Effective asset management is crucial for improving the reliability, resilience, and cost efficiency of distribution networks throughout the asset life cycle. Distribution transformers are among the most critical components, as their failures can cause extensive service interruptions and substantial economic impacts. Therefore, robust and transparent maintenance prioritization strategies are essential, particularly for utilities managing several transformers. Traditional time-based maintenance, while simple to implement, often results in inefficient resource allocation. Condition-based maintenance provides a more effective alternative; however, its performance depends strongly on the reliability of indicator selection and weighting. This study proposes a systematic weighting framework for distribution transformer maintenance prioritization using a multi-criteria decision-making (MCDM) approach. Each transformer is evaluated across two dimensions, including health condition and operational impact, based on indicators identified from the literature and expert judgment. To address uncertainty and judgmental inconsistency, particularly when the consistency ratio (CR) exceeds the conventional threshold of 0.10, the Fuzzy Analytic Hierarchy Process (FAHP) is employed. Seven condition parameters characterize transformer health, while impact is quantified using five indicators reflecting failure consequences. The proposed framework offers a transparent, repeatable, and defensible decision-support tool, enabling utilities to prioritize maintenance actions, optimize resource allocation, and mitigate operational risks in distribution networks.

Electromagnetic compatibility (EMC) is an essential requirement for the disturbance-free operation of equipment connected to electricity networks. The process of EMC coordination always starts with a detailed characterisation of the interference mechanism that has to be protected. Based on this characterisation, appropriate indices for the quantification of the mechanism have to be introduced. Finally, based on these indices, compatibility levels, immunity testing procedures, including test levels and emission limits, are established that form the best possible trade-off of sharing costs, risks and responsibilities between all involved stakeholders. Recently, flicker in LED lamps caused by interharmonic distortion was identified as a new interference mechanism which is not yet covered by the existing EMC coordination in the IEC 61000 series of standards. This article proposes a novel EMC coordination framework to address this interference mechanism. It shall serve as information for standardisation committees in IEC TC77/SC77A and IEC TC34 to extend or update the relevant standards. The article follows the process for EMC coordination for this new mechanism, starting from a detailed characterisation of it, proceeding to define suitable indices and measurement methods to capture it and finally proposing compatibility levels, immunity testing procedures, test levels and emission limits.

Electromagnetic compatibility (EMC) is an essential requirement for the disturbance free operation of equipment connected to electricity networks. To ensure a holistic overall approach to EMC, known interference mechanisms have to be protected by introducing indices for their proper quantification and by establishing suitable emission limits and immunity test levels that form the best possible trade-off of sharing costs, risks and responsibilities between all involved stakeholders (usually network operators and manufacturers). Recently, flicker in modern lamps caused by interharmonic distortion was identified as a new interference phenomenon which is not yet covered by the existing EMC coordination framework in IEC 61000 or IEEE. A new EMC coordination framework addressing this interference phenomenon is proposed in this paper and it is intended to serve as guidance for standardization committees to extend or update the relevant standards. The process for implementing EMC coordination is followed step-by-step in the proposed framework starting from characterizing the phenomena, then defining suitable indices and measurement methods to capture the phenomena, and finally proposing a set of limits.

This work addresses a limitation in power system harmonic analysis due to the challenges of converting complex time domain models to the harmonic domain. A linear approximation, in the form of a Norton equivalent, is the simplest model necessary to describe harmonic coupling. This work expands how the Norton equivalent can be created. A general approach is developed from first principles, where a methodological starting point is established for linearising all models. Its versatility is demonstrated by converting a model of transformer magnetising current hysteresis. For this purpose, a modification is made to the classic Preisach model of hysteresis for time-periodic input and output. A new data driven method fits test results of a small transformer to the Preisach model. Results show an improved accuracy in the Norton equivalent's frequency coupling matrices over models that only consider magnetic saturation.

