Multi-parametric gas sensing for transformer monitoring using an optical fiber sensor array

Abstract

The maintenance and inspection of power transformers can be a time-consuming task for electric utilities, but it is a necessity for maintaining electrical grid reliability. A standard strategy for diagnosis of fault conditions in an oil-filled transformer is to periodically acquire oil samples and perform dissolved gas analysis (DGA). Aging and temperature variation can induce varying concentrations of hydrogen, methane, and other hydrocarbons, which all form as the oil degrades. Acetylene (C2H2) is generated only during localized, high-temperature events such as partial discharge, and its presence is a key marker for identifying these conditions..The development of optical fiber-based sensors to fill the role of DGA offers several advantages, including the option to implement real-time, in-situ, or even spatially resolved (distributed or quasi-distributed) sensing schemes. The evanescent field approach, in conjunction with tailored sensing materials, provides a cheap and scalable solution to this problem. However, this solution is oftentimes hampered by long-term stability and cross-sensitivity issues. One solution is to gather data from multiple optical fiber sensors designed to eliminate cross-sensitivity and calibrate drift. In this work, a multi-sensor array is developed to target multiple gas species relevant to transformer monitoring (C2H2, CH4, H2). This approach, combined with machine learning models such as support vector machines (SVM), can be used to identify the gas species present at concentrations relevant to DGA (ppm levels) with dramatically increased accuracy.

Plasmonic and interferometric optical fiber sensors for electrical system monitoring applications

“…To rectify this problem, multiple sensors can be used in tandem targeting distinct species. When employing electronic sensors, a sensor array is commonly referred to as an "electronic nose" [46]; the compact nature of optical fibers makes a similar approach feasible, where multiple sensing elements can be combined as a "photonic nose", in parallel as a fiber sensing bundle [47] or in series on a single fiber [30]. Of promise as a future alternative to current DGA methods, is the extension of the fiber optic-based sensing platform to the equivalent of the "photonic nose" application in which one or more functionalized sensing layers are interrogated at one or more wavelengths of interest to allow for multivariate sensing of complex gas mixtures with capability for individual analyte discrimination.…”

“…This poses a challenge for operational power transformer monitoring, because these gas species can be present at quantities over several orders of magnitude in oil samples and may make it difficult to distinguish acetylene at the 1-10 ppm level, which may be an early indicator of electrical faults. The "photonic nose" concept was leveraged in labscale, gas-phase testing of relevant gas species (H2, CH4, C2H2, CO) at concentrations spanning 10-5000 ppm [47]. In this approach, a selective Ni/SiO2 acetylene sensor was co-packaged with sensors targeting hydrogen (AuPd) and methane (PIM-1/ITO), and all three sensors in the multi-sensor bundle were monitored simultaneously in real-time and exposed to a randomized gas schedule.…”

“…The system is designed to mimic an oil filled transformer, with the ability to simulate electric discharge events, and an array of on-board diagnostic equipment to cross-validate sensor response. Fiber sensor bundles were constructed using the same sensors tested in oil and gas-phase, as in [47] (Ni/SiO2, AuPd, PIM-1/ITO) with an additional fourth sensor, also targeted at hydrogen detection, based on a Pd/SiO2 sensing layer [30]. The bundle was embedded in a PVC pipe for mechanical support and inserted into the system through an access hatch in the top (Fig.…”