06-09-2012, 04:08 PM
DESIGN OF IEC 61850 BASED SUBSTATION AUTOMATION SYSTEMS
ACCORDING TO CUSTOMER REQUIREMENTS
DESIGN OF IEC 61850.pdf (Size: 348.04 KB / Downloads: 45)
INTRODUCTION
The standard IEC 61850 „Communication Networks and Systems in Substations“ will provide
interoperability between the electronic devices (IEDs) for protection, monitoring, metering, control
and automation in substations. Interoperability and free allocation of functions opens up a vast range
of possible solutions, but the consideration of customer requirements and commercially available
equipment will scale down this range to a handful of them. It is important both for utilities and
Substation Automation system providers to understand this process. This design process will be
outlined in the following chapters.
THE IMPACT OF IEC 61850 ON SUBSTATION AUTOMATION
The basic functionality of Substation Automation is given by its tasks and will not be changed by IEC
61850. On a first look, also the system architecture is not so much changed. Nevertheless,
communication is the backbone of SA and, therefore, IEC 61850 the most important key for designing
systems. A lot of inherent features in IEC 61850 like the use of object oriented data model, the
selection of mainstream communication technology allow responding very dedicated to requirements
stated in customer specifications not by chance but based on standardized rules. Therefore, these
features support designing optimized systems. Optimization includes not only functional performance
but also economic aspects like investment, availability, expandability and maintainability, i.e. all life
cycle costs. For specification, design and engineering, the most important feature of IEC 61850 is its
support to strong formal description of the substation and its automation system. The use of this strong
description facility will be mentioned in all steps below if applicable. If the customer is not providing
this formal specification, this task is left for the system integrator or provider to use its power for the
SA system design.
CUSTOMER SPECIFICATION
General
The customer specification has to include three areas of requirements, i.e. the functionality needed, the
performance requested, and all constraints applicable. The functionality refers mainly to the given
single-line diagram of the substation and the protection and control functions of the substation
automation system. The performance includes not only the reaction times on certain events but also
figures for reliability and availability. The constraints may include but are not restricted to given
switchgear (process) interfaces, to interfaces needed for remote network control centers or remote
maintenance systems. Constraints include also the geographical situation on-site, i.e. the distances
between components, building space, shielding and grounding facilities, and last not least the
existence of prescribed IED types. There might be non-technical constraints like requested quality
certificates, preferred project management procedures, documentation needs and training requirements
etc. The last ones are, however, outside the scope of this paper.
Performance
Performance comprises a wide range of topics such as response time, safety and reliability. These
requirements guide the allocation of LNs and their related functions to devices, and strongly influence
the structure of the communication system. Response time requirements can be subdivided into
average response time requirements, which are not process critical, and absolute worst case
requirements, whose deviation might lead to dangerous process states. If the performance
requirements are safety related or not, depends on the function using this data. Therefore, they should
be specified per function. For safety it might be sufficient to specify the degree of safety to be met as a
safety probability per function, typically a failure probability of 10-5/h to 10–6 /h for protection related
functions.
CONCLUSIONS
The design process with IEC 61850 is very similar to the common one. It depends partly on the given
prerequisites represented by topology constraints or predetermined devices. Nevertheless, based on the
inherent properties of IEC 61850, optimized Substation Automation systems can be designed, which
are not expensive and un-maintainable singular solutions, but reliable systems based on a global,
future-proof standard. The communication system has been proven to be scalable supporting the
requested availability. It was also shown that the availability is not only a communication issue but
also a matter of redundant functions in separated IEDs.
The free allocation of functions has been used in a very conservative way only. More freedom based
both on state-of-the-art in technology and acceptance by the utilities will improve the optimization
supported by IEC 61850, but ever existing constraints will always control the process as described in
this paper above.