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Integration of solar photovoltaic systems to low-voltage distribution networks is witnessing an unprecedented growth in many parts of the world. Although solar photovoltaic generation is of significant benefit from a number of angles, exceedance of hosting capacity levels by such installations in low-voltage distribution networks continue to cause significant technical challenges in network operation, especially to the management of network voltage. Modern smart inverters are equipped with Volt-VAr and Volt-Watt control capabilities, which can assist in the management of network voltage levels. This paper provides a detailed analysis of the influence of different connection standards which cover these strategies on solar photovoltaic hosting capacity and their applicability in low-voltage distribution networks. Smart inverters with differing Volt-VAr and Volt-Watt control functions are modelled in the DIgSILENT PowerFactory platform. Influence of different connection standards on solar photovoltaic hosting capacity is analysed to investigate the most beneficial connection approach/es to address the issue of voltage violations. Furthermore, the work presented in this paper provides a greater understanding on the hosting capacity improvement by employing advanced inverter control functions where such improvements are subjected to locational aspects of inverters in low-voltage distribution systems.

It is well known that three-phase induction motors have to be derated in the presence of supply voltage unbalance (negative sequence) exceeding a stipulated limit of 1% based on several widely used standards. Generally, voltage unbalance limits are decided based on the magnitude of negative sequence voltage unbalance factor which is quantified as the ratio of negative sequence voltage to positive sequence voltage. However, a specified voltage unbalance magnitude can arise as a result of numerous possibilities of the three phase supply voltages. Therefore, it is hypothesised that the current derating curve, which defines a derating factor that is dependent on the magnitude of the voltage unbalance, is not optimal and may not be economical and/or safe for some voltage unbalance conditions. To examine the validity of this hypothesis, modelling and experimental validation need to be carried out considering motor losses and temperature rise which are the main factors that help determine the derating factor of an induction motor. Realising these requirements, the emphasis of this study is to examine the dependency of losses, temperature rise and torque oscillations of a three-phase induction motor on the complex nature of voltage unbalance through calorimetric and finite element simulation-based studies. The outcomes are expected to assist in the development of suitable derating factors.

This letter proposes an analytical approach to estimate local and the network wide influence of a static compensator (STATCOM), configured for voltage unbalance (VU) mitigation. In addition, it provides guidelines for determining the most appropriate location for active mitigation. The proposed generalised formulation is able to demonstrate the VU mitigation provided by a STATCOM regardless of the control strategy used or the network conditions.

Integration of Distributed Generation (DG) has occupied a great interest in modern power engineering due to its significant merits over the conventional power generation techniques. However, several aspects such as climatic conditions, land and fuel availability, DG location and DG size need to be carefully considered to harness the best results from integrating DG units for power networks. Among them, sizing of DG units has taken a prominent place as it affects the network operation as well as the cost aspect. Optimizing the sizes of prospective DG units that are intended to be integrated for a given network will facilitate in gaining the expected merits such as minimizing active power losses and voltage deviations without causing any stability, protection and power quality issue. The existing methodologies for determining optimal DG sizes are rather sophisticated. This paper presents a robust mathematical solving approach based on Lagrange Multiplier Method (LMM) for determining the optimal DG sizes for minimizing the active power losses and voltage deviations. The problem is formulated and solved as a multi objective function. Validation of the proposed mathematical solution strategy was tested using the IEEE-6 and IEEE-33 standard test bus systems. Results demonstrate the effectiveness of the proposed methodology.

With the increased interest in controlling and managing voltage unbalance (VU), network operators are now increasingly being motivated to obtain the state of their networks with greater details. Distribution system state estimation (DSSE) is a prominent tool that enables network operators to estimate the level, location, and related impacts of VU. DSSE techniques developed to date which use the polynomial or exponential load models are deficient in recognizing VU attenuation associated with three-phase induction motors (IMs) that are directly connected to the ac network. Adoption of adequate three-phase models of IMs, which are used in full unbalanced load flow, into the existing DSSE techniques is not feasible due to several factors including requirement of extensive data, additional computational efforts, and major constraints related to incorporating the necessary modifications. As a solution, this paper proposes a novel formulation for postprocessing the results of current DSSE techniques to reflect the aforementioned behavior of IMs. Simulations are carried out using the IEEE 13 bus distribution network for a range of scenarios to verify the developed methodology. The work presented in relation to VU attenuation in interconnected networks also complements the existing treatise in IEC documentation that only deals with radial networks.

