TRANSFORMER and Its operation
Table of Contents
TRANSFORMER | what is Transformer
Principle Of Operation of Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductor. A varying current in the first or primary winding creates a varying Magnetic flux in the Transformer core,. And thus a varying magnetic field through the Secondary winding. This varying Magnetic field induces a varying electromotive force EMF or voltage in the Secondary winding. This effect is called mutual Induction.
When a load is connected to the Secondary,. Electricity will flow through the Secondary winding, Travelling from the primary circuit to the Transformer and then to the load. The ratio of the number of turns in the Secondary to the number of turns in the primary determines the induced voltage in the Secondary winding of an ideal Transformer, which is Expressed as follows:
A Transformer enables an Alternating current (AC) voltage to be “stepped up” by making greater than. Or “stepped down” by making less than by carefully Choosing the ratio of turns.
Basic Principle of Transformer
Construction of Transformer
Laminated steel cores
Transformer use at power or audio Frequencies typically have cores made of high permeability Si steel. Due to the steel’s much higher Permeability than that of free metal,. The core serves to Significantly lower the magnetising current and confine the flux to a path that closely couples the windings. Early Transformer designers quickly realised. That cores made of solid iron resulted in Unaffordable Eddy-current losses, so they developed cores that were made of bundles of insulated iron wires to lessen this impact. A Principle that has been used ever since was used in later designs to build the core by stacking layers of thin steel laminations. There is a thin Non-conducting layer of Insulation between each lamination and its Neighbours. The minimum Cross-sectional area for the core to prevent Saturation is indicated by the Universal Transformer Equation.
Laminations reduce the magnitude of eddy currents by limiting them to highly elliptical paths with little flux. Thicker laminations reduce losses but are more time- and Money-consuming to build. High frequency Transformers Typically use thin laminations, and some types of these laminations are so thin that they can operate at frequencies of up to 10 kHz.
The term “E-I Transformer” refers to a common laminated core design that is made of Interlaced stacks of E-shaped steel sheets capped with shaped pieces. Despite having more losses on average, this design is very cost-effective to produce. A steel strip is wound around a Rectangular form to create the cut-core or C-core type, which is then made by bonding the layers together. Then it is split in half, creating two C shapes, and the core is put together by Connecting the two C halves with a steel strap. They benefit from the flux being always parallel to the metal grains, which lowers Reluctance.
Because a steel core is permanent, it keeps its static magnetic field even after power is turned off. Resuming power will result in a significant inrush until the remaining magnetism’s impact is reduced, typically after a few cycles of the applied alternating current. It is necessary to choose fuses or other Overcurrent protection mechanisms to let this safe inrush pass. Induced currents from geomagnetic disturbances during solar storms can cause saturation of the core and operation of transformer protection devices on Transformers connected to long, overhead power transmission lines.
By using cores made of a low-loss, high-permeability silicon steel or amorphous (non-crystalline) metal alloy, distribution Transformers can achieve low no-load losses. The lower losses at light load make up for the core material’s higher initial cost over the course of the Transformer’s lifespan.
Circuits that operate above mains Frequencies and up to a few tens of kilohertz, like Switch-mode power supplies, use Powdered iron cores. High Electrical Resistivity and high Magnetic permeance are combined in these materials. Cores Constructed from ferrites, a type of Non-conductive magnetic ceramic material, are typical for frequencies above the VHF band. The Coupling Coefficient (and bandwidth) of tuned Radio-frequency circuits can be adjusted by moving the cores of some Radio-frequency Transformers, which are sometimes referred to as “slugs.” Toroidal Transformers are Constructed around a Ring-shaped core,. Which Depending on the operating Frequency,. May be made from a long strip of silicon steel or perm alloy wound into a coil, Powdered iron, or ferrite.
By Ensuring that the grain Boundaries are Optimally aligned,. A strip construction raises the Efficiency of the Transformer by Lowering core Reluctance. The air gaps present during the construction of an E-I core are Eliminated by the closed ring shape. Although more expensive cores with Circular Cross-sections are also available, the Cross-section of the ring is Typically square or Rectangular. The primary and Secondary coils are frequently wound tightly together to completely cover the surface of the core. This reduces the length of wire required and offers Screening to reduce Electromagnetic field generation caused by the Magnetic field of the core.
