What is a transformer? Transformer device. Electrical transformers. Energy losses in the transformer
We continue our acquaintance with electronic components and in this article we will look at device and principle of operation of the transformer.
Transformers have found wide application in radio and electrical engineering and are used for the transmission and distribution of electrical energy in power supply networks, for powering radio equipment circuits, in converter devices, as welding transformers, etc.
Transformer designed to convert alternating voltage of one value into alternating voltage of another value.
In most cases, a transformer consists of a closed magnetic circuit (core) with two windings located on it that are not electrically connected to each other. The magnetic core is made of ferromagnetic material, and the windings are wound with insulated copper wire and placed on the magnetic core.
One winding is connected to an alternating current source and is called primary(I), voltage is removed from the other winding to power the load and the winding is called secondary(II). A schematic diagram of a simple transformer with two windings is shown in the figure below.
1. The principle of operation of the transformer.
The operating principle of the transformer is based on phenomenon of electromagnetic induction.
If alternating voltage is applied to the primary winding U1, then alternating current will flow through the turns of the winding Io, which will create around the winding and in the magnetic core alternating magnetic field. Magnetic field produces magnetic flux Fo, which, passing along the magnetic circuit, crosses the turns of the primary and secondary windings and induces (induces) alternating EMF in them - e1 And e2. And if you connect a voltmeter to the terminals of the secondary winding, it will show the presence of output voltage U2, which will be approximately equal to the induced emf e2.
When a load, for example an incandescent lamp, is connected to the secondary winding, a current arises in the primary winding I1, forming an alternating magnetic flux in the magnetic circuit F1 varying at the same frequency as the current I1. Under the influence of an alternating magnetic flux, a current arises in the secondary winding circuit I2, which in turn creates a counteracting magnetic flux according to Lenz’s law F2, seeking to demagnetize the magnetic flux generating it.
As a result of the demagnetizing effect of the flow F2 Magnetic flux is established in the magnetic circuit Fo equal to the flux difference F1 And F2 and being part of the flow F1, i.e.
Resultant magnetic flux Fo ensures the transfer of magnetic energy from the primary winding to the secondary winding and induces an electromotive force in the secondary winding e2, under the influence of which current flows in the secondary circuit I2. It is due to the presence of magnetic flux Fo and there is a current I2, which will be the greater the more Fo. But at the same time, the greater the current I2, the greater the counterflow F2 and therefore less Fo.
From the above it follows that at certain values of the magnetic flux F1 and resistances secondary winding And loads the corresponding EMF values are set e2, current I2 and flow F2, ensuring the balance of magnetic fluxes in the magnetic circuit, expressed by the formula given above.
Thus, the flux difference F1 And F2 cannot be zero, since in this case there would be no main thread Fo, and without it the flow could not exist F2 and current I2. Therefore, the magnetic flux F1, created by the primary current I1, always more magnetic flux F2, created by the secondary current I2.
The magnitude of the magnetic flux depends on the current creating it and on the number of turns of the winding through which it passes.
The voltage of the secondary winding depends on ratio of the number of turns in the windings. With the same number of turns, the voltage on the secondary winding will be approximately equal to the voltage supplied to the primary winding, and such a transformer is called dividing.
If the secondary winding contains more turns than the primary, then the voltage developed in it will be greater than the voltage supplied to the primary winding, and such a transformer is called increasing.
If the secondary winding contains fewer turns than the primary, then its voltage will be less than the voltage supplied to the primary winding, and such a transformer is called downward.
Hence. By selecting the number of turns of windings at a given input voltage U1 get the desired output voltage U2. To do this, they use special methods for calculating the parameters of transformers, with the help of which the windings are calculated, the cross-section of the wires is selected, the number of turns is determined, as well as the thickness and type of the magnetic core.
The transformer can only operate in alternating current circuits. If its primary winding is connected to a direct current source, then a magnetic flux is formed in the magnetic circuit, constant in time, in magnitude and direction. In this case, an alternating voltage will not be induced in the primary and secondary windings, and therefore, electrical energy will not be transferred from the primary circuit to the secondary. However, if a pulsating current flows in the primary winding of the transformer, then an alternating voltage will be induced in the secondary winding, the frequency of which will be equal to the ripple frequency of the current in the primary winding.
2. Transformer design.
2.1. Magnetic core. Magnetic materials.
Purpose magnetic circuit consists in creating a closed path for the magnetic flux with minimal magnetic resistance. Therefore, magnetic cores for transformers are made of materials with high magnetic permeability in strong alternating magnetic fields. The materials must have low eddy current losses so as not to overheat the magnetic core at sufficiently high values of magnetic induction, be fairly cheap and not require complex mechanical and thermal treatment.
