Energy Losses a Transformer

Only in an ideal transformer the power output is equal to the input power. In actual transformers the output power is always less than the input power because of unavoidable energy losses. These losses are:

(1)    Copper loss. There is loss of power due to Joule heating in the primary and secondary windings.
(2)    Iron Loss. This is due to the eddy currents being produced in the core of the transformation. This is minimized by using a laminated iron core.
(3)    Hysteresis loss. During each cycle of A.C., the core is taken through a complete cycle of magnetization. The energy expended in this process is finally converted into heat and is, therefore, wasted. This is minimized by using silicon-iron for preparing the core. The hysteresis loop for this material is very narrow.
(4)    Leakage of magnetic flux. Due to leakage, all the magnetic flux produced in the core by the primary is not linked with the secondary. They may pass through air. The loss due to this cause is minimized by using a shell type of core.

Uses of Transformers

(1)    The step-up and step-down transformers are used in a.c. electrical power distribution for the domestic and industrial purposes.
(2)    The audio-frequency transformers are used in radio receivers, radio-telephony, radio-telegraphy and in televisions.
(3)    The radio frequency transformers are used in radio-communications at frequencies of the order of mega-cycles.
(4)    The impedance transformers are used for matching the impedance between two circuits in radio communication.
(5)    The constant current and constant voltage transformer are designed to give constant output current and voltage respectively even when the input voltage varies considerably.

Uses of transformer in long distance power transmission:

Advantages of high voltage in transmission:

Suppose we want to transmit a give power (VI) = 44,000 W from a generating station to a distant city. It can be transmitted (i) at a voltage of 220V and an current of 220A or (ii) at a voltage of 22000 V and a current of 2 A. Following are the losses which occur in the transmission:

(a)    When the current is flowing through the line wires, the energy (I2Rt) will be lost as heat. This would be greater in the first case.
(b)    The voltage drop along the line wire is equal to (RI). Again this loss is great in the first case.
(c)    The line wires, which are to carry the high current, will have to be made thick. Such wires will be expensive.

Thus from the above example it is clear that from the point of view of both efficiency and economy, the power must be transmitted at high voltage and at low current.

If we make use of D.C., transformation of voltage is not possible. If A.C. is used, voltage can be stepped up or stepped down by using transformers. Hence A.C. transmission is preferred to D.C. transmission.

The A.C. voltage generated at the power stations is stepped up by means of a transformer to 66,000 V and is transmitted to various sub-stations at the consumer end. The sub-stations employ suitable transformers to step down the voltage to 440 for supplying to the industry and to 220 volt for domestic use.