Ferroresonant UPSs
These UPSs, which
are another hybrid
technology, keep the inverter in standby mode
similar to line-interactive and standby UPSs. The
protected system however, is powered from the
utility through the ferroresonant transformer.
The
transformer provides voltage regulation and power
conditioning for disturbances such as electrical line
noise. The ferroresonant transformer also maintains
a reserve of energy that is usually sufficient to power
most computers (i.e. PCs) briefly when a total outage
occurs. This keeps the computer supplied with
power within most input requirements until the
inverter is switched on.
In cases where the input frequency is unstable,
the ferroresonant topology subjects the load to
some voltage excursions in addition to frequency
fluctuations. When the frequency variations exceed
a pre-set limit, the unit supplies stable voltage and
frequency to the load through the backup battery
and inverter.
Ferroresonant technology is particularly sensitive
to sudden current surges on the load input
which may cause a significant change in the output
voltage of the UPS. In general, ferroresonant UPSs
that use transformers are often larger in size and
produce heat which can impact sensitive components
in a computer and batteries in the UPS.
These
UPSs work best with most non-computer technology
or linear loads such as monitors, heaters and lights.
Applications