Magnetic materials, used for the manufacture of magnetic cores, are produced in the form of separate sheets, or in the form of long tapes of a certain thickness and width and are called electrical steels.
Sheet steels (GOST 802-58) are produced by hot and cold rolling, strip textured steels (GOST 9925-61) only by cold rolling.
Also used are iron-nickel alloys with high magnetic permeability, for example, permalloy, permindur, etc. (GOST 10160-62), and low-frequency soft magnetic ferrites.
For the manufacture of a variety of relatively inexpensive transformers, they are widely used electrical steels, which have a low cost and allow the transformer to operate both with and without constant magnetization of the magnetic circuit. Cold-rolled steels, which have better characteristics compared to hot-rolled steels, have found the greatest application.
Alloys with high magnetic permeability used for the manufacture of pulse transformers and transformers designed to operate at elevated and high frequencies of 50 - 100 kHz.
The disadvantage of such alloys is their high cost. For example, the cost of permalloy is 10–20 times higher than the cost of electrical steel, and permendur is 150 times higher. However, in some cases their use can significantly reduce the weight, volume and even the total cost of the transformer.
Another disadvantage is the strong influence of permanent magnetization and alternating magnetic fields on the magnetic permeability, as well as low resistance to mechanical influences - shock, pressure, etc.
From soft magnetic low frequency ferrites manufactured with high initial permeability pressed magnetic cores, which are used for the manufacture of pulse transformers and transformers operating at high frequencies from 50 - 100 kHz. The advantage of ferrites is their low cost, but the disadvantage is low saturation induction (0.4 - 0.5 T) and strong temperature and amplitude instability of magnetic permeability. Therefore, they are used only in weak fields.
The choice of magnetic materials is made based on electromagnetic characteristics, taking into account the operating conditions and purpose of the transformer.
2.2. Types of magnetic circuits.
Magnetic cores of transformers are divided into laminated(stamped) and tape(twisted), made from sheet materials and pressed from ferrites.
Laminated Magnetic cores are assembled from flat stamped plates of the appropriate shape. Moreover, the plates can be made from almost any, even very fragile, materials, which is an advantage of these magnetic cores.
Tape Magnetic cores are made of a thin tape wound in the form of a spiral, the turns of which are firmly connected to each other. The advantage of strip magnetic cores is the full use of the properties of magnetic materials, which makes it possible to reduce the weight, size and cost of the transformer.
Depending on the type of magnetic circuit, transformers are divided into rod, armored And toroidal. Moreover, each of these types can be either rod or tape.
Rod.
In magnetic circuits rod type windings are located on two rods ( rod called the part of the magnetic circuit on which the windings are placed). This complicates the design of the transformer, but reduces the winding thickness, which helps reduce leakage inductance, wire consumption and increases the cooling surface.
Rod magnetic cores are used in output transformers with a low level of interference, since they are insensitive to the effects of external low-frequency magnetic fields. This is explained by the fact that, under the influence of an external magnetic field, voltages that are opposite in phase are induced in both coils, which, when the turns of the windings are equal, compensate each other. As a rule, high and medium power transformers are made of rod type.
Armored.
In the magnetic circuit armor type the winding is located on the central rod. This simplifies the transformer design, allows for more complete use of the winding window, and also provides some mechanical protection for the winding. Therefore, such magnetic circuits are most widely used.
Some disadvantage of armored magnetic cores is their increased sensitivity to low-frequency magnetic fields, which makes them unsuitable for use as output transformers with low noise levels. Most often, medium-power transformers and microtransformers are armored.
Toroidal.
Toroidal or ring transformers make it possible to make fuller use of the magnetic properties of the material, have low dissipation fluxes and create a very weak external magnetic field, which is especially important in high-frequency and pulse transformers. But due to the complexity of manufacturing the windings, they were not widely used. Most often they are made from ferrite.
To reduce losses due to eddy currents, laminated magnetic circuits are assembled from stamped plates 0.35 - 0.5 mm thick, which are coated on one side with a layer of varnish 0.01 mm thick or an oxide film.
The tape for tape magnetic cores has a thickness from a few hundredths to 0.35 mm and is also covered with an electrically insulating and at the same time adhesive suspension or oxide film. And the thinner the insulation layer, the denser the cross-section of the magnetic circuit is filled with magnetic material, the smaller the overall dimensions of the transformer.
