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Transformer working principle and detailed introduction
【 Source: 】 【 Release time:2012-09-19 】 【 Typeface:Large In Small
To know the working principle of the transformer, the first to know its function, it is nothing more than the voltage transformation; impedance transformation; isolation; regulator ( saturated magnetic transformer ), the iron core transformer is used the general shape of E type and C type iron core. It is simple in principle but according to different using occasions ( for different purposes) transformer winding process will be different requirements. Power transformers are widely used. Transformer can be classified according to purpose: distribution transformers, power transformers, transformer, combined transformer, dry type transformer, single-phase transformer, rectifier transformers, electric furnace transformer, reactor, transformer, lightning protection and variable resistance

To know the working principle of the transformer, the first to know its function, it is nothing more than the voltage transformation; impedance transformation; isolation; regulator ( saturated magnetic transformer ), the iron core transformer is used the general shape of E type and C type iron core. It is simple in principle but according to different using occasions ( for different purposes) transformer winding process will be different requirements. Power transformers are widely used.

Transformer can be classified according to purpose:

Distribution transformers, power transformers, transformer, combined transformer, dry type transformer, single-phase transformer, transformer, rectifier transformers, reactors, impedance transformer, lightning protection transformer, box type transformer, box type transformer.

The most basic type of transformer, including the two coils around a wire, and each other with the inductive method called together. When an AC current ( with a known frequency ) tend to be one of the coils, coil will be induced in another group with the same frequency of the AC voltage, and the sensed voltage depends on the two coils and the magnetic exchange coupling chain level.

Generally refers to the connection of AC power to the coil is called a " coil " ( Primary coil ); and the cross in the coil voltage called the primary voltage. ". At the time of the two coil induced voltage may be greater or less than a voltage, is composed of a coil and the two coil question turns ratio of the decision. Therefore, transformer step-up and step-down transformer is divided into two.

Most transformers have a fixed iron core, which is wound on one and two coil. Iron based magnetic materials with high conductivity, most of the magnetic flux confined to the core, therefore, two sets of coils to get a high degree of magnetic coupling. In some transformers, coils and between the two cores tightly integrated, and its first and two voltage ratio is almost two of the number of turns of the coil is the same as. Therefore, the transformer turns ratio, and can be used as step-down transformer step-up or reference index. Due to the function of the boost and buck, making the transformer has become an important adjunct of modern power system, enhance the long-distance transmission of electricity transmission voltage makes more economical, as step-down transformer, it makes more diversified power utilization, we can say, if no transformer, then the modern industry can not achieve real current development status.

[1] electronic transformer in addition to smaller volume, in power transformers and electronic transformers two, and there was no clear line of demarcation. General 60Hz power network power are very large, it may be covered with a Delta region as the large capacity. Electronic device power limit, usually confined to the rectification, amplification, and other system components, some of which part belongs to the magnifying power, but as is the case with the electric power system power capacity compared to, it still belongs to the scope of small power.

A variety of electronic equipment used to the transformer, the reason is: to provide various voltage classes to ensure normal system operation; providing system in different potential operation part is electrically isolated; the alternating current with high impedance, but the DC is providing a low impedance; in different electrical potential, maintain or modified waveform and frequency response. " Impedance " one of important concepts, which is one of its electronic properties, it designed a device, whereby when the circuit impedance lines from a class to another class, which is to use a device - transformer.

Transformers - the principle of electromagnetic induction, from one circuit to another circuit for transmitting electrical energy or signals to an electric power transmission is an important element or as a signal transmission

Transformers 1 - static electromagnetic device

The transformer can be an alternating current voltage can be transformed into the frequency of the alternating current voltage to another

The main constituent of the transformer is an iron core and sleeve in the core of the two windings.

The principle of transformer

The coil is connected with a power supply, receiving power, called a winding

The coil is connected to the load, out of AC power, known as the two primary winding

A two winding winding

Voltage phase U1 voltage phasor U2

Current phase I1 current phasor I2

Electromotive force EMF phasor phasor E1 E2

N1 N2 turns turns

At the same time chain once, two winding magnetic flux phasor is φ m, the flux is called main magnetic flux

Supplementary transformer working principle:

The transformer is transform AC voltage, current and impedance of the device, when the primary coil electric current, the iron core ( or core) can generate an alternating magnetic flux, so that the secondary coil induced voltage ( or current ).

