Streaming electrification study of transformer insulation system using a paper tube model

Abstract

A simple flow model was designed to simulate oil flow in the insulation ducts of power transformers. It consisted of an annular paper tube, relaxation tanks, pump and flow controls. Both laminar and turbulent flow modes wer& studied in the temperature range 27 to 70 C. Current development was monitored as a function of temperature and flow velocity. The temperature dependence was approximately the Arrhenius type; no current peak was observed as reported for transformers, in the temperature range studied. The current increased linearly with flow velocity at low flow rates, and increased as the square of velocity at high flow rates with a gradual transition in the intermediate range of flow. development was characterized by a sharp rise initially as the flow was turned on, levelling off to a maximum after several minutes. Partial discharge patterns were observed in the volt-time plot, increasing in frequency and temperature at elevated temperatures and flow velocities. A strict application of the test results to transformers is not possible due to unknown parameters.

Development and calibration of a streaming electrification model for a cellulose duct

“…Oommen [16] and Tanaka et al [3] both assume that the number of ions available obey an Arrhenius temperature relationship Hence, the wall charge gradient boundary condition is tentatively postulated to follow a similar dependence, namely…”

Electrostatic Generation in Dielectric Fluids: The Viscoelectric Effect

“…Note that the unit exponents here do not exactly match those in the table above (i.e., the units of L φm and L mφ should be A ⋅ s 2 /m 3 not A ⋅ s 1.87 /m 2.74 ). However, several investigators, including Oomen and Lindgren [39], have found the current to increase with the square of the velocity at high flow rates, This apparent discrepancy is due to the fact that the Hazen-Williams equation is a relatively simple approximation to the pressure gradient -flow rate behavior in pipes over the complete turbulent region. A better approximation is given by the Darcy-Weisbach equation (see Potter and Wiggert [40]), ∇(p/ρ) = (f/D)V 2 /2 = [8f/(π 2 D 5 )]Q 2 (8) where f is the pipe "friction factor," ∇(p/ρ) is (∆p/ρL), and L and D are the pipe length and diameter.…”

“…The laminar flow of a dielectric liquid in a circular horizontal pipe has been treated analytically by Walmsley and Woodford [41] and experimentally studied by Touchard [42]. Oommen and Lindgren [39] also studied it experimentally in a horizontal annulus. In both cases the current was found to be a linear function of the mean flow velocity V. For laminar flow in a circular horizontal pipe, the pressure gradient is:…”

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

“…It was found that the effective oil velocity did not exceed 0.6 m/s for the coil and its insulation structures for 240 MVA oil-forced power transformers [31]. In addition, some national grids have their own rules to keep the oil-flow velocity below 1 m/s [31][32][33][34]. When the flow velocity decreases, the oil flow will turn to be the state of laminar flow accompanying with the decrease of the electrified tendency [34].…”