Transformer Principle Problem 20, Transformer Principle Problem

Transformer ABCDyāyāygi is a device that uses the principle of electromagnetic induction to change the alternating voltage, and the main components are the primary coil, the secondary coil and the core (magnetic core). In electrical equipment and wireless circuits, it is often used for voltage lifting, impedance matching, safety isolation, etc. The main functions of the transformer are:

voltage conversion; Current conversion, impedance conversion; Isolation; voltage regulation (magnetic saturation transformer); autotransformers; High-voltage transformers (dry-type and oil-immersed), etc., the commonly used core shapes of transformers generally include E type and C type core, XED type, ED type CD type.

Transformers can be divided into distribution transformers, power transformers, fully sealed transformers, combined transformers, dry-type transformers, single-phase transformers, electric furnace transformers, rectifier transformers, reactors, anti-interference transformers, lightning protection transformers, box-type transformers, test transformers, corner transformers, high-current transformers, and excitation transformers.

In its most basic form, a transformer consists of two sets of coils wound with wires wound and inductively weighed together with each other. When an alternating current (with a known frequency) flows through one of the coils, an alternating voltage of the same frequency is induced in the other coil, and the magnitude of the induced voltage depends on the degree of coupling and cross-linking of 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, which is determined by the ratio of turns between the primary coil and the secondary coil.

Therefore, transformers are divided into two types: step-up and step-down transformers.

Most transformers have a fixed core with primary and secondary coils wound around them. Due to the high permeability of iron, most of the magnetic flux is confined to the core, so a fairly high degree of magnetic coupling can be obtained between the two sets of coils. In some transformers, the coil and the core are tightly bonded and the ratio of the primary and secondary voltages is almost the same as the ratio of the number of turns of the coil.

Therefore, the turn-to-turn ratio of the transformer can generally be used as a reference index for the step-up or step-down of the transformer. Due to the function of step-up and step-down, the transformer has become one of the important appendages of the modern power system, and the transmission voltage is increased to make the long-distance transmission of power more economical, as for the step-down transformer, it makes the power application more diversified, so to speak, without the transformer, the modern industry can not achieve the current situation of development.

In addition to the small size of electronic transformers, there is no clear dividing line between power transformers and electronic transformers. In general, the power supply for a 50Hz power network is very large, and it may cover the capacity of half a continent. The power limit of an electronic device is usually limited by the ability of rectification, amplification, and other components of the system, some of which are amplified power, but when compared with the power generation capacity of the power system, it still falls under the scope of small power.

Electricity generates magnetism, magnetism generates electricity, hehe.

Hehe. The magnetic field of the core passes through the core and transmits energy from the primary coil to the secondary coil.

The secondary coil is equivalent to cutting magnetic field lines, and when a part of the closed circuit is lifted to cut magnetic field lines in a magnetic field, the conductor will induce an electric current.

Because the secondary coil is also wound around the core.

The iron core plays the role of magnetic conduction.

It has been explained many times.

When the primary side of the transformer applies the alternating voltage U1, and the current flowing through the primary winding is i1, the current will produce alternating magnetic flux in the iron core, so that the primary winding and the secondary winding have electromagnetic contact, according to the principle of electromagnetic induction, the alternating magnetic flux will induce electromotive force through these two windings, and its magnitude is proportional to the maximum value of the winding turns and the main magnetic flux, the voltage on the side with more winding turns is high, and the voltage on the side with fewer winding turns is low, when the secondary side of the transformer is open, that is, when the transformer is no-load, The voltage of the primary and secondary terminals is proportional to the number of turns of the primary and secondary windings, and the transformer plays the purpose of transforming the voltage.

