ABB Remote I/O RIO600 Installation And Commissioning Manual page 96

Section 6
Commissioning
88
Function block
VMHAI
U_A HiAThd
U_B
U_C
BLOCK
GUID-DC5C6BCF-D48D-48D5-9B33-7F14CE94F7BC V1 EN
Figure 50: Function block
Functionality
The distortion monitoring 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
U_B
U_C
BLOCK
GUID-59E5E9BC-90DB-4467-860E-B0470C220118 V1 EN
Figure 51: Functional module diagram
Distortion measurement
The distortion measurement module measures harmonics up to the 8
total harmonic distortion (THD) is calculated from the measured harmonic
components with the formula.
N
2
Uk
∑
k 2
=
THD
=
U 1
GUID-E60DDDB4-1527-49FF-92C6-2F9768515268 V1 EN
th
Uk = k harmonic component
U1 = the voltage fundamental component amplitude
Demand calculation
The demand value for THD is calculated separately for each phase. If any of the
calculated total demand distortion values is above the THD alarm limit setting, the
HiAThd output is activated.
Distortion
Demand
measure-
calculation
ment
1MRS757488 H
HiAThd
th
harmonic. The
(Equation 6)
Installation and Commissioning Manual
RIO600