A refined general summation law for VU emission assessment in radial networks

• A discussion on the existing methods for voltage unbalance emission allocation and assessment in distribution networks.
• Development of a statistical approach for voltage unbalance emission assessment.
• Development of a new general summation law for aggregating randomly varying voltage unbalance levels.
• Several case studies demonstrating the validity of the methods presented.

Voltage unbalance (VU) management of power systems requires the development of well researched engineering practices to maintain acceptable VU levels while utilising the total VU absorption capacity of the power system. In this regard, IEC/TR 61000-3-13:2008 prescribes a VU emission allocation methodology based on a stochastic approach which uses a general summation law in order to aggregate numerous sources of unbalance to take into account their random variations. On the other hand, recent deterministic studies on VU emission assessment at the post-connection stage of unbalanced installations present a complex VU factor based approach to determine constituent components of the post-connection VU emission at a point of evaluation. The primary objective of the work presented in this paper is to develop statistical approaches for compliance assessment using the outcomes of the deterministic methodologies on VU emission assessment, thus refining the existing general summation law. A revised general summation law is established, introducing weighting factors to evaluate the influences made by different sources of unbalance separately, in order to assess VU emission in radial networks.