Voltage And Current Unbalance; Harmonic Calculations - AEMC 8335 Power Pad User Manual

Voltage and Current Unbalance

(three-phase connection - over one second)
These are calculated from the filtered RMS vector values (over one second)
VFrms[i] and Afrms[i] (ideally the fundamental vectors of the signals).
NOTE: The operations are vector operations in complex notation with
Forward phase-to-neutral voltage (vector)
1
Vrms = ( VFrms
+
3
Reverse phase-to-neutral voltage (vector)
1
Vrms = ( VFrms
−
3
Phase-to-neutral voltage unbalance (vector)
Vrms
−
Vunb =
Vrms
+
Forward current (vector)
1
Arms = ( AFrms
+
3
Reverse current (vector)
1
Arms = ( AFrms
−
3
Current unbalance (vector)
Arms
−
Aunb =
Arms
+

Harmonic Calculations

(excluding neutral – over 4 consecutive periods every second)
Harmonic bins are calculated by FFT with 16 bit resolution (1024 samples on 4
cycles) without windowing (IEC 1000-4-7). From the real parts bk and the imagi-
nary parts ak, the harmonic factor is calculated for each order (j) and for each
phase (i) (Vharm[i][j], Uharm[i][j], and Aharm[i][j]) with respect to the fundamental
and the angles Vph[i][j], Uph[i][j], and Aph[i][j] with respect to the fundamental.
This calculation is accomplished using the following principle:
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116
[ ] [ ]
0 + a ⋅ VFrms 1 +
[ ] [ ]
2
0 + a ⋅ VFrms 1
[ ] [ ]
0 + a ⋅ AFrms 1 +
[ ] [ ]
2
0 + a ⋅ AFrms 1
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[ ]
2
a ⋅ VFrms 2 )
[ ]
+ a ⋅ VFrms 2 )
[ ]
2
a ⋅ AFrms 2 )
[ ]
+ a ⋅ AFrms 2 )
Power Quality Analyzer Model 8335
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