Propagation of Electrical Trees under the Influence of Mechanical Stresses: A Short Review

The present paper deals with the phenomenon of electrical treeing in solid insulation, under the influence of mechanical stresses. In this short review, it is indicated that mechanical stressing can affect the propagation of electrical trees and –depending on whether it is tensile or compressive- it can facilitate (or render more difficult) the breakdown. In aged insulating materials, electrical trees can appear very quickly and can lead to breakdown

Some Observations on the Dielectric Breakdown and the Importance of Cavities in Insulating Materials used for Cables and Electrical Machines

Partial discharges (PD) contribute greatly to the ageing and the breakdown of solid insulating materials. In the present paper, some conductivity measurements are performed relating the conductivity of inner walls of an enclosed cavity to the behaviour of PD in the case of polyethylene and of epoxy resin. The temporary decrease of the PD magnitude is explained in terms of the increase of the cavity inner wall conductivity. The PD behaviour is studied in epoxy resin samples and is explained with the aid of Pedersen's model. Scanning Electron Microscope (SEM) photographs indicate the sort of damage suffered by the cavity walls under electrical stress

Massive Hemoperitoneum from Uterine Leiomyoma Associated with Diffuse Myometrial Venous Congestion

Hemoperitoneum is a rare complication of uterine leiomyomas. Increased abdominal pressure during mechanical stress (i.e., trauma, intercourse, or menstruation) may lead to the rupture of superficial veins overlying the leyomioma. A 39-year-old woman presented with intra-abdominal bleeding without any evidence of mechanical stress. The bleeding was caused by a uterine superficial vein overlying a subserosal leiomyoma. After hysterectomy, histopathologic findings revealed diffuse venous ectasia throughout the whole uterus. Diffuse myometrial venous congestion should be considered a possible predisposing factor to spontaneous rupture of the superficial vesse