Voltage unbalance emission assessment in interconnected power systems

The International Electrotechnical Commission (IEC) Technical Report IEC/TR 61000-3-13:2008 considers voltage unbalance (VU) emission assessment as a key aspect of the VU management of power systems. Compliance assessment of unbalanced installations at the post connection stage is essential to ensure that the limits set by the IEC VU emission allocation methodology in the pre-connection stage are met. Although VU is known to be caused by load asymmetries and inherent network asymmetries, locating all VU emission sources is not a straightforward process, especially in a network with interconnections. Such assessment methodologies should ensure that the contributions from various sources of unbalance to the total VU emission are determined using data which is not overly demanding. This paper presents deterministic methodologies which can be used to assess constituent components of post-connection VU level at the point of evaluation in an interconnected network utilising post connection voltage/current measurements and known system parameters. The theoretical bases are developed to cover different load types including induction motors. Emission assessment outcomes of different study systems obtained by employing the proposed methodologies are verified using unbalanced load flow analysis.