Power transformers play a crucial role in maintaining power flow throughout the electrical grid. It ensures steady and reliable supply of energy to consumers. India’s power transformer market is buzzing with activity, driven by a confluence of factors. The market is expected to grow due to rising electricity demand amidst ambitious renewable energy goals. New transformer technologies are being developed to minimise these losses and improve the overall grid efficiency. While efficiency remains paramount, there is a growing focus on faster return on investment (payback time) for transformer projects. This is influencing technical decisions, including transformer design, material selection and maintenance strategies. Essentially, new technologies need to be not only efficient but also cost-effective in the long run.
Technologies
At present, the market has prioritised digitalisation, smart grid integration and sustainable solutions for transformers. Research and development in new core steels and innovative insulation techniques are underway to minimise energy losses and improve cooling efficiency.
Dry-type transformers: Dry-type transformers offer a versatile and safe solution for voltage transformation within the power grid. They function by efficiently increasing (step-up) or decreasing (step-down) voltage levels. This is particularly valuable when converting high-voltage transmission lines to voltages suitable for industrial or residential use.
A key advantage of dry-type transformers lies in their air-cooling mechanism, eliminating the need for potentially hazardous liquids such as oil or silicone for cooling the electrical core and coils. This “dry” design makes them well suited for indoor applications, where traditional oil-filled transformers pose safety concerns.
Furthermore, dry-type transformers have minimal maintenance requirements and a proven track record of reliable service. Unlike their liquid-filled counterparts, they utilise environmentally friendly high-temperature insulation systems. This translates into a safer and more dependable power source that eliminates the need for fire-resistant enclosures, containment basins, or the emission of toxic gases. These significant safety features enable the installation of dry-type transformers within buildings, often positioned near the point of maximum power consumption. This strategic placement enhances the overall energy efficiency by minimising costly power losses across primary and secondary lines.
Smart transformer: The rise of smart grids necessitates advanced transformers with intelligent capabilities. These “smart transformers” play a critical role in optimising power distribution through features such as autonomous voltage regulation, seamless smart grid integration and real-time communication. They deliver the exact amount of power required, minimising inefficiencies and fluctuations. Embedded with advanced controls, smart transformers offer self-diagnostics and enable remote monitoring of key components, ensuring proactive maintenance and component longevity.
Beyond efficiency, smart transformers enhance grid resilience through dynamic control of power flow, improved power quality and better fault current management. Advancements in design, modularity and recovery strategies are further improving grid resilience.
The environmental impact of smart transformers is significant. By directly reducing energy consumption and extending equipment lifespan, they contribute to a greener power grid. Their ability to dynamically manage power during peak demand ensures consistent voltage optimisation even under changing loads. Overall, smart transformers are a key technology for a more efficient, reliable and sustainable power grid.
Phase-shifting transformers: Phase-shifting transformers (PSTs) are specialised transformers employed within three-phase electric transmission networks to manage the active power flow. They achieve this by regulating the voltage phase angle difference between two specific points on the grid.
The core principle behind PSTs involves injecting a phase-shifted voltage source into the transmission line. This is accomplished through a combination of two transformers – a series-connected transformer directly in the line and a shunt transformer feeding the series unit. The specific configuration of these transformers induces the desired phase shift.
PSTs offer a simple, robust and reliable solution for power flow control. They can be employed in both preventive and curative control strategies. In the preventive mode, a permanent phase shift is introduced to redistribute power flow across the grid, alleviating stress on specific lines in case of outages. In contrast, in a curative mode, the phase shift remains minimal during normal operation, but can be automatically adjusted to reduce power flow on overloaded lines and prevent them from tripping offline. This dynamic power flow management allows for maximising the capacity of the transmission network by utilising lines closer to their thermal limits.
HVDC transformers: High-voltage direct current (HVDC) transformers play a crucial role in high-voltage transmission systems. These specialised transformers perform the critical function of converting alternating current (AC) to direct current (DC) and vice versa. This capability makes them particularly valuable in HVDC transmission systems, which utilise direct current for long-distance electricity transmission.
