02/02
73
From Bypass Supply to Normal Operation
The load is supplied by static switch; the sequence of controls to
commutate load on inverters is:
•
The oscillator of one of the two inverters starts to
synchronise with mains and imposes its frequency to the
system, closing the relays that connect it to parallel-
synchronisation bus.
•
The oscillator of the other inverter sees system frequency
and starts to synchronize with it.
•
When the second oscillator is synchronous with the system
closes its relays and connects itself to parallel-
synchronization bus, ceasing to synchronize with the bus and
using mains as reference.
•
The two oscillators are now in parallel and one may be
disconnected only turning off its Inverter.
•
The two-inverter static switches close the load each to its
inverter; drives to SCRs of both bypass static switches are
removed.
•
Relays that connect inverter control to parallel-current-
sharing bus are closed, after a small delay parallel-current
sharing circuits are enabled; relays are opened only turning
off its inverter.
From Normal Operation to Bypass Supply
In case of detection of bad output voltage, overload time expiration,
overtemperature of inverter, 11 at least one module sees that mains is
good, both inverter static switches are opened and static switches are
driven on.
UPS module failure
In case of failure of one of the two modules there is a strong
unbalance in output current sharing: that causes a turn-off of the
inverter involved; on UPS board is displayed number 44, on panel
message:
'INV : PARALLEL ERROR':
The block of the inverter is permanent; it can be removed only
pressing 'Reset Button' on UPS board.
As in the other cases of Inverter off on one of the two modules, the
load in supplied by the other Inverter if its rating allows it, otherwise
load is commutated on bypass.
7400M - Series UPS User Manual
Single Module and 1+N Parallel System