Transformer composed of an iron core ( or core) and the coil, coil having two or more than two winding, which is connected to the power of the primary coil winding is called, the remainder is called the secondary coil windings.

2 the ideal transformer

At once, two winding resistance and iron loss,

Meanwhile the coupling coefficient K=1 of transformers called ideal transformer

Description of ideal transformer electromotive force balance equation

E1 ( T ) = -N1 D φ/dt

E2 ( T ) = -N2 D φ/dt

If a, two winding voltage, electric potential of instantaneous values according to sine regularity,

There are

Without core loss, according to the principle of conservation of energy available

Thus, a two winding voltage and current effective value relationship

Let K=N1/N2, called the turn ratio ( also known as the voltage ratio ), then the

Two. The transformer structure

1 core

Transformer core is main magnetic circuit. Usually made with high Si content, thickness are respectively 0.35 mm.3mm.27 mm,

Surface coated with insulating paint for hot or cold rolled silicon steel sheet piled up

Core is divided into a core column and horizontal slice of two parts, a winding iron core column; transverse slice is a closed magnetic circuit with

The basic structure of central core and shell type two

2 winding

Transformer winding is part of the circuit,

It is with double wire insulated wire or enamelled round wire wound into

Transformer is the basic principle of the electromagnetic induction principle, the single phase double winding transformer as an example to illustrate the basic principle: when the primary side winding voltage plus the code 1, currentÍ 1, in the core of it generates alternating magnetic flux 1, these flux called main flux, in which role, both windings Induction EMFÉ1 respectively,É2, EMF formula is: E=4.44fNØM

Type : E-- induction voltage effective value

F-- frequency

N-- turns

Øm-- main flux maximum

As a result of the two winding and a secondary winding turns, EMF E1 and E2 have different sizes, when omitting resistance compressive drop, voltage code 1 and code 2 size is also different.

When the two sides of the transformer no-load, one side only the main magnetic flux flowing through the current (Í 0 ), the current known as the excitation current. When the two side load flow through the load currentÍ2, also in the core of magnetic flux, tries hard to change the main magnetic flux, but a constant voltage, main magnetic flux is constant, one side will flow through the two part of the current, a part as the excitation currentÍ 0, one part is used to balance theÍ 2, so this part of the current withÍ 2 changes. When the current multiplied by the number of turns, is the magnetic potential.

The role of balance is essentially the magnetic potential balance effect, transformer is through the magnetic potential balance effect achieved by the one or two side of the energy transfer.

Transformer technical parameters for different types of transformer has the corresponding technical requirements, can be the corresponding technical parameters. Such as power transformer main technical parameters are: the rated power, rated voltage, rated frequency and voltage ratio, working temperature rating, temperature, voltage regulation rate, insulation and moisture resistant, for general frequency the main technical parameters of transformer are: the transformation ratio, frequency characteristics, nonlinear distortion, magnetic shielding and electrostatic shielding, efficiency and so on.

A. voltage ratio:

Transformers two groups of coil number were N1 and N2, N1 for N2 primary, secondary. The primary coil and an AC voltage in the secondary coil ends, will produce induced electromotive force. When N2>N1, the induction electromotive force than primary the voltage applied is even higher, this transformer step-up transformer: called when the N2< N1, the induction electromotive force is lower than the primary voltage of the transformer, known as descending transformer primary secondary voltage and coil number of the following relations:

U1/U2=N1/N2

Type N called voltage ratio ( the ratio of the number of laps ). When n<1, N1>N2, U1>U2, the transformer is a step-down transformer step-up transformer. And vice versa.

Another current ratio I1/I2=N2/N1

Electric power P1=P2

Note that the above equation in the ideal transformer coil set up only one side

When there is a two pair of coils P1=P2+P3, U1/N1=U2/N2=U3/N3, current must use power relationship to ask, have more than one when this analogy

B. efficiency of transformer:

At rated power, the power output of the transformer and the ratio of input power, called the efficiency of transformer, i.e.

