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HT33 Series User Manual
Frequency converters mode
Parallel operation redundancy mode
3.2.1 Normal Mode
The UPS inverter power modules continuously supply the critical AC load. The rectifier/charger
derives power from the AC mains input source and supplies DC power to the inverter while
simultaneously FLOAT or BOOST charging its associated backup battery.
3.2.2 Battery Mode
Upon failure of the AC mains input power; the inverter power modules, which obtains power from the
battery, supplies the critical AC load. There is no interruption in power to the critical load upon failure.
After restoration of the AC mains input power, the “Normal Mode” operation will continue automatically
without the necessity of user intervention.
Note: UPS can also be started through battery (charged) mode via battery cold start function upon
failure of the AC mains. Therefore, the battery power can be used independently to improve the
utilization rate of UPS.
3.2.3 Auto-Restart Mode
The battery may become exhausted following an extended AC mains failure. The inverter shuts
down when the battery reaches the End of Discharge voltage (EOD). The UPS may be programmed to
“Auto Recovery after EOD” after a delay time if the AC main recovers. This mode and any delay time are
programmed by the commissioning engineer.
During the process of delay time, the battery will be charged by UPS to prevent any risks to load
equipment from future mains failure.
3.2.4 Bypass Mode
If the inverter overload capacity is exceeded under normal mode, or if the inverter becomes
unavailable for any reason, the static transfer switch will perform a transfer of the load from the inverter
to the bypass source, with no interruption in power to the critical AC load.
3.2.5 Maintenance Mode
A manual bypass switch is available to ensure continuity of supply to the critical load when the UPS
becomes unavailable e.g. during a maintenance procedure.
It is noticed that after UPS system supplies the power with the bypass mode, the maintenance
bypass switch Q3 is closed, and Q1, Q2, Q4 and battery switches are disconnected. For type below
30KVA, after UPS system supplies the power with the bypass mode, the rotary switch is switched onto
the maintenance bypass, and Q1, Q2 and battery switches are disconnected.
Warning: Hazard may occur after transferring to maintenance bypass
After UPS being transferred to maintenance bypass, power module and bypass module do not work
with no display on LCD, and input and output terminals as well as N bus are charged.
3.2.6 ECO Mode
If economical (ECO) mode is selected, the double-conversion UPS will stop to work so as to save
energy. During the operation of ECO mode, the load power will be supplied by bypass preferentially.
When bypass power is within the range of normal frequency and voltage, load power will be supplied by
bypass, or the system will transfer to inverter output, followed by load power interruption which extends