High frequency (HF) emissions in the range of 2-150 kHz (or Supraharmonics) originating due to the internal switching operation of power electronic devices are an emerging power quality concern in electricity distribution networks. Among many HF sources, electric vehicle (EV) chargers play an important role. However, the present understanding related to the behaviour of HF emissions due to EV charging is limited. Therefore, in this paper, HF emissions caused by charging of two EVs using their on-board chargers and a DC fast charging station are investigated. The findings of the study are expected to improve understanding related to HF emissions from EVs and provide important insights into modelling of EV chargers for HF studies.

In addition to the low order harmonics, power electronic systems tend to emit high frequency emissions (HF) in the range of 2 - 150 kHz where photovoltaic (PV) inverters play an important role. The recent high penetration of PV inverters in electricity distribution networks has necessitated the development of PV inverter models suitable for HF studies. Some of the major concerns associated with this work include selecting a suitable modelling approach, building experimental setups and achieving a compromise between the simplicity and the accuracy of the model. Based on research undertaken using commercially available single-phase PV inverters, this paper presents in detail how the aforementioned concerns can be handled to develop inverter models that are suitable for HF emission studies.

Voltage unbalance (VU) emission assessment is a challenging task due to the complex interactions between the sources of voltage unbalance. Consequently, to account for transferred voltage unbalance from neighbouring busbars, IEC/TR 61000-3-13 has introduced influence and transfer coefficients in the VU allocation and emission assessment process. However, no generalised practical approaches exist to evaluate these coefficients where as IEC guidelines suggest some approximations based on simulations and field measurements. As an alternative, this paper proposes a sensitivity analysis of network VU to unbalanced installations that can be employed in VU emission assessment. The proposed methodology uses readily available inputs and utilises a linearised approach to determine the network wide sensitivity of VU to unbalanced installations which makes it feasible for practical implementation.

This paper presents a comprehensive analysis on the operating performance of three-phase Induction Motors (IMs) driven by unbalanced supply voltages. It is a well known fact that three-phase IMs are adversely affected by the presence of unbalanced supply voltages and it is required to derate the output power wisely for efficient and safer operation of the motor. There is a certain guidance given in NEMA MG1-1993 to decide a suitable derating level, however limitations and drawbacks of such practices have been identified. Although voltage unbalance is a well-defined concept, existence of numerous voltage unbalance conditions have led to problematic prediction of IM performance in terms of temperature rise and motor derating. Thus, different study approaches, their findings, limitations and shortcomings are critically reviewed in this paper in order to develop a comprehensive derating mechanism for three-phase IMs.

Solar photovoltaics (PV) have received increasing attention in recent years due to a number of well-known reasons. Diverse technical merits, declining costs and comparatively simple installations have influenced an unprecedented growth of solar PV systems in many parts of the world. Together with this, there are technical challenges which the network operators have to address in order to maximise the hosting capacity of solar PV generation in low-voltage (LV) grids. Among these challenges, the steady-state voltage rise and line overloading have been the main issues of concern. In order to comply with stipulated network limits, distribution network service providers (DNSPs) are compelled to develop comprehensive techniques for the evaluation of acceptable solar PV hosting capacity levels.

Proliferation of solar photovoltaic (PV) generation in low voltage (LV) distribution networks has imposed a set of challenges in network operation and control. Voltage rise is currently the main constraint that limits solar PV capacity increase in LV networks. Together with this, there is a growing need for a generalised and versatile tool which utilities can use to deal with customer requests for new solar PV connections. This paper proposes a generalised approach to assess solar PV hosting capacity (HC) subjected to over-voltage curtailment based on a Nomogram representation, which facilitates reasonable modeling insights for HC assessment in LV networks. In addition, solar PV connection criteria are further developed using the Nomogram representation of HC evaluation. The proposed Nomogram based approach for HC assessment and connection criteria will contribute to further improvement of available guidelines on solar PV connections in LV networks.

