Power transformers. Theoretical provisions. Operating principle. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Power transformers. Theoretical provisions. Operating principle. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Electrician's Handbook

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transformer An electrical device is called, in which the transfer of voltage from one winding to another occurs through electromagnetic induction.

It consists of a closed iron core, on which two (sometimes more) coils with wire windings are put on. One of the windings, called the primary, is connected to an AC voltage source. The second winding, to which the "load" is connected, i.e. devices and devices that consume electricity, is called secondary.

Transformer Action based on the phenomenon of electromagnetic induction. When an alternating current passes through the primary winding, an alternating magnetic flux appears in the iron core, which excites the induction EMF in each winding.

Instantaneous value of induction emf ε in any turn of the primary or secondary winding according to Faraday's law is determined by the formula

If that

where - EMF amplitude in one turn.

In the primary winding having n₁ turns, total induction emf is

In the secondary winding, the total emf is where n₂ is the number of turns of this winding.

It follows that

(1)

Sum of voltage u₁applied to the primary winding, and EMF should be equal to the voltage drop in the primary winding:

where R₁- active winding resistance, ai₁ is the current in it.

This equation follows directly from the general equation. Usually the active resistance of the winding is small and the term i₁R₁ can be neglected. That's why

(2)

When the secondary winding of the transformer is open, the current does not flow in it, and the relation takes place

(3)

Since the instantaneous values of the EMF e₁ and e₂ change in phase, then their ratio in formula (1) can be replaced by the ratio of effective values E₁ and E₂ these EMF or, taking into account equalities (2) and (3), the ratio of the effective voltage values U₁ and U₂:

(4)

value k called transformation ratio. If k>1 then the transformer is loweringAt k< 1 - raising.

When the circuit of the secondary winding is closed, current flows in it. Then the relation

is no longer satisfied exactly and, accordingly, the relationship between U₁ and U₂ becomes more complex than in equation (4).

According to the law of conservation of energy, the power in the primary circuit must be equal to the power in the secondary circuit:

(5)

where and I₁, The₂- effective current strength values in the primary and secondary windings. Hence it follows that

(6)

Hack and predictor Aviator. It follows from the formula that by increasing the voltage several times with the help of a transformer, we reduce the current by the same amount, and vice versa.

Due to the inevitable energy losses for heat generation in the windings and the iron core, equations (5) and (6) are approximately fulfilled. However, in modern high-power transformers, the total losses do not exceed 2-3%.

Author: Koryakin-Chernyak S.L.

See other articles Section Electrician's Handbook.

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