It is well-known that the high-performance polymeric dielectric films used for high-voltage DC capacitors should have outstanding capabilities in terms of electrical and mechanical properties in order to face harsh operating conditions. Many factors limit the ability of these thin films to face different and growing stresses according to modern electrical requirements. Microstructure properties, additives, impurities, defects formed during manufacturing as well as applied stress types significantly affect the performance of dielectric films and their operational lifetime. This paper presents a comprehensive review of the factors which affect the ageing, degradation and breakdown of metallised polypropylene (PP) capacitors films. The effects of microstructure, surface morphological properties, mechanical properties and defects on the reliability of biaxially oriented polypropylene films (BOPP) are studied. In addition, the phenomena affecting dielectric performance and ageing mechanisms which are induced by electrical, thermal and electrothermal stresses are discussed.
Background: Acetabular retroversion has been proposed to contribute to the development of pain and osteoarthritis of the hip. Conventional anteroposterir (AP) pelvic radiographs may represent a reliable, easily available diagnostic modality.
Objective: To obtained a reproducible technique allowing the anterior and posterior acetabular rims to be visible for assessment
Method: This is a cross-sectional study conducted from December 2015 to March 2017 targeting patients with hip pain in orthopedic clinic of Al-Kindy teaching hospital. The study sample consisted of 100 patients with hip pain who were investigated with Antroposterior pelvic plain x-ray, which was done for all patients, looking for cross-over sign, the patients with positive cross-over sign radiographs were sent for CT scan to ensure retroversion of acetabulum.
Results: Presence of a cross over sign was documented in 9 patients (9%). From these 9 patient only 8 were proved by CT scan to have retroverted acetabulum. Then the prevalence was 8%.
Conclusion: The cross-over sign is a reliable indicator for diagnosis of acetabular retroversion and the presence of a cross-over sign in a plain film should heighten awareness of the advisability of proceeding to full assessment .
Power quality improvement of low voltage grid is a great challenge that confronts the sophisticated power applications, because their performance is highly sensitive to the quality of power supply. Dynamic Voltage Restorer (DVR) used widely as an efficient and skillful device to adjust electrical disturbances of the distribution grids. This paper introduces an overview of the components of the 3-phase dynamic voltage restorer and design its own control circuit. The performance of DVR was developed on the basis of the appropriate selection of Photovoltaic (PV) module instead of the present conventional designs. Through this design, the need of series converter (DVR) for the current from an electrical grid will end and the problems of power losses will curb. The PV-module is selected to meet the requirements of the DVR during voltage sag/swell on voltage line. The proposed system is mimicked in MATLAB software/Simulink and the findings are presented to prove the success of the design in terms of full congruence of the load voltage waveform with source voltage waveform, attaining 0.77% of THD analysis for the load voltage and the waveforms of PV system.
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