They are designed and configured with powerful engineering tools by highly trained staff. The maintenance of Digital SAS (DSAS) is different from that of conventional SAS because:

• DSAS pose new questions on how to ensure the effectiveness of maintenance over their whole life
• The professional profile of maintenance specialists has been changing with the technological evolution. This has an impact on the maintenance on DSAS

This new technology implies a change in the roles carried out by the traditional actors in the maintenance of DSAS and imposes different strategies for their maintenance practice in order to take into consideration new constraints,  such as software configuration and maintenance.  The approach for the maintenance of DSAS has to take into account system availability, total cost of ownership and the possibility of modification, extension or partial replacement of components. Specification, design, configuration, training and documentation are key elements contributing to the ability of the utilities to maintain a SAS during its lifetime. The Technical Brochure gives some guidance for stakeholders in DSAS maintenance - utilities and vendors.

Life Cycle and Maintenance Strategies of DSAS: When deciding the life cycle strategy of DSAS, utilities should take into account all aspects, from initial investment costs to decommissioning. The main contributing factors which have to be defined for their life-cycle strategy are identified in the Brochure. These factors also form the base for the definition of the utility's maintenance strategy during the life cycle of a DSAS shown bellow. 
The Technical Brochure briefly describes the different types of maintenance. As far as DSAS is concerned, the self-supervision implemented in these systems allows a reduction of preventive maintenance. It results in a shift away from preventive maintenance towards corrective maintenance.
The Brochure also describes different strategies for the outsourcing of maintenance.
Conservation of knowledge and skills for the maintenance of DSAS is a vital issue for utilities. Compared with conventional SAS, maintenance of DSAS requires a higher level of training and skills. 

Specification and testing:   Specifications of the DSAS should contain requirements related to the maintenance policy of the utility. It is important to ensure that the maintenance operations are feasible under the conditions defined by the utility.  These conditions include the global availability of the DSAS, safety conditions and acceptable degraded operation.  Level of specifications and maintenance principles can vary greatly between large and small utilities, between different voltage levels and depending on type and importance of substations. 

As with the other technical requirements in the DSAS specification, the approval and test process of the utility has to include the verification of the maintenance requirements.  Maintenance and test procedures following maintenance operations should be included in the DSAS documentation.

The maintenance tests in conventional bays are organized on the basis of "one equipment = one function." In a DSAS, one function can either be integrated together with other functions in the same device (Functional Integration) or can be distributed over several devices. The testing procedure has to take into account the implementation of the functions and cannot always be performed as an almost independent procedure for each function. Attention must be paid to the maintenance tools, which may experience maintenance constraints similar to the DSAS itself.

Overview of Utility Maintenance Practices for DSAS: Based on a questionnaire prepared by the WG, an insight into the current practice of maintenance of DSAS has been obtained and analyzed. Some key points are:

• There still seems to be a considerable amount of time-based maintenance on DSAS. The potential offered by self-supervision of DSAS is not completely used
• The average period for configuration modification is about 4 years, but there is a significant variation in the answers received
• About half of the utilities state that they use a comprehensive asset management system for DSAS
• Almost all interviewed utilities have trained maintenance staff
• Almost all utilities have a particular strategy for spare-parts, analyzed in the Brochure

Biography:
Volker Leitloff (1965), studied Electrical Engineering at the university of Stuttgart/Germany from where he earned the Dipl-Ing. degree in 1991. From 1991 to 1994 he prepared his PhD-thesis at the Laboratoire d'Electrotechnique de Grenoble and received the Dr. INPG degree from the Institut National Polytechnique de Grenoble (INPG) in 1994. From 1994 to 2002, he was with the R&D Division of Electricité de France were he worked successively on network protection and on transformers and network technology. Since 2003, he has been  with the French Transmission Network Operator RTE where he works on protection of transmission networks and substation control. He is the French member of the CIGRE Study Committee B5, past convenor of CIGRE WG B5.06 on DSAS Maintenance and actual and past member of WG 34.10, B5.10, B5.13 and B5.43.