116
Power Quality Analyzer Model 8335
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)
[ ]
[ ]
[ ]
)
2
VFrms
a
1
VFrms
a
0
VFrms
(
3
1
Vrms
2
⋅
+
⋅
+
=
+
Reverse phase-to-neutral voltage (vector)
[ ]
[ ]
[ ]
)
2
VFrms
a
1
VFrms
a
0
VFrms
(
3
1
Vrms
2
⋅
+
⋅
+
=
−
Phase-to-neutral voltage unbalance (vector)
+
−
Vrms
Vrms
=
Vunb
Forward current (vector)
[ ]
[ ]
[ ]
)
2
AFrms
a
1
AFrms
a
0
AFrms
(
3
1
Arms
2
⋅
+
⋅
+
=
+
Reverse current (vector)
[ ]
[ ]
[ ]
)
2
AFrms
a
1
AFrms
a
0
AFrms
(
3
1
Arms
2
⋅
+
⋅
+
=
−
Current unbalance (vector)
+
−
Arms
Arms
=
Aunb
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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