The primary advantage of HVDC transmission lies in its efficiency over long distances, compared to traditional AC transmission. HVDC transmission systems experience lower power losses, making them the preferred choice for transmitting electricity across vast distances, such as subsea or underground cables, or through geographical obstacles like mountains. HVDC transformers are specifically designed to operate at high voltages, typically ranging from 100 kV to 800 kV. Their application becomes most relevant when AC transmission proves impractical or cost-prohibitive. This often occurs in scenarios involving long-distance power transmission or geographical challenges such as underwater or mountainous terrain.
Ester-oil transformers: Ester-oil transformers utilise natural or synthetic esters as a coolant and insulating medium, instead of mineral oil derived from petroleum. Unlike mineral oil, ester oils are readily biodegradable, minimising environmental impact in case of spills or leaks. It has a much higher flash point than mineral oil, significantly reducing fire risk in substations. Some ester oils offer extended transformer life and potentially higher operational efficiency, compared to mineral oil. BHEL has invested in research and development to manufacture ester oil transformers domestically, aligning with India’s push for Make in India. Power Grid Corporation of India Limited has also adopted ester oil transformers for grid modernisation due to their improved safety and environmental profile, aligning with stricter environmental regulations.
On-load tap changers transformers: An on-load tap changers transformer (OLTC) is a special type of transformer that can adjust its voltage ratio, while it is still in operation (connected to the grid and delivering power). Traditional transformers require the power to be interrupted to make adjustments, leading to service disruptions. OLTCs achieve voltage adjustment through a mechanism that physically changes the number of turns within the transformer windings. This adjustment alters the voltage ratio between the input and output, allowing for precise control of the voltage delivered to consumers. It enables real-time voltage regulation, ensuring consistent and stable voltage delivery to consumers, even with fluctuating power demands. By maintaining optimal voltage levels, OLTCs minimise energy losses within the power grid, leading to improved efficiency. The ability to adjust voltage on-load helps prevent voltage sags (voltage dips) and surges, improving grid reliability and reducing the risk of outages. OLTCs play a vital role in integrating renewable energy sources such as solar and wind into the grid. These renewables have variable output and OLTCs help manage these fluctuations, ensuring grid stability. BHEL developed 500 MVA, 765/400/33 kV, 1-phase interconnecting transformers, meeting the requirement of fixed I2 R loss without OLTC as per the Central Electricity Authority standard specification for transformers and reactors.
Coupling transformers: Within the power grid, flexible AC transmission systems (FACTS) rely on coupling transformers to enhance control, stability and power transfer capabilities. These transformers act as a bridge between the high-voltage grid (such as 220 kV or 400 kV) and a FACTS device called a static synchronous compensator (STATCOM). A STATCOM injects dynamic and adjustable amounts of reactive power to maintain grid stability, but it cannot directly connect to high-voltage lines. The coupling transformer solves this by enabling a two-way flow of power between STATCOM and the grid. Unlike traditional transformers with tap changers, the STATCOM itself controls the voltage of the coupling transformer. The step-up function (increasing voltage) of the coupling transformer is critical. Special design considerations ensure it meets these demands. Strategically placed STATCOM devices, connected through coupling transformers, improve the grid’s ability to handle loads, enhance stability and minimise power losses through optimisation. In essence, coupling transformers play a vital role in FACTS by contributing to a more efficient and stable power transmission network.
The way forward
Transformer technology has undergone a remarkable transformation in recent years. Manufacturers have reached a significant milestone by developing equipment capable of handling the highest power transmission voltage in the world (1,200 kV). These advancements extend beyond just voltage levels – specific design features have improved dramatically.
This progress translates to lighter transformers with lower energy losses and reduced noise levels, even as their power ratings and voltage capabilities have increased. The key to these achievements lies in the development and utilisation of cutting-edge materials and advanced design tools.
However, the evolving power market landscape presents new challenges. The rapid growth across generation, transmission and distribution segments has significantly heightened grid complexity. This, coupled with the increasing penetration of renewable energy sources, has spurred further innovation in transformer technology. Several factors such as the need to minimise transmission and distribution losses for grid security, consumer safety and environmental reasons are driving this. The rising demand for shorter payback times on transformer projects has influenced design choices, material selection and maintenance strategies. In essence, transformer technology is adapting to meet the demands of a more complex and dynamic power grid.