Recently, along with the considered “traditional” types of magnetic cores, new forms have been used, which include “cable” type magnetic cores, “inverted torus”, coil type, etc.
Let's leave it at that for now. Let's continue in .
Good luck!
Literature:
1. V. A. Volgov - “Parts and components of radio-electronic equipment”, Energia, Moscow 1977
2. V. N. Vanin - “Current Transformers”, Publishing House “Energia” Moscow 1966 Leningrad.
3. I. I. Belopolsky - “Calculation of transformers and chokes of low power”, M-L, Gosenergoizdat, 1963.
4. G. N. Petrov - “Transformers. Volume 1. Fundamentals of Theory", State Energy Publishing House, Moscow 1934 Leningrad.
5. V. G. Borisov, “Young Radio Amateur”, Moscow, “Radio and Communications” 1992
A transformer is a static electromagnetic device containing from two to several windings located on a common magnetic circuit and thus inductively connected to each other. A transformer is used to convert alternating current electrical energy through electromagnetic induction without changing the frequency of the current. Transformers are used both to convert alternating voltage and in various fields of electrical engineering and electronics.
To be fair, we note that in some cases a transformer may contain only one winding (autotransformer), and the core may be completely absent (HF transformer), however, in most cases, transformers have a core (magnetic circuit) made of, and two or more insulated tape or wire windings covered by a common magnetic flux, but first things first. Let's look at what types of transformers there are, how they are designed and what they are used for.
This type of low-frequency (50-60 Hz) transformers is used in electrical networks, as well as in installations for receiving and converting electrical energy. Why is it called power? Because it is this type of transformers that is used to supply and receive electricity to and from power lines, where the voltage can reach 1150 kV.
In city power grids the voltage reaches 10 kV. Through this, the voltage is also reduced to 0.4 kV, 380/220 volts, required by consumers.
Structurally, a typical power transformer may contain two, three or more windings located on an armored electrical steel core, and some of the lower voltage windings may be powered in parallel (split winding transformer).
This is convenient for increasing the voltage received simultaneously from several generators. As a rule, the power transformer is placed in a tank with transformer oil, and in the case of particularly powerful units, an active cooling system is added.
Three-phase power transformers with a capacity of up to 4000 kVA are installed at substations and power plants. Three-phase ones are more common, since losses are up to 15% less than with three single-phase ones.
Network transformer
Back in the 80s and 90s, network transformers could be found in almost any electrical appliance. With the help of a network transformer (usually single-phase), the voltage of a household network of 220 volts with a frequency of 50 Hz is reduced to the level required by the electrical appliance, for example 5, 12, 24 or 48 volts.
Often mains transformers are designed with multiple secondary windings so that multiple voltage sources can be used to power different parts of the circuit. In particular, TN transformers (incandescent transformer) could always (and still can) be found in circuits where radio tubes were present.
Modern network transformers are structurally made on W-shaped, rod or toroidal cores from a set of electrical steel plates, on which the windings are wound. The toroidal shape of the magnetic core makes it possible to obtain a more compact transformer.
If we compare transformers of equal overall power on toroidal and W-shaped cores, then the toroidal one will take up less space, moreover, the surface area of the toroidal magnetic circuit is completely covered by the windings, there is no empty yoke, as is the case with armored W-shaped or rod cores. In particular, welding transformers with a power of up to 6 kW can be classified as network ones. Network transformers, of course, belong to low-frequency transformers.
One of the varieties of low-frequency transformer is an autotransformer, in which the secondary winding is part of the primary or the primary is part of the secondary. That is, in an autotransformer the windings are connected not only magnetically, but also electrically. Several conclusions are made from a single winding, and allow you to get different voltages from just one winding.
The main advantage of an autotransformer is its lower cost, since less wire is consumed for the windings, less steel for the core, and as a result the weight is less than that of a conventional transformer. The disadvantage is the lack of galvanic isolation of the windings.
Autotransformers are used in automatic control devices and are also widely used in high-voltage power grids. Three-phase autotransformers with windings connected in a triangle or star in electrical networks are in great demand today.
Power autotransformers are produced with powers up to hundreds of megawatts. Autotransformers are also used to start powerful AC motors. Autotransformers are especially suitable for low transformation ratios.
A special case of an autotransformer is a laboratory autotransformer (LATR). It allows you to smoothly regulate the voltage supplied to the consumer. The LATR design has a single winding, which has an uninsulated “path” from turn to turn, that is, it is possible to connect to each of the turns of the winding. Contact with the track is ensured by a sliding carbon brush, which is controlled by a rotary handle.
