5. Are the following sentences True or False?

1. The transformer consists of three coils placed close to each other.

2. Energy would be transferred by means of magnetic field from coil 1 to coil 2.

3. The coils are wound on the on a laminated iron core are not isolated from each other.

4. On small transformer, natural cooling is satisfactory.

5. The surface area of the tank cannot be increased.

6. In electric power systems, transformers are used to transfer electric energy.

7. The level of 20 kv is the most economical for distribution of smaller quantities over long distances.

6. Make up the plan to the text and retell it.

7. Give the summary of the text.

A wide variety of transformers designs are used for different applications, though they share several common features. Important common transformer types include:

AUTOTRANSFORMER

An autotransformer has only a single winding with two end terminals, plus a third at an intermediate tap point. The primary voltage is applied across two of the terminals, and the secondary voltage taken from one of these and the third terminal. The primary and secondary circuits therefore have a number of winding turns in common.

POLYPHASE TRANSFORMERS

For three-phase supplies a bank of three individual single-phase transformers can be used, or all three phases can be incorporated as a single three-phase transformer. In this case, the magnetic circuits are connected together, the core thus containing a three-phase flow of flux. A number of winding configurations are possible, giving rise to different attributes and phase shifts. One particular polyphase configuration is the zigzag transformer, used for grounding and in the suppression of harmonic currents.

AUDIO TRANSFORMER

Audio transformers are those specifically designed for the use in audio circuits. They can be used to block radio frequency interference or the DC component of an audio signal, to split or combine audio signals, or to provide impedance matching between high and low impedance circuits, such as between a high impedance tube amplifier output and a low impedance loudspeaker or between a high impedance instrument and the low impedance input of a mixing console.

Unit 17 (part 2). Transformers

1. Words to remember.

primary winding – первичная обмотка

secondary winding – вторичная обмотка

coupling –связь, соединение

step-up transformer – повышающий трансформатор

step-down transformer – понижающий трансформатор

wound – наматывать

transfer – передавать

turn – виток

2. Read the text. How the transformer works

Fundamentally a transformer consists of two or more windings placed on a common iron core. All transformers have a primary winding and one or more secondary windings. The core of a transformer is made of laminated iron and links the coils of insulated wire that are wound around it. There is no electrical connection between the primary and the secondary; the coupling between them is through magnetic fields. This is why transformers are sometimes used for no other purpose than to isolate one circuit from another electrically. When this is done, the transformer used for this purpose is called an isolating transformer.

The winding that is connected to the source of power is called the primary, and the winding connected to the load is called the secondary. The essential function of the conventional power transformer is to transfer power from the primary to the secondary with a minimum of losses. In the process of transferring energy from primary to secondary, the voltage delivered to the load may be made higher or lower than the primary voltage. The load may be some household appliance, an industrial electrical device, or even another transformer.

Transformers are found to be as close to 100 percent efficient as possible. That is, all the power in the primary should be transferred to the secondary. This is done by selecting the proper core material, winding the primary and secondary close to each other, and a number of other careful designs.

Thus, assuming 100 percent transformer efficiency, it can then be assumed that the relationship between the primary and secondary voltages will be the same as the relationship between their turns. If the secondary has more turns than the primary it can be said that the transformer is operating as a step-up transformer; if the secondary has fewer turns than the primary we say that the transformer is operating as a step-down transformer.