Presence of an Uninterruptible Power Supply (UPS)

The electrical power from a UPS is supplied from a storage unit: batteries or inertia wheel. This system prevent any power failure. The back-up time of the system is limited: from several minutes to several hours.

The simultaneous presence of a back-up generator and a UPS unit is used for permanently supply loads for which no failure is acceptable (Fig. D19). The back-up time of the battery must be compatible with the maximum time for the generator to start up and take over the load supply.

A UPS unit is also used to supply loads that are sensitive to power quality (generating a “clean” voltage that is independent of the network).

Main characteristics to be considered for implementing a UPS:

• Sensitivity of loads to power interruptions (see § 3.9 for definition),
• Sensitivity of loads to disturbances (see § 3.10 for definition).

The presence of a UPS unit is essential if and only if no failure is acceptable.

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Fig. D19: Example of connection for a UPS