When the secondary side of the transformer is connected to the load, under the action of electromotive force E2, there will be a secondary current through, and the electromotive force generated by the current will also act on the same iron core to play the role of reverse demagnetization, but because the main magnetic flux depends on the power supply voltage, and U1 basically remains unchanged, the primary winding current will automatically increase a component to produce the magnetokinetic potential F1 to offset the magnetokinetic potential F2 generated by the secondary winding current, under the action of the primary and secondary winding currents L1 and L2, The total magnetokinetic potential acting on the iron core (excluding the no-load current i0), f1+f2=0, since f1=i1n1, f2=i2n2, so i1n1+i2n2=0, it can be seen from the equation that i1 and i2 are in phase, so.

i1/i2=n2/n1=1/k

It can be seen from the formula that the primary and secondary current ratio and the primary and secondary voltage ratio are the reciprocal of each other, and the power of the primary and secondary windings of the transformer is basically unchanged, (because the loss of the transformer itself is relatively small compared with its transmission power), the size of the secondary winding current i2 depends on the needs of the load, so the size of the primary winding current i1 also depends on the needs of the load, and the transformer plays the role of power transfer.

This is a transformer that uses the magnetic saturation properties of the core to turn the input sine wave voltage into a narrow pulse-shaped output voltage. It can be used for ignition of burners, triggering of thyristors, etc. The pulse transformer structure is the original winding sleeve made of silicon steel with a larger cross-section.

u1/u2=k=2，u1=2u2。

i2/i1=k=2，i1=。

u2 i2=r2=100, so: u1 i1=(2 u1=400i1. According to KVL:

i1r1+u1=10v, so: 100i1+400i1=10, i1=.

The above calculations should have been calculated using the phasor method, but since the circuit is a pure resistive circuit, the effective values were used to calculate the calculations, and the results are not wrong.

u1=400i1=400×。

u2=u1/2=4v，i2=2i1=2×。

In the question, u=10v, so the answer c is correct.

The answer is c, you can convert the secondary resistance to the primary, and the square of the 100 ohm multiplication ratio is 400 ohms. Therefore, the primary total resistance is 500 ohms, the current is U 500 =, the secondary voltage is U * 400 500 2 = volts, the secondary current is like b d It is impossible at a glance, two closed circuits, there is a voltage and current can not be 0

You don't need to calculate to know that a is wrong, unless the conversion ratio is 1, the secondary resistance can be on a par with the primary resistor, and the voltage can be divided into one-half.

With the law of conservation of energy. The energy consumed by the secondary stage is provided by the pre-stage.

u1i1=u2²/100

When there is an electric current passing through the primary coil, the electric field is converted into a magnetic field, and the primary coil and the secondary coil are on the same magnetic ring, and the electric field is induced on the secondary coil to form a voltage.

If you don't understand the theory, just remember the correspondence between the turn ratio and the voltage ratio.

Generally, a transformer consists of two (or more) windings wound around a magnetically conducting material (core, magnetic ring, etc.). The input power supply is called the primary (primary side), and the transformer output is called the secondary (secondary side).

The transformer can only play the role of voltage conversion for the alternating current, and after adding the alternating current to the primary side, due to the continuous change of the polarity of the alternating current, a magnetic field with changing polarity is also generated on the iron core. The windings of the secondary side are in a changing magnetic field and therefore also induce a constantly changing positive and negative electromotive force. The voltage ratio of the primary and secondary sides is directly proportional to the number of turns of the coil.

When a sinusoidal alternating voltage U1 is applied to both ends of the primary coil, there is an alternating current i1 in the wire and an alternating flux 1 is generated, which follows the core through the primary and secondary coils to form a closed magnetic circuit. The mutual inductance potential U2 is induced in the secondary coil, and at the same time, 1 also induces a self-inductance e1 on the primary coil, and the direction of E1 is opposite to the direction of the applied voltage U1 and the amplitude is similar, thus limiting the size of i1. In order to maintain the existence of magnetic flux 1, there needs to be a certain amount of electrical energy consumption, and the transformer itself also has a certain loss, although the secondary is not connected to the load at this time, there is still a certain current in the primary coil, this current is called "no-load current".

If the secondary is connected to the load, the secondary coil will produce the current i2, and thus produce the direction of the magnetic flux 2, 2 is opposite to 1, plays the role of canceling each other, so that the total magnetic flux in the iron core is reduced, so that the primary self-inductance voltage e1 is reduced, and the result is that i1 increases, and it can be seen that the primary current has a close relationship with the secondary load. When the secondary load current increases, i1 increases, 1 also increases, and the increase in 1 exactly complements the part of the magnetic flux that is offset by 2 to keep the total magnetic flux in the core constant. If the loss of the transformer is not taken into account, it can be considered that the power consumed by the secondary load of an ideal transformer is the electrical power obtained from the primary power supply.

