Properties of Acoustic Emission Signals Coming from Partial Discharges Caused by Modeled Sources Immersed in Transformer Oil

Abstract

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...

Anusual Application of Partial Discharges to Diagnose of High Voltage Power Transformers

“…There was interesting a comparison of results coming from acoustic emission method basing on registration of AE signals recorded at several dozen points of lateral walls of the transformer. AE signal were subjected to numerical treatment basing on original method elaborated by Witos, named by its creator as "modified maximum volume method" [6,[16][17][18][19]. The result of above activities was maps of ADC descriptors (Fig.…”

Analysis of Properties Characteristic for Acoustic Emission Signals Recorded On-Line in Power Oil Transformers

“…Recorded AE signals have been put to filtration within the band of 110-200 kHz, and next basic characteristics, amplitude distributions and AE descriptor with an acronym ADC [1][2][3][4][5] were worked up. Basing on kriging method, the descriptor maps on lateral walls of trans- Positions of measuring points in the measuring network are also marked on the maps.…”

“…Author's method used to analyze AE signals [1][2][3][4][5][6], applied to signals recorded in power oil transformers, enables us to elaborate the method how to investigate AE signals in power oil transformers which includes successively: recording of signals, calculation of amplitude distributions of signals, calculation of defined AE descriptors, working up of descriptor maps on lateral walls of transformer tanks, location of AE sources according to these maps by means of the method of maximum loudness (modified by the authors), and analysis of properties characteristic for signals recorded at points lying in the vicinity of identified sources. Presented stages of analysis are realized repeatedly within different frequency bands which enable to distinguish signals coming from different types of sources such as partial discharges (PD), Barkhausen's effect, oil circulation, and outer acoustic interferences.…”

“…In order to investigate transformers an author's measuring system called AE DEMA-COMP [1][2][3][4][5][6] was applied; such a system has been equipped with AE sensors D9241A type, produced by Euro Physical Acoustic Corporation. Investigations concern two oil power transformers with transformer ratio of 120/20/6 kV and rated power of 25 MVA.…”

Location and Identification of Acoustic Signals Recorded in Power Oil Transformers within the Band of 20-180 kHz

“…In order to investigate transformers an author's measuring system called AE DEMA-COMP [1][2][3][4][5][6] was applied; such a system has been equipped with AE sensors D9241A type, produced by Euro Physical Acoustic Corporation. AE signals have been recorded at chosen measuring points, accessible for measurement.…”