Recognising that the experience gained on HVDC transmission systems could be of value throughout the industry, CIGRÉ Study Committee 14 established Working Group 04, Performance of DC Schemes, with terms of referencewhich included an obligation to collect information on all systems in
commercial service.

It was considered that such information could be useful in the planning, design, construction and operation of new projects. It was also envisaged that the sharing of operational performance data could be of benefit to those concerned with the operation of existing HVDC links or those planning new HVDC links.

It was clear that such reports were best prepared in accordance with a standardized procedure so that, with time, the accumulated data from several systems would establish a basis against which performance could be judged.

General information collected includes a system description, main circuit data and a simplified one-line diagram for each scheme. This descriptive information is compiled in a Compendium. The Compendium is revised biennially with the pages distributed to Regular Members of SC14.

The Regular Members may be contacted to obtain the latest copy of the Compendium or revised pages as required. The Compendium or revised pages may also be obtained through the Chair or Secretary of WG 14.04. Furthermore, operational performance data is collected annually from each scheme in commercial operation.

Performance data include reliability, availability and maintenance statistics. Reliability data are confined to failures or events which result in loss of transfer capability. Statistic are categorized in order to indicate which type of equipment caused the reduction in the transmission capacity.

With the exception of recording thyristor failures, data on component failures not causing a loss of transmission capacity are not recorded. Reliability data on individual components such as capacitors, relays or circuit breakers is more appropriately kept by groups directly involved with each respective apparatus. Working Group 04 summarizes the performance statistics for all reporting schemes every two year in a CIGRÉ paper entitled “A Survey of the Reliability of HVDC Systems Throughout the World.”

As the equipment and techniques of HVDC transmission developed, for example, the replacement of mercury- arc valves by thyristor valves in new projects; it has been necessary to revise or supplement the procedure from time to time. This revision of the Protocol will provide more accurate data on scheduled or planned outages, reporting of system capacity and commutation failures summarized as follows:

a) Outages taken for major reconfiguration shall not be reported.
b) Scheduled outages will include work that may be postponed until a suitable time during light load periods—usually night or weekend. Outages of this type will include work on redundant systems such as the controls where there is the philosophy of the owner to schedule an outage for this activity.
c) Maximum capacity has been clarified to include capacity available through utilizing redundant equipment when system may be loaded over normal conditions.
d) Inverter end commutation failures during ac faults will be reported when ac bus voltage drops below 90 percent rather than 85 percent.

Another category has been added to commutation failures related to control problems.Scheduled equipment unavailability (SEU) has less significance than forced equipment unavailability (FEU) in comparing different systems since scheduled outages may be taken during reduced system loading conditions or when some reduction in power transfer capability is acceptable.

Discretionary outages for maintaining redundant equipment are also considered within the SEU category. Accordingly, SEU is intended to be used mainly by owners over a long period of time for general comparison or for comparisons of their own needs, and not intended to be used for evaluating reliability of availability performance in RAM design or under RAM warranties.

This revised Protocol has been distributed to SC14 members for ballot last quarter, 1996 and was approved in March 1997. The Protocol will supersede the earlier issues and should be used for reporting 1996 performance and beyond.

NOTE—General terms relevant to HVDC transmission with explanatory figures are to be found in the International Electrotechnical Commission publication 633, “Terminology for High-voltage Direct Current Transmission” to which reference should be made.

Please observe that the time should be given in “decimal hours” i.e., 6 h:30 min = 6.5 hours.

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