Upuli Jayatunga

Voltage Unbalance Emission Assessment in Radial Power Systems

Voltage unbalance (VU) emission assessment is an integral part in the VU management process where loads are allocated a portion of the unbalance absorption capacity of the power system. The International Electrotechnical Commission Report IEC/TR 61000-3-13:2008 prescribes a VU emission allocation methodology establishing the fact that the VU can arise at the point of common connection (PCC) due to both upstream network unbalance and load unbalance. Although this is the case for emission allocation, approaches for post connection emission assessment do not exist except for cases where the load is the only contributor to the VU at the PCC. Such assessment methods require separation of the post connection VU emission level into its constituent parts. In developing suitable methodologies for this purpose, the pre- and post-connection data requirements need to be given due consideration to ensure that such data can be easily established. This paper presents systematic, theoretical bases which can be used to assess the individual VU emission contributions made by the upstream source, asymmetrical line and the load for a radial power system. The methodology covers different load configurations including induction motors. Assessments obtained employing the theoretical bases on the study system were verified by using unbalanced load flow analysis in MATLAB and using DIgSILENT PowerFactory software.

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 postconnection stage is essential to ensure that the limits set by the IEC VU emission allocation methodology in the preconnection 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. These assessment methodologies should ensure that the contributions from various sources of unbalance to the total VU emission are determined using data which are not overly demanding. This paper presents deterministic methodologies which can be used to assess constituent components of the postconnection VU level at the point of evaluation in an interconnected network utilizing postconnection 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 usingInternational Electrotechnical Commission (IEC) Technical Report IEC/TR 61000-3-13:2008 unbalanced load-flow analysis.

Voltage unbalance emission assessment: Sources of contribution and their ranking

Determining sources of voltage unbalance (VU) and quantifying their individual contributions in an interconnected network is a complex task due to multiple interactions that take place between them. Post-connection VU emission assessment techniques in relation to customer installations are important not only in compliance assessment according to IEC/TR 61000-3-13:2008 Limits - Assessment of emission limits for the connection of unbalanced installations to MV, HV and EHV power systems, but also in determining the various emission contributors in the power system being considered. This paper presents a case study on the application of a recently developed post-connection VU emission assessment methodology to a 66 kV interconnected sub-transmission network owned and operated by an Australian network service provider. The study incorporates the evaluation of constituent components of the resultant VU factors at busbar levels, identification of the dominant emission contributors and a methodology for ranking of the emission contributions made by the asymmetrical transmission lines in the network. Outcomes obtained through the VU emission assessment methodology are validated using three-phase, unbalanced load flow analysis.

Voltage unbalance management in power systems based on IEC 61000-3-13:2008: Implications on the use of ‘k uE factor’

Voltage unbalance emission allocation principles prescribed in IEC61000-3-13:2008 Technical Report utilise a factor, kuE, which allows separation of the total voltage unbalance that arises at a point of evaluation due to both the load under consideration and the supply network. As per the definition given, this factor (kuE) accounts for the unbalance emission that arises due to the load whereas (1-kuE) accounts for unbalance that arises due to the network. The technical report prescribes a range of values from which a suitable value can be chosen based on the system characteristics, however, no systematic methodologies exist to-date to determine the kuE factor. Hence, the sensitivity of the kuE factor to various system parameters cannot be examined. The work presented in this paper examines the sensitivity of this factor to system characteristics covering line asymmetry, load type and the level of load unbalance. While giving a systematic methodology for the evaluation of kuE it is demonstrated that the use of a constant kuE factor as given in IEC61000-3-13:2008 can lead to erroneous outcomes under certain conditions.

A review of recent investigations with reference to IEC/TR 61000-3-13 on voltage unbalance emission allocation

The Technical Report IEC/TR 61000-3-13:2008 provides guiding principles for coordinating voltage unbalance between various voltage levels of a power system through the allocation of emission limits to installations. This report is based on widely accepted concepts and principles in relation to voltage unbalance. With regard to some of the key ideas used in this report, investigations have been carried out which have enabled the development of deeper insights making the voltage unbalance allocation process more comprehensive. The key aspects which have been considered in detail include: voltage unbalance which arises as a result of lines and voltage unbalance propagation in HV-MV, MV-LV power systems. In addition, a robust voltage unbalance allocation method has been developed which overcomes some difficulties associated where a uniform voltage unbalance planning level is adopted across all bus bars with the same voltage level classification (ie, MV or HV or EHV). With regard to voltage unbalance emission assessment a novel technique has also been developed which was verified through the application to an interconnected power system where the methodology allows identification of the contributors to voltage unbalance at a selected bus bar.

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 postconnection stage is essential to ensure that the limits set by the IEC VU emission allocation methodology in the preconnection 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. These assessment methodologies should ensure that the contributions from various sources of unbalance to the total VU emission are determined using data which are not overly demanding. This paper presents deterministic methodologies which can be used to assess constituent components of the postconnection VU level at the point of evaluation in an interconnected network utilizing postconnection 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.

Voltage unbalance emission assessment in radial power systems

Voltage unbalance (VU) emission assessment is an integral part in the VU-management process where loads are allocated a portion of the unbalance absorption capacity of the power system. The International Electrotechnical Commission Report IEC/TR 61000-3-13:2008 prescribes a VU emission allocation methodology establishing the fact that the VU can arise at the point of common connection (PCC) due to upstream network unbalance and load unbalance. Although this is the case for emission allocation, approaches for post connection emission assessment do not exist except for cases where the load is the only contributor to the VU at the PCC. Such assessment methods require separation of the post connection VU emission level into its constituent parts. In developing suitable methodologies for this purpose, the pre and postconnection data requirements need to be given due consideration to ensure that such data can be easily established. This paper presents systematic, theoretical bases which can be used to assess the individual VU emission contributions made by the upstream source, asymmetrical line, and the load for a radial power system. The methodology covers different load configurations including induction motors. Assessments obtained by employing the theoretical bases on the study system were verified by using unbalanced load-flow analysis in MATLAB and using DIgSILENT PowerFactory software.