This way you can get effective voltages of different magnitudes across the load. Typical single-phase LATRs allow voltage from 0 to 250 volts, and three-phase ones - from 0 to 450 volts. LATRs with a power of 0.5 to 10 kW are very popular in laboratories for setting up electrical equipment.
It is called a transformer, the primary winding of which is connected to a current source, and the secondary winding is connected to protective or measuring devices that have low internal resistance. The most common type of current transformer is the instrument current transformer.
The primary winding of a current transformer (usually just one turn, one wire) is connected in series to the circuit in which the alternating current is to be measured. The result is that the current of the secondary winding is proportional to the current of the primary, and the secondary winding must be loaded, otherwise the voltage of the secondary winding may turn out to be high enough to break through the insulation. In addition, if the secondary winding of the CT is opened, the magnetic circuit will simply burn out from the induced uncompensated currents.
The design of the current transformer is a core made of laminated silicon cold-rolled electrical steel, on which one or more insulated secondary windings are wound. The primary winding is often just a busbar, or a wire with a measured current passed through the magnetic circuit window (by the way, they work on this principle). The main characteristic of a current transformer is its transformation ratio, for example 100/5 A.
Current transformers are used quite widely to measure current and in relay protection circuits. They are safe because the measured and secondary circuits are galvanically isolated from each other. Typically, industrial current transformers are produced with two or more groups of secondary windings, one of which is connected to protective devices, the other to a measuring device, such as meters.
Almost all modern network power supplies, various inverters, welding machines, and other power and low-power electrical converters use pulse transformers. Today, switching circuits have almost completely replaced heavy low-frequency transformers with laminated steel cores.
A typical pulse transformer is a transformer made with a ferrite core. The shape of the core (magnetic core) can be completely different: ring, rod, cup, W-shaped, U-shaped. The advantage of ferrites over transformer steel is obvious - ferrite-based transformers can operate at frequencies of up to 500 kHz or more.
Since the pulse transformer is a high-frequency transformer, its dimensions decrease significantly with increasing frequency. The windings require less wire, and to obtain high-frequency current in the primary circuit, a field-effect or bipolar transistor is sufficient, sometimes several, depending on the topology of the pulse power circuit (forward - 1, push-pull - 2, half-bridge - 2, bridge - 4).
To be fair, we note that if a flyback power supply circuit is used, then the transformer is essentially a dual choke, since the processes of accumulation and release of electricity into the secondary circuit are separated in time, that is, they do not occur simultaneously, therefore, with a flyback control circuit, it is still a choke, but not a transformer.
Pulse circuits with transformers and chokes on ferrite are found everywhere today, from ballasts for energy-saving lamps and chargers for various gadgets, to welding machines and powerful inverters.
To measure the magnitude and (or) direction of current in pulsed circuits, pulsed current transformers are often used, which are a ferrite core, often ring-shaped (toroidal), with a single winding. A wire is passed through the core ring, the current in which needs to be examined, and the winding itself is loaded with a resistor.
For example, a ring contains 1000 turns of wire, then the ratio of the currents of the primary (threaded wire) and secondary winding will be 1000 to 1. If the ring winding is loaded with a resistor of a known value, then the measured voltage on it will be proportional to the winding current, which means the measured current is 1000 times more current through this resistor.
The industry produces pulse current transformers with different transformation ratios. The developer can only connect a resistor and a measurement circuit to such a transformer. If you need to know the direction of the current, and not its magnitude, then the winding of the current transformer is simply loaded with two opposing zener diodes.
Communication between electrical machines and transformers
The courses on electrical machines taught in all electrical engineering specialties at educational institutions always include electrical transformers. Essentially, an electrical transformer is not an electrical machine, but an electrical apparatus, since it does not have moving parts, the presence of which is a characteristic feature of any machine as a type of mechanism. For this reason, the mentioned courses should, in order to avoid misunderstandings, be called “courses on electrical machines and electrical transformers”.
The inclusion of transformers in all electrical machine courses is due to two reasons. One of them is of historical origin: the same factories that built AC electrical machines also built transformers, since only the presence of transformers gave AC machines that advantage over DC machines, which ultimately led to their dominance in industry. And now it is impossible to imagine a large installation of alternating electric current without transformers.
However, as the production of alternating current machines and transformers developed, it became necessary to concentrate the production of transformers at special transformer-building plants. The fact is that, due to the possibility of transmitting alternating current electricity using transformers over long distances, the increase in the higher voltage of transformers was much faster than the increase in voltage of alternating current electrical machines.
