Sources of Electrical Power

The basic purpose of a source is to supply power to a load. A source is therefore, connected to the load as shown in Figure below. The source may supply either dc (direct current) or ac (alternating current). The terminology dc as employed here stands for any quantity that is steady, unchanging and unidirectional in nature. Similarly, the terminology ac stands to specify any quantity which is alternating in nature, I.e., its magnitude is changing in both the positive and negative directions with time. Unless stated otherwise, the term ac represents sinusoidal variations.

Power Sources

There are some sources of power

For dc power there are batteries, dc generators and rectification-type dc supply.

Similarly for ac power there are alternators and oscillators or signal generators.

Batteries (cell)

The battery is the most common dc voltage source. The term battery is derived from the expression “battery of cells”.

A battery consists of a series or parallel combination of two or more similar cells.

A cell is the fundamental source of electrical energy. Cells can be divided into primary and secondary types.

The secondary cell is rechargeable, whereas the primary is not.

The battery used in a car is of secondary type, since it can be recharged. But the cell used in a torch are of primary type, as they cannot be recharged.

Cells* and batteries produced electrical power at the expense of the chemical energy, and all have the same basic construction. Each has two electrodes (one positive and other negative) which are immersed in an electrolyte. Electrolytes are chemical change compounds. When dissolved in a solution, the decompose into positive and negative ions. These ions carry the charge inside the cell from one electrode to the other.

Note – An exception is the solar cell, which converts light energy into electrical energy.

Generators

The dc generator is quite different from the batteries. It has a rotating shaft. When this shaft is rotated at the specific speed by some external agency (such as steam turbine or water turbine), a voltage of rated value appears across its terminal. Generally a generator is capable of giving higher voltage and power than a battery.

Rectification-type Supply

The dc supply most frequently used in an electronics laboratory is of this type. It contains a rectifier which converts ac voltage to the dc voltage. The adaptor of mobile, laptop also is this type power source.

Alternators

The alternator is quite similar to the dc generator in terms of construction and working. When its shaft is rotated, an alternating current voltage is generated across its terminals. This type of alternators are used in most electric power stations.

Oscillators or Signal Generators

An oscillator is the equipment which supplies ac voltages. This voltage is used as a signal to test the working of different electronic circuits. The frequency of the ac signal supplied by this instrument can be varied.

Some signal generators are capable of giving other type of waveforms, such as triangular, square, etc., in addition to the ac wave.

Sources of Electrical Power