Transformer Types In electrical engineering, a transformer is a machine or device that inductively transfers electrical power from one circuit, which is running at one set of current and voltage levels, to another set of circuits, which are running at different sets of current and voltage levels. The majority of transformers are designed to meet certain application specifications, including those for greater impedance, constant current, or constant voltage.
Power, instrument, tap-changing, auto, RF, audio, and other types of transformers are ubiquitous in the electrical transmission system, various industries, and electronic applications. Although they vary in size, rating, and form from one another, they all work on the same fundamental premise. This article describes several different kinds of transformers, so let’s take a look at them.
Electric Motor Power Transformer
Power transmission lines, substations, and producing stations all make use of power transformers, which can either reduce or increase voltage. Low current goes over the transmission line because the voltage is raised using a step-up power transformer. Consequently, there is a decrease in I2R losses in the transmission lines. Industries rely on step-down power transformers to provide loads at the voltages specified by the transformers.
The electrical components get their juice from a few of the power transformers as well. Depending on its use, the power transformer can be either a single-phase or a three-phase unit. Power transformers typically include tap changing transformers, auto transformers, and distribution transformers, each with their own set of distinctive characteristics. What follows is a discussion of a few power transformers.
Transformer with a Laminated Core
These transformers are available in milliwatt to megawatt ranges and are the most popular. Electric power transmission and appliance low-voltage supply both make use of this sort of transformer. To lessen the impact of eddy currents, this transformer has a laminated core. A core made of thin steel, CRGO, or CRNGO ‘E’ and ‘I’ laminations is utilized in low and high power transformers, whether they are single phase or three phase. Bolts hold the laminated boards together. Around the core’s center limb, a former winds the primary and secondary windings. For tiny equipment, these transformers with split bobbin offer excellent insulation between the windings. It is possible to reduce electromagnetic interference by using shields between the primary and secondary.
Electric Core Toroidal Transformers
One of the numerous benefits of this transformer type over the laminated core variety is the reduction of stray or external magnetic fields, which allows for more efficient and quiet operation. These are ideal for applications that run on low or high voltage because of their compact size and reduced weight. A ribbon of steel is formed by cutting a highly efficient donut-shaped core constructed of grain-oriented silicon iron. Like a very taut clock spring, copper windings encircle this core.
Toroidal core transformers are more costly than EI laminated core transformers. Toroidal transformers, in contrast to EI laminated type transformers, are smaller and lighter for a given rating. Enhanced efficiency and less magnetic field leakage are further benefits. A few tens of VAs to thousands of VAs are available for these. The standard installation method is a bolt through a single hole in the middle, accompanied by washers and rubber pads.
Transformer for Autos
A typical transformer has two or three windings; an auto transformer, on the other hand, has just one winding, which serves as the primary and secondary. Unlike in a conventional transformer, where the two windings are physically separated, with this design the portion of the single winding that is shared by the primary and secondary is electrically coupled. Therefore, this transformer is capable of both induction and conduction. This uses a single winding to encase a laminated core, with primary and secondary windings split along its length.
Auto transformers can be categorized as either step-up or step-down. The voltage induced in the secondary is low in a step-down auto transformer because the whole winding functions as the primary and the remaining portion as the secondary. In contrast, a step-up transformer will work in the other way. Star or delta connected auto transformers, which are three phase power transformers, are utilized in power distribution systems. In most cases, however, high-power applications call for star-connected auto transformers.
The secondary connection of a variable auto transformer uses a sliding carbon brush, and there are a number of tappings on the single winding. As a result, the secondary voltage is changeable and equal to the turns ratio of the total winding to the tapping when the carbon brush is slid.
The stators of auto transformers provide the safe starting of a wide variety of electrical devices, including synchronous motors, induction motors, and others. Additionally, these serve as boosters and transformers for furnaces.
