MI 2892 Power Master
Theory and internal operation
164
For unbalance calculus, instrument use the fundamental component of the voltage input signals (U
1
, U
2
,
U
3
), measured over a 10/12-cycle time interval.
The negative sequence ratio u
-
, expressed as a percentage, is evaluated by:
100
(%)
U
U
u
(67)
The zero sequence ratio u
0
, expressed as a percentage, is evaluated by:
100
(%)
0
0
U
U
u
(68)
Note: In 3W systems zero sequence components U
0
and I
0
are by definition zero.
The supply current unbalance is evaluated in same fashion.
5.1.12
Underdeviation and overdeviation
Voltage Underdeviation (U
Under
) and Overdeviation (U
Over
) measurement method: Standard compliance:
IEC 61000-4-30 Class A (Section 5.12)
Basic measurement for the Underdeviation and Overdeviation is RMS voltage magnitude measured over
a 10/12-cycle time interval. Each RMS voltage magnitude (i) obtained through recording campaign is
compared to nominal voltage U
Nom
from which we express two vectors according to the formulas below:
Nom
RMS
Nom
Nom
RMS
i
RMS
i
Under
U
U
U
U
U
U
U
)
12
/
10
(
)
12
/
10
(
),
12
/
10
(
,
if
if
(69)
Nom
RMS
Nom
Nom
RMS
i
RMS
i
Over
U
U
U
U
U
U
U
)
12
/
10
(
)
12
/
10
(
),
12
/
10
(
,
if
if
(70)
Aggregation is performed on the end of recording interval as:
%
1
2
,
Nom
n
i
i
Under
Nom
Under
U
n
U
U
U
(71)
%
1
2
,
Nom
n
i
i
Over
Nom
Over
U
n
U
U
U
(72)
Underdeviation and overdeviation parameters may be useful when it is important to avoid, for example,
having sustained undervoltages being cancelled in data by sustained overvoltages.
Note: Underdeviation and Overdeviation parameters are always positive values.
5.1.13
Voltage events
Measurement method
Standard compliance: IEC 61000-4-30 Class A (Section 5.4)
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.
