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WG C2.23 System Restoration Procedures and Practices

WG C2.23 System Restoration Procedures and Practices 

While all System Operators have similar objectives to restore power as quickly and smoothly as possible following a power outage, procedures and practices may vary due to system or market differences.  In addition these restorations may not always proceed as planned.  Working Group C2.23 has conducted a review of system restoration procedures and practices adopted by System Operators to determine ways to improve effectiveness and efficiency and reduce associated risks.  The findings have been published in Technical Brochure 712 and the Australian member on the working group was Mark Miller. 

Working Group C2.23 has completed a review of the system restoration methods and processes adopted by various transmission system operators (SOs) to evaluate both common and unique approaches applied to various aspects of system restoration. The working group has also reviewed a number of recent disturbances for lessons learnt from restoration experiences to identify challenges and explore ways to improve the effectiveness and efficiency of system restoration.

The working group surveyed 18 SOs in 7 key areas related to system restoration and made the following observations and conclusions:

a.  In general, most SOs adopt a range of common approaches in various aspects of system restoration including:

    • Acquiring system awareness,
    • Developing restoration plans,
    • Providing training and conducting drills involving operating personnel and restoration participants,
    • Communicating with other operating entities such as neighboring SOs and DSOs, government agencies and the general public.

b At present, apart from the difference in system characteristics and installed facilities, there does not appear to be any particular approach adopted by an SO that is superior or inferior.

c. Most SOs have well-structured system restoration plans, communication facilities, communication protocol with government agencies, regulators, general public and other operating entities, adequate training and preparedness including black start and resynchronizing capabilities, etc.,

d. There are certain enhancements that may be worth considering to further improve restoration effectiveness and efficiency where these are not yet installed, including:

  i.  Adopting state of the art awareness and analytical capabilities such as:

        • Advanced SCADA and EMS functionality including wide-area security assessment or a fully integrated control landscape including SCADA/EMS, PMU within Wide-Area Control Systems and
        • Advanced analytics tools such as dynamic security analysis

ii    Adding private phone lines and satellite phones instead of public phones to enhance voice communication capability.

iii   Expanding the operations team resource to provide key information needed to support communications to external stakeholders. 
iv   Providing predictive monitoring of black start source performance.
v    Monitoring distributed generation, defining rules for restoration strategies to avoid reconnection until the frequency is stable and using storage systems such as pumped hydro plants as an alternative to end-use customer loads where possible.
vi   Developing a full set of rules with accompanying tool capabilities to aid operation and re-paralleling of islands, and developing operating procedures aided by automated or computer assisted capabilities.
vii  Developing a process and the necessary capabilities to assess frequency, voltage and angle differences, and initiate actions to reduce these differences to within the re-parallel setting thresholds prior to executing island resynchronisation.
viii Improving the effectiveness of voltage control by including pre-determined tolerances, dispatching reactive resources including shunt devices, and operator training.

e.  Future trends and developments:

i.   A separate Joint Working Group (C2/C6.36) is assessing potential challenges and possible contributions by distributed energy resources on system restoration.
ii.  HVDC links (VSC or LCC) can be used to aid system restoration including providing active and reactive support during black start and building the pathway between small and large generating units.
iii. The use of phasor monitoring units and other advanced technologies can enhance awareness and restoration process.

The survey provides an indication of general industry practice required to prepare for system restart. This is particularly relevant for the National Electricity Market in Australia as the appropriate balance between the costs and benefits of such activities has been a topic of some debate 

The Technical Brochure (TB) 712 can be viewed on e-CIGRE and is free to members

The cost to non members is €90.