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Transformer Characteristic Parameters
Sep 30, 2017

The transformer is a device which USES the principle of electromagnetic induction to change the ac voltage. The main components are primary coils, secondary coils and core (cores). The main functions are: voltage transformation, current transformation, impedance transformation, isolation, stabilization (magnetic saturation transformer), etc. According to use can be divided into: power transformer and special transformer (electric furnace change, rectifier, power frequency transformer, voltage regulator, mining, audio transformers, intermediate frequency transformer, high frequency transformer, impact transformer, instrument transformer, electronic transformer, reactor, transformer, etc.). The circuit symbol is often used as the beginning of the number. Example: T01, T201, etc.

A transformer consists of an iron core (or a magnet) and a coil. The coil has two or more windings, of which the winding is called a primary coil and the rest is called a secondary coil. It can transform ac voltage, current and impedance. The simplest core transformer consists of an iron core made of a soft magnetic material and a coil consisting of two or more turns on the core

The purpose of the core is to strengthen the magnetic coupling between the two coils. In order to reduce the eddy current and magnetic hysteresis loss in the iron core, the core is formed by the laminated silicon steel sheet. There is no electrical connection between the two coils and the coil is made of insulated copper wire (or aluminum wire). One coil connection is called a primary coil (or coils), and another coil is called a secondary coil (or a secondary coil). The actual transformer is very complex, inevitably exist copper loss (resistance heating coil), fever (core) iron loss and magnetic flux leakage (such as air closed magnetic induction line), in order to simplify the discussion here only introduce the ideal transformer. Ideal transformer conditions are: ignoring the leakage flux, ignoring the resistance of the original and the coils, ignoring the loss of the core, and ignoring the no-load current (the current in the coils of the coil of the coils). For example, the power transformer is close to the ideal transformer in full load operation (the output rating of the secondary coil is rated).

A transformer is a stationary electrical appliance made from the principle of electromagnetic induction. When the coil of the transformer is connected to the ac power supply, the alternating magnetic flux is generated in the core, and the alternating magnetic flux is expressed in phi. Phi is the same in the original, in the coils, phi is also a harmonic function, and the table is phi equals phi phi, phi, phi, omega, omega t. According to Faraday electromagnetic induction law, the induction electromotive force in the original and secondary coil is e1= -n1d phi/dt, e2= -n2d phi/dt. The number of turns of N1, N2, and coils. Figure illustrates the U1 = - e1, U2 = e2 (primary coil quantities with the Angle of the 1, said secondary coil quantities by 2) Angle under standard, its complex RMS for U1 = - e1 = jN1 Φ omega, U2 = e2 = - jN2 Φ omega, for k = N1 / N2, said strain ratio of the transformer. The ratio of the effective value of the voltage of the transformer original and the coils is equal to the ratio of the number of turns, and the difference between the voltage of the original and the coils is PI.

Characteristic parameters

Working frequency

Transformer core loss and frequency relationship is very high, so it should be designed and used according to the frequency of use, which is called frequency of work.

Rated power

In the specified frequency and voltage, the transformer can work long term without exceeding the specified temperature rise output power.

Rated voltage

The voltage applied on the coil of a transformer shall not exceed the specified value in work.

Voltage than

The ratio between primary voltage and secondary voltage of transformer, the difference between the ratio of the no-load voltage and the load voltage ratio.

No-load current

When the transformer secondary opens, the primary still has a certain current, which is called the no-load current. The no-load current is composed of magnetizing current (which produces flux) and iron loss current (caused by core loss). For the 50Hz power transformer, the no-load current is basically the magnetic current.

No-load loss

The power loss of the transformer in primary test when the secondary opening of the transformer. The main loss is the core loss, and the second is the loss (copper loss) generated by the no-load current in the primary coil copper resistance, which is very small.


The percentage of secondary power P2 with primary power P1. The more power the transformer is rated, the more efficient it is.

Insulation resistance

The insulation between the coil and the core of the transformer is shown. The insulation resistance is related to the performance, temperature and humidity of the insulating materials used.

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