At the current stage of development of AC electric machines, the highest rational voltage for them is 36 kV. At the same time, the highest voltage in actually implemented electrical transformers reached 1150 kV. Such high voltages of transformers and their operation on overhead power lines exposed to lightning discharges have given rise to many specific transformer problems that are alien to electrical machines.
This led to technological problems in production that were so different from the technological problems of electrical engineering that the separation of transformers into independent production became inevitable. Thus, the first reason - the production connection that made transformers related to electrical machines - disappeared.
The second reason is of a fundamental nature, consisting in the fact that the electrical transformers used in practice, as well as electrical machines, are based on, and remains an unshakable connection between them. At the same time, to understand many phenomena in alternating current machines, knowledge of the physical processes occurring in transformers is absolutely necessary and, in addition, the theory of a large class of alternating current machines can be reduced to the theory of transformers, which makes their theoretical consideration easier.
Because of this, in the theory of alternating current machines, the theory of transformers occupies a strong place, from which, however, it does not follow that transformers can be called electrical machines. In addition, you need to keep in mind that transformers have a different target setting and energy conversion process than electrical machines.
The purpose of an electrical machine is to convert mechanical energy into electrical energy (generator) or, conversely, electrical energy into mechanical energy (motor), meanwhile, in a transformer we are dealing with the conversion of alternating current electrical energy of one type into alternating current electrical energy current of a different type.
In this article we will look at what a transformer is. Types of transformers will be described, the principle of operation and design will also not be ignored. It is worth noting that this is a type of static (stationary) AC machines that are used for various purposes not only in everyday life, but also in industry. For example, to account for electricity consumption. But first things first.
What is this device?
It is an electrical static machine that is used to convert current or voltage. Moreover, several types of devices can be distinguished depending on which network the power is supplied from. Thus, three-phase ones have three network windings, which are connected according to the “star” or “delta” circuit. An analogy can be drawn in this with asynchronous electric motors. There are various types of power transformers, which will be discussed below.
But in everyday life, devices are used that have one network winding. In addition, there is at least one secondary, which serves to power the devices. For example, in lamp technology they use several secondary windings. There was a need to obtain several voltage values from one device: 6.3 V, 250 V. In addition, you can find current transformers in everyday life. They are installed in electricity meters and serve to operate the control device.
Design
It is difficult to identify the basis of the transformer, but if you rely on weight, then this is undoubtedly the core (magnetic circuit). It is made of steel sheets that are assembled together and tightly tied together. This allows you to obtain the maximum possible cross-section of the magnetic core. But not only steel can be used; cores are often made from ferromagnetic materials. This is a substance whose properties are very similar to metal, but has a slightly different structure. There are certain types of transformers; photos of the main structures are given in the article.
The design contains at least two windings. One (primary) is supplied with supply voltage. From the second, third, Nth, a reduced voltage is removed with a frequency and shape similar to the input one. The power windings consist of copper wire. It is wound on a frame located around the magnetic core. When voltage is applied to the primary circuit, a variable appears which induces an EMF in the secondary winding. As a result, a certain potential difference appears at the output.
Power transformers
These types include those that convert electricity into the grid. This is not only a transformer installed at substations. The types of power transformers are varied; they serve not only to reduce the voltage from 110 kV, for example, to 6 kV, in the case of a substation. These include devices used in power supplies for household radio equipment. In fact, the design is similar for all, there are common components.
Even the species of which are diverse have a similar structure. There are just some minor nuances, for example, power machines at substations are equipped with an oil cooling system, while welding machines operate without it. But the latter have adjustable output current. This is necessary for welding metals of different thicknesses. Well, devices used in everyday life are completely devoid of such adjustments.
Autotransformers
An autotransformer is one of the types in which the primary and secondary windings are directly connected. This allows you to obtain not only an electrical connection in the device, but also an electromagnetic one. Typically, an autotransformer has three terminals, and this allows you to obtain different voltage values. A distinctive feature of autotransformers is high But there is also one significant drawback - the primary and are not electrically isolated from each other. Such a transformer is used for the most part to regulate consumer power. Types of transformers for other purposes are discussed below.
Measuring
For use in electrical installations of alternating current, a special type of transformer has been created - measuring. Thanks to them, the limits of measuring devices are increased. In addition, they allow you to measure the current flowing through it without an electrical connection to the power wire. In other words, without a galvanic connection, it is possible to control the current flow in the circuit. But two types of measuring devices can be distinguished - voltage and current transformers. There are different types of current transformers, their differences are in dimensions and areas of application.
