Interpretation of Harmonic Contribution Indices with respect to Calculated Emission Limits

The general process of evaluating harmonic emissions of a customer installation consists of two stages. In the first (planning) stage, emission limits are calculated based on the procedures provided in standards or guidelines. In the second (operating) stage, the “actual” contribution of the customer installation to the voltage harmonic distortion during operation is assessed and compared with the calculated emission limits. Several methods for the contribution assessment exist, but it is not clear how the determined contribution should be compared with the limits calculated in the planning stage. Some aspects and considerations as to how the emission limits can be compared with the common indices for harmonic contribution assessment are presented in this paper. After a brief introduction of the commonly used procedures and calculation methods, an example of a simplified low voltage test system with three customer installations is used for the calculation and comparison of all relevant indices.