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Alarm 74:
In a parallel system, with N+M configuration, where:
N: nr equipment to size the system according to the maximum permissible load.
M: nr redundant equipment in the system. It is equivalent to over sizing the
UPS’s in the system, in order to continue supplying the maximum
permissible load without overloading it. Usually, this value is fixed to “1”.
The alarm is displayed when the load exceeds the maximum permissible load
by N equipment. In this condition, the equipment will not be overloaded
individually, meanwhile the load doesn’t exceed the maximum load of N+M.
Example: Assuming that a parallel system of 2+1 equipment of 20 kVA
(N=2, M=1).
If the load of the system is lower than 40 kVA.
Any overload alarm is displayed (if it is not exceeded the individual overload
for phase for each equipment).
If the load of the system is higher than 40 kVA. The alarm 74 “Loss of
redundancy” is displayed.
If the load of the system is higher than 60 kVA. Beside the alarm 74 “Loss of
redundancy”, there will also be (as a minimum, among others), alarm 2
“Inverter overload” in all the equipment in the system.
Alarm 75:
This alarm can be displayed for two reasons:
Input contactor from the equipment faults (it doesn’t close properly). It is shown
when the DC bus voltage is not kept at a certain level when closing the input
contactor. Input contactor from the equipment fails (it doesn’t close properly).
The system can retry the contactor test several times (see description of alarm 47).
Alarm 76:
After the first error in the parallel system communication, when one of the UPS’s
has already been chosen as a master in the system, a second error or break in the
communications has been detected by the slave equipment,
which will be blocked permanently (rectifier and inverter are shutdown, output
voltage is not supplied to the output of the system), by displaying this alarm.
Alarm 77:
Error in configuration memory.