Current transformers enable the conversion. In this case, the large current flowing in the circuit is reduced to a safe value. Moreover, the output is safe for control or measurement systems, alarm and protection devices. The primary winding is a piece of conductor with a secondary winding around it. A current of 1 or 5 Amperes is removed from the latter. But voltage transformers are designed for a different purpose. They perform voltage reduction to measure performance. With their help, protective devices are provided against high voltage circuits.
Pulse
This type of device is used for highly specialized purposes. It is necessary to convert a series of pulse signals. Moreover, the duration of one pulse can reach several tens of microseconds. Moreover, there is one small feature - only the amplitude of the signal changes, but not its shape. By the way, there are certain types of protection also equipped with circuits that prevent excess voltage or current.
As a rule, pulse devices are used in circuits in which a square-wave signal flows. Often this type of device is used in television technology. They convert short-duration video signal pulses with a very high duty cycle. Moreover, at the output you receive a signal in its original form, but with increased amplitude.
Conclusion
Now you know what a transformer is. We looked at the types of transformers and saw that they all have slight differences, despite the fact that the design is largely similar. Please note that safety precautions must be followed when working with any electrical devices. In addition, to service AC electrical networks, you must have an access group.
Transformers are devices designed to convert electricity. Their main task is to change the value of alternating voltage. Transformers are used both as independent devices and as components of other electrical devices.
Quite often, transformers are used to transmit electricity over long distances. Directly at power generating enterprises, they make it possible to significantly increase the voltage generated by the alternating current source.
By increasing the voltage to 1150 kW, transformers provide more economical transmission of electricity: electricity losses in wires are significantly reduced and it becomes possible to reduce the cross-sectional area of cables used in power lines.
The operating principle of the transformer is based on the effect of electromagnetic induction. The classic design consists of a metal magnetic core and electrically unconnected windings made of insulated wire. The winding to which electricity is supplied is called the primary winding. The second one, connected to devices that consume current, is called secondary.
After the transformer is connected to an alternating current source, its primary winding produces an alternating magnetic flux. It is transmitted through the magnetic circuit to the turns of the secondary winding, inducing an alternating EMF (electromotive force) in them. If there is a consumption device, an electric current arises in the secondary winding circuit.
The ratio between the input and output voltage of a transformer is directly proportional to the ratio of the number of turns of the corresponding windings.
This value is called the transformation coefficient: Ktr = W 1 /W 2 =U 1 /U 2, where:
- W1, W2 - number of turns of the primary and secondary windings, respectively;
- U1, U2 - input and output voltages, respectively.
The windings can be arranged either as separate coils or one on top of the other. For low-power devices, the windings are made of wire with cotton or enamel insulation. The micro transformer has windings made of aluminum foil with a thickness of no more than 20-30 microns. The insulating material is an oxide film obtained by natural oxidation of the foil.
TYPES AND TYPES OF TRANSFORMERS
Transformers are fairly widespread devices, so there are many varieties of them. According to design and purpose, they are divided into:
Autotransformers.
They have one winding with several taps. By switching between these taps you can get different voltage readings. The disadvantages include the lack of galvanic isolation between the input and output.
Pulse transformers.
Designed to convert a pulse signal of short duration (about ten microseconds). In this case, the pulse shape is distorted minimally. Typically used in video signal processing circuits.
Isolation transformer.
The design of this device provides for the complete absence of electrical connection between the primary and secondary windings, that is, it provides galvanic isolation between the input and output circuits. It is used to increase electrical safety and, as a rule, has a transformation ratio equal to unity.
Peak transformer.
Used to control semiconductor electrical devices such as thyristors. Converts sinusoidal AC voltage into spike-shaped pulses.
It is worth highlighting the method of classifying transformers according to the method of their cooling.
There are dry devices with natural air cooling in an open, protected and sealed housing design and with forced air cooling.
Liquid cooled devices can use different types of heat transfer fluid. Most often this is oil, but there are models where water or a liquid dielectric is used as a heat exchanger.
In addition, transformers with combined liquid-air cooling are produced. Moreover, each of the cooling methods can be either natural or with forced circulation.
CHARACTERISTICS OF TRANSFORMERS
The main technical characteristics of transformers include:
- voltage level: high voltage, low voltage, high potential;
- conversion method: up, down;
- number of phases: single or three phase;
- number of windings: two- and multi-winding;
- shape of the magnetic circuit: rod, toroidal, armored.
One of the main parameters is the rated power of the device, expressed in volt-amperes. The exact limits may vary slightly depending on the number of phases and other characteristics. However, as a rule, devices that convert up to several tens of volt-amperes are considered low-power.
