ABB Relion 620 Series - Function Block; Functionality; Operation Principle

10.2.1 Identification
Function description IEC 61850
identification
IEC 60617
identification
ANSI/IEEE
C37.2 device
number
Voltage total harmonic distortion VMHAI PQM3U PQM3V
10.2.2 Function block
Figure 572: Function block
10.2.3 Functionality
The voltage total harmonic distortion function VMHAI is used for monitoring the
voltage total harmonic distortion THD.
10.2.4 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.
Distortion
measure-
ment
Demand
calculation
BLOCK
ALARM
U_A_AB
U_B_BC
U_C_CA
Figure 573: 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
THD
U
U
k
k
N
=
=
∑
2
2
1
(Equation 194)
Power quality measurement functions
1MRS757644 H
1086 620 series
Technical Manual