Behaviour of electrical double layer under oil flow and voltage application inside a capacitive sensor

Abstract

This study presents an experimental investigation of the behaviour of electrical double layer (EDL) under oil flow and voltage application inside a capacitive sensor. This sensor is incorporated in a closed-loop filled with fresh transformer oil. The sensor configuration allows a potential application for risk assessment. The behaviour of EDL is investigated by recording the streaming and the capacitive current waveforms for grounded and energised middle copper-electrode cases and at different oil-flow velocities and temperatures. The effect of direct and alternating voltage energisation is examined for different wave shapes and frequencies. In addition, the physicochemical reaction coefficient, the wall space-charge density and the accumulated charges inside the sensor are calculated by the static and the dynamic methods. The results are interpreted in terms of EDL evolution, physicochemical reaction at the solid-liquid interface, relaxation time of charges and electron emission from the negatively energised electrode. The results reveal that the calculated wall space-charge density slightly decreases with the increase in the oil-flow velocity, contrary to the physicochemical reaction coefficient. For the case of AC energisation, the results show that there is an innocuous effect of the generated harmonic voltages on the oil-flow electrification phenomenon.

Measurement of Dielectric Liquid Electrification in the Shuttle System with Two Parallel Electrodes

“…The electrification current is also called a streaming current [33]. The structure between the solid surface and liquid is called an electric double layer [25,34,35]. The structure is presented in Figure 1.…”

Survey of different sensors employed for the power transformer monitoring

“…This sensor is placed in the oil and absorbs moisture from the oil until it reaches an equilibrium state [74]. Due to the high relative permittivity of the water, the capacitance of the sensor increases when moisture permeates the polymeric dielectric [75]. Therefore, by measuring the capacitance of the sensor, the amount of oil moisture can be determined [76].…”

Effects of multiple parameters on static electrification and breakdown strength of transformer oil

“…In order to reduce transformer manufacture costs, transformer insulation structures are designed to be more compact [3][4][5]. Many transformer manufacturers increase oil flow velocity to achieve the purpose of heat dissipation, and therefore the charge separation is more likely to occur on oil/pressboard interface [6][7][8][9][10]. Currently, the oil flow velocities have no instruction guidance of IEC standards.…”