JWG C4.42/CIRED Continuous assessment of low-order harmonic emissions from customer installations

Background:
Harmonic voltage distortion remains an important issue in power networks and utilities are fully aware of the impact this creates on power quality. With the increasing number of power electronic loads, harmonic interactions and inverter based generation, e.g. PV and wind, the issue is likely to become more exacerbated in the future. A proper determination and quantification policy for low-order harmonic emission levels could help restrain harmonic voltage distortion in power networks. For example, an incentive based policy could compel the customers to keep the harmonic emission levels inside required limits, but the assessment of the harmonic emissions remains a challenge. Basic guidelines on the assessment of the harmonic emission levels are provided within the IEC TR 61000-3-6. However, the detailed methods to determine the harmonic emission levels remain complex and highly difficult to be used in practice. The assessment should preferably run continuously with the statistical evaluation of results and not as a single-shot (at certain time instant) or two-step (before and after the connection of installation) procedure. In recent years many techniques were proposed to determine the harmonic emission levels but for various reasons none of them is widely used in practice, i.e. these methods require the knowledge of the actual network data in terms of system impedance. The aim of the work is to review the current industry practice and the new technologies and approaches available in this field and to propose practical guidelines for online monitoring and continuous assessment of low-order harmonic emissions from disturbing customer installations.

Scope:
1. Review of harmonic emission assessment methods with present background distortion based on the IEC approach (basic definition of emission)
2. Evaluation of methods for system harmonic impedance determination (invasive and non-invasive methods, reference impedance) with non-invasive methods being based on natural fluctuation of loads (regression methods)
3. Consideration of technical limitations related to harmonics measurements (CTs and VTs) and sensitivity analysis (measurement errors, system impedance estimation error)
4. Consideration of statistical assessment of results, i.e. 95% value in 1 week, aggregation of results (intervals 200 ms, 3 s, 10 min, …)
5. Recommendation and specification of a clearly defined methodology with clear instructions for practical implementation

Time Schedule : Start : May 2015 Final report : December 2018

Convener:Igor Papič (Slovenia)