Technical data

5 AC/DC Converter
MASTERGUARD Series SIII
UPS Systems from 60 to 800 kVA
6
MKA4CAT0UKSIII/Rev. 11-11/2004/UK
utility or generator) shall be 15%
(normal operation is guaranteed up to
8%). The maximum current THD
injected into the mains shall be 30%
but will be reduced to 5% for the units
above 200 kVA which shall have 12
pulse rectifiers and filters provided as
standard.
5.7 Operation with diesel generator
In order to obtain the required THD on
input voltage, the coordination
between diesel generator and UPS
shall be based on the generator’s sub-
transient reactance, as opposed to its
short-circuit reactance.
5.8 Capacity and charging
characteristics
The rectifier shall be capable of
supporting the inverter at nominal
power and supplying the batteries with
charging current. After discharge of the
battery the rectifier will power the
inverter and recharge the batteries. The
following charging methods for the
different types of accumulators are
available:
5.8.1 Sealed, maintenance-free lead
acid accumulators:
Charging at constant current up to the
maximum load voltage level.
Thereafter the loading voltage shall be
kept at a constant level within narrow
limits (single-step charging method).
5.4 Power factor (available only for
60-500kVA range)
The rectifier/battery charger control
provides an algorithm for input power
factor optimisation.
When batteries are fully charged, the
battery care algorithm puts them on
stand-by (see section 5.11 “Battery
Management”). It is in this condition
that the rectifier enters its PFC mode
(Power-Factor Control). In this mode it
is able to perform a dynamic real-time
maximisation of the input power
factor, compensating mains utility
fluctuations. The PFC makes it
possible to reach PF > 0.92 (>0.9 for
twelve-phase configurations) under
normal operating conditions. This
means time-average PF > 0.9 for most
typical applications.
Example: assuming a typical utility
MTBF of 200h and a 10h period for full
battery recharge results shall be:
PF = 0.75 10 hours
PF = 0.92 190 hours
PF
AVG
= (0.75*10+0.92*190)/200 = 0.91 200 hours
5.5 Residual ripple filtering
The rectifier output shall have a
residual voltage ripple of < 2% RMS,
with batteries disconnected.
5.6 Total harmonic distortion (THD)
of input voltage
The maximum voltage THD permitted
on the rectifier input (either from the
5.8.2 Sealed, low-maintenance lead
acid accumulators or NiCd
accumulators:
Charging at increased charging voltage
and constant charging current. If the
charging current falls short of a lower
threshold value the rectifier shall
automatically return to load voltage
level (two-step charging method).
5.9 Overvoltage protection
The rectifier/battery charger shall
automatically switch off if the DC
voltage exceeds the maximum value
associated with its operational status.
5.10 Shared battery operation
UPS in parallel configuration can
operate with common batteries (a
maximum of two UPS can share a
common battery bank). In this case the
batteries are recharged in parallel by
the rectifiers of the two UPS. The total
current supplied by the rectifiers is
divided equally, with a maximum
unbalance equal to the programmed
level of battery current limits.
Although this configuration leads to
optimisation of the initial economic
investment, it reduces reliability
advantages, which are usually offered
by parallel UPS systems (see chapter
14 for details).
5.3 Soft start
After applying the input voltage the
rectifier starts a programmable current
soft start (1-90 seconds). This
procedure results in a gradual and soft
walk-in of the current taken from the
input voltage supply network. This
ensures that any standby generator is
gradually introduced into the UPS
input, as shown in Figure 5. To avoid
the simultaneous start-up of different
rectifiers, it is possible to programme a
hold-off dedicated start delay (1-180
seconds) for each unit.
In addition, the UPS includes an ‘on
generator’ function which, when
activated via floating contact, provides
the possibility, of inhibiting either
battery charging, synchronisation of
the inverter to the direct line supply or
transfer to the direct line.
Figure 3. Rectifier soft start
AC
Imput
Current
Hold-off
Delay
(1- 180s)
Current
soft
start
(1-90 s)
TimeMains OKMains Failure
Tecnico-SIII-MG 10-11-2004 8:22 Pagina 6