Comparison of discharges measured from a generator´s terminals and from an antenna in front of the slots

Partial discharge (PD) measurements have been carried out off-line from the terminals of two generators at the Guri Power plant. In addition, an antenna (developed by Tennessee Valley Authority (TVA)) was used to detect the electromagnetic signal in front of each slot of the two stator windings. The characteristic PRPD (phase resolved partial discharge) signature of internal discharges was detected both from line end measurements and in front of every slot. Other features characteristic of specific defects, such as slot discharges, was detected both from the terminal and from the TVA probe only for one of the generators. In contradistinction, for the other generator, slot discharges were only seen with the TVA/PRPD measurements and not from the terminals. The advantages and the limits of the measurements made from both the line end terminals and with the TVA probe are further discussed based on the results from the two generators