GE P642, Technical Manual

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6.4.11 POWER AND ENERGY MEASUREMENT DATA FORMATS
The power and energy measurements are available in two data formats:
Data Type G29: an integer format using 3 registers
Data Type G125: a 32 bit floating point format using 2 registers
The G29 registers are listed in the first part of the MEASUREMENTS 2 column of the Courier database. The G125
equivalents appear at the end of the MEASUREMENTS 2 column.
Data type G29
Data type G29 consists of three registers:
The first register is the per unit (or normalised) power or energy measurement. It is a signed 16 bit quantity. This
register is of Data Type G28.
The second and third registers contain a multiplier to convert the per unit value to a real value. These are unsigned
32-bit quantities. These two registers together are of Data Type G27.
Thee overall power or energy value conveyed by the G29 data type is therefore G29 = G28 x G27.
The IED calculates the G28 per unit power or energy value as:
G28 = (measured secondary quantity/CT secondary)(110V/(VT secondary).
Since data type G28 is a signed 16-bit integer, its dynamic range is constrained to +/- 32768. You should take this
limitation into consideration for the energy measurements, as the G29 value will saturate a long time before the
equivalent G125 does.
The associated G27 multiplier is calculated as:
G27 = (CT primary)(VT primary/110V) when primary value measurements are selected
and
G27 = (CT secondary)(VT secondary/110V) when secondary value measurements are selected.
Due to the required truncations from floating point values to integer values in the calculations of the G29
component parts and its limited dynamic range, we only recommend using G29 values when the MODBUS master
cannot deal with the G125 IEEE754 floating point equivalents.
Note:
The G29 values must be read in whole multiples of three registers. It is not possible to read the G28 and G27 parts with
separate read commands.
Example of Data Type G29
Assuming the CT/VT configurations are as follows:
●
Main VT Primary 6.6 kV
● Main VT Secondary 110 V
●
Phase CT Primary 3150 A
● Phase CT Secondary 1 A
The Three-phase Active Power displayed on the measurement panel on the front display of the IED would be 21.94
MW
The registers related to the Three-phase Active Power are: 3x00327, 3x00328, 3x00329
Register Address Data read from these registers Format of the data
3x00327 116 G28
3x00328 2 G27
Chapter 16 - Communications P64x
362 P64x-TM-EN-1.3