This study introduces an advanced control strategy tailored for Type-IV wind turbines, focusing on the coordination between the machine-side converter (MSC) and the grid-side converter (GSC) under grid-forming (GFM) control. With the growing penetration of wind energy in power systems, it is crucial for these systems to operate as voltage sources, ensuring stable terminal voltage and frequency by dynamically adjusting both real and reactive power outputs. Unlike conventional approaches, this paper presents a strategy where the MSC manages the DClink voltage, while the GSC operates under a newly proposed fault-ride-through mechanism, which involves freezing the power synchronous loop (PSL) during grid disturbances. Additionally, a novel current limitation mechanism is introduced to protect the converter during both balanced and unbalanced faults. Comprehensive simulation results in PSCAD/EMTDC validate the effectiveness of this control scheme under diverse grid conditions, including low short circuit ratios (SCR), balanced and unbalanced faults, and frequency variation scenarios.

This study presents a volcanic resilience assessment for the electricity network in Taranaki, New Zealand, modelling the distribution system as a standalone Critical Infrastructure (CI) and incorporating key interfaces such as transmission Grid Exit Points and generator nodes. Previous volcanic risk assessment studies have identified potentially severe impacts on the electricity infrastructure, but have not included power flow analysis. This research addresses this gap and applies natural hazard risk assessment approaches and power system resilience analysis to assess system level impacts for a complex multi-hazard volcanic hazard scenario. The impact is estimated through power flow calculations and Monte Carlo-based outage analysis.

Identifying the topology of low-voltage (LV) networks is becoming increasingly important. Having precise and accurate topology information is crucial for future network operations and network modelling. Topology identification approaches based on smart-meter data typically rely on Root Mean Square (RMS) voltage, current, and power measurements, which are limited in accuracy due to factors such as time resolution, measurement intervals, and instrument errors. This paper presents a novel methodology for identifying distribution network topologies through the utilisation of smart-meter harmonic data. The methodology introduces, for the first time, the application of voltage Total Harmonic Distortion (THD) and individual harmonic components (V2–V20) as topology identifiers. The proposed approach leverages the unique properties of harmonic distortion to improve the accuracy of topology identification. This paper first analyses the influential factors affecting topology identification, establishing that harmonic distortion propagation patterns offer superior discrimination compared to RMS voltage. Through systematic investigation, the findings demonstrate the potential of harmonic-based analysis as a more effective alternative for topology identification in modern power distribution systems.

AbstractLarge geomagnetic storms are a space weather hazard to power transmission networks due to the effects of Geomagnetically Induced Currents (GICs). GIC can negatively impact power transmission systems through the generation of even‐order current and voltage harmonics due to half‐cycle transformer saturation. This study investigates a decade of even‐order voltage total harmonic distortion (hereon referred to as Even‐Order Total Harmonic Distortion (ETHD)) observations provided by Transpower New Zealand Ltd., the national system operator. We make use of ETHD measurements at 139 locations throughout New Zealand, monitored at 377 separate circuit breakers, focusing on 10 large geomagnetic disturbances during the period 2013–2023. Analysis identified 5 key substations, which appeared to act as sources of ETHD. The majority of these substations include single phase transformer banks, and evidence of significant GIC magnitudes. The ETHD from the source substations was found to propagate into the surrounding network, with the percentage distortion typically decaying away over distances of 150–200 km locally, that is, at a rate of −0.0043 %km−1. During the study period some significant changes occurred in the power network, that is, removal of the Halfway Bush (HWB) single phase bank transformer T4 in November 2017, and decommissioning of the New Plymouth substation in December 2019. Decommissioning of these two assets resulted in less ETHD occurring in the surrounding regions during subsequent geomagnetic storms. However, ETHD still increased at HWB with increasing levels of GIC, indicating that three phase transformer units were still susceptible to saturation, albeit with about 1/3 of the ETHD percentage exhibited by single phase transformers.

Harmonic modelling and experimental validation of an inverter-driven heat-pump (HP) under different power levels is considered in this paper. Preliminary results of a research activity, conducted first in New Zealand at the University of Canterbury (UC) and then in Italy at the University of Campania “Luigi Vanvitelli”, are reported. The aim is to investigate the impact of harmonics (and in future interharmonics) on the low voltage network produced by modern HPs. The starting point was a previous study conducted at the UC, where the harmonic emissions of six commercial heat-pumps were compared by means of lab. measurements and PSCAD models. The time-domain model developed in this paper is validated by experimental measurements made in the field. Very accurate results in terms of harmonic injection were obtained, which will allow its use in more comprehensive harmonic penetration studies in the time and frequency domains.

