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DNP 3.0 and MODBUS Data Structures
13.7
Individual Harmonic Voltages and Currents
DNP
Modbus
Quantity
Full Scale
Type:Index
Input Reg.
AI:128–227
30129-30228
A Voltage Individual Harmonic Data
Vmax=32767
(M = 128, P = 129)
±
180deg =
±
32767
AI:228–327
30229-30328
A Current Individual Harmonic Data
Imax=32767
(M = 228, P = 229)
±
180deg =
±
32767
AI:328–427
30329-30428
C Voltage Individual Harmonic Data
Vmax=32767
(M = 328, P = 329)
±
180deg =
±
32767
AI:428–527
30429-30528
C Current Individual Harmonic Data
Imax=32767
(M = 428, P = 429)
±
180deg =
±
32767
AI:528–627
30529-30628
B Voltage Individual Harmonic Data
Vmax=32767
(M = 528, P = 529)
±
180deg =
±
32767
AI:628–727
30629–30728
B Current Individual Harmonic Data
Imax=32767
(M = 628, P = 629)
±
180deg =
±
32767
Table 13.5: Individual Harmonic Voltages and Currents
Specifying DNP Type Index Values
DNP Harmonic Magnitude
=
M
+ 2(
n
−
1)
DNP Harmonic Phase Angle =
P
+ 2(
n
−
1)
where: M corresponds to magnitude in the table above, P corresponds to phase in the table above,
and n equals the harmonic number.
Example 1:
Specify the type index for the magnitude of the 3rd harmonic of the A-phase voltage.
Type Index Value =
M
+ 2(
n
−
1) = 128 + 2(3
−
1) = 132
Example 2:
Specify the type index for the phase angle of the 5th harmonic of the C-phase current.
Type Index Value =
P
+ 2(
n
−
1) = 429 + 2(5
−
1) = 437
Scaling and Resolution
Compute actual values from DNP readings as follows: divide the DNP reading by the full-scale
number of counts and multiply by the full scale range. For example, if the DNP reading for voltage
is 21069, and the maximum voltage value is 150, the actual voltage is determined as follows:
Measured Voltage = (21069
÷
32767)
×
150 = 96
.
45
volts
Remember that magnitudes are actual scaled primary values and the resolution is determined by
dividing the maximum primary value by the Full Scale count. For example, with a maximum
(1133A) current range of 2.5 Amps (CT ratio of 100), then the resolution is 250
÷
32767 = 0.0076
Amps. If the actual primary current is 96.5 Amps, then the DNP reading would be:
Expected Counts = (96
.
5
÷
250)
×
32767 = 12
,
648
counts
.