This International Standard is applicable to the measurement of partial discharges which occur in electrical apparatus, components or systems when tested with alternating voltages up to 400 Hz or with direct voltage. This standard - defines the terms used; - defines the quantities to be measured; - describes test and measuring circuits which may be used; - defines analogue and digital measuring methods required for common applications; - specifies methods for calibration and requirements of instruments used for calibration; - gives guidance on test procedures; - gives some assistance concerning the discrimination of partial discharges from external interference. The provisions of this standard should be used in the drafting of specifications relating to partial discharge measurements for specific power apparatus. It deals with electrical measurements of impulsive (short-duration) partial discharges, but reference is also made to non-electrical methods primarily used for partial discharge location (see annex F). Diagnosis of the behaviour of specific power apparatus can be aided by digital processing of partial discharge data (see annex E) and also by non-electrical methods that are primarily used for partial discharge location (see annex F). This standard is primarily concerned with electrical measurements of partial discharges made during tests with alternating voltage, but specific problems which arise when tests are made with direct voltage are considered in clause 11. The terminology, definitions, basic test circuits and procedures often also apply to tests with other frequencies, but special test procedures and measuring system characteristics, which are not considered in this standard, may be required. Annex A provides normative requirements for performance tests on calibrators.