What is AC Transformer
A transformer is an electrical device that transfers electrical energy from an alternating current circuit to one or more other circuits, also used primarily to increase or decrease voltage. A transformer is made of two electrically isolated coils that work on the Faraday principle of mutual induction. During this process, an emf is induced in the secondary coil of the transformer by a change in the magnetic flux flowing in the primary coil winding.
Benefits of AC Transformer
Isolation and Productivity
The conventional transformer has a simple design based on efficiency. In addition, it also provides galvanic isolation, as the two windings do not have any electrical connection between. It also transfers all the energy to a transformer in the process of magnetic coupling.
The basic structure of conventional transformers has remained the same over the past decades, but advances in material technology have resulted in higher saturation densities and lower hysteresis losses in transformers, resulting in an efficiency of about 97 per cent for even very efficient transformers.
Power Transmission and Distribution
AC transformers are considered to be one of the most important components of the power system, which includes power generation, transmission and distribution. Transformers have made it possible to distribute electric power over large distances at a reasonable cost.
Power transformers provide highly efficient and long-distance power transmission, which helps to step up the voltage to a higher level on the output. The distribution system is used by distribution transformers to step down high voltage.
Stepping Voltage and Current Up and Down
Transformers are important components in both power distribution and power electronic systems. They can reduce the high voltage in transmission at substations as well as increase the amount of current required by the end-users.
Efficiency in Terms of Costs
For voltage level change and isolation, a conventional transformer is a great alternative to a low-cost, high-efficiency transformer that does not have a high overall transformer cost.
Wide Range of Applications
The efficiency of the different types of transformers, regarding power, distribution, potential, and isolation, is almost the same. They all work on the same concept, although they have different applications.
Reversed Linked
Typically AC transformers can be reverse linked, which means the same transformer can be wired as step-up or step-down, depending on how it is installed by the manufacturer. The manufacturer must allow and specify this reversibility capability.
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Types of AC Transformers
Transformers with a step-up and a step-down function
Step-up transformers convert low voltage (LV) and high current on the primary side of the transformer to high voltage (HV) and low current on the secondary side. Step-down transformers convert the high voltage (HV) and low current to the secondary side’s low voltage (LV) and high current.
Single-Phase and Three-Phase Transformers
Single-phase transformers are less cost-efficient than three-phase power systems. However, when space is restricted, a bank of three single-phase transformers is preferable to a single three-phase transformer since it is easier to transport.
Transformers for electricity, distribution, and instrumentation
Power transformers are often used to scale up or decrease the voltage level in transmission networks. It is most efficient at or near full load; thus, it is used mostly at high or peak loads.
A distribution transformer reduces the voltage for distribution to household or commercial consumers. It features superb voltage control and runs 24 hours a day at 50% of full load for optimal efficiency.
Instrument transformers decrease large voltages and currents to smaller values than ordinary instruments can monitor.
Autotransformers with Two Windings
When the ratio of the high and low voltage sides is more than 2, a two-winding transformer is often employed. Using an autotransformer is more cost-effective when the ratio of high to low voltage sides is less than 2.
Oil Cooled and Dry Type Transformers
This category includes the transformer cooling system. Transformer oil is used to cool oil-cooled transformers. In the dry type transformer, air cooling is used.
Air-core transformers
Air-core transformers have two or more coils wound up in a solid insulating material or an insulating coil shape (i.e., the currents required for radio transmission) to transfer radio-frequency currents. Iron-core transformers provide similar functions in the audio frequency range.
Parts of AC Transformer
Core
The windings are held in place by the core of the transformer. The core is made up of soft iron, which helps to decrease Eddy current and hysteresis losses while also providing a low resistance channel for magnetic flux passage. Copper loss is directly proportional to the core diameter of the transformer, whereas iron loss is inversely proportional.
Conservator
The transformer oil is stored in the conservatory, with an airtight iron cylindrical drum installed above the transformer. It features a top vent and is only half-full with oil to allow temperature fluctuations. However, the main tank is full of oil, connected to the conservatory through a conduit.
Cooling Tubes
The transformer oil is cooled using cooling tubes. Oil may circulate naturally or artificially inside the transformer. When the oil temperature rises, hot oil rises, and cold oil falls naturally in natural circulation; however, an endless pump is utilised in forced circulation.
Insulating materials
Primary and secondary windings and the transformer core are isolated using insulating materials like paper and cardboard due to their high conductivity and flexibility. High conductivity reduces the quantity of copper required while also lowering losses. Furthermore, high ductility allows conductors to be easily bent into tight windings around the core, reducing copper use and winding volume.
