Specifications

16
Apparent power (in VA or kVA)
It is defined as:
PAPP =VX I
for single-phase load
PAPP = V x I x √
3
for three-phase loads
where V is the load voltage supply
and I is the current absorbed by the
load in normal load conditions.
This information is normally shown on
documents and/or load nameplates
though it may be shown as an
oversized value.
Active power (in W or kW)
It is defined as:
kW = kVA x cosϕ
(where cosϕ means power factor PF).
The cosϕ value of loads is very
seldom indicated, therefore a correct
UPS sizing requires measurements
of kVA absorbed by loads.
Experience, anyway, shows that
typical loads of computer feature a
PF between 0,65 and 0,8.
Considerations on the
misleading concept of
“computer power”
In the definition of the UPS rated
power, the parameter values, defined
as “computer power”, “switching
power”, “actual power”, power a
particular temperature value, etc. are
sometimes indicated.
Such arbitrary parameter values have
no relation with apparent power and
active power; they can be neither
quantified nor defined and therefore
must not be used for the correct
sizing of the UPS.
Crest Factor
A linear load absorbs a sinewave
current that shows an effective value
(I
EFF usually measured and declared)
and a peak value (I
PK
). The Crest
Factor value is defined as:
I
PK
CF =
IEFF
The nominal value for a linear load is
CF = 1,41. Most loads applied to
UPS’s are non- linear load: they
absorb distorted current with a CF
value greater than 1,41 and require
therefore higher peak currents thus
resulting in an increased distortion of
the output voltage than equivalent
linear loads. Directive EN62040-3,
indicates a typical non-linear load as
CF=3, used for UPS testing, which
may be used in the absence of other
data.
Overload
Overloads are temporary requests
from electrical equipment which
exceed regular operation absorption.
They are caused by current peaks
which may occur when one or more
users are switched on. In case the
overload exceeds the admissible
limits the UPS guarantees the energy
supply via the automatic bypass line.
For “On line” UPS’s the transfer is
effected without any break in power
(transfer time = 0 ms). The “bypass”
is a safety device with independent
protection and auxiliary supply able
to supply the load independently
from the UPS also when the UPS is
switched off or broken.
Input current harmonics
The UPS battery charger rectifier
absorbs a distorted current containing
harmonics that are multiples to the
reference 50Hz frequency. These
harmonics may cause voltage distortion
which may affect the normal operation
of non privileged user’s.
The harmonics level of AROS UPS's
complies with the present directive.
Howerver, in order to further reduce the
presence of these harmonics variuos
solutions are available such as the
installation of Active Filetrs (Power
Factor Controlled) or different Rectifier
designs.
Runtime
The batteries supplied with the UPS’s
are valve regulated batteries (VRLA)
known as sealed batteries with no
electrolyte top-up, very low gas
emission, suitable for installations in
offices and public places with no need
for special precautions. Batteries are
normally supplied with the UPS and
can either be installed in the same
cabinet or in additional ones. AROS
guarantees the power supply runtimes
specifying the apparent load power and
the power factor.
Remarks about the misleading
concept of “typycal autonomy”
In defing the runtime it is often used the
concept “typical autonomy (or runtime)”
which has nothing to do with the real
runtime based on the 100% load value
expressed in W or kW (active power).
The runtime that AROS shows on all its
documentation have been calculaterd
at 100% of the load.
Evaluation parameters