Liquid dielectric

About: Liquid dielectric is a research topic. Over the lifetime, 3702 publications have been published within this topic receiving 45150 citations.

Measurement and modeling of dielectric response of composite oil/paper insulation

Abstract: Moisture and aging strongly influence the dielectric properties of oil/cellulose insulation systems. Dielectric measurements can therefore be used for assessing the condition of the oil/paper insulation. In this paper, we report on measurements and modeling of recovery voltages and polarization and depolarization current measurements on composite oil/paper insulation. A numerical model allows us to model the response of the composite system from knowledge of the dielectric properties of the constituents (oil and paper). In particular we demonstrate the consistency between recovery voltages and polarization and depolarization current measurements and show the influence of material properties on dielectric response.

The electroosmotic droplet switch: Countering capillarity with electrokinetics

Abstract: Electroosmosis, originating in the double-layer of a small liquid-filled pore (size R) and driven by a voltage V, is shown to be effective in pumping against the capillary pressure of a larger liquid droplet (size B) provided the dimensionless parameter σR2/e|ζ|VB is small enough. Here σ is surface tension of the droplet liquid/gas interface, e is the liquid dielectric constant, and ζ is the zeta potential of the solid/liquid pair. As droplet size diminishes, the voltage required to pump eletroosmotically scales as V ∼ R2/B. Accordingly, the voltage needed to pump against smaller higher-pressure droplets can actually decrease provided the pump poresize scales down with droplet size appropriately. The technological implication of this favorable scaling is that electromechanical transducers made of moving droplets, so-called “droplet transducers,” become feasible. To illustrate, we demonstrate a switch whose bistable energy landscape derives from the surface energy of a droplet–droplet system and whose triggering derives from the electroosmosis effect. The switch is an electromechanical transducer characterized by individual addressability, fast switching time with low voltage, and no moving solid parts. We report experimental results for millimeter-scale droplets to verify key predictions of a mathematical model of the switch. With millimeter-size water droplets and micrometer-size pores, 5 V can yield switching times of 1 s. Switching time scales as B3/VR2. Two possible “grab-and-release” applications of arrays of switches are described. One mimics the controlled adhesion of an insect, the palm beetle; the other uses wettability to move a particle along a trajectory.

Dielectric properties of natural ester, synthetic ester midel 7131 and mineral oil diala D

Abstract: The insulating liquids used in industrial applications are typically mineral oils. In recent years however, significant attention has been paid to alternative insulating fluids, including synthetic and natural ester liquids. In order to expand their practical applications, it is important to have detailed information on their dielectric properties. In this present paper, the dielectric properties of synthetic ester, Midel 7131; mineral oil, Shell Diala D; and vegetable (rapeseed) oil have been investigated. It has been shown that Midel 7131 has a higher ac breakdown voltage (27.6 kV) as compared with Diala D oil (26.4 kV) and rapeseed oil (24.6 kV). However, the breakdown voltage of the Diala D oil has the smallest standard deviation (7%) amongst the tested liquids (13% for Midel 7131 and 11% for rapeseed oil). Statistical analysis of the breakdown voltages has been conducted and it has been shown that the ac breakdown voltages can be described by a normal distribution. dc I-V characteristics have been measured and the space charge saturation regime has been observed for all three liquids starting from ~9 kV for positive energisation and ~10 kV for negative energisation in the point-plane topology. Apparent mobilities of the charge carriers in the tested liquids have been obtained using I1/2-V curves; these mobilities can be used for calculation of the space charge influenced distribution of the electric field in liquid insulators stressed with dc voltage. Such analysis can be important for design and exploitation of HVDC power systems.

Analysis of partial discharge characteristics of natural esters as dielectric fluid for electric power apparatus applications

Abstract: Petroleum based mineral oils are generally used for electric power apparatus insulation and cooling applications. Since the conventionally used mineral oils are not biodegradable and difficult to decompose, there is a need for the development of alternate vegetable based insulation oils for such applications. Formation of partial discharges plays a major role in determining the life time of liquid insulation. Reports on partial discharge characteristics of thermal aged natural ester fluids for high voltage applications are scanty. The major aim of this research work is to understand the partial discharge characteristics of natural esters as a dielectric fluid for power transformer and other electric power apparatus insulation applications. Laboratory experiments are performed as per IEC (International Electro technical Commission) test procedures in order to understand the breakdown voltage and partial discharge characteristics of vegetable oils such as corn oil and palm oil under both virgin and thermal aged conditions. This paper presents a comparative assessment of the PD characteristics of thermal aged natural ester fluids with respect to mineral oil. Time and frequency domain analysis of PD pulse at both needle-plane and rod-plane electrode configurations are studied. Statistical analysis of PD pattern is also carried out. This analysis collects the typical PD patterns from natural ester fluids in order to find its suitability for power transformer and electric power apparatus applications.

Gapped resonant microwave apparatus for producing hyperthermia therapy of tumors

Abstract: Apparatus and process for elevating the temperature of a tumor (22) by hyperthermia without unduly heating healthy tissue surrounding the tumor containing tissue, and controlling generally the temperature distribution within any dielectric medium put in place of the tissue (20), which medium acts as a dielectric load in the microwave circuit. The apparatus comprises a gapped, resonant microwave circuit having matching media for matching the intrinsic impedance of the dielectric load to the intrinsic impedance of any medium within the waveguides (16) and 16') which serve to conduct the microwave beams to the tissue (20) to be treated. Heat may be removed from the dielectric fluid (38) of a dielectric matching medium by circulating the dielectric fluid to a heat exchanger (41).