George E. Mercier

Ultrasonic Sensing of Partial Discharges within Microfarad Value AC Capacitors

As new dielectric fluids and materials are introduced, partial discharge (P.D.) testing of microfarad value capacitors in the factory is assuming greater importance. However, the large capacitance restricLs the use of the common electrical methods for detecting small (1-20 pC) discharges, and bridge techniques are not economical for production line tests. For these reasons, the use of ultrasonic sensors for detecting P.D. within microfarad value capacitors was studied, and this resulted in the development of a combined acoustic waveguide probe, ultrasonic sensor and indicating meter, suitable for factory P.D. testing of capacitors.

High voltage power capacitor dielectrics recent developments

This paper discusses recent, new impregnant developments and evaluations for capacitor dielectrics. These dielectric fluids are isopropylbiphenyl (Wemcol), di-2 ethylhexyl phthalate plus trichlorobenzene (Dielektrol II) butylated monochlorodiphenyl oxide (Edisol) phenyl xylyl ethane (PXE) and benzyl neocaprate (BMC). The film-paper dielectrics impregnated with these were extensively tested for thermal stability under voltage and resistance to overvoltages with partial discharges: Considerable attention is now being devoted to practically significant partial discharge testing, to determine service reliability. Also included here is the evaluation of windings where one foil is narrower and folded at the edges to reduce the voltage stress at the foil edges.