SP121E Rev. 000 Siel S.p.A. Pag. 19 of 42
Issued date: 2005-05-06
GREEN POINT
The static bypass can support overloads greater than those supported by the inverter and enables the load to
be powered even if an internal fault within the UPS occurs.
The bypass has one fused at the input to the UPS.
11) Back feed protection
The back feed protection is installed in series with the bypass SCRs. When the mains power supply fails, and in
the event of a fault occurring with the SCRs, the back feed protection device prevents any current that could
cause an electric shock from back feeding to the incoming power supply connections.
Furthermore, when a mains supply failure occurs, an electromagnetic switch positioned at the rectifier input
opens, thus preventing any current back feed onto the electrical system prior to this point.
This device must be installed in electrical systems in accordance with the new CEI 11-20 regulation (I and II
category systems). This enables the user to work on the incoming power supply, after the power supply to the
UPS has been switched off via the supply isolator, and therefore no risk of any current back feed occurring from
the UPS.
12) SWMB (Maintenance by-pass), SWIN, SWOUT
The SWMB maintenance bypass switch directly connects the input to the UPS to the output load, thus
bypassing the internal sections of the UPS, the switch connects all of the incoming conductors (including the
neutral) to the corresponding output conductors without interruption to the load. Whilst the SWMB switch is
closed, the SWOUT, SWIN and FBAT switches can be opened, which enables the user to safely carry out
maintenance work within the UPS, whilst power to the load is maintained.
This method of operation is necessary for UPS systems of a certain size, where maintenance work is often
carried out on site, and therefore supplied as standard within the UPS.
The maintenance by-pass switch enables the load to be continually supplied, without altering the electrical
system. The bypass switch can also be used to re-connect power to the connected load in an event of an
emergency for whatever reason (overloads, high ambient temperature, total failure etc.), and can be left
switched on until such time as the UPS resumes normal operation condition.
The manual by-pass line is sized in accordance with the rated output of the UPS.
The UPS also enables the integration of an external maintenance bypass switch, therefore when the external
bypass is activated the UPS can report the condition and take the appropriate action.
7.3 Operating modes
The UPS can be configured to operate in one of the three general operating modes:
- ON-LINE;
- STAND-BY ON (equivalent to line interactive mode).
- Stand-by
The “Battery Operation mode”, “By-pass Operation mode” and “Maintenance By-pass Operation
mode” are common to all three of these system configured modes.
(134 pages)
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