User Manual 10H52258UM60 - Rev. 3 - 01/2019
48
APM 400/600
Introducing UPS Operations
Thus, when the bypass frequency is within the synchronization range, the inverter control circuit will synchronize
the inverter output frequency with the bypass frequency and phase.
The UPS is also equipped with a manual maintenance bypass switch that can be used to shut the UPS down
when it is necessary to carry out maintenance work. If the user closes this switch, the critical loads are supplied
by the bypass line via the maintenance bypass switch.
Warning
When the load is supplied by the bypass or maintenance bypass, the quality of the power supply is not
guaranteed
and the connected equipment is not protected against power failures or surges and sags
System Control Principle
Normal operation
Normal mode: In this mode, the UPS is supplied by normal mains input, while the rectifier and inverter operate
normally; the load is supplied via the inverter and the battery circuit breaker is closed so that the battery is in a
stable, floating charge state.
(Parallel System)
N.B.: As all the UPS module outputs are connected in parallel, the system checks that the
inverter control circuits are perfectly synchronized with one another and with the bypass, in terms of both
frequency and phase, and that their output voltages are the same. The current supplied to the load is distributed
automatically between all the connected UPS units. A warning message appears while synchronization is in
progress.
Mains abnormal
When the mains supply fails, or is outside the operating limits, the rectifier will stop working automatically, and
the load will be supplied by the battery (via the inverter).
The length of time that the UPS is able to continue supplying the load while in battery mode depends on the size
of the load and battery capacity. During this period, if the battery voltage reaches the EOD voltage, and the mains
power supply has still not been restored, the inverter will stop working automatically, and the UPS operator
control and display panel will display the corresponding alarm messages. If the system uses split bypass
configuration and the bypass is normal, the system will transfer to bypass.
Mains recovery
If the mains supply returns within normal operating limits within the permissible time, the rectifier will restart
automatically, supplying the load and charging the battery again. In this case, the power supply to the load is not
interrupted.
Disconnecting the battery
In order to disconnect the external battery from the UPS system when it is necessary to carry out maintenance
work, use the external isolating switch. In this condition, the UPS functions and steady state performance remain
unaffected, with the exception of the battery backup function (upon mains failure), .
UPS module failure
In the event of an inverter failure, the output fuse will blow and the STS will transfer the load automatically to the
bypass so that the supply of output power to the load is not interrupted. If this occurs, please contact your local
Vertiv customer service center assistance.
(Parallel System)
In the event of a fault in a single UPS module, it will be excluded automatically from the parallel
system. If the system is still capable of providing the necessary power, the remaining modules will continue to
supply the load without any interruption. If the remaining modules are no longer capable of fulfilling power
requirements, the load will automatically transfer to the bypass.
Overload
If the inverter is overloaded or the inverter current remains outside the defined specifications longer than the
stipulated time, the load will automatically transfer to the bypass without interrupting the power supply to the
load. If both the overload and current return within the specified limits, the load will be transferred back to the
inverter. In the event an output short circuit, the load will be transferred to the bypass and the inverter will shut
down. Five minutes later, the inverter will start up automatically. If the short circuit has been eliminated at this
point, the load will be transferred back to the inverter. The point at which the transfer occurs is determined by
