10
2. Current readings
Assume device settings: CT primary current = 200A; current input overload = 200% (10A).
Current engineering scales:
HI = Imax = CT primary current
×
2 = 200.00
×
2 = 400.00A
LO = 0A
If the raw data reading is 250 then the current reading in engineering units will be as follows:
Amps reading = 250
×
(400.00 - 0)/9999 + 0 = 10.00A
3. Power readings
a) Assume device settings (690V input, direct wiring): wiring configuration 4LN3; PT = 1; CT primary current = 200A.
Active Power engineering scales:
HI = Pmax = Vmax
×
Imax
×
3 = 828.0
×
(200.00
×
2)
×
3 = 993,600W = 993.6kW
LO = -Pmax = -993.6kW
If the raw data reading is 5500 then the power reading in engineering units will be as follows:
Watts reading = 5500
×
(993.6 - (-993.6))/9999 + (-993.6) = 99.469kW
If the raw data reading is 500 then the power reading in engineering units will be as follows:
Watts reading = 500
×
(993.6 - (-993.6))/9999 + (-993.6) = -894.23kW
b) Assume device settings (wiring via PT): wiring configuration 4LL3; PT = 120; CT primary current = 200A.
Active Power engineering scales:
HI = Pmax = Vmax
×
Imax
×
2 = (144
×
120)
×
(200.00
×
2)
×
2/1000 = 13824kW
LO = -Pmax = -13824kW
If the raw data reading is 5500 then the power reading in engineering units will be as follows:
Watts reading = 5500
×
(13824 - (-13824))/9999 + (-13824) = 1384kW
If the raw data reading is 500 then the power reading in engineering units will be as follows:
Watts reading = 500
×
(13824 - (-13824))/9999 + (-13824) = -12441kW
4. Power Factor readings
Power factor engineering scales:
HI = 1.000.
LO = -1.000.
If the raw data reading is 8900 then the power factor in engineering units will be as follows:
Power factor reading = 8900
×
(1.000 - (-1.000))/9999 + (-1.000) = 0.78
4.2.2 32-bit Modulo 10000 Format
The short energy registers 287-294, and 301-302 are transmitted in two contiguous 16-bit registers in modulo
10000 format. The first (low order) register contains the value mod 10000, and the second (high order) register
contains the value/10000. To get the true energy reading, the high order register value should be multiplied by
10,000 and added to the low order register.
4.2.3 32-bit Long Integer Format
In a 32-bit long integer format, data is transmitted in two adjacent 16-bit Modbus registers as unsigned (UINT32)
or signed (INT32) long integer (whole) numbers. The first register contains the low-order word (lower 16 bits) and
the second register contains the high order word (higher 16 bits) of the 32-bit long number. The low-order word
always starts at an even Modbus address. The value range for unsigned data is 0 to 4,294,967,295; for signed
data the range is -2,147,483,648 to 2,147,483,647.
A 32-bit data can be transmitted without conversion “as is”, or by using decimal pre-scaling to transform fractional
numbers to an integer format.
Fractional numbers are pre-multiplied by 10 in power N, where N is the number of digits in the fractional part. For
example, the frequency reading of 50.01 Hz is transmitted as 5001, having been pre-multiplied by 100. Whenever
a data register contains a fractional number, the register measurement unit is given with a multiplier
×
0.1,
×
0.01 or
×
0.001, showing an actual register resolution (the weight of the least significant decimal digit). To get an actual