The Poly Phase Transformer
Power grids and transmission lines, which use three-phase electric power systems, frequently use this sort of transformer to transmit extremely high voltages. Most systems use three-phase alternating current (AC) for generation, transmission, distribution, and usage, making these the most cost-effective. The three windings of this transformer are encircled by a three-legged core and placed in a tank. Possible configurations for the connections between the main and secondary windings include star-star, star-delta, delta-delta, and delta-star. Depending on the load or application, these three-phase transformers can be either step-up or step-down models. Since all of the windings share a core, the transformer’s efficiency is good since the leakage magnetic flux is low.
Cooled by Oil Transformers
Huge oil-cooled transformers are employed in a variety of units, including power distribution units, substations, and generating stations. The windings and core of these transformers are insulated and cooled by the use of conventional transformer oil, often known as mineral oil. Transformers that use oil as a cooling medium have their core and coils immersed in the oil. Transformers cooled by oil have superior insulation and heat conductivity compared to those cooled by air. Among these varieties are
Self-Cooling Transformers Immersed in Oil
This design uses conduction to transfer heat from the core and windings to the oil. As the oil’s temperature rises from its core and windings, it begins to flow throughout the tank and eventually reaches its walls, where it is naturally cooled by the surrounding air. Since this oil keeps circulating, it helps to lower atmospheric temperatures.
Transformers that are forced air cooled and immersed in oil
This cooling approach involves employing fans to direct pushed air onto the outside surface of the transformer, which improves heat dissipation. After a specific temperature is reached, these fans will turn on automatically.
Transformers that are embedded in oil and cooled by water.
The coils submerged in the oil at the very bottom of the tank are used to extract or dissipate heat in this type. Additional cooling of this water is accomplished in cooling towers, spray ponds, or heat exchangers.
Oil Immersed Forced Oil Cooled Transformers.
This sort uses a pump to circulate forced oil, which extracts heat. To dissipate the heat, the oil is pushed up to the windings and then returned via external radiators, where fans disperse the air. Extremely high-capacity transformers often employ air blast cooling radiators for this purpose.
Relay Devices for Grounding
Using these, a ground path can be established for systems that are either Wye connected, ungrounded stars, or delta connected. The system is kept at zero voltage, neutral, or ground thanks to this transformer’s low impedance link to ground. There is no way for the fault current to go back to ground when it happens on an ungrounded or isolated system. This results in an increase in voltage on the other two lines while the defective line remains grounded. The insulation of the transformer and other parts are overstressed as a result. Therefore, to avoid this, a grounding transformer is necessary.
These often take the shape of single-winding transformers with a zigzag layout, though they can also feature a unique star-delta arrangement. The primary’s star connection is linked to the supply system, while the secondary’s delta connection is left unloaded. Grounding transformers have lower power ratings than power transformers since the load on the secondary is only applied for a short period of time, in the case of a malfunction. The purpose of these is to support the load without it, and in the event that one of the lines goes grounded, it will continue to supply current to the load. The result is a grounding transformer that is both smaller and cheaper than a continuous duty power transformer. Utility, industrial, and electrical transmission networks are the most common users of these.
Detectors of Leakage
By slackly connecting the main and secondary windings, their design achieves a high leakage inductance in comparison to other transformers. We also refer to these as stray-field transformers. The intrinsic current limitation helps to minimize overloads, and the loose coupling between the primary and secondary windings contributes to this. This means that the input and output currents are always below the thermal overload threshold, even in the event of a secondary short circuit. When the electrode comes into contact with the workpiece during arc welding, this sort of transformer is most commonly utilized as a welding transformer to generate short circuit currents. These currents are limited, though, because of the high leakage inductance. High voltage discharge lamps and extra-low voltage uses (e.g., door bell installations and children’s toys) that are likely to experience frequent short circuit circumstances are other potential uses for these transformers.
Transformer with Resonance
A high-voltage transformer has two high-Q coils, one primary and one secondary, wound on a ferrite or air core and connected across the windings. By connecting an inductor and a capacitor, two LC circuits are created. In some cases, the capacitor alone is a resonant coil.
