This article will take an in-depth look at electric transformers.
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This chapter will discuss what electric transformers are, how they are made, and how they function.
Electric transformers are stationary devices that transfer electrical power between circuits while maintaining the same frequency. They are designed to either increase or decrease voltage levels, which results in a corresponding decrease or increase in electric current. The operation of a transformer is based on the principles of electromagnetic induction and mutual induction.
Electric transformers operate based on Faraday's laws of electromagnetic induction. Their core principle is that electricity can create magnetism, and, conversely, magnetism can generate electricity.
Magnetism is a fundamental aspect of every electrical mechanism. Electric transformers utilize these magnetic properties to adjust voltage levels, either increasing or decreasing them. By varying the strength of the magnetic field within the transformer, changes are induced that generate electrical force or power. When a conductive wire, such as copper, interacts with this process, electrons flow through the wire, enabling the transmission of electricity.
Electric transformers can either increase or decrease voltage levels based on the arrangement of the coils around their core. As alternating current flows through the transformer, it causes the magnetic field to fluctuate. The core is wrapped with an output wire, and the changing magnetic field induces a current in this wire.
To transfer electricity over long distances or between power plants, it must be transported at higher voltages to efficiently cover the distance. At the receiving end, the voltage is reduced to lower levels to prevent damage to equipment and avoid potential electrical hazards. Power plants use smaller substations to gradually reduce the high voltage into manageable levels. In local areas, including residential homes, transformers further step down the voltage to levels suitable for household appliances, such as stoves. air conditioners, Laptops, heaters, and televisions require lower voltage levels. In industrial settings, where machines and equipment often operate at higher voltages, transformers that step up the voltage are commonly used to meet these needs.
To step down the voltage, an electric transformer requires more turns of wire on the primary winding and fewer turns on the secondary winding. Conversely, to step up the voltage, it needs fewer turns on the primary winding and more on the secondary winding. It is uncommon for both windings to have an equal number of turns, as this would result in no change in voltage, merely transferring the same voltage from one circuit to another.
All electric transformers experience some energy loss, usually in the form of heat, regardless of their design. As static devices, transformers can be difficult to control and cool. Excessive heat can damage or degrade the insulation on the transformer’s wiring. To manage this, transformers can be cooled in two primary ways: air cooling and oil cooling. Air cooling involves directing blasts of air onto the coils to dissipate heat and lower the temperature.
Ambient air can also be used to dissipate heat by carrying away hot air particles as it flows through the coils. Alternatively, immersing the transformer in oil or water can help cool it down. The two sets of coils, or windings, in an electric transformer are linked by a magnetic core, typically made of iron or ferrite, and are laminated with copper or enamel-coated materials.
For efficient operation, an electric transformer comprises several key components, including those listed and described below.
This component supports the primary and secondary windings while providing a low reluctance path for electromagnetic flux. It is made from stacked thin sheets of high-grade oriented steel, separated by a thin insulating material. To minimize hysteresis and eddy currents, the core steel has a carbon content below 0.1%, and silicon is often added to further reduce eddy currents. In a three-phase transformer, each limb of the core carries the primary and secondary windings for each phase, with yokes magnetically coupling these limbs. The core can be constructed in two main ways: core type and shell type. In the shell type construction, the core surrounds the windings.
Each phase of a transformer includes two sets of windings: the primary winding and the secondary winding. These windings are made of multiple turns of copper or aluminum conductors, insulated from each other and from the transformer core. The configuration and type of windings are determined by factors such as current rating, short circuit strength, temperature rise, impedance, and voltage surges.
The winding rated for higher voltage is known as the HV winding (high voltage winding), while the winding rated for lower voltage is referred to as the LV winding (low voltage winding).
Based on voltage ratings, high voltage windings have thinner conductors compared to low voltage windings and are arranged around the low voltage windings, which are positioned closer to the core. In shell-type transformers, the high voltage windings are placed between the low voltage coils and may be divided into multiple sections. In core-type transformers, the windings are categorized into four types, with the choice depending on factors such as current carrying capacity and the number of turns.
Insulation is vital for transformers, as inadequate insulation can result in significant damage. Insulating materials must have high dielectric strength, the capability to withstand high temperatures, and robust mechanical properties. Common insulating materials include cotton, synthetic fibers, and paper. These insulators are positioned between the windings and the core, as well as between current-carrying parts and between the windings themselves.
The tank serves two primary functions: it protects the core and windings from external environmental factors and contains the oil. It also provides support for other transformer components and accessories.
These tanks are usually made by rolling steel plates into container shapes. To reduce weight, aluminum sheets can be used instead of steel, although this increases costs because aluminum is more expensive than steel.
In oil-immersed transformers, the oil serves several purposes: it provides extra insulation between conducting parts, helps cool the transformer, and assists in identifying faulty areas.
