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Condition monitoring is playing an increasingly important role within electrical power networks, where its use can help to reduce maintenance costs, improve supply reliability and permit increased utilization of equipment capacity by providing a measure of actual operating conditions as an alternative to relying on more stringent 'worst case scenario' assumptions. In this context, energy harvesting may have a role to play in that it offers the possibility of realizing autonomous, selfpowering sensors that communicate their data wirelessly. In the vicinity of electrical transmission and distribution equipment, alternating magnetic fields at the power frequency offer a potential source of energy that does not require hard-wiring or batteries. There are many potentially useful locations for sensors where the level of magnetic flux density may be sufficient to provide enough power for a low-power wireless sensor node. This paper describes a 'free-standing' inductive harvester for use in positions where there is an ambient magnetic field due to conductors that are remote and/or inaccessible. Using data from surveys of magnetic flux density levels at two substations, optimum core and coil designs for the harvester were obtained through theoretical analysis and experiment. A demonstrator was then constructed in which a wireless sensor becomes selfpowering when immersed in a 50 Hz magnetic field. Laboratory results show that this system can deliver a useful average power of 300 µW when placed in a magnetic flux density of 18 µT rms .

The thermal decomposition of the acetates of calcium, sodium, silver and copper(II) have been investigated using thermogravimetry and differential thermal analysis, together with analysis of the gaseous products formed during the decomposition process. The results indicate that the major organic product formed is either acetone or acetic acid, depending on whether the final solid product is the oxide or the metal Much work has been published on the thermal decomposition of metal acetates (see for example refs. [1][2][3][4]) although interest has mainly been centred on the nature of the solid products formed. The acetates of the Group IIA metals have been extensively studied and it has been shown [5,6] that decomposition yields the corresponding carbonate, with acetone as the other major product. The decomposition of calcium acetate has, in fact, long been used as a student exercise to demonstrate the formation of acetone. It is generally accepted that breakdown of the acetate group is a complicated process, since the formation of oxides of carbon plus hydrocarbons can lead to many side reactions occurring.We have studied the decomposition of the acetates of sodium, copper and silver using thermogravimetry (TG) and differential thermal analysis (DTA). The processes have also been investigated using a flow system, which enables decomposition products either to be trapped out or collected in gas bulbs for subsequent identification. To check the results produced by this equipment, the thermal decomposition of calcium acetate has also been studied. ExperimentalThe samples of sodium acetate used were Analar grade material, whereas the samples of cupric and calcium acetate were general laboratory reagent grade (not less than 98 % and 95 % pure, respectively). Silver acetate was prepared by mixing equal volumes of 1 M aqueous solutions of Analar silver nitrate and sodium acetate. The precipitated silver acetate was filtered, washed with distilled water, recrystallized from hot distilled water, and dried at room temperature in a vacuum oven.

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