1MAC050144-MB C
Section 8
Measurement functions
615 series ANSI
569
Technical Manual
Figure 305:
Functional module diagram
8.10.4.1
Distortion measurement
The distortion measurement module measures harmonics up to the 11th harmonic. The
total demand distortion TDD is calculated from the measured harmonic components with
the formula:
(Equation 74)
I
k
k
th
harmonic component
I
max_demand
The maximum demand current measured by IA, IB, IC
If IA, IB, IC are not available in the configuration or the measured maximum demand
current is less than the
Initial Dmd current
setting,
Initial Dmd current
is used for
I
max_demand
.
8.10.4.2
Demand calculation
The demand value for TDD is calculated separately for each phase. If any of the calculated
total demand distortion values is above the set alarm limit
TDD alarm limit
, the ALARM
output is activated.
The demand calculation window is set with the
Demand interval
setting. It has seven
window lengths from "1 minute" to "180 minutes". The window type can be set with the
Demand window
setting. The available options are "Sliding" and "Nonsliding".
The activation of the BLOCK input blocks the ALARM output.
8.10.4.3
Application
In standards, the power quality is defined through the characteristics of the supply voltage.
Transients, short-duration and long-duration voltage variations, unbalance and waveform
distortions are the key characteristics describing power quality. Power quality is, however,
Distortion
measure-
ment
Demand
calculation
BLOCK
ALARM
I_A
I_B
I_C
demand
k
N
k
I
I
TDD
max_
2
2
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