SUBSTATIONS SESSION Chairman: Ernst GOCKENBACH Reporter: Mark WALDRON

Session overview Six presentations in 150 minutes Speakers have 15 minutes for presentation Maximum 5 minutes will be allowed for questions & discussion on each presentation A minimum of 20 minutes allocated for general discussion and/or responses to prepared questions.

Session 3 questions (1) Question 1 Reliability & dependability will be critically important for UHV equipment but, as described in the session papers, switching devices and other equipment for UHV are quite complex e.g. the incorporation of resistors into switching devices. Is the increased complexity in equipment design a concern for long term reliability of the UHV systems and what measures/techniques have been applied during design and testing to mitigate this risk. Question 2 Differing solutions have been proposed with regard to substation layouts (double busbar, 1.5 circuit-breaker, double circuit-breaker) and the preferred technology (AIS, GIS, MTS). Can participants provide greater insight into the decision making process in these areas to ensure the optimum solution taking into account factors such as operational constraints and requirements (e.g. outage planning and fault resilience), technology, investment cost, impact upon the environment (space, visual amenity etc), impact of the environment on the equipment (pollution, seismic etc)? Does the large physical dimensioning of AIS equipment insulation pose any particular problems either for design or maintenance?

Session 3 questions (2) Question 3 Session papers have demonstrated that the insulation coordination design of UHV systems needs to consider all equipment as part of an integrated approach. For example the inclusion, or not, of switching resistors within circuit-breakers and disconnectors and knowledge of the precise characteristics of surge arresters can have a significant impact upon the design and testing of other substation equipment such as transformers. Various solutions have been presented. Do participants believe that the present “project specific” design approach delivers the optimum solution or would it be appropriate to standardize more elements of design and reduce variation? Is there an optimum solution or do differing approaches have equal merits? Who is ultimately responsible for the performance of the overall design? Question 4 Various difficulties have been presented regarding the testing of UHV equipment both in the laboratory (making & breaking tests, dielectric testing etc) and at site (HV testing of GIS etc). Large laboratories and suppliers have responded to these challenges with extensions and/or variations of existing test techniques leading to increasing size of test equipment and costs. Are there significant breakthroughs within reach which could simplify the techniques and methods available for testing of UHV equipment and installations? Does theoretical modelling and study have a greater role to play in the verification process for UHV?

Session 3 questions (3) Question 5 To date, insulation coordination practice for UHV is largely based on extension of the procedures and data from lower voltage installations; an approach which appears to be quite robust. Do participant believe that there are areas where existing techniques, knowledge, or information on the performance of basic insulation media are lacking and where more detailed investigation is required? Are there specific examples of problems that have been experienced in this area? Question 6 The switching duties required of disconnectors (e.g. busbar transfer switching) and earthing switches (induced current switching) at UHV levels can be quite onerous and the transients produced can be severe, particularly within GIS. The devices in question are, typically, developments of existing designs which have been developed to cater for increasing duties which were not originally envisaged. Are existing devices, either with or without switching resistors, the optimum solution for long term operation? Are there alternative solutions available using different technology or is it possible to minimise the use of disconnectors by adapting other equipment and/or the substation layout?