For a given power level, toroidal transformers are more effective than the less expensive laminated E-I types. Additional benefits over E-I types include smaller size (roughly half that of E-I types), lighter weight (roughly half that of E-I types), less mechanical hum (making them superior in audio amplifiers), a lower exterior magnetic field (roughly one tenth that of E-I types), low off-load losses (making them more effective in standby circuits), single-bolt mounting, and a wider variety of shapes. The main drawbacks are higher costs and a limited amount of power (see “Classification” above). In comparison to laminated E-I types, toroidal transformers frequently display higher inrush current due to the absence of a residual gap in the magnetic path.
In order to reduce losses, physical size, and weight of a Switched-mode power supply, ferrite toroidal cores are used at higher frequencies, typically between a few tens of kilohertz and hundreds of megahertz. The more expensive winding labour involved in Toroidal Transformer construction is a disadvantage. This is because every time a single turn is added to a coil, the entire length of the coil winding must pass through the core aperture. Toroidal Transformers are therefore rare above ratings of a few kVA. By splitting and forcing open a toroidal core in small distribution transformers, a bobbin containing primary and secondary windings can be inserted, Providing some of the advantages of a Toroidal core.
A working Transformer can be created without a physical core by simply placing the windings close to one another,. A configuration known as a “air-core” transformer. Since the magnetic circuit is made up primarily of air, any loss caused by Hysteresis in the core material is eliminated by an Air-core Transformer. Such designs are not suitable for use in power distribution. Because the leakage inductance is invariably high, leading to very poor regulation. Despite this, they Frequently work in radio-frequency applications due to their extremely high bandwidth, which is maintained by carefully overlapping the primary and secondary windings.
In spite of the high leakage Inductance, they are also used for resonant transformers like Tesla coils where they can achieve relatively low loss.
Depending on the application, different conducting materials are used for the windings, but in every case, the individual turns must be electrically isolated from one another to guarantee that the current flows through every turn. For small power and signal transformers, where the potential difference between adjacent turns is present and currents are low.
Cut through the transformer windings to see. Insulator in white. Green spiral: Silicon steel that is grain oriented. Black: Copper with no oxygen is used for the primary winding. Secondary winding in red. Toroidal transformer, top left. Correct, but E-core would be comparable to C-core. The windings in black are made of film. Top: The capacitance between the ends of both windings is equally low. Since the majority of cores are at least moderately conductive, insulation is also necessary. Bottom: The secondary winding’s lowest capacitance is required for low-power, high-voltage transformers. Bottom left: An increase in capacitance would result from less leakage.
Multiple-stranded conductors are also used in large power transformers because, without them, high-current windings would have an uneven distribution of current, even at low power frequencies. Each strand is individually insulated, and the strands are set up so that at different points in the winding or throughout the entire winding, each section takes up different relative positions in the entire conductor. The transposition lowers eddy current losses in the winding by balancing the current flowing through each conductor strand. The stranded conductor is easier to manufacture because it is more flexible than a solid conductor of equivalent size.
In order to improve high-frequency response, the windings of signal Transformers may be arranged to reduce leakage inductance and stray capacitance. This is accomplished by cutting each coil into layers of sections, which are then layered between the sections of the other winding. A stacked type or Interleaved winding is what this is.
For the purpose of controlling voltage regulation, power Transformers frequently have internal connections or taps at intermediate points on the winding, typically on the side with the higher voltage. Such taps are typically manually operated, with automatic on-load tap changers reserved for higher power rated or Specialised Transformers Supplying Transmission or distribution circuits or certain utilisation loads like furnace Transformers due to cost and reliability considerations. The impedance of each speaker can be changed using taps on the Audio-frequency Transformers that Distribute audio to public address loudspeakers.
