TRANSFORMERS

The transformer is a device for changing the electric current from one voltage to another. As a matter of fact, it is used for increasing or decreasing voltage. A simple transformer is a kind of induction coil. It is well-known that in its usual form it has no moving parts. On the whole, it requires very little maintenance provided it is not misused and is not damaged by lightning. We may say that the principle parts of a transformer are two windings, that is coils, and an iron core. They call the coil which is supplied with current the “primary winding”, or just “ primary”, for short. The winding from which they take the current is referred to as the “secondary winding” or “secondary” , for short. It is not new to you that the former is connected to the source of supply, the latter being connected to the load. When the number of turns of wire on the secondary is the same as the number on the primary, the secondary voltage is the same primary, and we get what is called a “one-to-one” transformer. In case, however, the number of turns on the secondary winding is greater than the input voltage and the transformer is called a step-up transformer. On the other hand, the secondary turns being fewer in number than the primary, the transformer is known as a step-down transformer.

O. Translate the given sentences, pick out all electrical terms and learn them.

1. In Russia, the use of transformers for supplying current to arc lamps was suggested for the

first time in 1876 by Yablochkov, the inventor of the arc lamp.

2. A good deal of work on transformer design was done by another Russian scientist,

I.F.Usaguin, who suggested the transformer as a source of power for loads other arc

lamps.

3. A transformer is a device which depends for its action on mutual induction and which

serves to convert electric power in an A-C system at one voltage or current into electric

power at some other voltage or current without change in the frequency.

4. An elementary transformer consists of a steel core which carries two windings insulated

from both the core and each other.

5. The winding connected to the supply circuit is called the primary and the winding

connected to the receiver circuit is the secondary.

6. The alternating current traversing the primary sets up an alternating magnetic field which

interlinks the secondary and induces an EMF in it.

7. Since the magnetic field is an alternating field, the induced EMF in the secondary is

likewise alternating at a frequency equals to that of the current in the primary.

8. The magnitudes of the two EMFs depend on the frequency of the magnetizing current, the

number of turns in the windings, and the magnetic flux in the core.

9. The difference between the EMFs and the terminal voltages is so small that the terminal

voltages of the primary and secondary are practically proportional to the number of turns.

10. The difference between the EMF and the terminal voltage of the primary is especially small,

when the secondary is open and the current in it is zero.

11. The current flowing in the primary when the secondary is open-circuited is very small

( 3.5 to 10 per cent of the load current); and is known as the exciting ( or magnetizing,

or no-load) current of a transformer. Also, the secondary terminal voltage is equal to the

EMF induced in it.

12. In Russian terminology the ratio of two voltages is referred to as the transformation ratio, it is

designated by the letter k.

13 .When the transformers reduce the applied voltage, they are called step-up transformers .Their

transformation ratio is greater than unity.

14. When the transformers raise the applied voltage, they are called step-down transformers.

Their ratio is transformation ratio is less than unity.

15. When the primary of a transformer is connected to an A-C source and the secondary is open,

the transformer is said to be at no-load ( there is no load on the secondary).

Р. Translate the following sentences from Russian into English, using new words and

words combinations.

Q. Answer the following questions to the exercise N.

1. What is a transformer?

2. What is a transformer used for?

3. Are there any moving parts in a transformer?

4. What are the principal parts of a transformer?

5. How many windings are there in a transformer?

6. What winding is connected to a load?

7. What is the purpose of a step-down transformer?

8. What is known as a step-up transformer?

Date: 2014-12-28; view: 1785