Nanotechnology has been applied in the electrical industry for the enhancement of insulation properties. The compactness of the electrical machines has resulted in the requirement and creation of next‐generation insulating fluid with inflated dielectric properties. In this study, the magnetic nanoparticles are used in different concentrations to form stable nanofluids comprising ester‐based oils and two different electrode structures. The host fluids are synthetic ester oil and rapeseed oil, and magnetic nanoparticles used are iron (II, III) oxide, cobalt (II, III) oxide, and iron phosphide. Furthermore, the breakdown tests are analysed using Weibull statistical distribution.

An electret‐based electrostatic energy harvester featuring tuneable resonance frequency, small size, light weight, and high output power was designed and its performance predicted by the finite element method and verified by experiment. The device consists of a resilient fluorinated polyethylene propylene (FEP) electret film that is metallised on one side with a small seismic mass attached to its centre and an arc‐shaped counter electrode. In principle, such an energy harvester is mechanically a mass‐spring system and electrically a self‐bias voltage variable capacitor and converts vibrational energy into electrical energy by electromechanical coupling. For an energy harvester sample with dimensions of 30 × 10 × 9 mm for which the last dimension denotes the initial depth of the centre of the harvester, the resonance frequency can be tuned from 17 to 70 Hz by stretching the length of the FEP film loaded with a given seismic mass of 0.06 g. For a seismic mass of 0.1 g, the harvester generated a power up to 797 μW to a matching resistor at its resonance frequency of 17 Hz at an acceleration of 1×g, where g is the gravity of the earth. Such energy harvesters are promising candidates for use in self‐powered electronic devices and wireless sensor network nodes.

The authors report the key findings from an experimental study that explored the use of activated bentonite for the reclamation of thermally aged ester‐based transformer nanofluids to improve their insulation performance. Bentonite activated with acid treatment caused an increase in the specific surface area and pore volume of bentonite compared to the bentonite sample before treatment, thus imparting an improved adsorption capability. Physico‐chemical diagnostic studies were carried out to characterise the activated bentonite. The insulation performance of the reclaimed natural ester and nano‐filled ester fluid samples was assessed by measuring the corona inception voltage and breakdown voltage of each fluid sample, apart form measuring the flow electrification current using the spinning disk method. The results revealed that the reclamation process improved the corona inception voltage, dissipation factor and the breakdown voltage of the base ester fluid sample due to attraction of carbon particles to activated bentonite, but no significant variation was observed with nanofluids due to the depletion of the electrical double layer. The flow electrification current of ester and ester nanofluids reduced after treatment with activated bentonite, may be attributed to the interaction between copper and bentonite that alters the double layer formation responsible for the separation of charges.

A nanostructured film of NiCo₂O₄ has been prepared using a hydrothermal technique by simply using separate precursors to obtain nanoneedle‐like architecture for electrochromic applications. A homogeneous film consisting of packed nanoneedles with moderate density, appearing translucent white in colour, has been obtained and characterized using XRD and Raman spectroscopy techniques for confirming the composition and structure. Electrochemical analysis of the film reveals that the film shows good electrochromic properties under the anodic scan of potential with strong stability. The mechanism of the electrode under the transformation from natural white to opaque dark brown colour has been understood with the help of an in situ optical absorption spectroscopy technique. The electrode is found electrochromically active with a bias of up to 2 V and shows 50% optical contrast which makes it a good candidate for application in a solid state electrochromic device.