Terminals inside transformers are used to connect incoming and outgoing cables. They are linked to bushings, which are attached to the ends of the windings. Bushings act as insulators, creating a barrier between the terminals and the tank, and provide a safe path for conductors connecting the terminals to the windings. Most bushings are made from materials like epoxy resins and porcelain.
The oil conservator is located above the tank and bushings. It typically features a rubber bladder to manage oil expansion and contraction due to temperature fluctuations. A level indicator on the conservator displays the oil level. The oil conservator is connected to the main tank by a pipe.
Breathers are used in oil-immersed transformers to keep the oil moisture-free. As temperature changes cause the oil to expand and contract, air flows in and out of the conservator tank. The breather, located at the end of the pipe that allows air to enter and exit the conservator, ensures that this air is free of moisture. It removes moisture using silica gel, providing dry air for the conservator.
Heat in a transformer is generated by the power dissipation during the conversion process. Dry-type transformers rely on natural air for cooling, whereas oil-immersed transformers employ various cooling methods. Cooling fans and radiators are added to the transformer tank depending on factors like power rating, power loss, and cooling needs. The cooling process transfers heat from the core and windings to the surrounding oil, which is then dissipated through the radiator. For larger transformers, forced cooling is used, with cooling radiators integrated into the system to improve heat dissipation.
The explosion vent serves as an emergency release for oil and gas buildup inside a transformer. Positioned above the conservator tank, it consists of a metal pipe with a diaphragm at one end. If a fault causes the oil pressure inside the tank to reach dangerous levels, the diaphragm will rupture at a predetermined pressure, allowing the internal forces to be safely vented into the atmosphere.
Tap changers are used to adjust the secondary voltage of electric transformers by modifying the turns ratio to achieve the desired voltage level. There are two types of tap changers: on-load and off-load. Off-load tap changers are used when the transformer is not supplying any load, while on-load tap changers can adjust the voltage without interrupting the current flow to the load.
The Buchholz relay is employed in oil-immersed transformers rated above 500 kVA. It functions by detecting faults through the presence of oil and gas. The relay identifies gases released when short circuits within the transformer generate sufficient heat to decompose the oil. When these gases are detected, the Buchholz relay activates an alarm and triggers the circuit breaker to interrupt the current flow to the primary winding, thus stopping the flow of electricity.
In addition to the components mentioned, transformers also use pressure sensors and temperature sensors. Larger transformers may include additional features such as indicators, heat exchangers for efficient cooling, and protection relays.
All transformers operate based on Faraday's laws, but they can be classified or designed in different ways according to their specific applications and requirements.
These types of electric transformers are considered highly efficient due to their use of multiple iron plates with excellent magnetic properties.
In this type of electric transformer, the magnetizing and demagnetizing processes happen quickly, making it a highly preferred option. The iron plates are usually made of silicon steel and coated with insulating paint to minimize heat generation during the transformer's operation.
All electric transformers use the process of induction to convert electricity, rather than a direct conductive connection. Therefore, they can technically be classified as isolation transformers. The primary function of an isolation transformer is to transfer electrical power from one source to another device, isolating the electrical device from the power source. While they share similarities with other types of transformers, isolation transformers are specifically designed to isolate electricity or the electrical device from the power source. Some applications of isolation transformers include... isolation transformer ...include use in uninterruptible power supplies, robotics, test and measurement systems, motor controls and industrial control panels, and data communication systems.
These electric transformers efficiently manage energy loss in high-frequency applications due to the use of ferrite cores with high magnetic permeability. They feature an E-type configuration and can be customized and shaped to suit various functions.
These transformers are ideal for applications such as power transformation and modification, as they efficiently convert lower voltages to higher voltages while reducing amperage and minimizing resistance effects. The conversion process involves electrical energy passing through two sets of coils, with the second set having more windings, forming a complete coil assembly. Some applications of step-up transformers require only a single set of windings, while others may need an additional tertiary set of windings.
All electric transformers require two sets of coils to complete the conversion process. These coil windings are mounted on a core made of ferrite compound or a laminated core, with the coils themselves being either enamel-coated or bare copper. Step-up transformers utilize coil windings made from alloys such as aluminum, nickel, copper, chromium, and steel, which enhance their energy efficiency.
The voltage of a power transmission line refers to the measure of power transmission capacity in a transmission line. And these High voltage transformers are used to modify the voltage levels in power lines within high voltage contexts. These transformers handle voltages ranging from 600 to 5000 volts, where a volt measures electromotive force. High voltage electric transformers are commonly used for metering and providing protection in high voltage circuits. They are also utilized in electrostatic industrial and scientific applications.
These transformers have a donut shape, which helps minimize induction leakage by creating high inductance within the system. They feature short windings and are lighter than other transformers of the same rating. However, their winding process is slower, making them more expensive.
These transformers, which lack a magnetic core, are typically used in applications like radios and small electronic devices. They operate through flux linkage between two magnetically coupled coils or windings: the primary and secondary. The transformers generate flux using their windings and the surrounding air. For winding the coils, materials with low magnetic permeability, such as plastic tubing and cardboard, are used.
