Impact of IEC 61850 on Protection and Automation

Priorities

Automation of substations, with integrated protection and control systems and the use of the new IEC 61850 Standard are major industry trends. The application of IEC 61850 will be extended to further areas and its impact will demand continued review and study to detect any general problems, so that they can be addressed before they become too widespread. CIGRE SC B5 provides a unique channel of feedback to IEC in this respect.

Relevant issues related to the IEC 61850 standard are:

• Functional testing of IEC 61850 based systems
• Application of protection schemes based on IEC 61850
• Engineering Guidelines for IEC 61850 based systems
• Maintenance strategies for Substation Automation Systems
• Impact of security requirements on SAS

The introduction of digital hardware and numerical protection technology has greatly transformed the planning, operation and maintenance practices for protection systems. Design engineers now require appropriately adapted guidelines to support their work. Several working groups are preparing reports about on-going trends and offering recommendations for the protection of generators, transformers, shunt reactors, overhead lines or cables and busbars.

Modern numerical relays are highly integrated and contain a great number of protection and additional functions. Special attention is given to the increasing trend for functional integration. "Bay Units" for combined protection and control are now accepted at distribution levels and this trend may migrate to the transmission levels. Numerical relays are widely self-monitored. Regular routine testing will therefore be increasingly replaced by condition-based maintenance, depending on how comprehensive the self-monitoring is.



System-wide monitoring and protection

Wide area disturbances due to loss of stability or voltage collapse, still occur and may become more probable in the future, with higher system loading and by regularly operating plant and power systems towards their design limits and capabilities. On the other hand, wide-band communication links, adaptive digital protection and GPS synchronized data acquisition provide platforms for novel system wide monitoring and protection techniques. In many countries a large part of the business is the retrofitting of existing plants and systems because of life-expiry, or because of recommendations about the need to change current practices. The development of life-cycle maintenance and risk management strategies are therefore expected.

Software tools for dynamic simulation, management of relay settings, disturbance or fault record analysis, or how to write specifications are improving.

Emphasis on education is a challenge, considering that protection is generally not a topic dealt with to any significant depth by colleges and universities, and that engineers entering in the power engineering sector in general are becoming rare.

Numerical technology combined with advances in information management contributes to the more efficient management of power networks, but it introduces problems and issues in four main areas: level of integration, standardization, information management, wide area monitoring and protection.

The integration of ever more functions into fewer devices and systems has been an increasing trend - especially over the last 10 years or so. Figure 1 indicates the evolution of the number of devices for a protection and control system covering a station with six 220 kV lines and eight 16 kV feeders.

Protection function integration is now the norm and combined with high level of self-supervision in numerical protection devices actually supports a higher degree of integration - a trend that will continue in the future.

The modern protection technology facilitates new solutions and functions to tackle several fault management problems, such as the protection of combined cable-overhead lines (adaptive auto reclosing with ability to distinguish potentially transient overhead line arcing faults from solid cable faults) or the protection of parallel and/or multi-terminal lines.

Standardization

Standardization covers two main aspects: Typical Bay and Station levels and Communication.

Independently of the applied technology, it is possible to define the required functionality and performance of each protection and control function (tripping times, precision, etc) for each type of Bay, in each type of substation. Users can define additional requirements, such as the permitted level of functional integration, the physical scheme architecture, the requirements concerning DC auxiliary/tripping supplies, test facilities, wiring and inclusion of some specific devices. Functional requirements can also be listed at the Station level, covering HMI (Human Machine Interface), event and alarm lists, etc.

Specifications need only be functionality based, with reference to a single line diagram, rather than detailing specific protection system devices.

Communications

Communications in substations should assure interoperability between compliant Intelligent Electronic Devices and functions within the substation. They should be future-proofed, i.e. able to cope with the fast developments in communication technology compared to the more slowly evolving application domain of power systems.

These are very ambitious goals, which demand that all secondary substation devices and functions must be examined with regard to their communication performance and requirements.