Power Transformer
Power transformer is a kind of soft magnetic and electromagnetic component, the function is power transmission, voltage conversion and insulation isolation,
and has been widely used in power supply technology and power electronics technology.
According to the size of the transmission power, the power transformer can be divided into several grades: more than 10kVA for high power,
10kVA ~ 0.5kVA for medium power, 0.5kVA ~ 25VA for small power, and below 25VA for micro power.
sort
The classification of commonly used power transformers can be summarized as follows:
1, according to the number of phases:
(1) Single-phase power transformer: used for single-phase load and three-phase power transformer group.
(2) Three-phase power transformer: used for the rise and fall voltage of three-phase systems.
2, according to the cooling method:
(1) Dry power transformers: rely on air convection for cooling, generally used for local lighting, electronic lines and other small capacity power transformers.
(2) Oil-immersed power transformer: relying on oil as a cooling medium, such as oil-immersed self-cooling, oil-immersed air cooling, oil-immersed
water cooling, forced oil circulation, etc.
3. Divided by use:
(1) Power transformer: used for power transmission and distribution system up and down voltage.
(2) Instrument transformers: such as voltage transformers, current transformers, for measuring instruments and relay protection devices.
(3) Test transformer: can produce high voltage, high voltage test for electrical equipment.
(4) Special transformers: such as electric furnace transformer, rectifier transformer, adjustment transformer, etc.
4, according to the winding form:
(1) Double-winding transformer: used to connect two voltage levels in the power system.
(2) Three-winding transformer: generally used in power system regional substations to connect three voltage levels.
(3) Autotransformer: used to connect power systems with different voltages. It can also be used as an ordinary boost or drop transformer.
5, according to the core form:
(1) Core transformer: power transformer for high voltage.
(2) Amorphous alloy transformer: amorphous alloy core transformer is a new type of magnetic conductive material, no-load current drops by about 80%,
is a distribution transformer with ideal energy saving effect, especially suitable for rural power grids and developing regions and other places with low load rate.
(3) Shell transformer: special transformer for high current, such as electric furnace transformer, welding transformer; Or for electronic instruments and
television, radio and other power transformers.
principle
1, the power transformer is the output and input share a group of coils of the special transformer, boost and buck with different taps to achieve, less than
the common coil part of the tap voltage is reduced, more than the common coil part of the tap voltage is increased.
2, in fact, the principle is the same as the ordinary transformer, but his original coil is its secondary coil. The general transformer is a original coil on the
left through electromagnetic induction, so that the secondary coil on the right generates voltage, and the autotransformer is its own influence.
3, the autotransformer is only one winding transformer, when used as a step-down transformer, a part of the winding is drawn as a secondary winding; When
used as a booster transformer, the applied voltage is only applied to a partial turn of the winding. Usually the part of the winding that belongs to the primary and
secondary at the same time is called the common winding, the rest of the autotransformer is called the series winding, the same capacity of the autotransformer
compared with the ordinary transformer, not only small size, but also high efficiency, and the larger the transformer capacity, the higher the voltage. This
advantage becomes more and more prominent. Therefore, with the development of power system, the improvement of voltage level and the increase of
transmission capacity, autotransformer has been widely used because of its large capacity, small loss and low cost.
Feature
The most basic type of a power transformer consists of two sets of coils wrapped with wires and connected to each other in an inductive manner. When an AC
current (with a given frequency) flows through one group of coils, an AC voltage of the same frequency will be induced in the other group of coils, and the
magnitude of the induced voltage depends on the degree of coupling and magnetic linkage between the two coils.
Generally, the coil connected to the AC power supply is called the Primary coil; The voltage across this coil is called the primary voltage. The induced voltage
in the secondary coil may be greater or less than the primary voltage, depending on the ratio of turns between the primary coil and the secondary coil. Therefore,
the power transformer is divided into two kinds of boost transformer and buck transformer. Most power transformers have a fixed core, which is wound with primary
and secondary coils. Due to the high permeability of iron, most of the magnetic flux is confined to the core, so the two sets of coils can thus achieve a fairly high
degree of magnetic coupling. In some transformers, the coil and the core are so tightly combined that the ratio of the primary to secondary voltage is almost
the same as the ratio of the turns of the coil. Therefore, the turn ratio of the transformer can generally be used as a reference index for transformer boost or
buck. Because of this boost and buck function, the transformer has become one of the important appendages of the modern power system, increasing the
transmission voltage makes the long-distance transmission of power more economical, as for the buck transformer, it makes the use of power more diversified,
we can say that without transformers, the industry could not achieve the current development.
In addition to the small size of the power transformer, there is no clear dividing line between the power transformer and the electronic transformer. The power
supply that normally provides a 60Hz power network is very large, it may cover half the continental area as large as the capacity. The power limitations of electronic
devices are usually limited by the ability of rectification, amplification, and other components of the system, some of which are amplifiers, but which are still in the
range of small power when compared to the generating capacity of the power system.
Transformers are commonly used in various electronic equipment, the reason is: to provide a variety of voltage levels to ensure the normal operation of the system;
Provide electrical isolation of the parts of the system operating at different potentials; Provides high impedance to AC current, but low impedance to DC; Maintain
or modify the waveform and frequency response at different potentials.
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