5 Theory and internal operation
82
3
1
3
N
Pst
P
N
i
i
ltp
∑
=
=
p: 1,2,3
(22)
5.1.10 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
r
r
r
r
+
+
=
+
)
(
3
1
3
2
1
0
U
U
U
U
r
r
r
r
+
+
=
,
)
(
3
1
3
2
2
1
U
a
U
a
U
U
r
r
r
r
+
+
=
−
,
(23)
where
0
120
1
3
2
1
2
1
j
e
j
a
=
+
=
.
For unbalance calculus, instrument use the fundamental component of the voltage input
signals (U
1
, U
2
, U
3
), measured over a 10-cycle time interval.
The negative sequence ratio u
-
, expressed as a percentage, is evaluated by:
100
(%)
×
=
+
−
−
U
U
u
(24)
The zero sequence ratio u
0
, expressed as a percentage, is evaluated by:
100
(%)
0
0
×
=
+
U
U
u
(25)
Note:
In 3W systems zero sequence component U
0
is by definition zero.
The supply current unbalance is evaluated in same fashion.
5.1.11 Voltage
events
Voltage dips (U
Dip
), swells (U
Swell
), minimum (U
Rms(1/2)Min
) and maximum (U
Rms(1/2)Max
)
measurement method
Standard compliance: IEC 61000-4-30 Class A& S (Section 5.4.1)
The basic measurement for event is U
Rms(1/2)
.
U
Rms(1/2)
is value of the RMS voltage measured over 1 cycle, commencing at a
fundamental zero crossing and refreshed each half-cycle.
The cycle duration for U
Rms(1/2)
depends on the frequency, which is determined by the
last 10-cycle frequency measurement. The U
Rms(1/2)
value includes, by definition,
harmonics, interharmonics, mains signalling voltage, etc.
Voltage dip
Standard compliance: IEC 61000-4-30 Class S (Section 5.4.2)
The dip threshold is a percentage of Nominal voltage defined in EVENT SETUP menu.
The dip threshold can be set by the user according to the use. Instrument event
evaluation depends on Connection type:
