What is the working Principle of a Conventional Battery?
One of the primary requirements of any telephone system is that service shall be available to the subscribers at all times. The electrical energy required for signalling, switching, speech transmission etc. in telephone exchanges is derived either directly or indirectly from the public electricity system. In order to provide uninterrupted service, the exchange power supply system is designed to give continuous energy to the system. So provision is also made for an alternate source of supply in the event of mains failure. This emergency energy is derived from
- Batteries of secondary cells.
- A combination of battery and prime mover generator sets.
The secondary cells in general use in BSNL are of lead-acid type. Secondary cells are electrolytic cells for the generation of electric energy. These cells can be restored to its original condition after they are discharged. This restoration is done by passing a current in a direction opposite to the flow of current in the cell during the discharge.
General requirements of a good cell
- There must be no local action, i.e., little or no wastage of the materials when the cell is not delivering current.
- The e.m.f of the cell must be of such magnitude to enable the cell to deliver a reasonable amount of energy with moderate current.
- Frequent replacements of materials must not be necessary, and such materials must not be expensive.
- The internal resistance must be small.
There are three types of storage (secondary) cells in use. They are (1) lead-lead-acid type (2) Nickel-iron-alkaline and (3) Nickel-Cadmium alkaline type. They are commonly known as lead-acid type cell. These cells have electrodes of lead immersed in an electrolyte of dilute sulphuric acid in a suitable container.