Question

Sketch and describe an arrangement for automatic connection of emergency batteries upon loss of main power. Include in your answer:

(a) Means of obtaining d.c. charging supply from a.c. mains:

(b) A method of maintaining charge on lead acid batteries;

(c) The arrangement to check that batteries operate at loss of main power

(d) The length of time for which emergency batteries of passenger and cargo ships must provide power.

Answer 1

The DC charging supply is obtained from the main busbar. A transformer will step down the voltage to required charging voltage and a rectifier will provide DC voltage at required charging emf
When charging from a discharged state, emf is supplied through a branch ‘A’ at full charging voltage
A voltage monitor ‘V’ monitor the voltage of the cell and gets energised when cell its full charge emf of 2.2V/cell.
‘V’ closes contact V1 and energises contact ‘TC’, then TC 1 gets open and TC2 gets closed and current passes through a resistor for trickle charging.
When main power failure occurs, the contactor KM gets de-energised, so contacts KM1 & KM2 get open and KM3 & KM4 are closed.
Opening of KM1 & KM2 isolates the battery from charging circuit and KM3 and KM4 closes to allow the battery to supply to emergency services
A test switch provides means for testing the battery.

Part (a)

from the mainline through a bridge rectifier, which converts AC to DC.

Part (b)

Full charge/ Quick charge/ burst charge: when the battery is discharged on load or otherwise full charge switch is switched ON to charge the battery
Trickle charge/ float charge: batteries get discharged when not in use due to local actions so it is kept on trickle charge where very small amounts of current is supplied just to make up for the loss of charge.

Part (c)

test switch is pressed which simulates loss of main power and the charging contacts open and load contacts is made

Part (d)

for transitional power source 30 minutes for both passenger and cargo ship

✓ Verified Model Answer (Text Solution)