The grid connected solar PV systems have been significantly increased in the recent past mainly due to government policy initiatives around the globe for renewable energy developments. Diverse technical merits, comparatively simple installations and declining costs have influenced an unprecedented growth of solar PV. However, the technical challenges arising in distribution networks have to be systematically addressed in order to increase the solar PV hosting capacity (maximum solar PV penetration level without violating any operating constraint's) of LV distribution networks. This paper presents solar PV hosting capacity evaluation for a selected LV distribution network incorporating overvoltage issue and further the paper elaborates the effects of some operational changes and network upgrades for the enhancement of solar PV hosting capacity of the selected network.

Integration of Distributed Generation (DG) into power networks has taken a great interest in power industry because of its wide range of merits over the conventional methods of generation. Nevertheless, several aspects need to be considered before deploying them to the network for facilitating enhanced system performance. Optimal DG placement in terms of sizing and location are crucial in minimizing the active power loss and maintaining stipulated network voltage levels. This paper presents a novel analytical method for optimal DG placement by defining a new sensitivity index referred to as Loss-Voltage Sensitivity Index (LVSI) combining traditional Voltage Sensitivity Index (VSI) and Loss Sensitivity Index (LSI). The best location for DG allocation evaluated by new index reflects the conditions for minimum power loss and voltage deviations in the network effectively as both VSI and LSI are utilized in the new formulation. The proposed method was verified using the IEEE-6 bus test system considering several operating scenarios. Results show that proposed methodology is accurate in determining the optimal sites for allocating DG units.

Increasing solar PV penetration in LV distribution grids may potentially disrupt the nominal network operating conditions and result in power quality issues. Voltage rise has been reported to be the most prominent power quality issue with high solar PV penetration levels. In order to comply with stipulated network limits, distribution network service providers are compelled to develop comprehensive techniques for the evaluation of solar PV hosting capacity. This paper presents a generalised deterministic model that can be used to evaluate the PV hosting capacity of LV distribution networks. A safe limit of feeder level PV hosting capacity is defined based on the locational variation of solar PVs and feeder characteristics. The hosting capacity outcomes established using proposed method for different PV inverter operating scenarios are verified using simulations.

This paper investigates the impact of high frequency (HF) voltages in the range of 2 – 150 kHz present in the electricity distribution networks on the lifetime of electrolytic capacitors used as the DC link in switch mode power supplies (SMPS) of grid connected equipment. In this study, both time domain simulations and controlled laboratory experiments have been employed.

Network voltage unbalance (VU) is a potentially damaging power quality phenomenon for both utility and end consumer equipment. With the increased penetration of disturbing loads such as electrified railways, single phase distributed generators and line-to-line connected industrial loads, VU levels can be exacerbated. Consequently, network operators are increasingly diligent in maintaining the network-wide VU within stipulated limits. VU management in general, is a synergy of a number of tasks covering proper planning, operation and application of active VU mitigation techniques. Application of power quality conditioning equipment such as static compensators (STATCOMs) at appropriate locations is one such unbalance mitigation technique, which can be seen in practical networks. This paper gives a comprehensive analysis of STATCOM based VU mitigation taking into account the influence made by location and the impedance of STATCOM and comparatively evaluates the management and mitigation techniques of VU with respect to a practical 66 kV sub-transmission network.

The impact of supply voltage unbalance (VU) on three-phase induction motors (IMs) is well known in terms of extra losses and associated derating to ensure that the motors do not prematurely fail. Theoretical studies, experimental results and standards exist in this regard. However, the approaches taken in the past are not seen be exhaustive now considering the modern tools such as Finite Element Modelling (FEM) software. Also, the relevant documentation available to-date on the subject does not cover the level of variability in the outcomes such as extra losses that can arise when an IM is subjected to the same level of VU that can be produced in a range of different ways. This paper emphasises the importance of Positive Sequence Voltage and the Complex Voltage Unbalance Factor (CVUF) in analysing the losses of a motor under different VU scenarios. Statistical analysis of the losses of three-phase IMs operating under different supply voltage unbalance scenarios is presented in this paper giving special focus to the behaviour of the core loss and copper loss. Two dimensional (2D) FEM is used to model the electromagnetics of the motor and Bertotti core loss model is used to evaluate the core losses. The outcomes of this analysis will be useful in the process of developing improved and cost effective mechanism of derating for mains connected three-phase IMs as well as in their design optimisation.

