Honeywell EXCEL 5000 User Manual page 80

ALPHABETIC REFERENCE
74-5577–33 (US)
EN2B-0184 GE51 R0518 (Europe)
The following diagram illustrates the principal connections of XFM 35 and multiple
XFM 36-1/S/Rs:
The principle of operation is that XFM 35 implements the desired algorithm and
then outputs the actual kW shed/restore values to the XFM 36-1/S/Rs. A positive
kW value is a command to restore loads totaling that much kW. A negative kW
value is a command to shed loads of that much kW. The kW shed/restore values
can appear at output Po1, Po2, or Po3.
Po1 is the output for priority group 1. It has the lowest priority and is shed first. Po2
loads are shed next and Po3 loads are shed last.
Each sheddable load is controlled by an XFM 36-1/S/R. The XFM 36-1/S/Rs are
connected in the CARE control strategy in a series string. For priority group 1, for
example, XFM 35 output Po1 is connected to the Po input of the first XFM 36-
1/S/R. The Po output of the first XFM 36-1/S/R is then connected to the Po output
of the second XFM 36-1/S/R. The Po output of the second XFM 36-1/S/R is then
connected to the Po input of the third XFM 36-1/S/R. Up to 50 XFM 36-1s can be
connected in a string this manner. To complete priority group 1, the Po output of
the last XFM 36-1/S/R must be connected to the Po1 input of XFM 35. The XFM
36-1/S/Rs for priority groups 2 and 3 are connected similarly to XFM 35 Po2 and
Po3 inputs and outputs. In any group, the sequential load with the highest load
number (parameter 14) is shed first.
In basic system operation, XFM 35 outputs 0 kW to Po1, 2, or 3 if no loads are to
be shed or restored. However, if, for example, 500 kW must be shed in a system
where all loads are ON, -500 kW will be output from XFM 35 PO1. The first XFM
36-1/S/R will shed its load of, for example, 150 kW, and the remaining kW (-350) is
output to the PO input of the second XFM 36-1/S/R. The process continues until a
total of 500 kW is shed, or the remaining kW to be shed value is output into the
XFM 35 PO1 input. XFM 35 then outputs that value to its PO2 output, and the
priority group 2 XFM 36-1/S/Rs shed their loads as explained above. If necessary,
the process continues through the priority 3 loads. The order in which loads are
shed within a group depends primarily on whether a sequential or rotational
strategy exists for that group. Refer to the XFM 36-1/S/R section for more detail.
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EXCEL CARE CONTROL ICONS