11
LO = 0V
If the raw data reading is 8314 then the voltage reading in engineering units will be as follows:
Volts reading = 8314 × (17,280 - 0)/9999 + 0 = 14,368V
2. Current readings
Assume device settings: CT primary current = 200A; current input overload = 150% (7.5A).
Current engineering scales:
HI = Imax = CT primary current × 1.5 = 200 × 1.5 = 300A
LO = 0A
If the raw data reading is 250 then the current reading in engineering units will be as follows:
Amps reading = 250 × (300 - 0)/9999 + 0 = 7.5A
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 × (200 × 1.5) × 3 = 745,200W = 745.2kW
LO = -Pmax = -745.2kW
If the raw data reading is 5500 then the power reading in engineering units will be as follows:
Watts reading = 5500 × (745.2 - (-745.2))/9999 + (-745.2) = 74.6kW
If the raw data reading is 500 then the power reading in engineering units will be as follows:
Watts reading = 500 × (745.2 - (-745.2))/9999 + (-745.2) = -670.67kW
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 × 1.5) × 2/1000 = 10368kW
LO = -Pmax = -10368kW
If the raw data reading is 5500 then the power reading in engineering units will be as follows:
Watts reading = 5500 × (10368 - (-10368))/9999 + (-10368) = 1037.9kW
If the raw data reading is 500 then the power reading in engineering units will be as follows:
Watts reading = 500 × (10368 - (-10368))/9999 + (-10368) = -9331.1kW
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
Decimal Scaling
Decimal pre-scaling can be used to accommodate fractional numbers to an integer register format.
Fractional numbers 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 fractional number with specified precision, scale the register value with the
given multiplier. To write a fractional number into the register, divide the number by the given multiplier.
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