Nanotechnology applications for electrical transformers—A review

Highlights

• A state-of-the-art review of nanotechnology alternatives for transformers is shown.

• Performance of materials used in transformers can be enhanced by nanoparticles.

• Nanofluids, nano-insulation, nanostructured insulators are the main topics.

• A general prospective of nanomaterials applications for transformers is proposed.

Abstract

Nanoscience and nanotechnology applications have shown remarkable progress in several industrial fields, producing advance materials. Nowadays, there are a great number of technological developments and R&D projects regarding nanotechnology concepts to enhance performance and reliability of conventional materials. Electrical industry has taken advantage of these nanotechnology efforts looking for application in its components, such as in electrical transformers which are considered as key elements in the electricity network. This paper shows a comprehensive literature review on the applications of nanotechnology concepts for transformers, especially investigations related to insulating materials, dielectric fluids, outdoor insulators, monitoring systems and other components. Latest up to date literature on the applications regarding nanomaterials for transformers have been reviewed and reported. In addition, opportunities for future research and a general overview of nano-applications in electrical transformers are shown in this work.

Introduction

Electrical transformers are one of the most important components of the generation and distribution electricity network due to any fault in these elements will reduce the reliability of the power system and interrupt the power supply [1], [2]. Basically, transformers are static devices consisting of a winding, or two or more coupled windings, with or without a magnetic core, for inducing mutual coupling between circuits [3]. They also include a variety of inner construction materials, mainly metals and plastics. Insulating fluids with dielectric and thermal characteristics are incorporated in oil-immersed transformers while a polymeric resin is used to encapsulate all the inner components in dry-cast transformers.

In more than 100 years, electrical transformers have not suffered significant changes in regards of operation and functionality; however, manufacturers have reached important progresses regarding design topics with the aim to offer high-added value products with higher capacity, reliability and efficiency. On the other hand, some research and developments have been focused in both the enhancement of conventional materials and introduction of new materials. However, considering materials physics, it is clear that traditional materials are reaching their performance limits based on its properties-microstructure, which it has already reached in many cases. Therefore, many electrical transformer manufacturers have considered innovation and new technologies initiatives as alternatives to take competitive advantage against industrial competitors, for example advance materials or even nanoscience and nanotechnology which have emerged to revolutionize the material science in the last years.

Since the term of nanotechnology was conceptualized by Richard P. Feynman in his speech in 1959 [4], it has been carried out several investigations in physics, chemistry, mechanics, biology, etc., in which Feynman’s idea related to the manipulation of matter at molecular and atomic level (nanoscale) has been demonstrated. Nanotechnology can be defined as the understanding, control and manipulation of matter at nanoscales, as small as 100 nm to create materials with fundamentally new properties and functions [5]. Although nanotechnology is a new word, it is not a new topic since nature has been doing manipulation of the matter at nanometric levels to build its systems like plants and animals [6]. An extraordinary example of nanotechnology from the nature is given by the lotus flower, which always has its leaves clean although it grows in muddy waters. The water-repellent surface of lotus leaf and flower is due to the nanosized wax papillae on the upper side of each epidermal cell, so drops of water roll off free of dust and dirt particles, leaving the surface clean. This self-cleaning property of highly hydrophobic surfaces, termed as the lotus effect, has opened the possibilities of fabricating superhydrophobic surfaces for a variety of products [7], [8], [9]. Another popular example is given from a small lizard called gecko. The gecko lizard has the ability to adhere to vertical surfaces, even walk upside down on ceilings. This extraordinary climbing skill is due to on the sole of a gecko’s toes there are some one billion tiny adhesive hairs, about 200 nm in both width and length [10], [11], [12]. It is clear that these nanotechnology examples and others from nature have been taken to develop new nanomaterials with specific applications such as, paints and coatings with self-cleaning effects, high-performance glues and adhesives, etc.

In spite research and development regarding nanotechnology have increased in the current century, there are references of antiques decorative pieces which fortuitously have nanoparticles incorporated in its microstructure. For example, investigations have found that the beautiful colors of some old Chinese and Japanese ceramic pottery (1000 years ago) came from metallic nanoparticles of gold and cooper used in the colorant [13], [14], [15]. Another example is related to the ancient Damascus blades, which were very attractive and well-valued in Europe in the 17th century due to two qualities: wavy-like banding and extremely sharp edge. Recent analysis showed that the extraordinary characteristics of Damascus blades were attributed to cementite nanowires and carbon nanotubes in its microstructure [16], [17].

Nowadays, fields in micro- and nanoscience have achieved a relevant progress due to the technological collaboration between several disciplines such as material science, physics, chemistry, information technology, etc., and also by social, economic and politic aspects [18]. The International Electrotechnical Commission (IEC) is working on the standardization of the technologies relevant to electrotechnical products and systems in the field of nanotechnology in close cooperation with other committees of IEC and ISO. On the other hand, the ASTM International has released a standard to facilitate communication among members of the business, research, legal, government, and educational communities, ASTM E2456—06(2012) Standard Terminology Relating to Nanotechnology.

Nanotechnology comprises two approaches: bottom–up and top–down (Fig. 1). The first approach denominates as molecular nanotechnology, involves the building of organic and inorganic structures atom-by-atom or molecule-by-molecule. The second is related to size reduction of conventional materials at nanometric levels, i.e., bulk materials are broken down into nanoparticles by mechanical attrition and etching techniques [19].

Nanostructured materials have been extensively studied in the last years due to potential applications in electronics, biotechnology, medicine, engineering, etc. Investigations have demonstrated that materials performance can be dramatically altered by nanoparticles additions, for example higher mechanical resistance, hardness, ductility, wear resistance, dielectric and thermal capacity, magnetic properties, etc., therefore there is a great interest in nano-materials [20], [21].

Nanotechnology offers feasible technological alternatives not only for the enhancement of conventional materials, but also for the development of new materials for electrical transformers. This paper provides a state-of-the-art literature review of nanotechnology applications in electrical transformers and focuses on investigations regarding nanomaterials for transformers and its benefits over traditional materials. References of nanotechnology concepts for dielectric fluids, solid insulation, outdoor insulators and systems for monitoring & diagnosis (M&D), and other inner materials, are presented in this work. Finally, a general overview of nanotechnology alternatives for the next generation of electrical transformers is also proposed.