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Investigation results of acoustic emission signals coming from partial discharges within chosen generator coil bar, in relation to measurement results of apparent charge introduced by partial discharges sources, are presented in the article. Analysis is based on amplitude distributions calculated for acoustic emission signals, ordered at different measuring points for different values of the supply voltage. In order to assign acoustic emission signal to its advance degree a descriptor named by an acronym ADP (defined by authors) is calculated for each amplitude distribution. Descriptor families describing acoustic emission signals measured at particular measuring points (for different supply voltages) are presented in relation to apparent charge introduced by acoustic emission sources. These families concerning acoustic emission signals, measured at different measuring points for identical supply voltage, enable us to locate acoustic emission sources with maximum activity.

Investigation results concerning acoustic emission signals coming from partial discharges generated by modeled sources are presented in the paper. These sources have been made using different bushing ends (without any extra elements and with a thread or a pike) situated directly in the oil, but without screens typical for partial discharge investigations in a bushing. Measurements have been carried out using own measuring acoustic emission system DEMA-COMP and -in a parallel way -computer-aided partial discharges measuring system TE 571 (produced by the firm Haefely Trench). Fundamental and advanced analysis of acoustic emission signals has been made. These signals were recorded in 20 measuring situations which need to multiple installation of acoustic emission sensors. Conclusions resultant from own originate advanced analysis of signals content description of properties revealed by defined acoustic emission descriptors.PACS numbers: 43.40. Le, 77.22.Jp, 84.70.+p 1. Description of modeled sources, a measuring stand and measuring systemsAs a modeled partial discharges (PD) source, made and used during the investigations, was the bushing PTK 123/450/630 with additional ends (without any extra elements, with a thread or a pike) situated directly in the oil. This bushing was not equipped with screens typical for PD investigations.Investigations of PD generated by modeled sources have been carried out in High Voltage Laboratory of the firm ZTS IZO-ERG in Gliwice and precisely -on the measuring stand presented in Fig. 1. An integral element of this stand is the vat in shape of the cylinder (diameter of 900 mm, height of 1200 mm). PD sources have been placed inside the vat filled by the oil. Such PD sources and measuring conditions enable us to observe partial discharges in boundary of the voltage electrode and transformer oil as well as only in the oil.Acoustic emission (AE) sensors have been placed during investigations at measuring points P A , P B and P C on external surface of the vat within specially prepared clamps. Permanent magnets (elements of sensor clamps) ensured unchangeable position of sensors on vat walls during measurements as well as recurrent thickness of the couple layer (it is the cup grease which ensures good conditions of acoustic contact). Measurements have been carried out using in a parallel way own measuring AE system DEMA-COMP [1-8] and computer-aided PD mea- * corresponding author; e-mail: franciszek.witos@polsl.pl Fig. 1. Scheme of measuring stand used to investigate of PDs generated by modeled sources immersed in the oil fulfilling the vat; P A , P B , P C -measuring points fixed on external surface of the vat.suring system TE 571, produced by the firm Haefely Trench (investigations of other authors are published in [9][10][11][12][13][14][15][16][17][18]).Distances between a modeled source and AE sensors are of several tens of centimeters. These distances are typical for AE signals, generated in many real objects. Owing to that, results of analyses carried out for AE signals recorded...