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Chapter 12 Helpful information
variations as part of its normal operation, thereby preserving battery life. Because it
constantly rectifies AC to DC and then inverts the DC back to AC, the online UPS
produces an output that corrects for voltage and frequency deviations. For this reason,
double-conversion technology is the most common for critical load applications and the
most advantageous type of system for generator integration.
6. Consult with the manufacturers. Often you can avoid a range of potential problems
and the UPS not working on generator power by first ensuring that the generator
manufacturer has tested and approved the product's intended use with UPS units. To
ensure that the optimal UPS/generator size match is achieved, it is wise to consult with
both the UPS and the generator manufacturer prior to finalising a purchase. In addition,
capacities of prospective loads to be protected can generally be found in the
manufacturer's specifications.
Addtional solutions
The UPS won't operate online when powered by generator.
A common characteristic of generators is the normal output voltage distortion when supplying
power to non-linear loads such as computers. This output voltage distortion can be interpreted
by the UPS as unacceptable power quality, forcing the UPS to transfer to battery operation.
When the load is transferred to the battery, naturally the generator distortion will be reduced
or disappear, leading the UPS to attempt to transfer back to line operation. When the load is
reapplied to the generator, the distortion will return, leading the UPS to once again transfer to
battery. This cycle may repeat indefinitely at intervals of approximately 4 seconds. The answer
in this case is to choose a generator which will not distort, when the nonlinear computer load
is applied.
See
Step 2 Increase the generator size
additional information.
The UPS stays on battery power while attached to a generator
This is generally due to the generator being undersized. To prevent voltage distortion and
complications with a UPS, the generator must be selected so that it will supply the peak
current required by the computer load, not only the average current. It has been determined
experimentally that this typically requires that the generator have a rating at least 3 to 5 times
the rating of the entire load to be connected to the generator. However, due to wide
differences in output impedance for generators, it is not possible to specify an over-sizing
factor that guarantees compatibility with all systems.
See
Step 2 Increase the generator size
additional information.
222
in the
Considerations section
in the
Considerations section
6U Rack or Tower UPS RT8kVA and RT11kVA IUOMG
of this chapter for
of this chapter for
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