The tuned secondary oscillates sinusoidally with each pulse from a sawtooth, square wave, or other periodic alternating current source connected to the primary. Resonance generates high secondary voltage. These transformers create massive AC voltages. The electronic ballasts that turn on fluorescent lights also employ these. Radio transmitters, ignition systems, super heterodyne radio receivers, and others employ transformers.
Constant voltage transformers are also resonant. Strategically positioning the ferro-resonant tank circuit in the secondary and choosing the right core helps keep a transformer’s secondary voltage stable regardless of primary voltage variations. The secondary flux capacitor drains current when charged. Due to flux saturation, the load or secondary terminal voltage remains constant independent of input voltage variation.
These transformers, placed for safety, isolate the load or equipment from the power supply. The two circuits are electrically isolated but magnetically connected. Isolation transformers have 1:1 turns ratios. Transformer galvanic isolation prevents electric shock. Medical equipment uses transformers to prevent AC power leaking to patient devices. Shielded isolation transformers prevent coupling magnetic noise. These act as surge suppressors, noise filters, and isolation.
Instrument transformers prevent high voltage and current from damaging metering equipment, relays, instruments, and other control devices in the circuit where electrical quantities are monitored. These are made to extend the measuring range of ammeters, voltmeters, wattmeters, protection relays, energy meters, etc. Devices convert high-voltage circuits to measurement-ready voltage and current. This includes all voltage and current instrument transformers.
Instrument Transformer with Multiple Uses
A single unit of this sort can serve as both a voltage and current transformer. This kind of transformers is great for high voltage control systems like metering and protection because it reduces the voltage and current to a standard, quantifiable, low value. This makes the most efficient use of available space by reducing the need for mounting pads and supporting structures. Revenue metering and protective relaying are two of its primary uses.
Transformer for Pulse
By keeping the two circuits isolated, pulse transformers may transfer rectangular electric pulses of constant magnitude and rapid peak and fall times. Pulse transformers can be either small signal, medium power, or high voltage. Transformers with low leakage inductance, high open circuit inductance, and low distributed capacitance tolerance might lessen the rectangular pulse distortion. Digital logic circuits and telecommunications make use of smaller transformers known as signal type pulse transformers. When it comes to protection systems, power control circuits, camera flashes, and more, medium sized pulse transformers are the way to go. In order to shield the main side circuits from electrical load transients, these transformers necessitate low coupling capacitances. To connect the power semiconductors’ high-voltage gate terminals to the low-power control circuitry, high-frequency power converters require large-power pulse transformers. These find additional usage in pulsed power applications such as particle accelerators and radar systems.
RF transformers serve multiple purposes in electronic circuits, including maximum power transfer via impedance matching, DC isolation, voltage and current step-up or step-down, connecting unbalanced and balanced circuits, and many more. Connector packages, surface mount packages, and other configurations are available for these transformers. In RF transformers, the steel laminations have no purpose. You can adjust the windings of this transformer to a specific frequency—often between 30 KHz and 30 MHz—by adding a capacitor to one of the windings.
The transformers might have a balun type core, an air core, or a ferrite core. Printed circuit boards use air core RF transformers that are soldered onto a few rounds of wire. Superheterodyne radio receivers, which primarily use tuned type transformers, utilise ferrite core transformers. For balanced amplifiers and other unbalanced circuits that require mode rejection, balun transformers are an essential component.
Transformer for Audio
When it comes to audio circuits, the transformers used to transmit the signal are specifically constructed to handle audio signals. This sort of transformer operates within a frequency range of 20 Hz to 20 KHz. These have multiple uses, including increasing or decreasing the signal voltage, changing the circuit’s balance from balanced to unbalanced, lowering or raising the circuit’s impedance, electrically isolating one audio device from another, and blocking the DC component of current while allowing the AC signal through. A few examples of the many kinds of transformers found in audio equipment are: splitters, impedance converters, direct boxes, hum eliminators, loudspeaker toroidal AF transformers, moving-coil phono inputs, line outputs, inter-stage and power outputs, microphone outputs, and so on.