Overcoming local limitations in distribution networks with high solar photovoltaic (PV) generation is a challenging issue, unless appropriate planning strategies and regulations are in place. Determination of solar PV hosting capacity of a distribution network can help in maintaining secure and healthy operation of the electricity grid without violating grid operational limits, specially during the peak solar power generation periods. This paper presents a feeder-based PV hosting capacity evaluation approach to determine a safe limit. It is proposed to use simplified calculations to establish the feeder hosting capacity in lieu of detailed network analyses, which increases complexity. Probabilistic nature of the proposed approach accounts for the randomness of solar PV presence within distribution networks. Monte Carlo Simulations (MCS) are performed to analyse maximum limits for solar PV integration using DIgSILENT PowerFactory as the simulation platform.

With the high penetration of power electronic interfaces and the increased use of power line carrier communication, high frequency (HF) emissions (supraharmonics) in the range of 2–150 kHz are emerging as a new power quality issue in distribution networks. Both IEC 61000-4-7 and IEC 61000-4-30 recommend the use of a high pass (HP) filter during measurement/analysis of these emissions. However, the filters used so far in HF measurements have non-linear phase characteristics making phase details unsuitable for further analysis. As a solution, this paper proposes a digital, offline, zero-phase HP filter having near ideal magnitude characteristics and a zero phase response.

Determining the impact of the individual contributors to network voltage unbalance (VU) is a complex task due to the interaction between the sources of voltage unbalance in power systems. This becomes further complicated as the network itself contributes to network voltage unbalance when it is not symmetrical which is mostly the case in real networks. To account for the network asymmetry, the Technical Report IEC/TR 61000-3-13 which is used for the assessment of voltage unbalance emission limits applies a scaling factor K ue when apportioning the global allowance to end user consumers. Studies on the impact of the untransposed overhead lines on each and every individual busbar and on the overall network voltage unbalance are essential in: emission allocation studies, identification of power flow constraints, and in decision making related to future investments on VU mitigation. This paper proposes an effective methodology to determine the influence of different untransposed lines based on the results of balanced load flow studies. The methodology can be easily extended to obtain the influence of the other contributors as well.

Distributed Generation (DG) has become a key component in modern power industry due its significant advantages over the traditional power generation methods. Nevertheless, best expected outcomes can only be achieved with optimal allocation of DG resources where inappropriate allocation may impose problems in power system stability, protection and quality. This paper presents analytical approaches for optimizing the DG size, BESS (Battery Energy Storage Systems) capacities and power dispatch in Medium Voltage (MV) networks. Since most of the existing analytical approaches related to optimizing DG sizes for minimizing network losses and voltage deviations have considered individual objective function separately, both parameters may not be minimized simultaneously. Thus, in this paper, an analytical methodology was formulated based on an objective function built on new parameter Loss-Voltage Sensitivity Index (LVSI) that evaluates both minimum impact of network loss and voltage variations for optimizing the DG size. The results obtained from this approach were compared with a conventional Genetic Algorithm (GA) formulated by the authors. The BESS capacities are determined considering the effects of Load Proportionality Factor (LPF), State of Charge limits (SOC) of battery storages, number of load areas and the portion of daily off-peak solar generation period energy consumption expected to be served by each BESS unit. The significance of this BESS capacity determination methodology is highlighted as the BESS capacities can be numerically calculated whereas in existing work, they are heavily relying on conventional optimization techniques which do not give an idea about the internal behavior of parameters which determine the capacities of BESS units. Moreover, an optimal BESS dispatch algorithm is also presented in this paper for minimizing the energy losses and voltage deviations. The applicability of the proposed methodologies are verified using the standard IEEE-33 and IEEE-69 test bus systems. Simulations carried out in MATLAB is used to illustrate the accuracy and the appropriateness of the proposed approaches.

