ABB RELION 620 Series Technical Manual page 676

Section 8
Power quality measurement functions
8.1.5
670
I_A
Distortion
I_B measure-
ment
I_C
BLOCK
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Figure 337: 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
N
2
∑
I
k
k = 2
TDD =
I
max_ demand
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I
th
k harmonic component
k
I The maximum demand current measured by IA, IB, IC
max_demand
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
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.
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,
Demand
ALARM
calculation
1MAC504801-IB E
(Equation 101)
620 series ANSI
Technical Manual