Detection of dissolved gas in oil–insulated electrical apparatus by photoacoustic spectroscopy

One of the most effective and convenient ways to determine the early stages of potential faults in oil-insulated electrical apparatus and to monitor the development is to routinely detect and analyze the concentrations and fluctuations of potential fault gases [1]-[5]. This method has been widely used in power-grid operations and is effective in preventing the occurrence of catastrophic faults. In the past, the technology to detect mixed gas by electrochemical sensors offered effective early warnings of potential faults in electrical apparatus. Today, gas chromatography is widely used to accurately detect the composition of various gases dissolved in oil. Fault development can accurately be diagnosed by using gas chromatography together with various other means such as the Duval Triangle and key gas methods. After extended use, these techniques have been found to have drawbacks, namely, the need to routinely replace or calibrate chromatographic columns and sensors because their properties change with use, and the consumption of calibration and carrier gases with gas chromatography use [6], [7]. Photoacoustic spectroscopy, developed in the 1970s, is a spectral detection and analysis technology derived from a combination of spectroscopy and calorimetry. The method is powerful in physical chemistry research that involves inorganic or organic compounds, semiconductors, metallic materials, and high-polymer materials. It has found widespread application in various disciplines, such as physics, chemistry, biology, medicine, and geology. The major advantages associated with photoacoustic spectroscopy are that it (1) is characterized by high monitoring sensitivity because it directly measures the energy absorbed by gases without background noise; (2) uses easily available air instead of high-purity inert gases as the carrier gas without consuming the to-be-measured gas; (3) does not require chromatographic columns and sensors, which are easily contaminated, undergo aging, and require frequent replacement; (4) does not require a calibration gas, raising the prospect of realizing true maintenance-free operation; and (5) displays a high level of versatility because it even detects the contents of high-concentration gases in the oil tank of on-load tap changers [8]-[12]. Therefore, photoacoustic spectroscopy can greatly enhance the on-line monitoring of electrical system maintenance owing to its high stability, low drift, and maintenance-free features. Considering these technical characteristics, we devised a test platform by combining the technology with the headspace degassing technique. Thus, we investigated the application of photoacoustic spectroscopy to detecting concentrations of gases dissolved in oil-insulated electrical apparatus.