An Oil Flow Velocity In Situ Sensor for Power Transformers Based on Laser Doppler Effect

The assessment of the power transformers health status has garnered significant attention. The oil flow velocity serves as a critical parameter for assessing the severity of internal faults in oil-immersed power transformers, and its effective monitoring can accurately reflect the operational state of power transformers. The operational principle of the existing transformer heavy gas protection involves measuring the oil flow velocity during transformer faults through a mechanical device positioned at a specific pipeline location. However, this approach presents several challenges, including prolonged response times, a narrow monitoring range, and low measurement accuracy. To address these challenges, a fast-response, wide-range, high-accuracy, and long-lifespan in situ oil flow velocity sensor was designed and developed, drawing inspiration from the existing sensing technologies based on the laser Doppler effect and tailored to the operational environment of transformers. Test results for the key parameters of the sensor demonstrated that a measurement range of 0–3 m/s was achieved, with a maximum measurement error of 3.6%. Furthermore, the sensor is capable of operating for over 15 years in the complex operational environment of power transformers. Finally, application tests were conducted on a real scale 110-kV transformer, yielding a maximum measurement error of only 3%, with the flow velocity being accurately measurable under various conditions. The developed sensor offers a novel technical approach for the digital sensing of transformer oil velocity.

I. Introduction

The power transformers are the essential components of power transmission systems, and their operational health directly influences the reliability and stability of electricity supply [1]. The transformer oil exhibits superior insulation and heat dissipation properties, effectively preventing internal metal components from corrosion and oxidation. Consequently, it is widely utilized in power transformers to enhance performance and extend service life. Among various faults, penetrating arc discharge poses a significant threat to the integrity of the insulation structure within transformers [2], [3]. The occurrence of an arc discharge leads to rapid decomposition of the insulation materials, generating substantial gas in a short time frame, which results in a swift pressure increase within the oil tank [4], [5]. Additionally, a considerable volume of oil rapidly flows back into the transformer conservator from the tank. The oil flow velocity serves as a critical parameter indicative of arc fault severity [6]. Therefore, precise monitoring of oil flow velocity is crucial for effectively mitigating deflagration-related arc discharges.