Islanding detection during intended island operation of nested microgrid

In the future, functionalities like islanding detection must also operate during intended island operation of (MV+MV or MV+LV) nested microgrids. In this paper, healthy and faulty islanding detection of LV network connected generation unit during nested (MV+LV) microgrid islanded operation were studied by simulations with PSCAD model from real-life smart grid pilot. Main focus in the simulations was on the study and comparison of usage possibilities of combined (high-speed communication based transfer trip & fault detection/direction + voltage vector shift) and multi-criteria (voltage total harmonic distortion & voltage unbalance) based islanding detection schemes also during intended island operation of nested microgrid consisting only from inverter based generation units.fi=vertaisarvioitu|en=peerReviewed

Intermittent earth fault passage indication in compensated distribution networks

An intermittent or restriking earth fault is a special type of earth fault that is common mostly in compensated cable networks. A great deal of effort has gone into protection against this type of fault. However, locating this fault has not received much attention. Therefore, there is a need to have a reliable method for locating this fault to repair the damaged cable. In this paper, the principles of a new method developed for locating transient intermittent earth faults on distribution networks are presented. The proposed method employs negative and zero sequence currents, and no voltage measurement is required, which means the proposed method has the potential to reduce cost when implemented in practice. It is intended mainly for typical intermittent earth faults in cable distribution networks where the typical fault resistance is in the range of a few ohms. Real data obtained from practical field tests is used to explain the phenomenon. A series of disturbance recordings obtained from field tests validate the proposed method.©2021 Elsevier. This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication.fi=vertaisarvioitu|en=peerReviewed

Multi-objective active network management scheme studied in Sundom smart grid with MV and LV network connected DER units

Use of controllable, flexible, distributed energy resources (DER) in MV and LV networks will be in key role in order to improve local and system-wide grid resiliency and maximize utilization of renewable energy sources (RES). These resources will provide different technical services as part of future active network management (ANM) schemes. Therefore, future ANM and protection methods and solutions have to be adapted and developed so that active control and utilization of DER during both grid-connected and islanded operation modes is enabled. In this paper, multi-objective ANM scheme is studied by PSCAD simulations during grid-connected operation of Sundom Smart Grid. Based on the simulation results conclusions are stated, for example, related to preventing unwanted MV and LV network reactive power / voltage control interactions and potential mutual effects between voltage (U) and frequency (f) control functions (QU-, PU- and Pf -control) of DER units which are actively participating on studied multi-objective ANM scheme.fi=vertaisarvioitu|en=peerReviewed

Advanced islanding detection in grid interactive microgrids

In the future active network management and protectionsolutions have to enable utilization of intended islandoperation as well as active control and utilizationflexibilities during normal and islanded operation ofgrid interactive microgrids. In this paper, combinedislanding detection schemes for both MV and LVnetwork connected distributed generation units duringnormal grid-connected operation are studied.Utilization of active network management functionalityat MV level enables to control the reactive powerunbalance continuously in order to ensure reliableislanding detection without non-detection zone.Combined scheme also prevents maloperations due toother disturbances.fi=vertaisarvioitu|en=peerReviewed

Utilization of a mixture of CTs and current sensors in line differential protection applications

The popularity of Rogowski sensors is increasing due to their advantages over conventional CTs. Consequently, network utilities may sometimes end up facing a question whether it would be possible to use line differential protection on a line where the current measurements at the local end are based on CTs, whereas, the remote end measurements are based on current sensors. The main challenge in the use of such a combination in line differential protection applications is that while CTs may saturate, Rogowski sensors do not. Such issues were studied in a hardware-in-the-loop simulation setup. Based on the studies conducted, it appears that the use of mixture of CTs and current sensors for line differential protection applications is a feasible option provided that the CTs are properly dimensioned and that the protection settings are carefully chosen.fi=vertaisarvioitu|en=peerReviewed

Active and reactive power requirements at DSO-TSO interface : a cases study based on four European countries

The ENTSO-E network code for demand connection sets harmonized requirements for connecting large renewable energy generation units as well as demand response facilities and furthermore reactive power limits which need to be fulfilled at the interface between TSO and DSOs. In this paper, P/Q-measurements for several primary substations in four different countries (Austria, Finland, Germany and Slovenia) are investigated. For the investigated primary substations measurements of active and reactive power over a period of one year in 15-min resolutions were collected. Based on the investigations the impact of reactive power requirements at the TSO-DSO interface is addressed. Moreover, how and on which voltage level the reactive power could be balanced is discussed.fi=vertaisarvioitu|en=peerReviewed

A deep learning approach to earth fault classification and source localization

A portion of electrical feeders in distribution grids are prone to faults, often resulting in different types of earth faults, power quality disturbances as well as damaged equipment and outages. While in developed countries the amount of such feeders can be relatively low, the quota reaches as high as 20% for many developing countries. Tackling this issue requires (i) understanding the current status of the grid and the faults that occur and (ii) identifying the origin of the fault for preventing similar future faults. This process is however costly and time consuming as it requires many hours of tedious manual work from engineers, operators or field experts. In an effort to tackle this issue, we present in this work a machine learning based framework for automatized fault type classification and faulty feeder identification. We provide an empirical evaluation of our proposed framework on a dataset of recordings from a real grid, showing encouraging results