Mumbai University > Electronics Engineering > Sem7 > Power Electronics 2

Marks: 7M

Year: Dec 2013

Off-line UPS

• In the case of the off-line system, in normal operation power is supplied directly from ac mains.

• In the event of mains failure, a transfer switch disconnects the power line and connects the inverter to the load.

• When the mains power is restored, the load is reconnected to the power line.

• Although all manufacturer tries to minimize the switching delay but it could be as long as 25 milliseconds.

Operation:

Mode 1 (Mains ON)

• When the mains is ON, the power is supplied to the load via the normally ON mains static switch.

• The battery is charged through the charger.

Mode 2 (Mains OFF)

• When the mains is off, the main static switch gets open circuited and UPS static switch are closed automatically.

• Battery charging will stop and battery supplying power through inverter.

• The total time taken to sense the power failure and make a changeover from mains to UPS is about 5m sec.

Advantages:

• Fewer parts
• Lower operating temperature
• Lower initial cost
• Lower operating cost

Disadvantages:

• Extreme voltage distortion can require frequent battery usage
• Output frequency varies within a configurable range