Particularities of measuring partial discharges in stator windings insulation systems of high-voltage electrical machines

The purpose of the article is to provide potential tools that can make a significant contribution to the identification of partial discharges (PD). Different types of partial discharges occur in stator winding insulation and a few partial discharges may occur simultaneously. Internal partial discharges are electrical discharges that occur in voids in the insulation of the stator winding. In typical stator insulation systems that use epoxy bonded mica tapes, insulation degradation due to internal partial discharges is usually slow (many years or decades). External partial discharges (slot PD and surface PD in the end-winding) are more dangerous and lead to the destruction of the insulation in a short time (several months or years). Therefore, the identification of insulation defects is essential. The analysis of existing methods for identification of defects in the insulation of high-voltage electrical machines using the results of measuring the partial discharges characteristics is carried out. The advantages and disadvantages of each of the groups of identification methods are characterized. It is shown that among the models of knowledge representation in solving problems of diagnostics of insulation systems for high-voltage electrical machines, identification methods, including field tests using training samples, are among the most suitable ones. It is noted that detection of insulation defects and their identification cannot be carried out only by direct measurements of PD characteristics and other dielectric parameters (electrical resistance, dielectric loss, polarization index). For this, special computing programs based on pattern recognition methods should be used. Results are presented of identification of technological defects in the insulation of the stator winding at the stage of factory testing, obtained using the PD identification method developed by the authors

1. Sedding H. G., Stone G. C., Warren V. Progress in interpreting online partial discharge test results from motor and generator stator windings. CIGRE 2016; Paris, A1-202. (In Eng.)

2. Montanari G. C., Seri P. A Partial Discharge – Based health index for rotating machine condition evaluation. IEEE Elect. Insulation Magazine 2018; v. 34: 17 – 23. (In Eng.)

3. Ramesh P., Sumangala B., Vishwanath A. Novel approach to identify slot discharges in the presence of end winding corona discharges. IEEE Transactions on Dielectrics and Electrical Insulation 2019; v. 26 (5): 1385 – 1393. (In Eng.)

4. Montanari G. C., Seri P., Ghosh R., Cirioni L. Noise rejection and partial discharge source identification in insulation system under DC voltage supply. IEEE Transactions on Dielectrics and Electrical Insulation 2019; v. 26 (6): 1894 – 1902. (In Eng.)

5. Tanaka K. Prediction of residual breakdown electrical field strength of epoxy-mica paper insulating systems for the stator winding of large generators. IEEE Transaction Dielectrics Electrical Insulation 2015; v. 22: 1118 – 1123. (In Eng.)

6. Kunicki M., Cichoń A., Nagi L. Statistics based method for partial discharge identification in oil paper insulation systems. Electric Power Systems Research 2018; v.163 (B): 559 – 571. (In Eng.)

7. Stone G. R. Objective methods to interpret partial-discharge data on rotating-machine stator windings. IEEE Transaction on Industry Application 2016; v. 42 (1): 195 – 200. (In Eng.)

8. Akbari A., Rahimi M.,Werle P., Borsi H. Fault localization and analysis for a damaged hydrogenerator and a proposal to improve the standard for generator commissioning tests. IEEE Electrical Insulation Magazine 2019; v. 36 (3): 9 – 25. (In Eng.)

9. Kunicki M., Cichon A. Application of a phase resolved partial discharge pattern analysis for acoustic emission method in high voltage insulation systems diagnostics. Archives of acoustics 2018; v. 43 (2): 235 – 243. (In Eng.)

10. Deshpande A. Partial discharge source identification using phase window analysis of PRPD data. 19th International Symposium on High Voltage Engineering 2015; Plzen: 23 – 28. (In Eng.)