Register Value Update - ABB Relion 620 Series Protocol Manual

1MRS757645 B
3.4.5.1
620 series
Communication Protocol Manual
(
IEC 61850
Modbus value =
A070857 V1 EN
The range of the original IEC 61850 value can be seen in the Modbus memory map
point list.
All frequently updated data are readable from a sequential data area. Additionally,
there is a separate sequential data area for measurands and counters with a slow update
rate.

Register value update

The Modbus register values can be updated in three ways. For most registers, the
update method is predefined and fixed.
1. The most common method is updating through the internal IED event change
detection. When an analog value is changed, it is detected by the IED and sent
spontaneously to, for example, the IEC 61850 clients. This same value is also
cached in the Modbus database and made visible for the Modbus clients. Most
process values related to current and voltage measurements are mapped this way.
2. Some Modbus register values are mapped from the IED objects that are not part
of the IED change detection. These values are automatically scanned in the
background by the Modbus stack. The Modbus database cache is updated with a
new value when a change is noticed. Most diagnostics and demand values are
mapped this way.
3. A few Modbus register values are available so that the Modbus stack directly
reads the momentary value of the mapped source object. These values are never
cached in the Modbus database. They are only fetched from the source object at
the time of the Modbus client reading. Most registrations are mapped this way.
The Modbus data is derived from the internal IEC 61850 data model. The data model
has a predefined choice of objects which are subject to the internal IED change
detection, that is, the default IEC 61850 dataset. Since the requirements are that all
object changes should be noticed within 1...2 ms, the number of objects in this dataset
is limited by the CPU resources.
Methods 1 and 2 can be used regardless of whether the Modbus stack is integrated on
the same hardware as the application or not. Since data is always returned from the
Modbus cache, the response time is very fast and constant.
Method 3 can only be used if the Modbus stack is integrated on the same hardware as
the application. Several of these object types may be included in a Modbus scan. Since
all these Modbus registers must be fetched separately from the IED source objects, the
assembly of the response message may take a longer time, thus prolonging the
response time.
Vendor-specific implementation
)
Value scaleFactor
× +
Section 3
Offset
(Equation 1)
27