The Indian transformer industry has grown significantly since its inception five decades ago. Transformer manufacturers have also matured and demonstrated noteworthy technological advancements in recent years by developing equipment with the rating of 1,200 kV, the highest capacity power transmission system voltage in the world. There has been tremendous improvement in the specific design characteristics and properties of transformers over the past decades. While the power ratings and voltage levels have increased, related parameters such as weight, losses and sound level have improved. These improvements have been achieved through the development and application of advanced materials and design tools.
In recent years, the changing dynamics of the power market across the world have put an additional demand for transformer technology. The complexity of the grid has increased manifold with the rapid growth in the generation, transmission and distribution segments. Additional factors driving technology developments in the transformer industry include increasing penetration of renewable energy sources, as well as the need to reduce transmission and distribution losses in order to address grid security and consumer safety concerns, and to maintain environmental impacts. In addition to efficiency, the requirement of shorter payback time is also influencing technical decisions, including design, choice of materials and maintenance strategies.
The distribution segment is also fraught with aging infrastructure, high network losses and poor financial performances. To address these challenges, it is critical to strengthen the performance of sub transmission and distribution network. Smart Grids are the new watchword. The notion of smartness comes from intelligence being embedded into the electrical network. This smartness generally is expected to enhance value for the end consumer through enhanced and convenient availability of electricity. The need and necessity for Smart Grid in India is well established. It is in fact all the more relevant to be smart about the usage of energy and electricity to deliver low cost electricity. As India moves towards increased globalisation and as the present government rises to the challenges and opportunities of the 21st century, smart grids are taking center stage in the process of delivering safe, convenient and affordable power to all citizens. Development of smart grid increases the demand of smart and advance transformers for power system.
A solid-state transformer with managerial role in the electric distribution grid is generally called smart transformer. As an integral part of the smart grid, smart transformers work independently to constantly regulate voltage and maintain contact with the smart grid in order to allow remote administration if needed and to provide information and feedback about the power supply and the transformers themselves. Through a process known as voltage optimisation, a smart transformer provides the exact amount of power that is needed, and responds instantly to fluctuations within the power grid, acting as a voltage regulator to ensure that the optimised voltage is undisturbed.
Need of Smart Transformer
Today’s transformers include multiple intelligent electronic devices or control systems, which can assess the condition of the transformer system and make intelligent recommendations based on design and component data. With this, the operator can remotely monitor the behavior of the transformer core, windings, oil, tap changer and bushings, thereby, keeping a close watch on critical transformer components. Dynamic control of real and reactive power can optimise the efficiency of distribution systems, improve power quality in a more dynamic operating environment and limit fault current. Meanwhile, modeling and simulation can be applied to optimise current designs and explore new concepts that can facilitate system recovery in the event of failure. Modularised design components, standardisation and recovery concepts can help improve resilience.
Smart transformers directly reduce energy consumption.Therefore, it directly reduces greenhouse gas emissions as well. This makes them an important part of any energy retrofit or lighting retrofit. While smart transformers immediately reduce power consumption by providing a stable, optimal power supply that supplies electrical equipment with its ideal voltage, they also protect electrical equipment from power fluctuations – thereby, helping electrical equipment last longer. Additionally, through their smart grid connectivity, smart transformers can be administered dynamically, allowing facilities to monitor and manage the transformers directly during periods of power fluctuation, and helping them ensure that their power supply remains voltage optimised even when new demands are being placed upon it.
Most appliances are designed to work with a percentage of voltage away from the base. A smart transformer delivers voltage directly at the base, which means appliances work at their most efficient – they last longer and use less power. Smart transformers can help large commercial facilities use power more efficiently to save money, power and go greener. They have been successfully deployed to save energy for organisations. A smart transformer provides the exact amount of power that is needed, and responds instantly to fluctuations within the power grid, acting as a voltage regulator to ensure that the optimised voltage is undisturbed. STs are programmed to, as a default; provide voltage optimised power supply that directly addresses their facility’s energy needs.
Figure 1: A typical smart transformer hardware control
Characteristics of Smart Transformer
The basic requirements of smart transformer are cooling control tuned to load profile, voltage regulation, reliability, fault prediction – detection, energy efficiency and condition assessment. The smart transformers have some intelligence to meet the requirement of future power systems. Some important characteristics of smart transformers are as follows:
• They give exact amount of power that’s needed and respond instantly to fluctuations within the grid
• Smart transformers act as a voltage regulator and it ensures that the optimised voltage is undisturbed, because they directly reduce energy consumption & greenhouse gas emissions
• Smart transformers immediately reduce power consumption by providing a stable, optimal power supply that supplies electrical equipment with its ideal voltage
• They also protect electrical equipment with its ideal voltage
• Smart transformers as a default, provide a voltage optimised power supply that directly addresses their energy needs.
Smart Transformer Hardware Control System
The set of hardware control blocks include smart transformers, instrumentation, control gate drives, electronic On Load Tap Changer (OLTC), transformer builds the voltage regulation block, which is also responsible for the secondary voltage regulation.
The interface module blocks are data converters, which convert variables and events of the control system – and send them to the master module. In the master module the data of all the interface modules are packed and sent to the Programmable Logic Control (PLC) interface which converts the data to be sent through the medium voltage line. The data coming from a set of transformers are received by the gateway block, which concentrates and sends them to the wireless interface. From this block, the data are sent to the power utility where it is received and processed. A typical smart transformer hardware control is depicted in figure 1.
