G3200 using IEC61850 - How to detect if Modbus Slaves are offline



Goals and Symptoms

G3200 and PowerSCADA (or any IEC61850 Client Software): How to detect if the Modbus Slave is Offline to prevent invalid values?

Facts and Changes

Having G3200 Firmware v1.4, PM820 meter connected to G3200 over RS485 as a Modbus Slave, PowerSCADA (as IEC61850 Client) connected to G3200 on Ethernet port.
If the communication between the G3200 and the PM820 is broken, then the values (last values of the PM820) are still available over the G3200.
In this case, would be better to have all PM820 data become invalid or to have a way to trigger an alarm about this, wouldn't be?
Is there a possibility to change this in the CID file or in the G3200 firmware, or what is the solution?

Causes and Fixes

Current firmware implementation in G3200 doesn't support updating IEC 61850 data structure when the connected device (Modbus Slave) is offline.
PowerSCADA (or any other IEC61850 Client software) connected to G3200 should check the values of LLN0 and LPHD Logical Nodes under each Modbus Slave device defined in the CID file.
If It finds LLN0.ST.Mod = 5(OFF) then it should trigger an Advanced Alarm for that Modbus Slave device.

LLN0 and LPHD are the two logical nodes dedicated for physical device health and status.

Case1: When Modbus Slave device is "Online"
LPHD1.ST.PhyHealth = 1(OK)
LLN0.ST.Mod = 1(ON)

Case2: When Modbus Slave device is "Offline"
LPHD1.ST.PhyHealth = 3(Alarm)
LLN0.ST.Mod = 5(OFF)

G3200 updates the whole IEC 61850 data structure of the device if, and only if, the device is Online.
Then, it reads the data from device using Modbus functions and updates the IEC 61850 data structures.
If devices get disconnected, Measures, Quality and Timestamp won't be updated. However, the above mentioned nodes: "LPHD1.ST.PhyHealth" and "LLN0.ST.Mod" are updated and their values could serve as device status monitoring.

Created on 13th MAY 2013 by
Adrian Dicea
PowerSCADA Product Prime @ Expert Level - Global Technical Support

Related ranges: G3200, PowerSCADA, IEC61850, Modbus