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.

Trends on utilizing distributed renewable resources around the world have significantly increased the number of grid connected solar photovoltaic systems in low voltage networks. In Sri Lanka, low voltage systems are now available with the cumulative addition of the installed rooftop solar capacities is exceeding fifty percent of the rated capacity of the connected transformer. Thus, it is of vital importance to understand the technical impacts of solar photovoltaic additions in large scales on the operating performance of the networks and how to mitigate those issues. In this study, a futuristic solution is proposed with the formation of smart grid type operation, to effectively utilize the daytime solar photovoltaic generation in low voltage systems within the distribution transformer service area. Distribution transformer based smart grid, which operates with controlling mechanisms, loads, rooftop solar and battery storage systems is proposed for an urban low voltage distribution network in Sri Lanka which have more than forty percent of solar penetration level based on transformer capacity. The detailed network was modeled in MATLAB/SIMULINK simulation platform in order to develop different operating scenarios. The base model was validated with the field data available with transformer meter.

There is a growth of high frequency (HF) emissions in the range of 2–150 kHz (also known as Supraharmonics) in electricity distribution networks, primarily due to the increasing number and capacity of AC grid connected equipment having power electronic interfaces. Although PV inverters are a major HF source in electricity distribution networks, PV inverter models that are suitable for HF emission studies are yet to be developed. To this end, a generic method that can be used to develop HF models of small-scale (

Recent government policy initiatives have significantly increased the number of grid connected solar PV systems in distribution networks. Thus, it is of vital importance to understand the technical impacts of high penetration levels of solar PV systems on the operating performance of these networks. This paper presents an analysis of power quality aspects of an urban low voltage (LV) distribution network with high solar PV penetration levels in Sri Lanka. The study includes three-phase load flow analysis carried out by modeling the selected network in DIgSILENT PowerFactory simulation platform using 15 - minute load data. Effects on net power flows and voltages of the LV network, which have been verified using field measurements, are discussed. Factors influencing the hosting capacity of solar PV are investigated by analysing technical impacts at varying solar PV penetration levels.

Due to the increasing number and capacity of grid connected power electronic interfaces associated with distributed generating systems, there is increasing concern on the associated power quality problems. Amongst these, high frequency (HF) emissions (referred to as Supraharmonics) in the range 2–150 kHz has become a topic of growing interest within power quality research communities. An increasingly prominent grid connected devices which can contribute to these HF emissions are the photovoltaic (PV) systems. In this paper, HF emissions from seven small (output power ≤ 10kW), grid-tied, photovoltaic inverters (both single phase inverters and three phase inverter composed of three single phase inverters) are analysed using measurements carried out under controlled conditions in laboratory environments. It is shown that under fixed network conditions, these HF emissions are affected by the MPPT (Maximum Power Point Tracking) voltage and the output power level of the PV inverter. Moreover, a strong correlation between the behaviour of HF emissions and the topologies of inverters was observed; an important factor in developing high frequency models of PV inverters.

The concept of the micro grid is still growing with regard to co-ordination strategies and the development of proper controllers to enhance the reliability aspects under different operating modes. In this context,due to the growing interest of renewable energy sources droop based inverter dominated micro grids are one of the fastest emerging technologies. This research paper aims to study reactive power sharing and voltage variation under different scenarios in an inverter dominated islanded micro grid. In this regard, non-linear equations that describe the model have been derived and an averaged model is used in the derivation of the mathematical model resulting in simplified equations which are used to model large signal equivalent circuits in PLECS software. In addition, the impact of load perturbations, filter parameters, line impedances and droop variations are analyzed

