On the addition of degrees of freedom to force-balanced linkages

The design of shaking-force balanced linkages can be approached by deriving these linkages from balanced linkage architectures. When desired, a possible step is to add degrees-of-freedom (dof), for instance by substituting a link with a n-dof equivalent linkage for which the balanced design of the other links is not affected. This paper shows how the coupler link of a shaking-force balanced 4R four-bar linkage, applied as a 5R five-bar linkage, can be substituted with an equivalent 2-dof pantograph

The effect of water content on the electrical properties of transformer oil

The condition monitoring of insulating oil used in high voltage apparatus is based on assessing its electrical, physical and chemical properties. During their service life, these apparatuses such as transformers are subjected to several stresses which reduce their insulating capacity. Water and oxygen are the most important factors that accelerate the aging and degradation of transformer oil. There is a strong relationship between the presence of water in oil and the degradation of its electrical properties. This paper presents an experimental investigation to quantify and correlate the change in water content in transformer oil and its effect on their electrical properties. For this purpose, three samples of oil are used: new uninhibited, regenerated and used oil. A physical treatment using a MAXEI station is applied to the three samples to reduce their water content. The treatment is an operation of filtration, degassing and dehydration which is a necessary step before injection of the oil in transformer and during maintenance operations. During the physical treatment, the electrical properties of the oil samples are measured. The breakdown voltage, the dielectric loss factor, the permittivity and the resistivity were measured in according to the standards IEC 60156 and IEC 60247. The results revealed that for the three oil samples; new, regenerated and used, the electrical properties are strongly correlated with the change in water content in oil. The breakdown voltage and resistivity increase considerably when the water content is reduced. If the water content is reduced under 5 ppm, the breakdown voltage remains practically constant. The dielectric loss factor decreases by the water content variation. By decreasing the water content in oil, the insulating properties of transformer oil are improved. The analysis of the results shows that a strong correlation exists between the breakdown voltage, resistivity and the presence of water in oil