Estimation of Moisture Content in Dielectrics Using a Four-Element Model of Capacitive Sensors
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mation of Moisture Content in Dielectrics Using a Four-Element Model of Capacitive Sensors I. N. Vorotnikova, *, M. A. Mastepanenkoa, Sh. Zh. Gabrielyana, and S. V. Mishukova aStavropol
State Agrarian University, Stavropol, 355017 Russia *e-mail: [email protected]
Received April 27, 2020; revised May 20, 2020; accepted June 1, 2020
Abstract—Disadvantages of existing methods for determining moisture content in insulating liquids used in laboratories of power plants are considered and revealed. A method is proposed for determining moisture content in liquid dielectrics based on the measurement of parameters of multielement two-terminal networks in steady-state and transient modes. The results of the studies as applied to transformer oils are presented. Keywords: dielectric, transformer oil, multielement two-terminal network, dielectric breakdown, capacitive sensor DOI: 10.3103/S1068371220070123
INTRODUCTION The presence of water in liquid dielectrics, such as petroleum oils (transformer, cable, condenser), vegetable oils, and synthetic isolating liquids, leads to an abrupt increase in the corrosive effect caused by naphthenic acids and accelerates the formation of precipitates, which negatively affects the main operational characteristics thereof, such as breakdown voltage, owing to increasing electrical conductivity and a decreasing dielectric strength. Let us consider methods for determining moisture content in liquid dielectrics—for example, in transformer oils. The methods for determining the presence of water therein known for today can be divided into standardized methods such as a hydrocalcium method, a chromatographic method, and a coulometric method, as well as unstandardized methods, such as ESR spectroscopy (electron spin resonance), NMR spectroscopy (nuclear magnetic resonance), and infrared and luminescent spectroscopy. The application of these methods requires laboratory conditions and highly qualified personnel skilled in working with toxic chemicals and substances that pose dangers of explosion and fire, as well as with expensive equipment. These methods are time consuming and do not provide a rapid analysis of transformer oils on the spot, which leads to additional costs for energy enterprises. To date, the dialectometric method is the most promising method for determining moisture content. The main core of this method consists in determining the parameters of a capacitive sensor having the form of a two-terminal network consisting of a two-, three-, or
four-element equivalent circuit involving resistors or capacitors. For liquid dielectrics, in particular, transformer oils, a four-element model of a capacitive sensor [1] consisting of three parallel circuits—resistive one R1x, capacitive one C1x, and mixed one R2x–C2x (Fig. 1)—is preferable. EXPERIMENTAL To determine the parameters of the aforementioned model, a method for determining the parameters of multielement two-terminal networks (M2TNs) can be applied [2]. The study concerning liquid dielectrics—in particular, transformer oi
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