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What is a Transformer?

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what is a transformer?

A transformer is a static appliance used to adjust AC voltage, current and phase. It consists mainly of an iron core (or magnetic core) and a coil, which has two or more windings that are not connected to each other. When an AC voltage is added to one end, electromagnetic induction is caused in all the windings due to the phenomenon of magnetic induction. In this way, transformers enable the conversion of electrical energy between different voltage levels, thus meeting the working requirements of various electrical equipment. Transformers play an important role in the power system and are widely used in power transmission and distribution, power conversion of power equipment and other occasions.

transformer

Types of transformers

Transformers can be classified into various types based on their purpose, construction, and usage. Here are some types of transformers:

1.Step-Up Transformer & Step-Down Transformer: As per their names, step-up transformers increase the voltage level at output compared to input, while step-down transformers decrease the voltage level at the output compared to the input.

●Step-Up Transformer: A step-up transformer is used to increase the voltage. This is achieved by having more turns in the secondary winding than in the primary winding. These transformers are used in power plants for transmission, as the power is sent over large distances, and it's more efficient to transmit electricity when it's at a higher voltage.

●Step-Down Transformer: A step-down transformer does the opposite - it reduces the voltage. This is achieved by having fewer turns in the secondary winding than in the primary winding. Step-down transformers are commonly used in distribution stations, converting the high voltage from the transmission lines down to lower voltage levels suitable for households and businesses.

2.Power Transformer & Distribution Transformer: Power transformers are used in transmission networks, they have higher insulation levels and are available in ratings up to 1200MVA. Distribution transformers, on the other hand, provide final voltage transformation in the electric power distribution system, stepping down the voltage used in distribution lines to the level used by customers.

●Power Transformer: Power transformers are used in the transmission network of higher voltages for step up and step down application (400 kV, 200 kV, 110 kV, 66 kV, 33kV) and are generally rated above 200MVA. They are mainly used in power generation stations and transmission substations with high insulation level. Their size and cost are higher because they are designed for maximum efficiency at 100% load as they are always in full load conditions.

●Distribution Transformer: Distribution transformers deliver the final voltage transformation in the electric power distribution system, reducing high voltage to the lower voltage levels used in residential and light commercial service (usually less than 200 kV). They are smaller in size, designed for maximum efficiency at 60-70% load, as they are not always in full load conditions. These are commonly used in the distribution network for feeding to the consumer end.

3.Single-phase Transformer & Three-phase Transformer: These transformers are categorized by the type of supply system.

●Single-phase Transformer: These transformers take single-phase AC voltage, and the output is also single-phase. They have one primary and one secondary winding. Single-phase transformers are commonly used in low voltage applications in residential and commercial setups, like in distribution lines that deliver power to homes, and for powering single-phase devices and equipment.

●Three-phase Transformer: These transformers take three-phase AC voltage as input and deliver three-phase AC voltage as output. They are typically used in high power environments like industrial and commercial setups due to their ability to handle large power loads efficiently. Three-phase transformers are more economical for supplying large loads and large power distribution. Despite their size, they are more efficient and robust.

4.Core Type Transformer & Shell Type Transformer: These transformers are categorized by their construction. The coil windings in a core type transformer are placed around the core, while in a shell type transformer, the core is put around the coil windings.

●Core Type Transformer: In a Core type transformer, windings are cylindrical in shape and surround the core. They are usually wound on separate legs. The magnetic flux in core-type transformers follows a two-directional, or two-path, route. One portion of the windings is on one leg of the core and the other portion on the other leg. The cooling in these transformers is more effective as more surface area is exposed to the windings for the refrigerating effect. Core type transformers are simple in construction but have a significant amount of leakage flux.

●Shell Type Transformer: In Shell type transformers, the windings are surrounded by the core. The magnetic path consists of two parallel parts surrounded by a part that is in series with the parallel paths. This arrangement increases the mechanical strength and provides good protection for the windings. The flux in the shell-type transformer always completes its path, causing less leakage flux, resulting in high electrical efficiency. Shell type transformers are robust, compact and exhibit excellent short circuit withstand capability.

5.Outdoor Transformer & Indoor Transformer: These transformers are categorized based on their location in the electricity system, either outside or inside an infrastructure.

