Voltage fluctuations, flicker, harmonics and voltage unbalance in power systems are critical factors in the consideration of power quality. They have traditionally been prescribed in a number of IEC Technical Reports. With the changes that are taking place in power systems such as the connection of distributed generation systems at all voltage levels, it is timely to consider what revisions are needed to ensure the standards remain adequate. To this end, a Joint Working Group CIGRE / CIRED C4.40, has been established and is well under way to produce a Technical Brochure by the end of 2019. Australian contributors to this work are Sarath Perera, Vic Gosbell and Alex Baitch.
The IEC Technical Reports 61000-3-6 (harmonics at MV, HV, EHV), 61000-3-7 (voltage fluctuations and flicker at MV, HV and EHV), 61000-3-13 (voltage unbalance at MV, HV and EHV), and 61000-3-14 (harmonics, voltage fluctuations and flicker, and voltage unbalance at LV for large installations) deal with the assessment of emission limits for the connection of disturbing installations to the power system.
The scope of the Joint Working Group is to:
Evaluate the suitability of the general limit allocation process in systems containing distributed resources and develop recommended changes (this applies to all four reports).
Evaluate the suitability of existing indices and limits (e.g., 95th percentile) for use in reconfigurable systems and recommend changes (this applies to all four reports).
Evaluate the suitability of the existing approach for allocating harmonic limits for higher-frequencies (above 2 kHz) and recommend changes (this applies largely to 61000-3-6 and -3-14).
Assess the effectiveness of 61000-3-7, 3-13, and 3-14 when fluctuating or unbalanced distributed resources are present (at any voltage level) and recommend changes.
Review industry experience with the present versions of the Reports and recommend changes as needed, based on recent usage and experiences (this applies to all four reports).
Major deliverables are the revised versions to each technical report with highlighted changes for review by IEC.
Through the work undertaken so far, the working group has agreed how to take into account distributed generation in the limit allocation process, which applies to all disturbance types. A major Australian contribution on harmonics is the voltage droop method that is applicable to radial systems as an alternative approach for determining a customer allowance.
The Terms of Reference for this Joint Working Group can be downloaded HERE