The Transformer Usage and Choices

A transformer is a device that converts AC voltage (increases or decreases). A transformer consists of several windings (two or more) that are wound on a common ferromagnetic core. If the transformer consists of only one winding, then it is called an autotransformer. Modern current transformers are: rod, armor or toroidal. All three types of transformers have similar characteristics and reliability, but differ from each other in the manufacturing method. The use of the remanufactured transformer is essential here

• In rod-type transformers, the winding is wound on the core, and in rod-type transformers, the winding is included in the core. In the rod-type transformer, the windings are clearly visible, and only the lower and upper parts are visible from the core. The core of the armored transformer hides almost the entire winding. The windings of the rod-type transformer are located horizontally, while this arrangement in the armored transformer can be either vertical or horizontal.

Regardless of the type of transformer, it consists of these three functional parts: the magnetic system of the transformer (magnetic circuit), windings, as well as the cooling system.

Transformer Principle

In the transformer, it is customary to isolate the primary and secondary windings. Voltage is supplied to the primary winding, and from the secondary winding. The action of the transformer is based on the Faraday law (the law of electromagnetic induction): a time-varying magnetic flux through an area bounded by a circuit creates an electromotive force. The converse is also true: a changing electric current induces a changing magnetic field.

Transformer Modes

There are three modes of operation of the transformer: idle, short circuit mode, operating mode. The transformer is “idling” when the leads from the secondary windings are not connected anywhere. If the core of the transformer is made of soft magnetic material, then the open-circuit current indicates what losses in the transformer occur due to magnetization reversal of the core and eddy currents.

The Other Mode

In the short-circuit mode, the terminals of the secondary winding are short-circuited, and a small voltage is applied to the primary winding so that the short-circuit current is equal to the rated current of the transformer. The value of losses (power) can be calculated if the voltage in the secondary winding is multiplied by the short circuit current. This mode of the transformer finds its technical application in measuring transformers.

If the load is connected to the secondary winding, then a current appears in it, inducing a magnetic flux directed opposite to the magnetic flux in the primary winding. Now, in the primary winding, the EMF of the power source and the EMF of the power induction are not equal, therefore, the current in the primary winding increases until the magnetic flux reaches the previous value.

For a transformer in active load mode, the equality is true:

U_2 / U_1 = N_2 / N_1 , where U2, U1 are the instantaneous voltage at the ends of the secondary and primary windings, and N1, N2 is the number of turns in the primary and secondary winding. If U2> U1, the transformer is called a step-up, otherwise we have a step-down transformer. It is customary to characterize any transformer by the number k, where k is the transformation coefficient.