What is a Function in IEC 61850?

The term "Function" is used in a variety of flavors throughout the standard series IEC 61850. If you ask five experts, you may get six answers.
IEC TC 57 has proposed (57/1863/DC) to develop a new Technical report IEC 61850-6-100: "SCL Function Modelling for Substation Automation"
A "function" is more or less a synonym for operation or action ... as described in Wikipedia:
"A function model or functional model in systems engineering and software engineering is a structured representation of the functions (activities, actions, processes, operations) within the modeled system or subject area."
In my seminars I compare IEC 61850 with Logistics:



IEC 61850 defines simple and more and more complex functions. A schedule according to IEC 61850-90-10 defines a set of quite complex (or comprehensive) functions. In most cases the functions defined by IEC 61850 are just functional components that are used as bricks to build a comprehensive application function.
The brick-concept of IEEE 1550 (UCA 2.0) indicated the use of the standard models: the Bricks (which are now the Logical Nodes in IEC 61850).
IEC 61850-7-2 Services define functions (called services) that provide information logistics, e.g., for accessing the device information model, allow exchange of any value made available by a device based on events for real-time and non-real-time applications, or services for controlling a controllable item like a circuit breaker or a fan.
Functions may be composed using the standard IEC 61499 (Function blocks) as described in the following papers:
V. Vyatkin, G. Zhabelova, N. Higgins, K. Schwarz, and N.-K. C. Nair, Towards intelligent smart grid devices with IEC 61850 interoperability and IEC 61499 open control architecture, IEEE Conference on Transmission and Distribution, New Orleans, April, 2010
 N. Higgins, V. Vyatkin, N. Nair and K. Schwarz, “Intelligent Decentralised Power Distribution Automation with IEC 61850, IEC 61499 and Holonic Control“,IEEE Transactions on Systems, Machine and Cybernetics, Part C, 40(3), 2010,
J. Xu, C.-W.Yang, V. Vyatkin, S. Berber, Towards Implementation of IEC61850 GOOSE Messaging in IEC61499 Environment, IEEE Conference on Industrial Informatics (INDIN’13), Bochum, July 29-31, 2013
Click HERE for more papers.
More to come ... stay tuned to this blog!

What is “Control with Enhanced Security”?

The IEC 61850-7-2 Control Model defines several operation modes:

• Status Only
• Direct control
  - normal security: Operate, TimeActivatedOperate, Cancel
  - enhanced security: Operate, TimeActivatedOperate, Cancel, CommandTermination
• SBO control (Select Before Operate)
  - normal security: Select, Operate, TimeActivatedOperate, Cancel
  - enhanced security: SelectWithValue, Operate, TimeActivatedOperate, Cancel, 
     CommandTermination

Have you ever tried to understand, implement, or use the option “Control with enhanced security”? The term can be quite misleading for people to believe that it has something to do with Cyber Security! No, it is not linked to that kind of security – even every operate command shall be secured by communication security measures.

So, what is it then? Usually I have explained it with the following slide.

Here is a one of many understandable use-cases for a specific switchgear (based on an email exchange with a very good friend of mine – a real switchgear expert … that believes in IEC 61850):

The proper name should be “Control with Confirmed Feedback”, so that any interlocks in the switchgear (can be abstract as well), need to be in the De-active state for the switchgear to report “Command Termination”, which would mean: the Control Element is now ready for another Operate service request.

A circuit breaker (CB) spring (drive) mechanism may work that it is only charged when the CB is Opened or Tripped. Then the energy in the spring mechanism would be enough to perform a Close Operation as well as a Trip Operation.

As the Trip mechanism does not need spring re-charging, it is instantaneous. However, there is a big delay after the Trip operation which is needed for the spring to charge or reset the mechanism again.

Although the indication of Trip will be instantaneous and reported spontaneously, however the switchgear cannot accept a new command since the spring mechanism is being recharged. During this time, the unit will not transmit the ‘Command Termination’ message so that a new command cannot be initiated. Once the spring is successfully charged, a ‘Command Termination’ message is transferred.

The CB mechanism example given above is one of many… there are some linear actuators which can Over-shoot during the process of operating the switch, this is then re-adjusted (i.e., brought to the normal position) after the instantaneous status change. The extra time needed to re-align actuator position (or to bring the actuator in the dead zone), will be the time after which the ‘command termination’ message is sent out.

Lesson learned: Ask always the domain experts!

Any question on IEC 61850?

When to use Operate Service and when SetDataValues?

The IEC 61850-7-2 abstract services Operate and SetDataValues are both mapped to MMS Write in IEC 61850-8-1. So, what makes a MMS Write service an Operate or a SetDataValues?

The two services and the mapping are sketched here:

The first mapping is showing the Operate service (as part of the control model):

The Operate service is used in conjunction with the control model (defining state machines, select-before-operate, time-activated control,…). Control service models require a special information model: controllable Common Data Classes, e.g., SPC – Controllable Single Point. The model comprises attributes defined by the CDC and the service parameter ctlVal: these are shown in the MMS Variable as a structure “Oper” with the components: ctlVal, origin, ctlNum, T, Test, Check. These have to written at MMS level. These are always required for Operate even if you need just ctlVal !!

The settable DataObjects require the MMS Write as shown in the following figure:

In IEC 61850-7-3 it is defined exactly which services are to be used for the various attributes in the Common Data Classes. Example for controllable DataObjects:

 
Note that the FC=CO is defined in 8-1 !

Note also that client user interfaces (like the IEDScout) may use different service names than 7-2 or MMS.