Switching Cubical:
Switching cubical provides facility for floating any one or more batteries charging any one battery at a time and supervisory alarm for all the associated units. The switching cubical also incorporates the auto paralleling panel which contains the circuitry for sequential switching i.e. for switching ON and OFF automatically to suit exchange load, one or more float rectifiers whose output are in parallel. All the components are mounted on a steel frame with screwed panel at the sides. Float rectifier and battery chargers are installed on both sides of switching cubical.
There are two sets of battery having 24 cells each to provide 48V DC supply to exchange equipment. These battery cells are connected in parallel with float rectifier. The input to float rectifier is 30V AC from AC mains. In case when power from the AAC mains fails the switching cubical switch exchange load to battery set. Also when the power from AC mains recovers switching cubical switch the exchange load to float rectifier and connect the battery-to-battery charger for charging. The switches are so interlocked the exception for battery on charge other batteries remain connecting across the exchange during or after any switching operation. Thus switching cubical plays a vital role in power plant.
Battery Charger:
The battery charger is a part of power plant is an exchange and provides initial rectifier and boost charging for the batteries. The lead acid cell battery can be charged from 1.8 Volts per cell to 2.7 Volts per cell.
The equipment consist of: -
- Three phase step down main transformer (TRI) with links for main variation and tap changing switches.
- Ballast chokes (L1 to L3).
- Three phase full wave bridge rectifier.
Working:
The function of battery charger is to charge the battery sets of 24 cells each. Rotary switches SW1 to SW3 designed as coarse control medium control and fine control respectively control the DC output voltage of charger. The three switches in combination provide 63 steps control over a wide range. The switches are connected to top on TRI. This facilities the voltage control for 24 cells as well as when battery charger replaces float in emergency. The ballast chokes provided on the
Secondary side of TRI keeps the charging current with in + - 25% of its set value in spite of mains fluctuation of +\- 50%. Sassing the chokes when charger replaces provides for links LK4 to LK6 float rectifier under emergency link LK7 is provided to insolate battery charger from battery during servicing.
Use Of Battery Charger As A Float Rectifier:
Under emergency condition it may sometimes be found necessary to use the battery charger as a float rectifier. It is obvious that when the battery charger is required to supply the exchange load , its DC output should be ripple free This is possible by making use of the filter is to act as a stand by.
This input terminal of the filter unit is provided with a link LK1 (In float rectifier) so that in case of float rectifier failure. Its filter unit can be connected to battery charger. In such as event change link LK4 form A.B. to B.C. position.