The document discusses two main types of uninterruptible power supplies (UPS): online UPS systems and offline UPS systems. Online UPS systems have an inverter that continuously powers the load, providing near-instantaneous switching if the main power fails. Offline UPS systems only activate the inverter when main power fails, resulting in a brief power interruption of up to 5 milliseconds as the load switches to battery power. Both systems use batteries, typically lead-acid, to provide backup power when mains power is lost, with online UPS systems providing backup times of 10-30 minutes while offline UPS times are similar.

1. ON-Line and OFF-Line UPS
Dr. Varsha Degaonkar
Department of Electronics and Telecommunication
Hope Foundation’s
International Institute of Information Technology, I²IT
www.isquareit.edu.in

2. Contents
• ON-Line UPS
• OFF-Line UPS
• Battery AH
• Back Up Time
• Battery Charger Rating
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3. Uninterruptable Power Supplies (UPS)
Need and Objectives:
1) Provide uninterruptible AC power
2) Pure sinusoidal O/P with low distortion
3) Regulation
4) Transient suppression
5) Frequency stability
6) Isolation of load from mains
Types:
1) On line UPS system (inverter preferred or continuous)
2) Off line UPS system (line preferred)
3) Line inter-active system
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4. On-Line UPS System
(Inverter preferred or continuous)
Block diagram
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5. Operation of On-Line UPS System
(Inverter preferred or continuous)
Mode I: Mains ON
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6. Operation of On-Line UPS System
(Inverter preferred or continuous)
Mode I: Mains ON
• In On-line UPS, Regardless of the mains supply ON or OFF,
the inverter operated on battery works.
• As mains power is present, charging of batteries takes
place.
• The switching time is considered as zero for these
supplies.
• Batteries used are sealed maintenance free
• Low running time (~ 10 to 30 min).
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7. Operation of On-Line UPS System
(Inverter preferred or continuous)
Mode II: Mains OFF
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8. Operation of On-Line UPS System
(Inverter preferred or continuous)
Mode II: Mains OFF
• The UPS supplies power to load, when the mains is OFF,
till the batteries become discharged.
• The batteries will start charging once again when the
mains supply start again.
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9. Operation of On-Line UPS System
(Inverter preferred or continuous)
Mode III: UPS Fail / Standby
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10. Operation of On-Line UPS System
(Inverter preferred or continuous)
Mode III: UPS Fail / Standby
If any fault occurs, UPS inverter is bypassed using a Triac.
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11. OFF-Line UPS System (Line preferred)
Block Diagram:
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12. Operation of OFF-Line UPS System
(Line preferred)
Mode I: Mains ON
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13. Operation of OFF-Line UPS System
(Line preferred)
Mode I: Mains ON
• When the mains is ON, the inverter circuit is OFF.
• Load gets coupled straight to the Mains supply.
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14. Operation of OFF-Line UPS System
(Line preferred)
Mode II: Mains OFF
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15. Operation of OFF-Line UPS System
(Line preferred)
Mode II: Mains OFF
When the mains supply is OFF, then only inverter is switched
ON.
Switching time < 5 ms
The applications where small interruption is tolerated, these
are used.
Sealed or lead-acid batteries are used.
Running time ~ 10 to 30 min.
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16. Line Interactive UPS System
Mode I: Mains ON
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Mode II: Mains OFF

17. 1) Lead acid batteries.
2) Nickel-Cadmium (Ni Cd) batteries
3) Sealed maintenance free batteries (SMF)
Lead acid batteries are most commonly used in
UPS.
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Batteries Used in UPS System

18. Battery Capacity: Ampere Hour (AH)-
𝐴𝑚𝑝𝑒𝑟𝑒 𝐻𝑜𝑢𝑟 = 𝐴𝐻 = 𝐼 × Δ𝑇 | 𝑚𝑖𝑛
I = Constant Discharge current
Δ𝑇 = Time period beyond which voltage of
battery decreases below the voltage level (final
discharge voltage)
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Batteries Used in UPS System

19. Battery Charging:
The battery Charging profile dependent on the type of the
battery chemistry.
Following figure shows the profile for Lead Acid Batteries:
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Batteries Used in UPS System

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Battery Efficiency

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Battery Efficiency

22. References:
Source: http://www.circuitstoday.com/ups-uninterruptable-power-supplies
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23. Thank you
www.isquareit.edu.in
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