ABB Relion REC670 Applications Manual page 417

1MRK 511 358-UEN A
Set the CD-port to 9–2LE communication using only LHMI. All other settings are also available
from PCM600.
Factors influencing the accuracy of the sampled values from the merging unit are, for example,
anti aliasing filters, frequency range, step response, truncating, A/D conversion inaccuracy,
time tagging accuracy etc.
In principle, the accuracy of the current and voltage transformers, together with the merging
unit, will have the same quality as the direct input of currents and voltages.
The process bus physical layout can be arranged in several ways, described in Annex B of the
standard, depending on what are the needs for sampled data in a substation.
SDM600
IEC18000011 V1 EN-US
Figure 200: Example of a station configuration with separated process bus and station
The IED can get analog values simultaneously from a classical CT or VT and from a Merging
Unit, like in this example:
The merging units (MU) are called so because they can gather analog values from one or more
measuring transformers, sample the data and send the data over process bus to other clients
(or subscribers) in the system. Some merging units are able to get data from classical
measuring transformers, others from non-conventional measuring transducers and yet others
can pick up data from both types. The electronic part of a non-conventional measuring
transducer (like a Rogowski coil or a capacitive divider) can represent a MU by itself as long as
it can send sampled data over process bus.
Application manual
Maintenance Center Network Control Center
Engineering
Computer HMI
Firewall
Workstation
VPN
AFS 6xx
AFS 6xx
SAM600
SAM600
bus
Printer
Events Printer
WAMS
AFS 6xx
Gateway
AFS 6xx
SAM600
Section 18
Station communication
IEC 6185 0
FOX615
NSD570
IET600 PCM600 ITT600
IEC18000011-1-en.vsdx
411