For uninterrupted power supply ( UPS ),the important component is a battery unit for UPS.The battery are used to store DC energy which is later used to supply a block of energy to a load,often in the form of a high current for a short time example to charge mechanism springs in switch gear,fire fighting system,emergency lighting, emergency instrumentation power for control panels and control devices and starter motors on engines generator.
Battery for UPS must in good condition and well maintain to ensure it can operating in full capacity when it needed.If the battery failure during interruption of power supply,it can cause serious damage and high cost for operation recovery.
Types of battery
Normally for industry used applications are invariable of two kinds of battery,It have a advantage and disadvantage depend on our application :
1) Lead-acid (Pb).
2) Nickel-cadmium (NiCd).
A battery consists of a number of cells connected in series. The series connection is necessary to create sufficient load voltage. Each cell has a low voltage which is peculiar to the type of cell and independent of the current and rating of the cell. The cell voltages are shown in Table 17.1.
How to recharge the batteries for UPS?
The maximum cell voltages during charging should not exceed 2.7 volts per cell for Pb cells and 1.85 volts per cell for NiCd cells.Suppose a nominal voltage of 110 DC is required then at least 54 Pb cells or 89 NiCd cells would be required.The size of a battery is defined as its ampere-hour capacity, since capacity is related to charge (Q) which equals current (I ) × time (T ).
If there is a total failure from the main supply then it will usually be necessary to maintain the continuous current for 4 hours so that the state of the plant will be known during the failure. During this time it would be expected that the main supply would be restored.
Hence the 4 hours can be used as the operating cycle of the battery in the event that the charger is unable to supply current.
For the battery storage and compartment it may be installed in several ways.Example it can install integral with the charger, in a separate cubicle or on open racks.
The choice usually depends upon the physical size of the complete battery.If we plan to used a large battery,it are more suited to an open rack installation.