Electromagnetic equipment, which contains several windings located on the same wire and inductively connected, is called a transformer. The device is necessary for converting electricity to current using magnetic induction without changing its frequency. Different types of transformer windings are used in many areas of electrical engineering and electronics.
Content
- Work principles
- Power unit
- Network device
- Features of the autotransformer
- Current equipment
- Pulse design
- Scope of application
Work principles
Any transformer has two or more windings in its construction. They are interconnected by electromagnetic induction and can be made of wire or tapes covered with a layer of insulation. The windings are attached to a magnetic core made of soft ferromagnetic material. If the device has only one such element, then it is called an autotransformer.
The design includes certain details:
- expansion tank with a lid;
- insulator;
- magnetic circuit (core);
- radiators;
- two windings - low and high voltage.
The principle of operation of transformers is studied even in the school physics course, so it is easy to understand even for a student. The first winding receives voltage, as a result of which an alternating current begins to flow in it. It creates a magnetic flux in the core, under the influence of which an electromotive force appears in two elements. The secondary winding closes due to the load, after which an alternating current begins to flow in it, for which the parameters - voltage and its curve, frequency and number of phases - differ.
There are several types of transformers according to certain parameters:
-
the number of phases - three- and single-phase; - the number of windings - three- and two-winding;
- type of insulation - oil, dry and with a filler that does not burn;
- type of cooling - with natural and forced oil, air and nitrogen blanket.
And also distinguish between power, network, automatic, pulse transformers and electric current devices. They differ in design, functionality and operating principles.
Power unit
Power transformer Is a low-frequency unit that is used in electrical networks to convert energy. The device got its name due to the fact that it is used to receive and transmit current to power lines, where the voltage indicator in some cases reaches 1200 kV. In cities, it is within 10 kV, it is thanks to the power transformers that it drops to 0.4 kV (220 and 320 V), which are needed by consumers.
The design of the device may contain two or more windings, they are located on an armored magnetic circuit made of technical steel. Some of the elements can be powered individually. This is convenient when receiving voltage from several generators at the same time.
Typically, power equipment is placed in an oil tank, sometimes a cooling system complements it. The unit is installed at substations; three-phase transformers are more common, since they reduce energy losses by 15%.
Network device
Network devices - types of current transformers that appeared in the 80s. It is this device that can convert a household voltage of 220 V into an indicator consumed by electrical appliances - 48, 24, 12 or 5 volts. Sometimes the units are made with several secondary windings, so you can use several power sources at once. In the circuits of any radio tube, there is always a network incandescent transformer.
In modern equipment, the core has the shape of the letter W or a rod; it is made of electrical steel plates on which the windings are wound. The transformer with compact dimensions has a toroidal magnetic circuit. At the same time, its power is not inferior to models with larger sizes and cores of other shapes. The network also includes welding devices with a power of up to 6 kW.
Features of the autotransformer
If you are interested in what kind of transformers there are, then among the low-frequency ones you can single out automatic equipment. In such units, the primary winding is also secondary at the same time. That is, the elements are connected not only by induction, but also by electricity. There are several leads from one winding, so it can give different voltages at the same time. The cost of the device is lower than that of other types of transformers. This is due to the consumption of a smaller number of wires for one winding, steel for the magnetic circuit and a small mass.
Autotransformers are used in automatic control devices and high-voltage networks. Equipment with windings connected in a delta or star is in great demand in modern electricity systems. Power units have a capacity of up to 100-200 MW. It is advisable to use them with small transformation ratios.
Another type of autotransformer is laboratory instrument. With its help, you can smoothly control the voltage before supplying it to the consumer. By design, this is a transformer with one winding, which has bare turns of wires. That is, it becomes possible to connect to each loop separately.
Contact is assisted by a sliding brush that can be operated with a rotary knob. During the load, voltages of different magnitudes come out, single-phase units give out an indicator from 0 to 250 V, and three-phase ones - up to 450 volts. Laboratories use less powerful designs to tune electrical equipment.
Current equipment
Current transformer Is a device, the primary winding of which is connected to a power source, and the secondary one is connected to measuring devices with low internal resistance. The first element - one wire or coil - is connected to the circuit in a sequential way to measure alternating current. In this case, the indicator of the secondary winding, which must be under a load with a high voltage capable of breaking through the insulation, is proportional to the first. If you open it, then the magnetic circuit will simply burn out from the uncompensated current.
In the design, the core is made of cold-rolled silicon steel, one secondary winding is wound around it. The primary part is usually a busbar or a wire with a current passed through the hole in the core. A high transformation ratio is the main advantage of such a unit. Current transformers are often used to measure electricity and in various relay protection schemes.
Since the circuits are isolated from each other, the use of the equipment is considered safe. Industrial units are available with several groups of secondary windings. One of them is connected to the protective equipment, and the second to the measuring device - the meter.
Pulse design
Pulse transformers are installed in welding machines, power supplies, inverters and current converters with low and medium power. These devices have long supplanted heavy low frequency equipment. The device has the form of a transformer with a ferrite core in the shape of the letters P or W, a rod, a cup or a ring. Their advantage over other materials is the ability to operate at frequencies above 500 kHz.
Since this is a high-frequency unit, its dimensions are also insignificant. Less wire is required per winding, and one or more field-effect transistors will be sufficient to generate current. Number of additional equipment depends on the topology of the power supply circuits:
-
forward - one device; - two-stroke - 2;
- half-bridge - 2;
- pavement - 4.
The transformer acts as a choke when a flyback power supply is used. After all, then the processes of accumulation and delivery of electrical energy into the secondary circuit are separated by a certain period of time. Pulse transformers with ferrite cores can be found almost everywhere today. They are used in energy-saving lamps, welding machines and inverters, as well as chargers for mobile phones, laptops and tablets.
A pulsed current unit is needed to measure the direction of electricity. The equipment is based on a ring-shaped ferrite core with one winding. A wire is passed through the ring, and the element with turns receives a load on the resistor.
Manufacturers produce different models of transformers with some differences in performance factors. To find out the direction of electricity, the winding is loaded with two opposite zener diodes.
Scope of application
The school physics course gave the students some understanding of the operation and application of transformers. For example, that the loss of power is always directly proportional to the square of the electric current, so you need to increase the voltage to transmit electricity over a significant distance. On the contrary, before the current is transferred to consumers, the indicator must be lowered. It is for this that various types of transformers are used.
And also the equipment is used in power supply circuits for household appliances. Units with several groups of windings are installed in televisions, computer monitors. They power the circuits, perform the functions of a transistor and a kinescope. The device of transformers is also studied in school lessons.
Without transformers, electrical networks and some types of equipment will not be able to function normally, therefore it is necessary at least superficially to know the device of the units, the principles of their operation, design features and differences in different models. This will allow you to independently troubleshoot some home appliances, industrial equipment, and mobile gadgets.