Smart transformers when used at the PCC, it controls the active power exchange between a microgrid and the utility grid dependent on the state of both networks and other information communicated to the smart transformers.
To control the active power, the smart transformer uses its taps that change the microgrid side voltage at the PCC.
Role of Smart Transformer in Smart Grid
The role of smart transformer in smart grid operation is as follows:
• Smart transformers are controlled dynamically allowing facilities to monitor and manage the transformers directly during the period of power fluctuations – and helping them ensure that their power supply remains voltage optimised even when new demands are being placed upon it.
• The power transfer between a microgrid and the utility grid is actively controlled without the need for communication to all microgrid elements.
• Protect the power system from load disturbances by isolating source and load harmonics, transients and voltage sags.
• Enhance the power quality by summarising the loads to the mains with identical phase current even for unbalanced loads.
• Providing unity power factor with sinusoidal currents under non-linear loads.
• Coordinate fault re-closing over sub-grids zones when connecting to other smart transformers
• Accept direct connection to future medium voltage DC power transmission, low voltage DC grid, storage systems and renewable energy systems.
Transformers serve as a hub for collection and distribution of energy and are a key component of a successful transition to a smart grid. Some transformers are located where grid communication is mature enough to allow or require interaction, while others are not. Transformers used in power transmission are immediate candidates for integration into smart grid technology and immediately will benefit from reliability and efficiency improvements that result from some of the new online monitoring technologies. Transformers used mainly for distribution circuits probably will be affected more as the smart grid matures. Most of today’s transformers are not ready for the smart grid because they were placed into service years before the age of interactive information transfer. Building the next generation of transformers will require incorporating remote monitoring of a wide range of transformer and system parameters.
There is already an increased use of digital monitoring in transformers. Vital statistics such as temperature, pressure and vacuum levels are being collected and transmitted in real time to a central clearing house. Many transformer manufacturers are recognising this growing demand for online transformer monitoring products and diagnostic services and are investing in building them, especially for step-up transmission high-voltage transformers. These technologies will be critical for improving grid reliability and helping utilities avoid transformer failures and resultant blackouts. They also will reduce maintenance costs and defer capital expenditures by extending a transformer’s useful life. Typical monitoring parameters for Smart Grid Integration are as given below:
i. Transformer tank pressure and vacuum,
ii. Oil and winding temperature,
iii. Pressure relief device operation,
iv. Sudden pressure relay operation,
v. Oil level,
vi. Water content in oil,
vii. Fans on/off operation indicator,
viii. Loss of control power indicator,
ix. Ambient temperature,
x. Input current and voltage,
xi. Output current and voltage,
Transformers in place already use smart devices for load switching. In the coming years, the move will be toward monitoring systems that promote transformer reliability. Ensuring reliability on the grid by replacing equipment before it fails and anticipating upcoming problems is on what transformer manufacturers will focus.
Benefits of Smart Transformers
The smart transformers are designed to monitor and manage power supply during fluctuations and ensure that it is voltage optimised even when new demands are being placed upon it. Other benefits and functions of smart transformers include:
• Protecting the power system from load disturbances by isolating the source from load harmonics, transients and voltage sags.
• Providing unity power factor with sinusoidal currents under non-linear loads.
• Enhancing power quality by summarising loads to the mains with identical phase current even for unbalanced loads.
• Reducing grid losses and improving power supply reliability.
• Provides ability to utilise input or output in AC or DC power.
• Protects the load from power supply disturbances.
• Eliminates the tap changer requirement.
• Provides backup and reduces outages length.
• Control voltage and frequency levels will reduce the system losses.
• Provide reactive power compensation and system harmonic filtering.
• In substations, it could be used to feed control equipment or to feed DC micro grid.
As one of the main components in distribution stations, transformers fulfill an important task: They are responsible for the final customers being supplied with the correct voltage. Grid operators must, therefore, guarantee a low voltage supply within the allowed voltage band for every household. However, the rising in feed of renewable energies overstrain many transformer substations. Considerable voltage fluctuations are the consequence and can even lead to an infringement of the permissible voltage band. Increasing trend towards regulated distribution transformers in case of non-compliance with the voltage quality criteria due to the decentralised supply from renewable energies, grid operators are forced to a costly expansion of the distribution grid.
Green and Efficient Transformers
The goal of reducing the industry’s carbon footprint has led to a rise in demand for energy-efficient transformers. Developed countries and emerging countries are focusing on developing new standards and adopting energy efficient equipment. The growing environmental consciousness has further pushed manufacturers to develop green transformers that are composed of biodegradable materials like ester fluids. Transformers can be filled with esters due to their higher flash points compared to mineral oil. This provides safety against fires, which are common in conventional transformers. Green transformers have additional features like hermetically sealed tanks, lower noise levels and reduced losses. Their uptake is expected to accelerate in the near future as utilities seek sustainable and safe solutions, particularly, in highly populated urban areas.
Smart transformers are intelligent enough to meet the requirements of upcoming power systems, which is why these will be highly popular in the future. The smart transformer can also help in overcoming several issues associated with distribution network and smart grid operation, which are difficult to deal with conventional off-load and on-load tap changer transformers, some of the attributes of smart transformers are reduction in grid losses and improved power quality and supply reliability.
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