Specifications

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1.1POWER SUPPLY PROBLEMS
1.2EFFECTS OF POWER SUPPLY
PROBLEMS ON EQUIPMENT
2.1UPS's: FOUR GOOD REASONS
FOR INSTALLING THEM
2.1.1GENERAL CONSIDERATIONS REGARDING OPERATION
2.1.2CONFIGURATIONS
figure A: UPS in VFI configuration
figure B: UPS in VI configuration
POWER SUPPLY PROBLEMS
[and the solutions to them]
inverter
Line Conditioner
EMI
FILTER
AC
AC
AC
DC
output
BATTERY
AC
DC
mains
disturbances
mains conditioner
bypass
inverter converter
AC
DC
AC
AC
DC
AC
manual bypass
static
B
A
T
T
E
R
Y
mains output
manual bypass
bypass
convertor
inverter static switch
Electric energy consists of a single-phase or three-
phase waveform characterized by:
• frequency;
• amplitude;
• a form (possible wave distortion);
• symmetry of the system (only for three-phase).
Even if the sinewave may be virtually prefect at the
source, this is not the case when it reaches the
equipment where various disturbances may be
observed such as:
• transient overvoltages;
• ownouts;
• frequency fluctuations;
• interruptions.
These disturbances are usually caused by the
transmission and distribution of power supply,
weather (storms, frost, wind, etc.) and industrial
conditions (machine faults, equipment with polluting
current, mains events, etc.). Therefore, despite
constant improvements to the distribution network
and the quality of the “electricity product”,
disturbances are still frequent and complete
elimination of these would indeed prove costly.
In this sector too, manufacturers have made consid-
erable progress in their efforts to reduce the vul-
nerability of equipment to disturbances (optimized
immunity to overvoltages, tolerance to brownouts of
up 10 or 20% or even of outages lasting from 5 to 10 ms).
On the other hand, the increasing complexity of
many computer and industrial applications, the use
of high performance PLCs and use of the continuous
cycle in industrial processes and telecommunications
systems means that the consequences of these dis-
turbances are ever more dramatic. They may even in-
volve losses of productivity, deterioration of prod-
uct quality, serious risks for people and equipment
and may even undermine the very existence of a
company. Computer systems and, generally, all de-
vices that require a disturbance-free power supply
must be suitably protected. The effects in terms of
premature aging of equipment and deterioration of
reliability and efficiency are less visible and there-
fore more detrimental.
1. To provide power in the case of a blackout: this is
the classical, although not the most important,
function of an UPS.
2. To provide a QUALITY POWER SUPPLY by filtering and
stabilizing the power source which may be the
mains supply or a generator and may be affected
by considerable disturbances.
3. INDEPENDENT MANAGEMENT: with a UPS, the user’s
worries are over. In a blackout, the UPS will auto-
matically safeguard all programs that are open
and, in the case of a fault, can alert service
technicians.
4.CONSIDERABLY IMPROVE RELIABILITY of the power
system, using redundant solutions that guarantee
power quality and continuity even in the case of
faults
system, using redundant solutions that guarantee
power quality and continuity even in the case of
faults
UPS's usually consist of three main blocks:
- a rectifier-battery charger to convert ac current
into dc current and to charge the battery;
- a set of batteries (usually of the sealed lead-acid
type) to store the energy and recover it instanta-
neously, according to requirements, for periods of
5 to 30 minutes or even longer;
- a static converter (inverter) to convert this dc
voltage into an ac voltage with perfectly filtered
and stabilized voltage and/or frequency.
These three functions can be integrated with addi-
tional capabilities: an automatic bypass for power
supply in the case of overloads or UPS faults, a man-
ual bypass that permits complete isolation of the
UPS and various local or remote signaling and main-
tenance options.
Many different types of UPS have been developed in
response to specific customer requirements for
availability and quality of power supply intended for
different types of loads, from a few Watts to many
Megawatts. The current classification according to
performance is indicated in the ENV 50091-3 prelimi-
nary specifications which identify three types of UPS:
VFI (Voltage and Frequency Independent): more gen-
erally known as ON LINE or DOUBLE CONVERSION where
the output of the UPS is independent of any fluc-
tuations in the power voltage (mains) and frequency
variations are maintained within the limits pre-
scribed by the ENV 61000-2-2 (CEI 110-10) specifica-
tions. This type of UPS can operate as a frequency
converter (see fig. A).
VFD (Voltage and Frequency Dependent): more com-
monly known as OFF LINE where the output of the UPS
depends on fluctuations of the power supply (mains)
voltage and frequency variations
VI (Voltage Independent): usually known as LINE IN-
TERACTIVE where voltage fluctuations are stabilized
with normal operating limits by passive/electronic
regulation devices
(see fig. B).