Over the past few years, the requirements of power utilities across the world have changed. This has necessitated equipment providers to make advancements in conductor, transformer and substation technologies. The adoption of the new substation technologies is driven by the reduced availability of space and the high price of real estate in urban and residential areas, which makes the setting up of new facilities difficult and costly. Transformer technology has been evolving over the years, with an increasing need to reduce transmission and distribution losses, address grid security and consumer safety concerns, and minimise environmental impact. Similarly, to eliminate faults on low tension lines and improve reliability, new conductor technologies are emerging. These are aimed at reducing faults to a large extent, eliminating theft by direct tapping and avoiding the overloading of distribution transformers (DTs).
Substations
Compact secondary substations
Compact secondary substations (CSSs) are type-tested assemblies that usually comprise an enclosure containing medium voltage switchgear, DTs, low voltage switchboards, connections and auxiliary equipment to supply low voltage energy from medium voltage systems. CSSs can also be used to step up voltage – for example, from 0.6 kV to 12 kV for specific applications like wind or solar farms. Typical medium voltage levels for CSSs are 12 kV, 24 kV and 36 kV. For CSSs, one or two oil-immersed hermetically sealed or dry-type transformers can be installed, and the transformer bushings can be located on the top or side of the transformer as per customer needs. Transformers with capacities of 200-1,600 kVA can be installed in CSSs. Various safety considerations also emphasise the use of this technology, particularly internal arc fault-tested CSSs.
Gas-insulated switchgear
High voltage gas-insulated switchgear (GIS) is compact, metal-encapsulated switchgear comprising high voltage components like circuit breakers and disconnectors, which can be safely operated in confined spaces. The robust and low-maintenance GIS-based design minimises the substation footprint by as much as 70 per cent, enabling it to be installed indoors, in busy urban areas and in harsh environments. GIS is available for voltages ranging from 12 kV to 800 kV. Different types of gas-insulated metal-enclosed switchgears are available, such as isolated-phase GIS, integrated three-phase GIS, hybrid GIS and compact GIS.
Transformers
Dry-type transformers
Ventilated dry-type transformers continue to grow in popularity around the world as they have several advantages over conventional transformers. They offer enhanced safety because there are no fluids to spill, explode or burn, and the use of special papers inside them does not support combustion in the air. As dry-type transformers can be located close to their loads (inside factories, schools, hospitals and apartments), low voltage lines can be shortened, leading to a reduction of associated losses. These transformers can be designed with a temperature rise up to 150 K, requiring less conductor and core steel, also resulting in lower initial costs. Their reduced size and weight contribute to the ease of installation and the smaller cores result in lower no-load losses. Dry-type transformers have enhanced overload capabilities and can accommodate heavy harmonic content as they have a large reserve temperature capability. They are insensitive to moisture and humidity, which is found in marine applications.
Retrofilling wet transformers with synthetic ester oil
The use of synthetic ester oil instead of mineral oil in oil-filled transformers is another emerging option. Ester oil is easily biodegradable and non-corrosive, and offers superior fire performance and moisture tolerance. Retrofilling transformers with synthetic esters helps increase water content with the moisture migration from paper insulation, making the insulation resistance rise from less than 20 MW to 80 MW. By using more water, synthetic ester delays the ageing of paper insulation.
Conductors
Aerial bunched cables/conductors
Aerial-bunched cables (ABCs) are an innovative concept for overhead power distribution. When compared to conventional bare conductor overhead distribution systems, they provide more safety, reliability and system economy, and lower power losses due to reduced installation and maintenance and operation costs. They are ideal for rural distribution, especially for installations in difficult terrain like hilly areas, forest areas and coastal areas.
ABCs are the preferred choice for power distribution in congested urban areas because of their rerouting flexibility. In comparison with bare overhead distribution lines, ABCs have high reliability in maintaining services because power and neutral conductors are insulated with the best dielectric medium. ABCs have lower fault rates on account of their protection against line and ground faults as well as high insulation resistance. When compared to other distribution conductors, these cables have better adaptability and can run concurrently with existing overhead bare conductor systems without any interference. Their high capacitance and low inductance lead to lower line impedance and better voltage regulation.
Going forward, it is essential for discoms to introduce and incorporate new technologies in order to reduce distribution losses and strengthen infrastructure.