mod_eprivacy

Mechanical and electrical phenomena of droplets under the influence of high electric fields

Description

The generation of singular water drops instead of a continuous water film on the hydrophobic surfaces of high voltage outdoor plastic isolators suppresses electric leakage over the surface and significantly improves the isolator capacity. However, the degree of hydrophobicity deteriorates through climatic influences and partial electrical discharges from the edges of drops or from dry-zone edges are even worse. This can lead to the complete loss of hydrophobicity and subsequent chemical and thermal damage to the isolator surfaces. The change in form of drops and in structure of drop coating influences the electric field distribution decisively and is therefore essential for the optimization of isolator field calculation for isolators under wet conditions. In this project, which is closely linked with TP-A5, the drop dynamics under the influence of high electric fields at varying relevant parameters such as surface and drop properties, classification of the electric field and environmental conditions is to be modeled. Furthermore, the onset of electrical partial discharges is to be calculated, which is determined by the electric field as well as the varying drops contours. The goal is to obtain an increased understanding of the fundamental mechanisms and influencing parameters as well as the expansion of existing aging models of plastic isolators and new insights for their optimization.

The project consists of experimental studies which are to obtain input data and a validation for the numerical calculations (in particular TP-A5) and will be extended to numerical simulations at a later stage. The long term goal is to simulate the electric field distribution and the resulting forces on the drops, as well as the resulting deformation and finally the resulting onset of electrical partial discharges. In the first phase of the project the necessary field strength for the onset of partial discharges is determined experimentally by varying different parameters and is the reference with models from the literature. This is done with basic arrangements with non-deformable drop replicas. For the experimental investigation a high-speed camera is used to determine the typical deformations of real drops, which will be used for the field simulations, as long as the drop deformation cannot be simulated yet. For the experimental validation of the modeling different parameters are varied: the direction and type of the electric field (AC, DC, pulsed field), volume, viscosity, conductivity and permittivity as well as the charge of the droplet, surface tension, texture and slope of the isolator, ambient conditions (density of the air, humidity). The previously developed video recording technology is optimized (resolution, depth of field). The experimental determination of the necessary field strength for the onset of partial discharges (electric process) is extended by the localization of partial discharge locations (UV camera).

In cooperation with TP-B1 and TP-C3 future investigations about icing subcooled sessile drops as well as supercooled drops in free fall and the associated charge separation under the influence of high electric fields are planned. Supercooled drops are found in thunderclouds for example. The influence of strong electric fields on the behavior of charged and uncharged drops is to be studied. A special goal is to experimentally investigate the influence of strong electric fields on the freezing behavior. Furthermore, the mechanisms for charge separation in a thundercloud will be better understood.

Team

Prof. Dr.-Ing. Volker Hinrichsen

Prof. Dr.-Ing. Volker Hinrichsen

Director subarea C5 This email address is being protected from spambots. You need JavaScript enabled to view it. +49 6151 16-20430
Jens-Michael Löwe, M. Sc.

Jens-Michael Löwe, M. Sc.

C5 This email address is being protected from spambots. You need JavaScript enabled to view it. +49 6151 16-20468
215216

Publications

2016

J. Löwe, M. Secklehner and V. Hinrichsen,
Investigation of surface charges on polymeric insulators and the influence of sessile droplets
International Electrical Insulation Conference
(INSUCON) 2017, 2016, ’Abstract submitted and accepted’

Nazemi, M. H.:
Experimental Investigations on Water Droplets on Polymeric Insulating Surfaces under the Impact of High Electric Fields.
Dissertation, Technische Universität Darmstadt, 2016.

2015

M.H. Nazemi and V. Hinrichsen,
Partial Discharge Inception Electric Field Strength of Water Droplets on Polymeric Insulating Surfaces,
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 22, No. 2, pp. 1088-1096, April 2015.

M.H. Nazemi and V. Hinrichsen,
Experimental Investigations on Partial Discharge Characteristics of Water Droplets on Polymeric Insulating Surfaces at AC, DC and Combined AC-DC Vol-tages,
IEEE Transactions on Dielectric and Electrical Insulation, Vol. 22, No. 4, pp. 2261-2270, August 2015.

2013

Nazemi, M. H., Hinrichsen, V., Gjonaj E.:
Investigations on Partial Discharges of Polymeric Insulators in the Presence of Oscillating Water Droplets on the Surface.
4. ETG-Fachtagung Grenzflächen in elektrischen Isoliersystemen, 2013.

Nazemi, M.H., Hinrichsen, V.
Experimental Investigations on Water Droplet Oscillation and partial Discharge Inception Voltage on Polymeric Insulating Surfaces under the Influence of AC Electric Field Stress
IEEE trans. on Dielectric and Electrical Insulation, 20(2) (2013), 443-453

Nazemi, M.H., Hinrichsen, V.
Partial discharge investigation and electric field analysis of different oscillation modes of water droplet on the surface of polymeric insulator under tangential AC electric field stress
ICSD 2013, IEEE International Conference on Solid Dielectrics, Bologna, Italy (2013), 194-197

Nazemi, M.H., Hinrichsen, V.
Partial Discharge of Water Droplets on Polymeric Insulating Surfaces
NSUCON 2013, 12th international insulation conference, Birmingham, UK (2013)

Songoro, H., Nazemi, M.H., Gjonaj, E., Hinrichsen, V., Weiland, T.
Water droplet oscillation on the hydrophobic surface of polymeric insulators under AC electric field stress
ISH 2013, 18th Sympo- sium on High Voltage Engineering (2013), Seoul, South Korea, accepted

Sunday, August 25, 2019