The measurement at power frequencies of power factor, dissipation factor or watts loss and capacitance or charging current; or equivalent quantities which define the electric circuit constants of the test specimen in the voltage range of approximately 80 volts to 50 kilovolts or higher. (2) Alternating-voltage corona measurements. The determination of the presence of corona discharge in the test specimen, usually related to the magnitude of the applied power-frequency voltage. The presence and the severity of corona are usually determined by indirect means; for example, by the resultant increase in dielectric loss or by the measurement of high-frequency components in the current. (3) Alternating-voltage distribution measurements. The measurement of the potential of the terminal electrodes and of one or more defined points between the high- and low-voltage electrodes of the test specimen, usually with applied voltage of power frequency. (4) Direct low- and high-voltage insulation resistance measurements. The measurement of the current-voltage relationship of the test specimen with the application, for a specified time, of direct voltage in the range of approximately 500 volts to 75 kilovolts or higher.

The primary purpose of this Guide is to present and discuss the applicability and limitations of the various measurement methods now in use, or available, for testing the electrical insulation of power apparatus in the field. Although factory tests assure the initial quality and condition, electric apparatus is subject, during shipment and installation and in operation, to influences which may affect the insulation and shorten its useful life. As a result the practice has grown of testing the insulation in the field from time to time to determine its suitability for service and to detect deterioration which can often be checked or prevented by suitable maintenance procedures. Various electrical characteristics of the dielectric have been suggested, and used, as criteria for judging the quality and condition of insulation. In this Guide the instruments and measurement techniques for determining these electrical characteristics are presented. The Guide is a summary of the present state of the art and is intended to serve as an aid in obtaining reliable and accurate data. The interpretation of data as it relates to the quality or serviceability of insulation is beyond the scope of this publication.

- Superseded.