Manual

Rockwell Automation Publication 1407-UM001G-EN-P - April 2013 139
CGCM Unit Software Interface Chapter 6
Energy Metering Considerations
Energy metering values (kW_Hrs, kVAR_Hrs, and kVA_Hrs) are provided using
a REAL data type. Values are expressed in a 32-bit floating-point format with a
precision of 7 digits. The table lists the theoretical range of a REAL value.
The energy values accumulate when the average generator line current is no less
than 1% of generator rated current. The limit that can be represented by an
energy tag is expressed by the following formulas:
When the energy tag value reaches (8,388,600 * rated kVA * % of rated load) and
the unit is still providing the same load level or less, the value will not update.
For instance, a 30 MVA machine operating at 10% load will yield an energy tag
limit of :
(8,338,600 * .1 * 30000) = 25,015,800,000 kVAh, or 2.50158 x 10
10
kVAh
When the energy tag value exceeds 8,338,600, rounding of the value begins to
occur.
The energy values are not retentive. When the 1407-CGCM unit powers up or
re-establishes a connection with the controller, the energy presets in the
Unscheduled Write table are written to the energy metering values.
Data Table
kW_Hrs Limit 8,338,600 rated kW % of rated load=
kVAR_Hrs Limit 8,338,600 rated kVAR % of rated load=
kVA_Hrs Limit 8,338,600 rated kVA % of rated load=
Table 12 - Unscheduled Read Data Table, Assembly Instance 5
Byte Size in
Bytes
Type Tag Name Description Units Range
0 4 Real AvgPF Average Power Factor PF -1…1
4 4 Real PhA_PF Phase A Power Factor
8 4 Real PhB_PF Phase B Power Factor
12 4 Real PhC_PF Phase C Power Factor
16 4 Real Total_kVA Total kVA kVA 0…3E+09
20 4 Real PhA_kVA Phase A kVA
24 4 Real PhB_kVA Phase B kVA
28 4 Real PhC_kVA Phase C kVA