Application - ABB RELION Series Technical Manual

Section 10
Power quality measurement functions
10.1.5
674
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 CMMXU
max_demand
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.

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 problem
concerning voltage or current that results in a failure or misoperation of customer
equipment is a power quality problem.
Harmonic distortion in a power system is caused by nonlinear devices. Electronic
power converter loads constitute the most important class of nonlinear loads in a
power system. The switch mode power supplies in a number of single-phase
electronic equipment, such as personal computers, printers and copiers, have a very
high third-harmonic content in the current. Three-phase electronic power converters,
that is, dc/ac drives, however, do not generate third-harmonic currents. Still, they can
be significant sources of harmonics.
Power quality monitoring is an essential service that utilities can provide for their
industrial and key customers. Not only can a monitoring system provide information
1MRS758755 A
(Equation 75)
REC615 and RER615
Technical Manual