MI 2792 PowerQ4 Plus
Theory and internal operation
108
Figure 5.7: Curve of equal severity (Pst=1) for rectangular voltage changes on LV
power supply systems
P
st
p
1min
– is a short flicker estimation based on 1-minute interval. It is calculated as
running average and is used to get quick preview of 10 minutes.
P
st
p
– short term flicker is calculated according to IEC 61000-4-15
P
lt
p
– long term flicker is calculated according to the following equation:
3
1
3
N
Pst
P
N
i
i
ltp
p: 1,2,3
(24)
5.1.11 Voltage and current unbalance
Standard compliance: IEC 61000-4-30 Class A (Section 5.7.1)
The supply voltage unbalance is evaluated using the method of symmetrical
components. In addition to the positive sequence component U
+
, under unbalanced
conditions there also exists negative sequence component U
-
and zero sequence
component U
0
. These quantities are calculated according to the following equations:
)
(
3
1
3
2
2
1
U
a
U
a
U
U
)
(
3
1
3
2
1
0
U
U
U
U
,
)
(
3
1
3
2
2
1
U
a
U
a
U
U
,
(25)
