Introduction

Albertino J. Cerejo Meneses received his Licenciatura degree in Electrical Engineering from the Faculdade de Engenharia, Universidade do Porto, Porto, Portugal, in 1977.
He is with Rede Eléctrica Nacional, S.A. (the Portuguese TSO) since 1980; he was Head of the Operations Department (South) from 1994 to 1998 and Head of the Telecommunications Department from 1998 to 2001. He is Head of the Systems Department since 2001. Mr. Meneses is member of the Portuguese professional association of engineers. He is currently the Portuguese representative in Study Committee B5 (Protection and Local Control) of CIGRE.

In response to the 12 questions posed by the Special Reporter, 38 prepared contributions were received, of which 35 were presented at the session.

This article intends to briefly summarize the findings, the discussions and the conclusions of the session.

Special Protection Schemes

Concerning the questions about costs, risks and telecommunications issues (questions nº 1 and 3), contributions focused on the importance of availability and reliability of the communication systems and mentioned the need to carefully design communications architectures in order to meet the requirements for performance and security (e.g. ensuring system redundancy and implementing voting schemes and self-healing solutions). On cost issues, there are expectations that economical gains from improved operational performance should outweigh high construction costs.

Regarding the question on cooperation issues (question nº 2), all contributions recognised the importance of close cooperation between countries, institutions such as CIGRE and EPRI, and also between manufacturers and utilities.

Concerning different approaches used in implementing network defense plans (question nº 4), some examples were given of the use of loss-of-synchronism detection (Brazil, Japan, France, and Western North American Power System), using either local or wide-area signals as well as adaptive or non-adaptive methods.
Regarding future developments and trends (question nº 5), while some contributions saw definite advantages in the use of centralized solutions, one contribution from the USA sees a need for hierarchical SPS, combining centralised and local decision, to ensure the implementation of adaptive solutions. Nevertheless, all contributions stressed that communication protocols will play a major role in the successful implementation of SPS.

Wide Area Protection Principles

In response to question nº 6, which addressed the comparison between traditional and new approaches to load shedding, there was a general consensus among all contributors that new voltage-dependent Wide Area Measurement (WAM) Systems resulted in a lesser amount of load shed, when compared with traditional under-frequency load shedding schemes.

Concerning the integration of Phasor Measurement Units (PMU) from different manufacturers and experiences on controlled tests with effective switching (question nº 7), the contributions mentioned the difficulties encountered in the integration process, stressing the need for a standard format of phasor measurement data, and reported both new PMU/WAMS projects (Brazil) and evolution in existing ones towards including WAM in closed-loop operation, aiming at an increased number of "meshed" WAM Systems within Europe.

Preventive Measures to mitigate Large Disturbances

Question nº 8 addressed the eventual influence of recent blackouts in the regulatory environment, as well as new system protection requirements resulting from regulatory or public opinion pressure. Two contributions (Brazil and USA) described the publication of specific more stringent protection requirements following recent blackouts. Actual implementation, however, will take time, as the need for accurate time-synchronization of all IEDs and recording of waveforms and voltage and frequency profiles is recognized.

Concerning the implementation of system-wide common criteria for protection and control systems, and the impact of the definition of critical fault clearing times (question nº 9), contributions reported the need to apply unit protection concepts, with redundant communication / teleprotection schemes.

In response to question nº 10, concerning decision-aid software tools, the contribution from the Netherlands described the development of a measuring device to complement the software tool - aiming to improve safety and reliability.

Question nº 11 addressed experiences in the specification and use of Line Differential Protections. Although some concerns were expressed, regarding the use of optical repeaters (Brazil) or personnel training issues (Spain), the majority of contributions reported that, with the availability of more powerful communication infrastructures, Line Differential Protections are now part of most national / utility guidelines for transmission line protection. The advantages mentioned include detection of very high resistance faults and immunity to power swings. Line differential protections are also seen as the best solution for the protection of series compensated lines. It must be noted that even in the cases where concerns were expressed, use of line differential protection is growing and the results are seen as very positive.

Service Restoration Practices

Only one paper was published under this category, discussing the service restoration part of the Brazilian Defense Plan, emphasizing a decentralized approach and steps taken towards the optimization of the process.

Question nº 12 tried to raise some discussion on restoration practices, comparing the requirement to keep manned substations to aid restoration with the implementation of redundant telecontrol, telecommunication or automation infrastructure / equipments. The only contribution to this question was received from the paper's authors, who explained the perceived need to keep at least some manned substations, especially in generation substations in "fluent" restoration corridors.

CONCLUSIONS

From the contributions received and the discussions in the session, a number of conclusions can be drawn. The main conclusions are grouped by discussion topic as follows:

1.Special Protection Schemes

• Reliable communications are essential;
• For implementation of new SPS, close cooperation between manufacturers, integrators and utilities will be crucial;
• There are definite advantages in using  centralized / hierarchical SPS;
• Communication protocols will play a major role in the successful implementation of SPS;
• Extensions of IEC61850 to cover communication between substations and to central levels are already being considered.

2.Wide Area Protection Principles

• Both WAP-based and voltage-dependent applications show improvements over traditional under-frequency load shedding (UFLS), regarding the amount of load shed;
• PMU implementation is in its 1st phase, evolving into "meshed" WAMS in Europe;
• Improvements in integration expected with newer equipments.

3.Preventive Measures to mitigate Large Disturbances

• Specific, more stringent requirements and regulations in place following recent blackouts;
• Some of those requirements imply de facto unit protection concepts (e.g. new Australian Electricity Rules);
• However, most utilities already use / specify in this way (e.g. redundant teleprotection schemes);
• Critical clearing times are defined in most national / utility guidelines for transmission line protection;
• Line Differential protections come of age as more powerful communication infrastructures become available. There are, however, some points to consider:
  • Integration of Distance function, to overcome communication failure;
  • Personnel training issues must be addressed, to avoid the "black box" syndrome.

4.Service Restoration Practices

• Not enough information to allow an overview and discussion of practices.

Biography

Albertino J. Cerejo Meneses received his Licenciatura degree in Electrical Engineering from the Faculdade de Engenharia, Universidade do Porto, Porto, Portugal, in 1977.
He is with Rede Eléctrica Nacional, S.A. (the Portuguese TSO) since 1980; he was Head of the Operations Department (South) from 1994 to 1998 and Head of the Telecommunications Department from 1998 to 2001. He is Head of the Systems Department since 2001. Mr. Meneses is member of the Portuguese professional association of engineers. He is currently the Portuguese representative in Study Committee B5 (Protection and Local Control) of CIGRE.