Breather
The breather is a silica gel-filled cylindrical container that keeps the air entering the tank dry. This is because moisture may disrupt the insulation and produce internal defects when the insulating oil interacts with it. The breather keeps moisture out of the air. The silica crystals in the breather absorb moisture from the air as it travels through them.
Windings
Windings are made up of many copper coil turns, which are bundled together and joined to make a full winding. The input-output supply or the voltage range may be used to wind the coils. Primary and secondary windings, which are the windings to which the input and output voltages are applied, are included in supply windings. Depending on their voltage range, windings may be categorised as high or low voltage.
Transformer oil
The core and the coils insulate and cool the oil. The core and windings must be completely immersed in mineral oil.
Tap Changer
Tap changers are used to compensate for voltage changes within the transformer. Onload and offload tap changers exist. Onload tap changers allow tapping to be altered without disconnecting the transformer from the supply; however, offload tap changers need the transformer to be detached.
Buchholz Relay
The Buchholz Relay detects flaws in the transformer by being installed above the connecting line that travels from the main tank to the conservator tank. It is powered by gases generated by transformer oil breakdown during internal problems. As a result, this gadget detects internal flaws in the transformer, allowing it to be protected.
Explosion Vent
The boiling oil in the transformer is ejected by the explosion vent during internal faults, preventing the transformer from exploding. This is usually positioned above the conservator tank’s level.
What Are the Main Uses of Transformers
Power transmission and distribution
Transformers are widely used in power systems. In power plants, large generators generate high-voltage alternating current. In order to transmit the power to distant users, transformers are needed to convert high voltage into low voltage to reduce the loss of transmission lines. In addition, in the distribution process of the power grid, high-voltage power needs to be further reduced to meet the needs of different types of users.
Power supply for electronic equipment
Transformers are also commonly used to supply low-voltage power required by various electronic devices. Inside electronic equipment, such as computers, TVs and stereos, stable low-voltage power is required to work. Transformers can convert high-voltage power provided by the public power grid into low-voltage power suitable for these devices.
Lighting system
Transformers are indispensable in urban and rural lighting systems. Transformers are used to reduce the power compression level required by lighting systems to meet different types of lamps and lighting needs. These transformers are usually installed in places such as street lights, buildings and public places to provide people with safe and reliable lighting conditions.
Industrial equipment
Various industrial equipment usually requires power supplies of different voltages. Transformers can convert one voltage to another as needed. For example, large mechanical equipment usually requires a higher voltage supply, and transformers can convert common voltage levels (such as 220V or 380V) to high voltages that meet the needs of the equipment.
Power load adjustment
In the power system, load refers to the electrical energy required by the electrical equipment connected to the system. Transformers can be used to adjust the load. To adapt to power demand at different times and locations. For example, during peak hours, transformers can transfer electrical energy from low-load areas to high-load areas to meet user needs.
Transportation system
Transformers are also widely used in transportation systems such as power, trains and subways. In the power system, transformers are used to transform voltage to meet the needs of long-distance power transmission and power supply. In train and subway systems, transformers are used to convert the electrical energy provided by the power grid into electrical energy suitable for supplying trains.
Frequency converter
Transformers are also commonly used in frequency converters. Frequency converters are a device that converts AC power into variable frequency AC power. Frequency converters are usually used to control the operation of motors, which can adjust the speed and torque of motors. They are widely used in air conditioners, water pumps, motor drive systems and other fields.
Self-Attention Mechanism
The key component of transformers is the self-attention mechanism. Self-attention allows the model to weigh the importance of different words in a sentence when encoding or decoding it. Each word in the input sequence is associated with three vectors: the query vector, the key vector, and the value vector. These vectors are used to calculate attention scores that determine how much focus should be given to each word when processing a particular word.
Multi-Head Attention
To improve the performance of self-attention, transformers use multiple sets of query, key, and value vectors called "heads." By using multiple attention heads, the model can learn different relationships between words in parallel and combine them to capture more complex patterns.
Positional Encoding
Since transformers do not inherently understand the order of words in a sequence, positional encoding is added to the input embeddings to provide information about the position of each word in the sequence. This allows the model to differentiate between words based on their position.
Feedforward Neural Networks
Transformers also include feedforward neural networks after the self-attention layers. These networks consist of fully connected layers with activation functions like ReLU (Rectified Linear Unit) and are applied independently to each position in the sequence.