The increasing integration of voltage source converters (VSCs) in the electric grid has significantly enhanced efficiency and reduced the carbon footprint of power networks. With the growing adoption of VSC, future networks are anticipated to be hybrid AC/DC systems. Analysis of these complex systems is critical for their planning, operation, and design. However, accurately simulating converters during symmetrical fault conditions in large hybrid AC/DC networks remains challenging due to the lack of comprehensive VSC models that account for AC and DC grid interactions. This paper tackles this issue by proposing a phase domain fault analysis method utilizing a quasi-static VSC model interface between the AC and DC grids. Verification studies conducted with PSCAD/EMTDC on the modified IEEE 30-bus network demonstrate the accuracy and effectiveness of the proposed method for symmetrical faults.

This paper presents an improved control strategy for a type-IV wind turbine using the machine-side converter to control the dc voltage and the grid-side converter operation in the grid-forming (GFM) control mode. When wind power becomes a considerable portion of the power system or even the only energy source, the wind power systems must operate as a voltage source to maintain the terminal voltage magnitude and frequency by adjusting the real and reactive power. The generator output power should track the power to the grid to maintain the DC voltage. This paper proposes the coordinated control of the generator’s output power with a DC-link voltage controller for the generator-side converter. A dynamic model of the grid-side converter operating in GFM control mode has been built, and the voltage and frequency regulation strategy is presented. Simulation results using PSCAD/EMTDC demonstrate the control performances under various grid conditions, i.e., a wide range of short circuit ratio (SCR) and islanding grid conditions.

The paper reports on the latest developments associated with the issues and challenges behind the choice of feasible interharmonic limits in distribution networks to be included in future International Standards as discussed within the interharmonic distortion task force (IHD-TF), which is formed in the framework of the Harmonics WG (519) of the IEEE PES T&D Committee.

This paper presents a nonlinear direct power control (DPC) strategy for grid-connected voltage source converters based on adopting instantaneous active and reactive power as dynamic variables. A general uniform expression with the instantaneous magnitude and phase for arbitrary three-phase signals has been established in this paper. The proposed model gives instantaneous relationships between the variables and no restrictions are imposed on the voltage or current waveform, i.e., the model is valid in the entire state space. A higher control layer, i.e., the power plant centralized controller, generates the reactive power command to support the point of common coupling voltage. A dynamic current limitation mechanism is included to protect the converter during grid faults. The stability of the control system is analyzed via the Lyapunov theory, and the system states are proven to converge to the desired equilibrium point asymptotically. Simulation results using PSCAD/EMTDC demonstrate that the grid-side converter using the proposed DPC approach has a fast response (less than 40 ms) along with very small power variation even with low SCR and is demonstrably superior to the latest DPC scheme in the literature under various grid conditions.

The development of solid-state devices has greatly increased the use of power electronic-based equipment. This equipment is nonlinear as when supplied with a sinusoid voltage the current waveform is non sinusoidal (i.e. contains harmonic components). Although these loads are nonlinear in the time-domain, however, they show linearity in the frequency-domain for a region around their operating point, which can be exploited. Moreover, in the frequency-domain the harmonic components exhibit phase-dependency. The tensor can represent this phase-dependency while complex numbers cannot, therefore analysing the electrical network using tensor representation rather than complex numbers is more accurate. Complex number can be shown to be a special case of a tensor. In the present work the application of tensors is for modelling the harmonics in a distribution system. Although time-domain programs, such as PSCAD/EMTDC, model accurately this phase-dependency the detail required, and computational cost make modelling a large distribution network unfeasible. Frequency-domain approach can model large networks efficiently, however, tensors rather than complex numbers must be used to capture the phase-dependency. Therefore, in the future, where the system is dominated by power electronic equipment, harmonic analysis software is better served using tensor representation rather than complex numbers. In order to use a tensor representation to solve for an electrical network a tensor is needed for each component in the system. The simulation accuracy is dependent on the tensor accuracy and over what range of distortion levels it is accurate. This paper introduces the use of tensor for harmonic analysis and looks at two methods for estimating the tensor for power electronic equipment. Namely Fourier Descriptors (FDs) and Average Admittances Locus (AAL). The evaluation is performed over a number of different distortion levels. An extensive set of simulations were performed using PSCAD/EMTDC to build a library of tensors for different nonlinear equipment. Laboratory tests were performed, also using different levels of voltage distortion, to verify the results obtained through simulation.

