819   APC and ASG

Created: 06 Feb 2012

Status: In Force (green)

Part: Part 7-3 (2010; Edition 2)





Category: Issue for edition 2 of this part


The CDC APC is described as a controlable analog process value. A controlable analog process value may be the position of a peterson coil or the position of a gate from a hydraulic gate. The control part of the data object based on that common data class provides the position the process equipment (gate or peterson coil) shall move to; the return value (FC=MX) provides the current position of the gate. Alternatly, a CDC exists, that allows a binary control (higher or lower). This is in line with what exists for tap changers (control of the tap position or binary control).

However, in 61850-7-4 and 61850-7-420, APC is frequently used as well for setpoints. In that case it is assumed that the return value of the object would be the value of the setpoint and not the process value.

This needs clarification. In addition, it is required to describe clearly what the difference between a setpoint and a setting is.


Use the CDC APC for both of the above described cases. In 7-4 (or any other part, that defines logical nodes with data objects) clearly state, what the return information (data attribute with FC MX) represents. As a better solution, the CDC APC shall be extended with a data attribute setPtVal (FC=MX) in addition to the data attribute mxVal (FC=MX) - these two data attributes beeing conditional. In 7-4 it shall be stated, which of the two DAs shall be used.

Regarding clarification between setpoint and setting: a setpoint will be set as part of operation (so it is a value that changes based on the process conditions). A setting is a configuration / system parameter that will stay constant within a certain context.

Discussion Created Status
Suggest to clarify in 7-3 as well, that the Interpretation of the Attribute mxVal is defined in the context of where the CDC is used (Part 7-4xx) 20 Nov 13 In Force (green)
10 May 12 In Force (green)
New decision based on phone call between Sub-Editor team: No change in 7-3, but clearly state in 7-4 or in any other LN that defines data objects based on APC for each data object, if the return information (data Attribute mxVal) is the setpoint that has been written (typically, if we have a regulation function behind) or if it is the return information from the controlled process object (typically if we directly control a process object). 21 Mar 12 Ballot Period


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