Theory Of Operation - ABB 6310408P Product Manual

1: Theory of Operation

The maintenance bypass panel (MBS) is designed to be used with the ABB POWER 827E inverter
plant. The main purpose of the MBS is to allow an AC load to be switched from its primary source
(Inverters) to an alternate source (commercial AC) and back to the primary source (Inverters) again.
This may be required, for example, when doing maintenance or upgrades to the Inverter Plant. The
transfer is done with a front panel mounted switch. The Inverter source and AC Line source are not
phase locked and the transfer is asynchronous, i.e., it occurs at random phase. For more information,
refer to schematic 4391036SD and 4391036SD-1 attached to the rear of this document.
A manual front panel "BYPASS" switch is used to select the load source. The "INVENTER." mode
selects the Inverter source and is the normal state. The unit is said to be in "BYPASS" mode when the
"UTILITY" (commercial AC) source is selected. There are front panel LEDs to indicate if the
"INVERTER" and "commercial AC" voltages are present, and to indicate if the unit is in BYPASS mode.
While the INVENTER and AC LEDs indicate the presence of those source voltages, they do not prevent
the load transfer from occurring. It is the operator's responsibility to know if the source that is being
transferred to is an energized source.
An alternate purpose of the MBS is to collect alarms from the inverter shelves and to extend these
alarms to the plant monitor. The status of the consolidated alarms is indicated by the upper three
LEDs on the front panel. Any Major alarm will light the Major LED and extend a form C transfer to the
plant monitor via a terminal block on the rear panel (see system schematic for details). A single Minor
alarm extend a minor alarm, however, two or more Minor alarms will generate a Major alarm and
retire (turn off) the Minor alarm. A Capacity alarm is an indication that an inverter shelf has exceeded
its programmed and/or equipped capacity. This alarm may be used as a prompt to add more inverter
capacity (i.e. shelves and modules). The load sharing capabilities of the 827E inverters will typically
cause multiple shelves to provide a Capacity Alarm at the same time, if configured and equipped
similarly. The Minor and Capacity alarms are extended to the plant monitor as form C transfers.
NOTE: The MBS is powered by a -48VDC battery input at the rear. If this input is not present, there
will be no LEDs lit on the front panel.
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