in substation, control unit, SCADA unit we use the battery bank for operation of relay and circuit breaker.

 At the condition of supply failure our SCADA system will not get shut down due the battery bank.

when supply will restore, we required supply to operate the panel to connect the load, which get form the battery bank

so for maintain this battery bank continuously charge we required the battery charger.

we used the float cum boost battery charger to charge the battery bank .

the diagram for float cum boost battery charger is as shown in fig.

CONSTRUCTION: -

It contains the three-phase ac supply with to battery charger is attached.

This three-phase ac supply is connected to the input of both float and boost battery charger.

Both the battery charger contains the rectifier circuit at output. Between the both charger there is VC contactor, which separate both from each other.

It also contain the battery bank of 110 v .

 WORKING: -

From fig, normally we charge the battery bank form the float charger.

The float charger input is connected to the 3-phase ac input supply. Then it converted this ac supply to dc and connected to the battery and also load because it performs two function:

1.sypply load.

2. charge the battery.

 When battery is completely dead at that condition battery is charged through boost charger which produce large voltage for small time of period to boost the charging.

 when we used boost charger at that time float charger is off and also VC contractor is disconnected.

 Boost charger can also supply the load but through diode to limit the voltage. because boost charger gives 2.6 voltage for each 2v battery, so for 110v it will be 143v and this voltage is not good to directly connected to the 110v load.

HOW TO CALCULATE FUSE RATING FOR MOTOR

Fuse rating for 40 HP  3 phase motor: -

Fuse rating for 30 kw 3 phase motor: -