This standard applies to the measurement of partial discharges during tests with alternating voltage, but general terms, definitions and requirements are usually also applicable for measurement of partial discharges during tests with direct voltage. Some special characteristics of partial discharge measurements under direct voltage are given in a separate clause and necessary references are made throughout the text. This standard is intended principally as a general guide to the drafting of specifications for specific apparatus.Measurements of partial discharges are made for the following main purposes:- to verify that the test object does not exhibit partial discharges greater than a specified magnitude, at a specified voltage;- to determine the voltage amplitude at which partial discharges of a specified low magnitude commence with increasing voltage and cease with decreasing voltage;- to determine the magnitude of the specified discharge quantity at a specified voltage.The partial discharges which are considered in this standard are localized electrical discharges in insulating media, restricted to only a part of the dielectric under test and only partially bridging the insulation between conductors. Discharges mostly occur in the form of individual pulses, which can be detected as electrical pulses in the external circuit connected to the test object. However, a more continuous form may also occur, the so-called pulseless discharge. This form will normally not be detected by the measurement methods described in this standard.Partial discharges may occur in cavities in solid insulation, in gas bubbles in liquid insulation or between layers of insulation with different dielectric characteristics. They may also occur at sharp edges or points of metallic surfaces.Even though they involve only small amounts of energy, partial discharges may lead to progressive deterioration of the dielectric properties of insulating materials; the definition and evaluation of such deterioration, however, is beyond the scope of this standard.Partial discharge measurements on cables and on apparatus having windings, such as transformers, generators and motors, are complicated by attenuation, resonance and travelling wave phenomena. Special requirements for tests on these objects are only briefly dealt with.This standard deals mainly with electrical measurements of partial discharges, but some reference is also made to non-electrical methods.
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