A series of tests was performed in winter 1996 to measure degradation of paper mulches with the help of physical and mechanical properties. Four types of paper used for mulching, kraft paper gauge 40, 60 and 80 and waxed paper were laid over soil in two growth chambers. They were kept under observation for 27 days under controlled temperature, humidity and light. Mulches were sprayed with water to simulate rain. Tensile and puncture tests were performed on each type of paper every day. Four mechanical properties; stress, strain, energy and tensile energy absorption were calculated from the force-deformation curve obtained by tensile test. Two mechanical properties; displacement and force to break were calculated from the force-deformation curve obtained by puncture test. A special die had to be designed to perform puncture tests. This design eliminated shear loading which otherwise would have been present in normal puncture tests. / Results showed that paper - 3 (kraft paper gauge - 80) was best suited for mulching as the mechanical properties were stable through 27 days with negligible fluctuations. Waxed paper required less force to break but was stable through 27 days of experimentation. / A three-way factorial model was developed to analyze the results statistically. A SAS program was written to model the results. The fitted model was in very good agreement with the actual values.

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A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in Engineering Date submitted: 28 August 2015 / Many generator transformers were installed many years ago during the initial commissioning of Eskom’s power stations. Many of these transformers have started showing signs of significant ageing of the paper insulation and hence require regular monitoring. There are two methods that are currently being employed to assess the degree of ageing of the paper insulation in a generator transformer, which are paper sampling and furan level measurement. This dissertation investigates an alternative method of predicting the degree of ageing of the paper insulation instead of what is used currently. This method uses the Arrhenius equation that relates time and temperature to determine the degree of degradation of organic materials. The reliability of the Arrhenius estimation method is assessed by comparing the predicted DP (Degree of polymerisation) values with the measured DP values of the same transformer paper insulation. The results obtained showed that there is reasonable correlation between the DP values estimated from the Arrhenius equation and the DP values estimated from the measured furan levels. The accuracy of the prediction method is reduced when the oil temperature greatly differs from the paper insulation temperature. The application of the Arrhenius equation to estimate the ageing of paper insulation is a great milestone in the quest to predict the remaining life of a transformer. It is the only method available to do this prediction and using online temperature measurement on transformers makes the method more reliable. / MT 2017