Medium-power devices are considered to be devices from several tens to several hundred, and high-power transformers operate with values from several hundred to several thousand volt-amperes.
Operating frequency - there are devices with a reduced frequency (less than the standard 50 Hz), industrial frequency - exactly 50 Hz, increased industrial frequency (from 400 to 2000 Hz) and high frequency (up to 1000 Hz).
AREA OF APPLICATION
Transformers are widely used both in industry and in everyday life. One of the main areas of their industrial application is the transmission of electricity over long distances and its redistribution.
Welding (electrothermal) transformers are no less famous. As the name implies, this type of device is used in electric welding and for supplying power to electrothermal installations. Also, a fairly wide area of application of transformers is to provide power supply to various equipment.
Depending on their purpose, transformers are divided into:
They are the most common type of industrial transformer. Used to increase and decrease voltage. Used in power lines. On the way from power generating facilities to the consumer, electricity can pass through step-up power transformers several times, depending on the remoteness of a particular consumer.
Before being supplied directly to consumer devices (machines, household and lighting devices), electricity undergoes reverse transformations, passing through power step-down transformers.
Current.
Remote measuring current transformers are used to ensure the operability of electricity metering circuits for the protection of power lines and power autotransformers. They have different sizes and performance characteristics. They can be placed in the housings of small devices or be separate, large devices.
Depending on the functions performed, the following types are distinguished:
- measuring - supplying current to measuring and control devices;
- protective - connected to protective circuits;
- intermediate - used for repeated conversion.
Voltages.
They are used to convert voltage to the required values. In addition, such devices are used in galvanic isolation circuits and electrical and radio measurements.
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Among modern electrical devices, one of the most common is the transformer. This unit is widely used in both household appliances and power electronics. Its action is to convert current. Moreover, the transformer can change its value both up and down.
A certain device has a variety of. They have some structural and functional differences. To understand what such equipment is, as well as the features of its operation, each type should be considered in detail.
Device
Existing today types of current transformers have certain common characteristics. The device has one, two or more windings in its system. They are located on one core. The transformers on sale today differ in their manufacturing method. Their reliability depends on the manufacturer. The performance characteristics of these types of equipment are also similar.
The transformer is not designed to convert direct current. Otherwise, it will lead to overheating of the conductor. Transformers are capable of operating exclusively with alternating, pulsed and pulsating current.
All types of presented equipment have three mandatory components. These include the magnetic core, cooling system and winding. The first component is also called the core.
Operating principle
Considering purpose and types of transformers, a few words should be said about their functional qualities. In such equipment there is a primary and secondary winding. The initial voltage is applied to the first coil. It needs to be raised or lowered.
Secondary windings may consist of one or more coils. Transformed voltage is transmitted from them. The operation of such a device is based on Faraday's law. The magnetic flux, which changes over time through an area limited by a contour, generates electromotive forces. In addition, a current that changes over time can induce a non-constant magnetic field.
In the diagrams, the transformer is depicted as two (or more) coils. There is a vertical line between the first and secondary windings. It represents the core (magnetic circuit). When performing the functions assigned to it, the transformer has low energy losses. This made the presented equipment in demand.
Operating modes
Existing types of transformer operation can be divided into 3 groups. These include idle, short circuit and operating mode. In the first case, the terminals of the secondary winding are not connected anywhere. In this mode, if the core is made of soft magnetic material, the current will show loss.
In the event of a short circuit, the terminals of the secondary winding coils are connected to each other. In this case, a slight voltage will be applied to the primary winding. This mode is present in measuring types of transformers.
With an active load, voltages arise at the ends of all types of windings. If this value is higher on the secondary winding, the transformer is called a step-up transformer. And vice versa. The degree of transformation is determined using a given coefficient.
Classification
There are several approaches to classifying the presented equipment. This allows you to understand its structure and functions. Existing types of current transformers can be classified according to purpose. In this case, voltage devices, measuring, laboratory, protective, and intermediate types are distinguished.
There are also several groups based on the installation method. The conditions in which the equipment can be operated depend on this. Transformers can be internal and external, stationary, busbar or support, as well as portable.
There can be one or several stages in the system. Based on the rated voltage, high-voltage and low-voltage devices are distinguished. Taking into account the type of insulation, several groups of transformers can also be distinguished. This indicator depends on the production technology. There are devices with compound, dry and oil-paper insulation.
According to the scope of application, there are power, household, welding, oil, autotransformers, etc.
Power transformer
Existing types of power transformers belong to low-frequency devices. They are used in power networks of enterprises, cities, towns, etc. Such equipment reduces the voltage in the network to the required value of 220 V.