In light of the clean energy vision, the uptake of Electric Vehicles (EVs), DERs, and other nonlinear devices has been increased and has led to a growing issue of harmonic distortion in Low Voltage (LV) distribution networks. A key enabler to operate the system better is the use of measurement data, such as Smartmeter data. However, obtaining actual harmonic time-series measurements of LV distribution networks remains a challenge, limiting research efforts to investigate innovating algorithms that use this time-series data. This paper introduces a novel approach to generate realistic synthetic smartmeter data of LV distribution networks. The paper discusses various methods for obtaining time-series harmonic data. Furthermore, this paper briefly addresses the privacy considerations related to harmonics measurements.

The ubiquitous Phase-locked loop (PLL) is used to synchronise power converters with the AC system. The limitations of the PLL when the AC system is weak are well known. This paper investigates the modelling and control of Grid-Side Voltage Source Converter (GS-VSC) of a wind-turbine under unbalanced network conditions and connected to a weak system. The proposed control scheme regulates the instantaneous active and reactive power at the PCC. The operation of the GS-VSC under unbalanced voltage condition is analysed and the concept of using different control target is present, which is independent of a PLL. A new current control scheme comprising of a central controller and a compensation controller is proposed. Simulation results using PSCAD/EMTDC are presented to validate the effectiveness of the proposed control scheme and to demonstrate the operation under unbalanced network conditions in a weak grid.

Over the past few decades, there have been rapid advances in solid-state technology as well as a reduction in cost. This, coupled with the functionality and efficiency improvements they afford, has resulted in a massive increase in the use of electronic devices. Where traditionally, there were a few well-known nonlinear loads that needed to be considered, now there are numerous low-power devices. Although individually insignificant, collectively, they are very significant. This paper presents a tensor-based harmonic analysis approach that is capable of capturing important interactions while being computationally efficient enough to model a large distribution system. Numerical experiments are used to highlight the advantages of the tensor framework. Numerous papers have investigated the tensor parametrisation or its mathematical equivalent-harmonically coupled admittance matrices (also known as frequency coupling matrices). However, this paper, for the first time, demonstrates how these models can be applied to perform harmonic modelling of a complete low voltage (LV) distribution system.

There are many challenges associated with including interharmonic voltage and current limits in future versions of international Standards (e.g. new IEEE Standard 519). This paper introduces a new definition of interharmonic subgroups based on IEC concept and aimed at overcoming the difficulty of the existing definition in IEC 61000-4-7 in limiting interharmonic distortion. The new subgroups are better able to address the main problem caused by interharmonics, which is light flicker (LF) produced by modern lamp technologies (e.g. LEDs) that cannot be assessed by the IEC Flickermeter (IEC 61000-4-15). A numerical case study is presented to show the effectiveness of the new definitions and, additionally, to test their robustness versus both the desynchronization of the window width used to perform the DFT with system fundamental frequency, and the accuracy requirement of the voltage measurement chain contained in IEC 61000-4-7.

There is a growing use of High Voltage Direct Current (HVDC) globally due to the many advantages of Direct Current (DC) transmission systems over Alternating Current (AC) transmission, including enabling transmission over long distances, higher transmission capacity and efficiency. Moreover, HVDC systems can be a great enabler in the transition to a low carbon electrical power system which is an important objective in today’s society. The objectives of the paper are to give a comprehensive overview of HVDC technology, its development, and present status, and to discuss its salient features, limitations and applications.

At present almost all the electric vehicle (EV) charging equipment is unidirectional, that is Grid-2-Vehic1e (G2V). There is great interest in bidirectional electric vehicle charging equipment due to the benefits this may bring. However, there is a lack of real experience and information regarding this technology. This paper reports on the first stage of a project to remedy this. The first stage is laboratory testing of the technology and the second is deployment and field experience over a year of the equipment’s use in a domestic home. As shown the harmonic performance of the bidirectional charger is very good.