The transformer can change the secondary voltage by changing the number of turns of the secondary coil as needed, but not the allowable load consumption.

The primary coil is alternating current that becomes an alternating magnetic field, and the secondary coil cuts the alternating magnetic field to generate an electromotive force and generates an electric current when there is a loop.

Electromagnetism, magneto-electrification. The current flow of the primary coil through the coil causes the core to produce alternating magnetic flux, which in turn causes the secondary coil to produce current.

1. Come to the ideal transformer.

The transformer is the source that can be seen.

bai an impedance converter du.

The input impedance of an ideal transformer depends on the DAO output impedance, and the ratio of the input impedance to the output impedance is the square of the ratio of the number of primary turns to the number of secondary turns.

When the secondary is open, the secondary impedance is infinite, and the primary impedance is also infinite. At this point, the primary energizing does not burn out the transformer. On the contrary, when the secondary short circuit is performed, the secondary impedance is infinitesimal and the primary impedance is also infinitesimal and the transformer will be burned when the primary is energized.

2. The actual transformer is different from the ideal transformer, when the secondary is open, the primary coil needs to establish an excitation magnetic field, and there is a certain loss, therefore, the input will have current, but in general, when the secondary is open, the input impedance of the transformer is the largest, the current is the smallest, and it will not burn out or heat up.

The primary BAI of the transformer is equivalent to one inductor and one DU resistor in series, although the electrical resistance is very small, but the inductive reactance of DAO is very large.

Alternating current can.

The inductance of the coil has an obstructive effect on the alternating current, and this obstruction is called inductance.

The inductive reactance is represented by XL, the inductance is represented by L, and the frequency is represented by F, then the formula for calculating the inductive reactance is:

xl= 2πfl

It can be seen that the greater the inductance l and frequency f, the greater the inductive reactance.

Whereas, the current through the transformer primary = voltage divided by the inductive reactance.

The primary no-load access power supply, at this time, the primary coil inductive reactance is very large, only a small current, not a short circuit. Therefore, it will not heat up violently or burn.

Since an iron core is placed in the coil, the coil and the core become a load.

The primary coil is not a short circuit, the primary coil has inductive reactance.

The transformer primary coil is out of the white and the short circuit is in the du

DAO occurs when the core is saturated; What you are talking about is the primary no-load access to the power back source, if the answer is AC, it will generally not be short-circuited, the primary is inductive L, plus the frequency of the AC power supply f, the inductive reactance is 2 fl, the greater the frequency, the greater the inductive reactance, and it will not be short-circuited. If it is connected to the DC power supply, it is a short circuit (f=0), and the transformer is not allowed to be directly connected to the DC power supply.

After the primary coil is energized.

Come, it will be in the iron core.

The alternating magnetic flux is generated from within, and this alternating flux will be used as DU for the primary coil, so that the primary DAO coil induces an electromotive force, which is in the opposite direction to the input AC voltage, which prevents the current from entering, so as to form a balance: the alternating magnetic flux generated by the input current can prevent the increase of the input current, and the input current is the so-called "magnetizing current, that is, the primary "no-load current" and "no-load current" of the transformer The size depends on the magnetic flux strength of the transformer core and the number of primary coils.

In the case of a Croatian named Nikola Tesla at the Edison Institute, he reasoned that if the primary coil was constantly turned on and off, so that it would flow continuously, wouldn't the secondary coil be able to continuously induce current? Due to the instantaneous switching of electric current, people do not notice the flickering of electric lights. This electric current, which changes in size and direction, is called alternating current.

Tesla found that this kind of hungry Xinzi device can increase or decrease the voltage of the tan, the more turns in the secondary coil, the higher the voltage induced, the turns ratio of the primary secondary coil is their voltage ratio, which is the basic principle of the transformer. Rotten.