Power transformers can have two or more windings. They are installed on an armor core. Most often, such a structural element is made of electrical steel. Such a transformer is placed in a tank with special oil. If the power of the equipment is high, it uses active cooling.
Three-phase power transformers are used for power plants. Their power is up to 4 thousand kW. These types of devices make it possible to achieve a 15% reduction in energy losses compared to three single-phase transformers.
Network varieties
In the 80s of the last century, the most common was network transformer. Types of transformers this type has been further developed. Today they are made on a W-like core, as well as rod or toroidal magnetic cores. The windings are installed on them.
Using such a device, the voltage coming from the household network is reduced to the required value (for example, 12, 24 V). Transformers with a toroidal core are considered the most compact. Its magnetic circuit is completely covered by windings. This avoids the appearance of an empty yoke.
Autotransformer
Existing types of transformer windings very diverse. They can be regulatory, basic, auxiliary. The autotransformer winding has the most original structure. This is a low frequency device. Its secondary winding is an integral part of the primary. They are connected, as in other types of transformers, magnetically. However, such a winding also communicates electrically.
Several terminals extend from one coil, allowing you to obtain voltages of different values. The advantage of this design is its low cost. Less wires will be required to install the winding. It is also possible to save on the amount of core material. The weight of the autotransformer will be less than that of other types of equipment.
However, this type of device does not have galvanic isolation. This is a disadvantage of autotransformers. Such equipment is used in automatic control technology, as well as in high-voltage communications. Today, three-phase autotransformers are very popular. Their connected winding forms a triangle or star.
Current and voltage transformer
Today there are also certain types of voltage transformers and current. It all depends on how the device functions. If it steps down the current, it is a current transformer. A certain category of devices has also been developed to regulate voltage.
The primary winding of the current transformer is connected to electricity, and the secondary winding is connected to measuring or protective devices. The first type of device is most often used. The coil with the primary winding is connected in series. It measures alternating current.
The core of such equipment is made of laminated electrical steel. It is produced by the cold-rolled method. The primary winding is most often a busbar. When operating such equipment, it is important to take into account the transformation ratio.
For industry, similar devices with several groups of secondary windings can be produced. One of them is connected to measuring instruments (for example, meters), and the second to protective equipment.
Pulse transformer
Considering what types of transformers are used today, it is impossible not to say a few words about the pulse varieties of the presented devices. They have almost completely replaced low-frequency heavy transformers. Their core is made not of charge steel, but of ferrite. The shape of the magnetic circuit can be very different, for example, cup, ring, Sh-like type.
Pulse type transformers can operate at high frequencies (500 kHz or more). Thanks to this feature, the dimensions of such products have been significantly reduced. Requires less wire to be used for winding.
Pulse transformers and chokes with ferrite cores are used everywhere today. They can be found in energy-saving light bulbs, chargers, powerful inverters, etc. Their scope of application is very wide.
Some pulse-type transformers use a reverse power supply circuit. In this case, the device is essentially a dual-type choke. At the same time, the processes of receiving and transmitting electricity do not occur simultaneously.
Pulse current transformer
To be able to measure the direction and magnitude of current, pulsed circuits often use a special transformer. Types of transformers This group has a ferrite core. Most often it has a single ring winding. A wire is threaded through its center. The current is studied in it. The winding is loaded onto a resistor.
The measurement is carried out according to a simple scheme. If the load is applied to a resistor of a known value, then the voltage when measured across it will be proportional to the winding current.
There are transformers of this type on sale with different transformation ratios. If you only need to know the direction of the current, the device is loaded with only two stabilizers built into the circuit.
Protection system
Transformers are reliable equipment. However, due to various damages, an emergency situation may occur. Therefore, various types of transformer protection.
Such systems disconnect equipment from the network if there is damage. Depending on the type of design, the protection may only disconnect power from the damaged part of the device. If a breakdown is detected, the system can generate a signal. In this case, various types of autotransformer protection are used.
Differential protection is necessary in case of violations of the integrity of windings, busbars and equipment inputs. If damage is detected from the outside, current cutting occurs. This is instant protection.
Gas protection is used in case of damage inside the tank. This may release gas. It also triggers when the oil level drops.
Overcurrent or directional protection helps protect equipment from overcurrents. Also, some designs may provide protection against short circuits to the frame and overload. The latter system acts on the signal, alerting personnel.
Having considered the design features and operating principle, you can understand what it is transformer. Types of transformers existing today differ in a number of ways. This affects their functionality.