Laminated core transformers feature a core made from laminated sheets of iron and nickel. The addition of nickel helps to reduce energy losses when the winding is energized. A major advantage of laminated core transformers is their ability to minimize eddy currents, which improves the efficient transfer of energy from the primary coil to the secondary coil.
These transformers operate with direct current (DC) because their flux density remains constant and does not cross zero. Pulse transformers are commonly used to connect load resistance with a pulse power source. For instance, they are employed in radar systems, including those on submarines, where radar transmitters need high voltages and high impedance, often with output tubes like magnetrons. Small pulse transformers can produce electrical surges, making them suitable for telecommunications and specialized applications such as camera flashes and radar equipment. Medium-sized pulse transformers are used in applications requiring electric circuits.
Current transformers are well-suited for measuring the flow of electricity in transmission lines. Unlike power transformers, which control voltage, current transformers are specifically designed to measure and monitor current flow for measurement purposes. Understanding their operation is crucial, as current transformers can also be used to regulate the flow of electricity to electronic devices.
These are power transformers and they are used to change the voltage capacity which is contained in a low voltage electrical transmission line. Compared to high voltage transformers these low voltage transformers are small enough that they can be held between two fingers as they also have a low weight. In most cases, these low voltage transformers transfer or convert 120 volts into 12 volts or 24 volts.
These electric transformers have a single winding, making them highly cost-effective. In autotransformers, this single winding serves as both the primary and secondary coil and features three taps for electrical connections. The advantages of autotransformers include their compact size, lower cost, and lighter weight. They are especially useful in systems with varying voltage levels.
Polyphase transformers have three or more conductors, with configurations that can extend up to 15 phases. They feature multiple windings on both the primary and secondary cores. Many polyphase transformers use a zigzag configuration, especially when grounding is required.
This is a type of electric transformer that can be used to derive a reference point for use in underground systems. The zig zag transformer is used in a number of industries due to its ability to provide a neutral point for grounding purposes. Some of the areas of use include petrochemicals, power distribution, and automotives. Zig zag transformers contain a primary coil but do not have a secondary coil although they all in all consist of six coils on three separate cores. The windings of a zig zag transformer are in two halves because the way the two halves of the windings interconnect results in the difference in winding patterns while connecting the coils and the core.
This transformer is classified as a polyphase transformer. While it is possible to create a three-phase transformer by connecting three single-phase transformers, using a dedicated three-phase transformer is more cost-effective. A three-phase transformer has three sets of primary and secondary windings, which can be arranged in delta or star configurations, such as delta-delta or star-star.
Three-phase transformers are crucial for directing and controlling electrical current from power lines to homes and businesses. A current transformer manages the flow of current from the electrical line to the areas or equipment that will use it. Power transformers are generally most effective and safe for operating electrical systems and individual appliances.
This type of transformer serves as a link between the grid and generators, transferring energy to substations. Due to its large size, it requires cooling, which is achieved using oil and cooling agents.
The system they use is costly due to its three-phase setup. However, despite the higher expense, it is more efficient than single-phase systems. These transformers are categorized into three groups based on their voltage ratings.
These transformers can act as step-down transformers, reducing high voltages to low voltages by transferring electrical energy through two coil stages, with the second stage having fewer windings. The amount of power generated may vary depending on the geographical location.
These transformers are used to isolate main power and voltage, and then convert it to a smaller ratio.
This chapter will discuss the applications and benefits of electric transformers.
Electric transformers are essential in our daily lives, as they adjust electrical current to meet the needs of various appliances. They manage voltage flow during charging, preventing unregulated voltage from causing electrical surges. This regulation helps safeguard appliances from potential damage.
Electric transformers are crucial in steel production, where they provide high voltages for melting and welding while delivering lower currents for cooling. In chemical processing, transformers are essential for powering electrolysis, which is used in processes like electroplating metals such as aluminum, copper, and zinc. They regulate the electrical current that drives these chemical reactions, ensuring precise control.
Electric transformers are cost-effective, providing a reliable and affordable solution for voltage transmission and isolation. Their various types enable a wide range of applications; for example, current transformers step down currents for measurement instruments. Additionally, transformers can be configured as either step-up or step-down devices, depending on their installation. Some models feature multiple taps on the primary winding to accommodate different input voltages.
Electric transformers require cooling because energy losses produce high temperatures that can reduce the lifespan of the insulating materials in the windings. They are not designed to handle direct current (DC). Maintenance can be challenging, as transformers are susceptible to issues such as oil leaks, overloading, and harmonics, which can cause damage.
Electric transformers are devices that transfer electricity between circuits by adjusting voltage levels while keeping the frequency constant. They are designed for use with alternating current (AC), so changes in supply voltage are affected by changes in supply current. Transformers can either step up or step down voltage levels, providing a safe and efficient power system for both industrial and residential applications.
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