Control Operation Rejections; Measurands; Class 2 Measurands - ABB RELION 620 Series Communication Protocol Manual

Section 3
Vendor-specific implementation
3.3.4.3
3.3.5
3.3.5.1
18
The relay cannot distinguish if the IEC 60870-5-103 client is of the Station or Remote
(NCC) type. However, it is possible to locally reject the control operations on the IEC
60870-5-103 client side based on this indication and information about the client type
(NCC or Station).

Control operation rejections

The IEC 60870-5-103 standard does not take into account that the IED could have
several remote client connections. It should be noticed that a remote control operation
could also be rejected if another remote client is performing a control operation at the
same time. The IED handles the remote command rejection in three different ways.
• Remote command to an existing object, while the IED is in Local mode or the IED
is in Remote mode, but control operation is blocked for some reason (Blocking
reasons include simultaneous control being performed by another remote client):
• The command is accepted on link level (Link ACK)
• The command is rejected on application level (Negative response,
COT=21)
• Remote command while the IED is still performing the previous command of the
same client:
• The command is rejected on link level (Link NAK, DFC=1)
• Remote command performed on a non-existing object:
• The command is rejected on link level (Link NAK, DFC=0)
In the last two cases the DFC flag is used to distinguish the faults.

Measurands

Measurand object transmission is defined by the IEC 60870-5-103 standard. The
standard does not define any method for transporting integer values like counters or
enumeral objects.
Measurands are transmitted as a set of Class 2 data, referred to as a Class 2 measurands
frame. According to the standard the coding of IEC 60870-5-103 measurand objects
must be 13 bit signed values in the range of -1...+1.
When an IEC 60870-5-103 measurand, for example phase current, is scaled as 2.4, it
means that the measurand value 1 corresponds to 2.4 × In, measurand value 0.5
corresponds to 1.2 × In, and so on. If the measurand value in this case exceeds 2.4 ×
In, the IEC 60870-5-103 object value saturates at its maximum value and an overflow
flag is set in the IEC 60870-5-103 object transmission.

Class 2 measurands

The interchangeable part of the IEC 60870-5-103 standard defines that only five Class
2 measurands frames exist. Measurands transmitted in these five Class 2 frames
1MRS757647 C
620 series
Communication Protocol Manual