Capacitor trends have evolved from their origins to crucial components for modern applications

Capacitor trends have evolved from their origins to crucial components for modern applications

Spokesperson: Dr. Venkatesh Raghavan, Global Head, BU PFC, TDK India

The humble capacitor has remained the same over the past 275 years: a piece of dielectric between two metal electrodes. But over the period, there have been significant changes in the materials (basically the dielectric and electrodes), design, construction, and manufacturing processes to keep pace with changing technological developments, standards, regulations, and customer requirements and applications, thus making them relevant and integral parts of the electrical power system even after 275 years!

From Leyden Jar to Modern Applications

In October 1745, Ewald Georg von Kleist of Pomerania in Germany invented the first recorded capacitor. A glass jar with water inside as one plate was held in the hand as the other plate. A wire in the mouth of the bottle received a charge from an electric machine and released it as a spark. In the same year, Dutch physicist Pieter van Musschenbroek independently invented a very similar capacitor. It was named the Leyden Jar after the University of Leyden, where van Musschenbroek worked. Benjamin Franklin investigated the Leyden jar and proved that the charge was stored in the glass, not the water, as others had assumed. The earliest unit of capacitance was the ‘jar’, equivalent to about one nano farad. Early capacitors were also known as condensers, a term still occasionally used today. It was coined by Alessandro Volta in 1782 regarding the device’s ability to store a higher electric charge density than a normal isolated conductor. In its simplest form, a capacitor is a dielectric between two conducting electrodes. Various dielectric materials used in capacitors include vacuum, air, gas, plastic film, ceramic, mica, paper, glass, metal oxides, etc. The electrodes are generally made of aluminium foil, metallised on various substrates such as paper and plastic films, electrolytic fluids, etc.

Present status

Over the past three centuries, the capacitor has evolved into one of the most versatile products found in most equipment: watches, home appliances, automobiles, aircraft, spacecraft, defence equipment, trains, almost every electronic piece of equipment, computers, cars, power systems, etc.

The capacitances span the widest range from a few PicoFarads (pF) to Farads, with voltage capability ranging from a few volts to a few kilovolts (kV) and banks up to a few megavolts (MV). The application spectrum includes frequencies from a few Hz (Hz) (in fact, from 0 Hz, DC) to a few megahertz (MHz), spanning a wide frequency spectrum.

Capacitors are one of the most efficient pieces of man-made power equipment, with the highest efficiency (in the order of 99.99%), low cost per unit of power handling capability (as low as Rs. 100/kvar), and high power density (volume per unit of power handling capability). No wonder the application spectrum is one of the widest, including energy storage and power conditioning (power factor correction, transient suppression, harmonic filtering, etc.). Signal filtering (coupling, decoupling), signal processing, sensors, tuned circuits, pulsed power, etc.

Some of the conventional applications in power systems

Firstly, simple capacitors store and release energy as needed, mitigating voltage surges and transients. They also enhance the power factor by supplying capacitive reactive current, thereby minimising reactive currents within the network. This loss reduction and improved voltage stability margins optimise network capacity and prolong equipment lifespans by maintaining lower operating temperatures. Capacitors integrated with series reactors block harmonic currents from entering while facilitating the required reactive current at the fundamental frequency. Configured as tuned harmonic filters, they establish a dedicated path for harmonics, significantly reducing harmonic distortion across the network. These applications collectively enhance the reliability and efficiency of power distribution systems.

Newer capacitor applications

Most of the future rolling stock is expected to deploy advanced power electronics with various capacitors. Apart from their higher reliability and longer life, these capacitors are expected to operate in environments characterised by higher operating temperatures and vibration and be very compact and lightweight.

The industrial sector, particularly converters, drives, and UPS systems, anticipates a rapid increase in power electronics usage, necessitating a wide array of capacitors for applications such as DC links, snubbers, and filters. Key priorities include cost-effectiveness, environmental friendliness, and high reliability.

Capacitors must exhibit exceptional reliability in medical equipment like MRI machines, laser systems, and cardiac defibrillators. This is crucial for sensitive applications such as life-saving devices.

The automotive industry, driven by electric and hybrid vehicles (EVs and HEVs), demands next-generation capacitors that excel in technology, reliability, compactness, lightweight design, and cost-efficiency.

Capacitors play a critical role in traditional and advanced power transmission (HVDC, SVC, FACTS, and smart grids). To meet diverse operational needs, they must possess high reliability, long operational life, safety, and customisation capabilities.

Renewable energy systems, including wind power converters, solar photovoltaics (SPVs), and hybrid systems, represent another significant market. Specialised capacitors are essential to optimise energy capture and integration into power networks, supporting the global shift towards sustainable energy sources.

The latest capacitor trends

There’s a growing move towards using eco-friendly materials like certified bio-films (BioPP films) and ISCC-certified materials to reduce products’ environmental impact. This shift is driven by increasing customer demands for assessments of products’ environmental impact throughout their lifecycle.

Manufacturers are also adopting responsible manufacturing practices by using green and renewable energy sources in their processes to cut down on carbon emissions. They’re using advanced design and simulation techniques, along with new materials and manufacturing methods, to improve capacitor performance while using less material, thus reducing environmental impact even further.

Another trend is developing capacitors that can better handle harmonics, which helps deal with increasing network pollution and new application demands. Advanced thermal designs and high-temperature materials ensure capacitors can withstand tough conditions in areas like renewable energy and electric vehicles.

Technological improvements in dielectrics allow higher energy densities, making capacitors potential alternatives to batteries in some applications due to their lower power loss and higher power density. Safety and reliability are becoming key features, going beyond basic compliance standards to ensure strong performance across different working conditions.

Future trends might include introducing self-healing technology in medium-voltage power capacitors and promising advancements in size, weight, cost-effectiveness, and environmental sustainability. Innovations could also include using nanotechnology for higher energy densities and operations at high temperatures, along with using thin, flexible glass dielectrics and thin film coatings for better performance and smaller size.

Integrating capacitors with other components to create modular solutions tailored for specific applications is also expected to grow, leading to more efficient and adaptable systems across industries, from power transmission to advanced electronics.

Though the capacitor in its basic form is more than 275 years old, the product has evolved to keep pace with changing technology and application requirements and still has relevance today. Capacitor, in some form, is present in our daily lives and is expected to continue to be an integral part of our daily lives. To keep pace with changing application requirements, capacitors are expected to be “greener” using greener materials and sustainable or responsible manufacturing processes, compact in size, have higher harmonic capability, have higher thermal capability, be safer and more reliable, use advanced dielectric materials to enhance energy density, etc.