WG C4.27 "Benchmarking of power quality performance in transmission systems"
Understanding and specifying technical performance of power systems is a critical factor in ensuring overall operating and capital costs are optimised. While reliability is often a key consideration, power quality is also important. PQ performance is influenced by regulatory and investment standards which may vary between System Operators. Benchmarking the adopted standards can be helpful in ensuring that the standards and associated costs are appropriate and can provide useful information to guide the setting of performance targets. CIGRE working group C4.27, was established in 2014 with a brief to investigate methods of benchmarking power quality (PQ) performance in transmission systems and has since produced Technical Brochure 718. Australia was represented by Sean Elphick from the Australian Power Quality and Reliability Centre (APQRC).
The specific scope of the working group was to develop a set of guidelines for benchmarking transmission technical performance based on:
- A review of the practical application and definitions of the indices proposed by C4 Technical Brochure 261 for transmission and sub-transmission systems.
- The definition of important “internal” indices such as circuit availability and line fault rates.
- Consideration of the implications for monitoring and reporting systems.
- Recommendations on how power systems can be described to assist transmission companies, regulators, and benchmarking companies in the identification of suitable peer groups.
- Highlighting what historical data, system descriptions and calculation methodologies need to be in place for effective benchmarking to be undertaken.
Highlights of the work undertaken and included in the technical brochure are:
- Identifying the power quality phenomena that are important for the purposes of benchmarking entire transmission systems. Five PQ parameters to define transmission system power quality were ultimately selected: voltage harmonic distortion, voltage flicker, voltage unbalance, voltage dips and short interruptions.
- Consideration of the different nature of PQ indices and development of different approaches to manage data related to continuous PQ phenomena (harmonics, flicker and unbalance) and event-based phenomena (voltage dips and short interruptions).
- Recommendations for the minimum set of indices that would adequately describe each of the PQ parameters for the purposes of transmission system benchmarking.
- Recognition that in order to allow for different parts of the system to be compared (benchmarked) or even for different transmission systems to be benchmarked against one another, two different sets of indices are required. This approach recognises that different network operators have different regulatory and investment regimes, which are the main drivers for system PQ performance. Furthermore, different network operators may have adopted different levels of PQ disturbances that are deemed acceptable to their system operations. It was determined that the minimum set of system indices should therefore include:
- A set of indices based on compliance against the limits adopted by the network operator as a measure of effectiveness of the technical standards and the policing of network access; and
- A set of indices based on the actual magnitude of the PQ parameters.
- Identification of the important system parameters and other technical and non-technical variables that must be considered when undertaking benchmarking in order to ensure that fair comparisons are made across sites and systems (i.e. ensure that apples are compared with apples).
- A general outline of the benchmarking process.
The outcomes from the working group are now being used by the APQRC as part of its ongoing Power Quality Compliance Auditing activities. A number of Transmission Network Service Providers operating within the National Electricity Market are currently utilising the APQRC for power quality benchmarking and ongoing compliance assessments.
The Technical Brochure (TB) 718 can be viewed on e-CIGRE and is free to members. The cost to non-members is €140.