Encoder-Decoder Architecture
In tasks like machine translation, transformers use an encoder-decoder architecture. The encoder processes the input sequence, while the decoder generates the output sequence. The decoder also includes an additional attention mechanism that helps it focus on relevant parts of the input sequence during the generation of the output.
Training
Transformers are trained using backpropagation and optimization algorithms like Adam to minimize a loss function, typically cross-entropy in NLP tasks. During training, the model learns to adjust the weights of its parameters to make accurate predictions.
Fine-Tuning and Transfer Learning
Transformers can be fine-tuned on specific tasks with relatively small amounts of task-specific data, making them highly versatile. Transfer learning techniques, such as pretraining on a large corpus of text data followed by fine-tuning on a smaller dataset for a specific task, have been particularly effective in NLP.
When Buying a Transformer – Things to Consider
Transformers are mainly used to change the voltage of the main power supply so that the much needed requirements can be accommodated. Different voltages can be provided by different transformers; but one important consideration to make while purchasing transformers is the voltage of the main power supply. The input voltage of the transformer to be purchased depends upon the main power supply, while the output voltage depends upon the requirement.
Transformers may also alter the frequency of voltage supply. This is especially important when the equipment is to be used in a different country where the main supply has a different frequency.
Transformers are available as single-phase and three-phase. The number of phases varies depending upon the requirement. Small homes and apartments generally require single phase transformers; while factories and industries require three-phase transformers as heavy equipment is used here.
The type and size of load are other important factors that are required to be considered when choosing a transformer.
Where are you planning to install the transformer? Is the transformer to be installed indoors or outdoors? Is the transformer to be placed near chemicals or other hazardous substances? All of this needs to be considered. If the transformer is to be installed outdoors, or near such hazardous substances, you need a transformer that is specially designed to withstand these harsh conditions.
What Are the Common Transformer Maintenance Procedures
Visual Inspection
One of the simplest and most effective transformer maintenance procedures is visual inspection. This involves checking the external condition of the transformer, such as the bushings, tank, radiator, valves, gauges, connections, and grounding. Visual inspection can reveal signs of physical damage, oil leaks, corrosion, overheating, or loose parts that may affect the performance or safety of the transformer. Visual inspection should be done at least once a year or more frequently depending on the environment and operating conditions.
Oil Testing
Another common transformer maintenance procedure is oil testing. Oil is the main insulating and cooling medium for most transformers, and its quality and condition can affect the transformer's functionality and lifespan. Oil testing can measure various parameters of the oil, such as moisture, acidity, dielectric strength, dissolved gases, and contaminants. These parameters can indicate the presence of faults, degradation, or aging in the transformer or its components. Oil testing should be done at least once every two years or more often if there are signs of deterioration or abnormality.
Winding Resistance Measurement
Winding resistance measurement is a transformer maintenance procedure that can assess the integrity and continuity of the transformer windings. Windings are the coils of conductors that carry the electric current and generate the magnetic field in the transformer. Winding resistance measurement can detect problems such as loose connections, broken strands, short circuits, or open circuits that may cause losses, inefficiencies, or failures in the transformer. Winding resistance measurement should be done every time the transformer is disconnected or reconnected to the power system.
Turns Ratio Test
Turns ratio test is a transformer maintenance procedure that can verify the voltage transformation ratio of the transformer. The voltage transformation ratio is the ratio of the number of turns in the primary winding to the number of turns in the secondary winding. It determines how much the voltage is stepped up or down by the transformer. Turns ratio test can detect errors or deviations in the turns ratio that may result from winding damage, tap changer malfunction, or core saturation. Turns ratio test should be done every time the transformer is serviced or relocated.
Insulation Resistance Test
Insulation resistance test is a transformer maintenance procedure that can evaluate the quality and condition of the insulation system of the transformer. The insulation system consists of the oil, paper, and other materials that isolate the windings and the core from each other and from the ground. Insulation resistance test can measure the resistance of the insulation system to the flow of electric current. A low resistance indicates a high leakage current, which may cause overheating, arcing, or breakdown of the insulation. Insulation resistance test should be done every time the transformer is de-energized or energized.
Dissolved Gas Analysis
Dissolved gas analysis is a transformer maintenance procedure that can identify and diagnose faults in the transformer by analyzing the gases dissolved in the oil. Faults such as overheating, arcing, sparking, or partial discharge can generate different types of gases, such as hydrogen, methane, ethylene, acetylene, or carbon monoxide. Dissolved gas analysis can measure the concentration and composition of these gases and determine the type, location, and severity of the fault. Dissolved gas analysis should be done regularly or whenever there is a suspicion of a fault in the transformer.
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