Powerware Uninterruptible Power Supply SOLA 4000 - Manual (Page 9)

SOLA 4000 - General System Description
JUE 401264 9
1 UPS Assembly
During overload or inverter failure conditions, SSI is switched off
and SSB is switched on, providing power supply from a backup
source (mains, output of another UPS system, diesel generator
set....). By always actuating both switches together for a short
period, an uninterrupted power supply during the switching is
ensured. This is an essential condition to reliably meet all power
supply requirements for connected sensitive equipment.
The control for each static switch (SSB and SSI) is performed
totally independently of each other, thus ensuring that a failure in
one static switch does not affect the other.
Switching Conditions, Inverter - Bypass The voltage and frequency of the bypass line have to be within
set tolerance limits, and the inverters have to be synchronised
with the bypass line.
Under inverter failure conditions:
(i) the UPS switches to bypass operation, for a single unit. (SSB
switches on, and SSI off).
(ii) for hot-standby units, the load is commutated to the second
inverter, and will switch to bypass only when no inverter is ready to
take the load.
(iii) in parallel systems, all units switch to bypass operation together
only if the load is more than the rated value for the remaining on-line
units.
If the conditions above for the bypass line and synchronisation
are not met:
• the inverter will continue to operate with reduced output voltage
under overload conditions, or
• the inverter will stop if an inverter failure occurs.
In this second case, the system will:
(i) commutate to a second standby-inverter in the case of a hot-
standby system
(ii) the remaining inverters will take the load in the case of a
parallel-redundant system or,
(iii) the UPS will commutate to the bypass supply with a very short
interruption of 10msec if the supplies are not synchronised, for the
case of a single UPS unit.
Under overload conditions, all UPS modules present will
switch to the bypass supply, and remain in bypass until the
overload is removed.
Switching Conditions, Bypass - Inverter a) The UPS switches automatically back to inverter operation
when inverter voltage and frequency are within tolerance limits,
the overload has been removed and the inverter is synchro-
nised with the bypass line (SSI switches on and SSB off).
b) If the UPS unsuccessfully attempts five times within 3 minutes
to switch to inverter operation, the UPS remains in bypass
operation and signals an alarm. After pressing the reset-button
once to reset the audible alarm, it should be pressed a second
time to automatically switch back to inverter operation.
c) If the UPS remains blocked on bypass operation and a mains
failure occurs, the UPS will switch automatically to inverter
operation if the inverter voltage and frequency are within
tolerance and the inverter is synchronised to the mains.