●Outdoor Transformer: These transformers are designed for installation outside buildings, exposed to weather and temperature changes, hence should be able to withstand these environmental factors. They are generally oil-filled, also known as Oil Immersed Transformers, which use transformer oil for cooling and insulation. Outdoor transformers come with added protection like weather-resistant enclosures to shield from moisture, dust, animals, and other environmental threats. They also need regular maintenance to ensure their robustness and longevity.

●Indoor Transformer: Indoor transformers, on the other hand, are designed for installation inside the buildings. They are generally dry-type transformers, which use air for cooling and are safer to use in populated areas due to their minimal fire hazard. Since they are shielded from harsh outdoor weather, they do not require the same level of protective measures as outdoor transformers. However, they still need a clean, dry, and well-ventilated space for safe operation.

6.Oil-Immersed Transformer & Dry Type Transformer: These transformers are categorized by the cooling method.

●Oil-Immersed Transformer: In Oil-Immersed transformers, the core and windings are immersed in transformer oil which acts as both, the cooling medium and the insulation to prevent arc formation. Transformer oil circulated through the transformer by natural convection dissipates the heat generated in the core and windings. This type of transformer is commonly used in power network and large industrial applications.

oil-immersed transformer

●Dry Type Transformer: Dry Type Transformers do not use liquid for the insulation purpose, but they use air or vacuum for the cooling purposes. In these transformers, cooling is done in natural air or forced air. These types of transformers are generally used in indoor installation, cities, buildings, and industrial plants for safety concerns and environmental reasons.

Dry Type Transformer

Transformer working principle

The working principle of a transformer is based on the principle of electromagnetic induction. When alternating current passes through the primary coil of the transformer, it produces a changing magnetic field. This alternating magnetic field then cuts through the secondary coil of the transformer, producing an electromagnetically induced electromotive force (voltage) in the secondary coil, which allows for energy transfer.

In simple terms, the working flow of a transformer is as follows:

1.An alternating current supply is passed through the primary coil (input side).

2.As the alternating current passes through the primary coil, it creates a changing magnetic field.

3.This alternating magnetic field moves along the iron core and cuts through the secondary coil (output side).

4.The electromagnetically induced electromotive force (voltage) that is produced in the secondary coil will depend on the turns ratio of the primary to the secondary coil.

This principle of the transformer can be used to either step-up or step-down voltages. If the secondary coil has more turns than the primary coil, the voltage is stepped up, creating a step-up transformer. Conversely, if the secondary coil has fewer turns than the primary coil, the voltages is stepped down, creating a step-down transformer. Finally, the output power from the secondary coil can be used by the connected circuit or device.

What are the main components of a transformer?

The main components of a transformer include:

1.Iron Core: The iron core is the main magnetic path part of the transformer, usually made up of silicon steel sheets, which is used to conduct magnetic flux.

2.Coils: The coils are the circuit part of the transformer. The coil connected to the power source is called the primary coil, while the coil responsible for transformer power output is called the secondary coil.

3.Insulation Materials: This includes insulation between coils, between coils and iron core, and among the layers within the coil itself.

4.Cooling System: This consists of the oil tank, insulation material, cooler, fan, etc. It is used to take away the heat generated during the operation of the transformer.

5.Protective Devices: These can include oil tanks, gas cushions, lightning protectors, temperature controllers, etc., used to prevent the transformer from overheating or internal short-circuiting.

6.Other Ancillary Equipment: This can include wiring terminals, lighting equipment, grounding devices, sampling ports, heating devices, etc.

What is the role of the cooling system of a transformer?

The primary function of a transformer's cooling system is to dissipate the heat generated within the transformer during its operation. When a transformer is in operation, resistive and magnetic losses, resulting from the flow of current and variations in magnetic flux, respectively, generate heat. This heat increases the internal temperature of the transformer.

If this heat cannot be removed efficiently, it could lead to the aging of various insulation materials inside the transformer, thereby reducing the lifespan of the transformer. It could also potentially cause short circuits or fire accidents.

Therefore, the presence of a cooling system is crucial for protecting the transformer and ensuring its regular, long-term, and safe operation. A cooling system typically comprises a cooler (radiator), cooling oil, fans, cooling water, and other equipment. Different types of transformers may employ different cooling methods, common ones being natural oil cooling, forced oil cooling, and air cooling.