Small-sized transformers used in household and office electronic equipment. classified according to the following main characteristics
■ according to the conditions of use and operation, taking into account the requirements for resistance to external influencing factors;
■ by functional purpose, which is determined by the types of electronic equipment;
■ by the parameters of the input electrical energy (operating voltage and frequency);
■ by design and technological parameters and characteristics, the main of which are design varieties of magnetic circuits.
Transformers for household and office electronic equipment are subdivided into performance groups and climatic performance categories based on resistance to mechanical factors. The classification of transformers according to the conditions of use and the requirements for each classification group for sinusoidal vibration and mechanical shock are given in table. 1.1. Requirements for the effect of ambient temperature, high humidity, atmospheric pressure and the classification of transformers according to these criteria are given in table. 1.2 Performance groups are selected based on the conditions of use of transformers and the required level of resistance in terms of mechanical and climatic influences. When choosing performance groups, the maximum degree of unification and the minimum possible number of performance groups of transformers of each class must be ensured.
Transformers whose performance group meets the most stringent requirements are preferred, all other things being equal.
The specific group of climatic and other versions is indicated in the technical specifications of the transformers
When using transformers with rigid characteristics in terms of resistance to external influencing factors (VVF), and transformers with less stringent requirements, individual or general protection is used as part of the equipment: depreciation, thermostatting, sealing, etc., while measures of individual protection of products in as part of the electronic equipment should ensure the possibility of using products manufactured according to reduced operational requirements.
As part of electronic equipment, devices and equipment for communication facilities (ACC), transformers can perform certain specified functions provided for by circuit solutions. The most widely used transformers are in power supply circuits of radio engineering devices, in rectifiers, filters, static converters, stabilizers, voltage and current regulators, audio frequency amplifiers. In converter circuits, using transformers, you can convert the main parameters of electrical energy in alternating current circuits: voltage, current, number of phases and shape of the curve. Each of the transformations, usually, is carried out simultaneously with the transfer of electricity by electromagnetic means to another electrical circuit, not directly connected with the circuit from which this energy is supplied. Transmission of energy by means of transformers is possible not only by electromagnetic means, but also by combined (electromagnetic-electric) one. Transformers with this type of power transmission are classified as autotransformers. There are practical schemes in which a transformer is also used to transmit electricity electromagnetically without converting it. This type of transformer, used to isolate one electrical circuit from another, is called an insulating transformer.
It should be noted that usually in transformers, the transformation of not one, but several of the above parameters of electrical energy is carried out simultaneously. Thus, voltage conversion always occurs with a change in current.
On the basis of their functional purpose, transformers can be classified into groups: power transformers, power converters and matching transformers.
Varieties of characteristics of low power supply transformers:
■ by voltage - low voltage, high voltage and high potential;
■ by the frequency of the supply network;
■ by the number of phases - single-phase, three-phase, six-phase, etc .;
■ by transformation ratio - increasing and decreasing;
■ by the number of windings - double-winding and multi-winding;
■ by the type of connection between the windings - transformers with electromagnetic coupling (with insulated windings) and transformers with electromagnetic and electrical coupling, that is, with coupled windings;
■ by the design of magnetic circuits;
■ according to the design of the windings - coil, wafer and toroidal;
• by design of the entire transformer - open, encapsulated and closed;
■ by designation - rectifier, filament, anode, anode-filament, etc.
The operating frequency of a transformer is one of the most important parameters that determines the main characteristics of a unit or unit, its purpose and scope of possible application. On this basis, transformers can be classified into transformers of reduced frequency (less than 50 Hz), industrial frequency (50 Hz), increased industrial frequency (400, 1 OOO, 2 OOO Hz), increased frequency (up to 10 kHz) and high frequency (over 10 kHz).
On the basis of input and output electricity, transformers can be divided into low-voltage, in which the voltage of any winding does not exceed 1000 V, and high-voltage, in which the voltage of any winding exceeds 1000 V.
Rated voltages of power supply systems, power sources, converters and connected to them receivers of electrical energy are determined in accordance with the requirements of GOST-
■ for sources and converters - 6; 12, 28.5; 42; 62; 115; 230 V for single phase alternating current and 42, 62, 230; 400; 690 V for three-phase alternating current;
■ for networks and receivers (transformers) - 6, 12, 27, 40, 60, 110, 220 V for single-phase alternating current and 40, 60, 220, 380, 660 V for three-phase alternating current.
