BLOCK
ALARM
Distortion
measure-
ment
I_A
I_B
I_C
Demand
calculation
GUID-E5EC5FFE-7679-445B-B327-A8B1759D90C4 V1 EN
Figure 409: Functional module diagram
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
TDD
I
I
k
k
N
demand
=
=
∑
2
2
max_
GUID-9F532219-6991-4F61-8DB6-0D6A0AA9AC29 V1 EN (Equation 97)
I
k
k
th
harmonic component
I
max_demand
The maximum demand current measured by CMMXU
If CMMXU is 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
.
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 "Non-
sliding".
The activation of the BLOCK input blocks the ALARM output.
10.1.5 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, a customer-driven issue. It could be said that any power
Section 10 1YHT530004D05 D
Power quality measurement functions
766 615 series
Technical Manual
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