Development of Acoustic Emission Sensor Optimized for Partial Discharge Monitoring in Power Transformers.

Sikorski Sikorski

doi:10.3390/s19081865

Abstract

The acoustic emission (AE) technique is one of the unconventional methods of partial discharges (PD) detection. It plays a particularly important role in oil-filled power transformers diagnostics because it enables the detection and online monitoring of PDs as well as localization of their sources. The performance of this technique highly depends on measurement system configuration but mostly on the type of applied AE sensor. The paper presents, in detail, the design and manufacturing stages of an ultrasensitive AE sensor optimized for partial discharge detection in power transformers. The design assumptions were formulated based on extensive laboratory research, which allowed for the identification of dominant acoustic frequencies emitted by partial discharges in oil–paper insulation. The Krimholtz–Leedom–Matthaei (KLM) model was used to iteratively find optimal material and geometric properties of the main structures of the prototype AE sensor. It has two sensing elements with opposite polarization direction and different heights. The fully differential design allowed to obtain the desired properties of the transducer, i.e., a two-resonant (68 kHz and 90 kHz) and wide (30–100 kHz) frequency response curve, high peak sensitivity (−61.1 dB ref. V/µbar), and low noise. The laboratory tests confirmed that the prototype transducer is characterized by ultrahigh sensitivity of partial discharge detection. Compared to commonly used commercial AE sensors, the average amplitude of PD pulses registered with the prototype sensor was a minimum of 5.2 dB higher, and a maximum of 19.8 dB higher.

Highlights

Power transformers are a strategic component of the electric power system
The results presented in the paper proved that almost all energy of acoustic emission (AE) pulses from partial discharges (PD) in oil was transmitted in the lower frequency band and the dominant frequency was about 25 kHz
Average power spectrum density (PSD) determined for registered acoustic emission signals emitted by surface discharges and registered with the use of use of ultrasonic sensor (a) discharges

Summary

Introduction

Power transformers are a strategic component of the electric power system. It is commonly believed that the oil–paper insulation system is designed in order to work reliably for 30–40 years. The asset management strategy developed by most power distribution companies, which is directed towards an extension of transformer life, results mostly from the high cost of the device purchased as well as long delivery time, reaching over a year. Such policy increases the probability of catastrophic failure occurrence, which is followed by a number of negative consequences, such as a threat to the life of the substation staff, significant economic losses, environmental hazards (oil leaks or fire), and local blackouts [1,2,3,4,5]. While analyzing cases of power transformer breakdowns described in the literature or reports of power distribution companies, one may notice that many of them are related to accelerated

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Conclusion