In addition to the above standardized voltage values, other rated voltages may be used:
■ 7 V - for generators in electrical systems of motorcycles and for power sources of motor vehicles;
■ 24 V single-phase current with a frequency of 50 Hz - for converters, networks and receivers for general industrial purposes;
■ 26 V (converters) and 2 V (receivers) of single-phase current with a frequency of 50 Hz and 400 Hz - for ship electrical equipment;
■ 36 V (sources, converters and receivers) of three-phase current with a frequency of 400 and 1000 Hz - for aviation equipment and aircraft;
■ 42 V - for single-phase and three-phase networks ;.
■ 120, 208 V (sources, converters) and 115, 220 V (receivers) with a frequency of 400 and 1000 Hz - for aviation equipment and aircraft;
■ 36 V with a frequency of 50 and 200 Hz (sources, converters, receivers) —for previously developed equipment and instruments;
■ 208 V (sources) and 200 V (receivers) of single-phase current with a frequency of 6000 Hz - for aircraft in technically justified cases.
For sources and converters, it is allowed to use an adjustable voltage setting, selected from the following range: 0.5; 1.0; 2.0; 3.0; 5.0; 10 and 15% from the nominal values. Permissible deviations from the nominal voltage values can be double-sided symmetrical and asymmetrical, as well as one-sided.
When operating ACC and telecommunication equipment, single-phase alternating voltage and phase voltages of three-phase current are used, which must correspond to the following values: rated voltage - 220 V; operating voltage - 187 ... 242 V inclusive for power supply from a general-purpose power grid; 213. .227 V inclusive for power supply of the equipment from the mains power supply through the regulation devices; voltage frequency - 50 Hz; frequency variation limits - 47.5 ... 52.5 Hz inclusive; permissible coefficient of nonlinear distortion - no more than 10%.
The nominal values of alternating voltages at the output of devices and power supplies and input supply voltages of functional units, PPPs, microcircuits and electronic equipment units containing transformers and drawn up by the main set of design documentation are selected from the range: 1,2; 2.4; 3.15; 5.0; 6.0 (6.3); 12.0 (12.6); 15.0; 24.0; 27.0; 36.0; 40.0; 60.0; 80.0; (110); 115; 127; 200; 220 and 380 V.
The variety of circuit solutions of transformers determines their classification according to the number of windings: one-, two- and multi-winding.
An example of single-winding transformers are autotransformers, in which, in addition to electromagnetic coupling, there is also a direct electrical connection between the primary and secondary windings. Autotransformers are not galvanically isolated. As already noted, in the autotransformer, the transmission of electrical energy is carried out in a combined way.
Fixed-ratio double-winding transformers have two windings (primary and secondary), and multi-winding transformers have multiple secondary windings. All windings of double-winding and multi-winding transformers are not electrically connected to each other.
The design and technological features of the classification of transformers are based on the design of the magnetic circuit or core, which determine the type of transformer. The design of the transformer is determined by the design of the magnetic circuit, and the name of the magnetic circuit is reflected in the name of the transformer. The industry manufactures armored, rod, ring (toroidal) magnetic circuits and magnetic circuits of complex (special) configurations. Armored transformers are manufactured on magnetic circuits of types Ш, ШЛ, Б, О, Х, Кв. etc. All transformer windings are located on the middle rod. The presence of only one coil, more complete filling of the magnetic circuit window with a winding wire, partial protection of the coil with windings from mechanical damage and its good magnetic shielding distinguish armored transformers favorably from other types.
Magnetic cores and transformer cores make up a large group of products manufactured by the industry in the form of unified designs according to design documentation that meets the requirements of GOST. Various types and sizes of magnetic circuits and cores are given in the relevant sections of the handbook. For the manufacture of magnetic circuits and cores, magnetically soft and magnetically hard magnetic materials are used, which have high magnetic permeability in strong magnetic fields, low eddy current losses and magnetization reversal. Belonging to a particular class of material is determined by the magnetization curve and the parameters of the hysteresis loop.
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