In a push-pull circuit, a centre is frequently used in the audio power Amplifier’s output stage. AM Transmitters’ Modulation Transformers are very similar. The windings of some Transformers are covered in epoxy resin for protection. By replacing the air spaces inside the Transformer’s Windings with epoxy. While it’s under vacuum, one can seal the Windings and help avoid the possibility of corona Formation as well as the absorption of dirt or water. This results in Transformers that are better suited for wet or dirty environments, but at a higher cost to produce.
Cutaway view of oil-filled power Transformer. The Conservator (Reservoir) at top provides Oil-to-atmosphere Isolation. Tank walls’ cooling fins provide required heat Dissipation balance.
High temperature damages winding insulation, even though Oil-filled Transformers are frequently still in use after more than fifty years. As a general rule,. The lifespan of a transformer is reduced by half for every 8 degrees Celsius in operating temperature. Dry and Liquid-immersed Transformers Frequently self-cool by natural convection. And radiation heat dissipation at the lower end of the power rating range. Transformers are frequently cooled by other methods as power ratings rise, including forced-air cooling, Forced-oil cooling, Water-cooling, or combinations of these.
Transformer oil, which cools and insulates the windings,. Is the dialectic coolant used in numerous outdoor utility and industrial service Transformers. Transformer oil is a highly refined mineral oil that naturally aids in maintaining the insulation on winding conductors,. Which is usually paper, at Acceptable insulation temperature ratings. To manage oil and winding Conductor insulation temperature conditions under varying, potentially challenging power loading conditions, monitoring, modelling, and forecasting are frequently required for high value transformer assets due to the centrality of the heat removal problem to all Electrical Apparatus. Building codes in many jurisdictions mandate. That indoor Liquid-filled Transformers either use a non-flammable liquid or are installed in Fire-resistant rooms.
Air-cooled dry Transformers are Preferred for indoor applications even at capacity ratings where oil-cooled construction would be more economical,. Because their cost is offset by the reduced building construction cost.
Radiators are frequently used in oil-filled tanks to allow natural convection of the oil through them. Some large transformers use Electric-powered fans, pumps,. Or heat Exchanger-based water cooling to circulate forced air, forced oil, or chilled water. In order to ensure that the Transformer is completely dry before the cooling oil is added,. Oil-filled Transformers go through extensive drying processes. By doing this, electrical failure under load is avoided. Buchholz relays are a possible addition to Oil-filled Transformers. These relays quickly De-energize the Transformer when they detect gas produced by internal arcing, Preventing catastrophic failure. The failure, rupture, and burning of Oil-filled Transformers can result in power outages and other losses. Walls, oil Containment, and Sprinkler systems for fire Suppression are frequently used in the installation of oil-filled transformers in order to protect them from fire.
The Insulation covering the Windings must be completely dried before the oil is introduced when building Oil-filled Transformers. There are numerous ways to dry things. All of them share the trait of being performed in a vacuum environment. It is Challenging to transfer energy (heat) to the insulation because of the vacuum. There are numerous Approaches to this. The active part is dried Traditionally by hot air being Circulated over it and then followed by periods of hot-air vacuum (HAV) drying. The use of Evaporated solvent that condenses on the colder active part is more typical for larger Transformers. The process can be completed at lower pressure and without the interference of extra oxygen, which is a benefit. Vapor-phase drying is a common name for this procedure (VPD).
Resistance heating can be used for distribution Transformers, which are smaller and have less Insulation weight. This technique Involves Injecting current into the windings to heat the insulation. The heating has the advantages of being highly controllable and being energy-efficient. Since the current is Injected at a frequency much lower than the grid’s nominal frequency,. Which is typically 50 or 60 Hz, the technique is known as Low-frequency heating (LFH). The Transformer’s Inductance has less of an impact at a lower Frequency,. Which allows for a reduction in the voltage required to induce the current. An older Transformer’s service can also be Performed using the LFH drying technique.
For circuit connections,. Wire leads will be brought out from the base of very small Transformers and connected directly to the ends of the coils. Larger Transformers may have heavy bolted Terminals, bus bars, or porcelain or Polymer-made High-voltage Insulated Bushings. Given that it must carefully control the electric field Gradient without Allowing the Transformer to leak oil,. A large bushing can be a complicated structure.