The rapid increase of the grid-connected solar photovoltaic (PV) has been reported to make a considerable impact on the power quality (PQ) in the grid. This paper discusses the generation and propagation of significant current/voltage harmonics which are caused by PV inverters in distribution networks. The impact made by high switching frequencies and different operating scenarios are studied by detailed modelling of PV inverters in a typical low voltage (LV) distribution network using PSCAD/EMTDC simulation platform. It was found that the PV inverter systems inject high frequency current harmonics at the switching frequency or associated side bands. Low order current harmonics are also significant due to the inability of switching control system of PV inverter to produce perfectly sinusoidal output. It is found that the amount of harmonics depend on the inverter control strategy, background distortion present at the point of connection (POC) and the percentage of inverter loading. Further, harmonic voltage distortion is found to be mainly dependent on the impedance of the distribution network where weak networks lead to give rise to higher voltage distortions. Moreover, harmonic resonances are significant due to the interaction of the inverter output impedance and the grid inductance. The current harmonics injected by single phase inverters have been found substantial and influential with regard to the energy transmission and increase losses.

Voltage unbalance propagation is an important aspect in relation to the voltage unbalance management process which aims to maintain acceptable voltage unbalance levels in the power system. The IEC Technical Report IEC/TR 61000-3-13:2008 incorporates the effects of voltage unbalance propagation in the voltage unbalance emission allocation methodology by introducing the voltage unbalance transfer coefficient, in order to evaluate the influence made by background voltage unbalance at the point of evaluation. However, no comprehensive approaches exist in the literature to evaluate these coefficients and the IEC work follows some approximations, which are deduced based on simulations and practical measurements. Recent work completed on voltage unbalance emission assessment at the post-connection stage of unbalanced installations allows separation of the voltage unbalance emission contribution made by upstream/surrounding unbalance sources as a constituent component of the resultant voltage unbalance emission level at the point of evaluation. These new methodologies implicitly deal with the important aspects of voltage unbalance propagation and allow the quantification of coefficients associated with voltage unbalance propagation, which is the main thrust of this study. The theoretical work completed by considering different types of loads in radial and interconnected networks is supplemented by the simulation results.

Detection of open live conductors is a challenging task in the power system operation since it acts as a high impedance fault. High impendence faults (HIF) characteristically has a very low current value which is often not detectable using conventional over current protection devices. Several methods of detecting these HIF have been put forward. These methods involve spectral analysis of currents, algorithms based on residual current analysis and detection of unbalanced voltages produced by the fault at the end of distribution line. This paper presents a method of detecting open conductor faults based on the sequence current component. Here the ratio of negative sequence current to positive sequence current is used as the detecting parameter and fault is detected through the unbalanced resulted in the system with the occurrence of the fault.

Load flow studies play a vital role in planning the future expansion of power system as well as for deciding the optimum operation of the existing power system. Three phase asymmetrical power flow studies are recommended for unbalanced power systems such as distribution networks. Unbalanced loading, single phase and two phase shunts make the system operation unbalanced leaving the application of conventional load flow techniques away from the scene. The paper presents an unbalanced power flow algorithm based on the current injection technique with full Newton-Raphson formulation. The proposed method is validated using IEEE four bus test network.

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.

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 (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 (VU) in power systems should be managed in a systematic manner in order to minimise its adverse effects on both customer equipment and supply utilities. It is a well known fact that three-phase induction motor performance can be significantly affected in the presence of supply voltage unbalance. It is also known that three-phase induction motors can help to reduce pre-existing network voltage unbalance levels. Recently undertaken research aligned with IEC/TR 61000-3-13:2008 Technical Report on voltage unbalance management (emission allocation and emission assessment) have quantified the contribution made by induction motors to the net voltage unbalance at a point of connection. It is perceived that loading level of three-phase induction motors will have an influence on this contribution. Hence, this study focuses on a sensitivity analysis of induction motor loading level on the voltage unbalance emission contribution to the point of connection. Simulation work undertaken indicates that increased loading levels on induction motors tend to exacerbate negative sequence voltage unbalance factor (VUF) at the point of connection in comparison to lightly loaded induction motors.

Voltage unbalance emission allocation principles prescribed in IEC61000-3-13:2008 Technical Report utilise a factor, k uE , 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 (k uE ) accounts for the unbalance emission that arises due to the load whereas (1-k uE ) 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 k uE factor. Hence, the sensitivity of the k uE 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 k uE it is demonstrated that the use of a constant k uE factor as given in IEC61000-3-13:2008 can lead to erroneous outcomes under certain conditions.

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.