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9Introduction
operation with an engine
generator set
See figure 11 below.
If a stand-by generator is included in the
installation, it is generally started automati-
cally in the event of a normal AC source
failure and connected to the main low volt-
age switchboard. It is disconnected when
normal AC source power is restored.
With such a system, the required battery
time may be reduced to the time neces-
sary for starting and bringing on line the
stand-by generator. The battery (D) sup-
plies power to the inverter (B) during the
transfers:
■ normal AC source to the generator;
■ generator to the normal AC source.
The transfer sequences described above
(normal AC source ➜ battery, battery ➜
generator, generator ➜ battery, and bat-
tery ➜ normal AC source) are fully auto-
matic. They in no way affect the load and
require no manual operation by the user.
output voltage quality
and continuity
The output voltage is stable in amplitude
and frequency and is free of interruptions or
transients outside specified tolerances, irre-
spective of normal AC source or load distur-
bances (outages, load step changes, etc.).
steady state voltage
regulation
For stable or slowly varying load condi-
tions, the inverter output voltage is regu-
lated to within ±0.5% in amplitude.
The frequency of the output voltage can
theoretically be regulated to within 0.1% of
the rated value, however the output fre-
quency range may be intentionally extend-
ed to a maximum of ±2 Hz so that the
inverter can remain synchronized with the
bypass AC source and its inherent fre-
quency fluctuations, thus enabling transfer
of the load to the bypass line at any time.
When the bypass AC source frequency
returns to within the specified tolerances,
the inverter is gradually re-synchronized to
the bypass line at a rate of 0.5 Hz to 2
Hz/s (as per the value personalized by the
after-sales support department), thus
avoiding exposing the load to sudden fre-
quency variations.
transient voltage regulation
The inverter output voltage is not notably
affected by instantaneous major variations
in load characteristics.
This is made possible by the PWM (Pulse
Width Modulation) chopping technique
and the microprocessor-based regulation
system that instantly compensates for any
variation. In particular, the inverter output
voltage remains within +/- 2% of the rated
voltage for load step changes of 0 to
100% or of 100 to 0%.
NOTE
The output frequency
range can be personalized
and if necessary modified
on the customer site by a
qualified MGE UPS SYS-
TEMS support technician
from ±0.25 Hz to ±2 Hz in
0.25 HZ steps.
When the bypass AC
source voltage moves out-
side this frequency range,
the inverter is desynchro-
nised and operates in
"free running" mode, with
the output frequency regu-
lated to a high level of
accuracy by a quartz
oscillator.
NOTE
To avoid load surges on
the generator, the rectifi-
er/charger is started with
a 10 second maximum
current consumption
walk-in (lasting 3 to 10
seconds, depending on
the percent load).
To avoid overloading an
undersized engine gener-
ator set, it is possible to
set a maximum power
level drawn by the nor-
mal AC input. Any addi-
tional power required is
supplied by the battery.
This modification can be
made on site by an MGE
UPS SYSTEMS field
engineer.
Example of an installation with an engine generator set
Fig. 11
HV system
Mains 2
Mains 1
Galaxy PW
G
A
B
D
C
generator
main LV switchboard
User’s Manual