ETA = ( P2 / P1 ) x100%

Type ofη is the efficiency of transformer; P1 for power input, P2 output power.

When the power output of the transformer P2 is equal to the input power of P1, efficiency ηis equal to 100%, the transformer will not produce any loss. But actually this transformer. Transformer is not when transmitting electric energy to cause a loss, this loss is mainly copper loss and iron loss.

Copper loss refers to the transformer coil resistance caused by the loss. When the current through the coil resistance heating, a part of electric energy is converted to heat and loss due to coil in general by the insulation copper wire wound together, so called the copper loss.

Transformers iron loss includes two aspects. One is the hysteresis loss, when the AC current through the transformer, the transformer silicon steel sheet magnetic lines of the direction and magnitude of change, make the silicon steel sheet in internal molecular friction, heat release, thus the loss of a part of the electric power, which is the hysteresis loss. Another is eddy current loss, when the transformer works . Core of magnetic field lines pass through, with flux lines perpendicular to the plane will produce the induced current, due to the current self into a closed loop circulation is formed, and a spiral, so called vortex vortex in the iron heating, energy consumption, this loss is called eddy current loss.

Efficiency of transformer and transformer power level has the close relation, usually higher power, loss and the output power is smaller, the efficiency is higher. Conversely, the power of small, efficiency is low.

C transformer power

Transformer iron core magnetic flux and voltage related. In the current excitation current is not with load increasing. Although increasing the load of not saturated iron core, the coil resistance loss increased, exceeding the rated capacity due to heat generated by the coil can not be timely released, coil will damage, if you use the coil is composed of superconducting materials, the increase of current does not cause fever, but inside the transformer and magnetic flux leakage caused by impedance, but the current increases, the output voltage will drop, the stronger current, output voltage is lower, so the transformer output power can not be unlimited. If you say no, transformer impedance, so when the transformer current will produce a particularly large electric power, make it very easy for transformer coil damaged, although you have a power transformer but not infinite. Can say, with the superconducting material and core material development, the same volume or weight of the transformer output will increase, but not infinite!

How to distinguish transformer parameter

Power transformers rated power, voltage, current and other parameters of the marker, a loss or disappear. Some commercial transformer does not mark any parameters. This is very inconvenient to use. Following the presentation of unmarked power transformer parameter distinguishing method. This method also has reference value to buy power transformer.

One, identifying power transformer

1 from the shape recognition of common power transformer iron core with E type and C type two. E type iron core transformer is a shell structure ( iron core coil wrapped ), using D41, D42 high quality silicon steel sheet as the core, is widely used. C type iron core transformer for cold rolled silicon steel strip as the core, magnetic leakage of small, small volume, a core structure ( coils wrapped core).

2 from the winding leading-out terminal number identifying power transformer commonly has two windings, whereby a primary and a secondary winding, thus having four terminals. Some power transformer in order to prevent noise and other interference, initial, often with a secondary winding shielding layer, the shielding layer is a ground terminal. Therefore, power transformer terminal is at least 4.

3 from the silicon steel sheet laminated identification by means of E type power transformer silicon steel sheet is * insert, E film and I film did not leave air gap, the core dovetail. Audio input, output transformer of E film and I film keeps a certain air gap, which is the difference between the power supply and power transformer audio transformer in the most intuitive method. As far as the C shape transformer, is generally a power transformer.

Two, estimation of power

Power transformer transmission power, depend on the core material and cross-sectional area. The cross-sectional area, regardless of E shaped shell type structure, or E shaped core structure ( including C shaped structure ), is refers to the winding of the package that stem cross-sectional area ( rectangle ). The measured core area of S, then press P = S2 / 1.5 estimate of power P. Type S unit is cm2.

For example: the measured a power transformer core area of S = 7cm2, estimate its power, P = S2 / 1.5 = 72 / 1.5 = 33W occurs from a variety of errors, the actual nominal power is 30W.

In three, the winding voltage measurement

To make an unmarked power transformer using, find the primary winding, and the distinction between the secondary winding of the output voltage is the most basic task. Now with an example of judging method.

Example: given a power transformer, a total of 10 terminals.

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