A perspective on online partial discharge monitoring for assessment of the condition of rotating machine stator winding insulation

PROJECT TITLE :

A perspective on online partial discharge monitoring for assessment of the condition of rotating machine stator winding insulation

ABSTRACT :

Partial discharges (PD) are tiny electrical sparks that can occur in liquid or solid insulation systems in high-voltage equipment, and will eventually cause failure of the equipment [one]?????????[three]. Partial discharge testing has been used for a lot of than eighty years as a factory quality management tool to seek out manufacturing defects that might eventually result in equipment failure. We tend to believe that Johnson was the first to measure PD on operating high-voltage equipment, in the Nineteen Forties [4]. His aim was to seek out an online technique to see whether or not stator winding coils or bars were vibrating excessively in the stator magnetic core. These vibrating coils result in abrasion of the high-voltage electrical insulation and to eventual failure. An indication of the insulation abrasion method was that PD (or what he referred to as slot discharge) occurred between the surface of the coil and therefore the stator core. By measuring the PD online, he could indirectly detect the movement of coils, which indicated that failure was possible. The measurement had to be created online as a result of, if the generator weren't operating, no magnetic forces would be engaged on the coils; thus, the air gaps that are a necessary precursor of PD wouldn't be as massive. Johnson was successful in identifying those generators that were suffering the foremost from this drawback, which was caused by the introduction of the primary thermoset insulation systems and by workmanship variations that were magnified by an inadequate methodology of securing the coils within the stator slots for the novel insulation system. The success of the Johnson online PD measuring system impressed different machine manufacturers and even some utilities to develop their own strategies [5], [half-dozen]. The most reason Johnson needed online PD measurement was that loose windings do not manufacture as abundant PD when the motor or generator is not operating. Therefore one in every of the important reasons for performing on-line PD tests is to monitor the condition of the equipment beneath traditional operating electri- al, thermal, and mechanical stresses. However, with the current stress on extending times between maintenance outages, and also the push to reduce testing costs normally, the most reason now given for on-line PD measurement is to avoid shutdown of the equipment, that would be necessary for an off-line PD check or alternative diagnostic test. Although we believe online PD monitoring was first applied to rotating machines, the identical reasons are valid for different electrical equipment, like oil paper cable joints or terminations, distribution class switchgear, gas-insulated switchgear, and power transformers [a pair of], [three].

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