Functionality - ABB RELION Series Technical Manual

1MRS758755 A
10.2.3
10.2.4
REC615 and RER615
Technical Manual

Functionality

The voltage total harmonic distortion function VMHAI is used for monitoring the
voltage total harmonic distortion THD.
Operation principle
The function can be enabled and disabled with the Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of VMHAI can be described with a module diagram. All the modules
in the diagram are explained in the next sections.
U_A_AB
U_B_BC
U_C_CA
BLOCK
GUID-615D1A8A-621A-4AFA-ABB0-C681208AE62C V1 EN
Figure 359: Functional module diagram
Distortion measurement
The distortion measurement module measures harmonics up to the 11th harmonic.
The total harmonic distortion THD for voltage is calculated from the measured
harmonic components with the formula
N
2
U
∑
k
k 2
=
THD
=
U
1
GUID-83A22E8C-5F4D-4332-A832-4E48B35550EF V1 EN
U
th
k harmonic component
k
U the voltage fundamental component amplitude
1
Demand calculation
The demand value for THD is calculated separately for each phase. If any of the
calculated demand THD values is above the set alarm limit THD 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.
Power quality measurement functions
Distortion
Demand
measure-
calculation
ment
Section 10
ALARM
(Equation 76)
677