Identifying earth faults on high-voltage overhead lines
In the joint ISOSTROSE project, the project partners are researching and developing a monitoring system for distribution grid transmission lines. This is aimed at precisely localising earth faults on high-voltage overhead lines in order to enable disturbances in the electricity grid to be quickly eliminated. After the theoretical phase, the scientists will carry out example monitoring in a test area. The engineers are concentrating on all facets of the task chain: on the one hand they are focussing on developing an exemplary, automated solution with hardware and software components for the power lines. On the other hand the developers are also focussing on integrated information and communications technology along the power lines, the transfer of the information to the grid control system as well as automated tools and procedures for necessary public safety measures such as preventive repairs.
The aim of the project is to carry our research on a sensor-based monitoring system that detects earth faults and the span where the earth fault is occurring in real time. This technology will make it possible to precisely narrow the fault to a few hundred metres. Based on this, measures for ensuring public safety can be effectively initiated and carried out. This will reduce line downtimes and related grid congestion.
The general approach is based on an independently working sensor system comprising earth fault sensors. These sensors are located directly on the power lines and continuously measure the locally flowing current, including the direction of the current flow. Different directions of current flow within a span mark the geographic location of the earth fault. A wireless connection along the transmission line transmits the data via transformer stations to the grid operator’s control system. In finding a solution to the research task, the consortium has drawn on the experience gained in the joint ASTROSE® project conducted by the German Federal Ministry of Education and Research.
An earth fault is an electrical connection between an energised conductor to the ground. This is a type of single-pole fault. It can be differentiated between restriking and transient earth faults. The special means by which 110 kV high-voltage grids are operated enables the grid to continue operating for a period of time when an earth fault occurs. A transient earth fault describes a momentary fault ranging from several milliseconds to a few seconds. These are usually arcing faults, which quickly extinguish themselves. These can be caused, for example, by branches or bird nests that are blown by the wind onto cables and create a brief electrical connection. The heat resulting from the arcing burns most objects, so that the cause of the fault is itself eliminated. Restriking earth faults, on the other hand, must be immediately detected and localised, since these can create a risk to third parties. The affected line is therefore shut down immediately. Transient earth faults occur about 65 times more frequently than restriking earth faults. Although it is difficult to determine faults in hindsight, grid operators always investigate such disturbances to make sure that the situation does not pose a threat to humans and animals.
Only a continuous detection of the earth faults can help
The reliable detection of earth faults provides a central task and challenge. Earth faults often last for just a few seconds or minutes. The earth fault sensors being researched must therefore record the current signals continuously. This requirement provides the basis for the scientific and technological research approaches being undertaken in the joint project.
- Energy-minimised sensor systems for measuring the earth faults in continuous measurement operation
- Innovative, more effective harvesting modules for continuously providing power to the earth fault sensors from the live conductor cables
- Communication strategies for ensuring the transmission of data to the ASTROSE® sensors, which then take over the transmission of the measurement signals
- Energy-optimised concepts for continuously recording the measured values and the secure, discontinuous dissemination of relevant readings via a wireless network
- Further development of the ASTROSE® communication structure for the secure, discontinuous transmission of the earth fault sensor data to the control system
- Modification of all system components in the sensor network for use on 110-kV transmission lines
- Further development of methods and algorithms for the sensor-assisted management of distribution grids
- Further development of tools for planning and constructing distribution grid lines with local, sensor-based monitoring
Innovative hardware and software developments will help to meet these challenges. In addition, new approaches for the installation, deployment and use in practice will be needed. The research topics are focussing on the components and equipment, intelligent grids, network planning, modular and meshed grids and the network operations management.
The following graphic illustrates the networking of the project partners based on their roles in the "energy distribution" value chain or the use of ISOSTROSE for this added value.
The project partners have two important milestones in their sights during the project. These envisage that:
- The system components (hardware and software) are researched in detail, and the laboratory testing of the components and the laboratory system are successfully completed. Production is authorised by the consortium.
- The ISOSTROSE monitoring system has been successfully tested in the field. The tests have been evaluated. There is documentation of the system and a proposal for its transfer to a pilot application.
11/2014 – 10/2017
Mitteldeutsche Netzgesellschaft Strom mbH
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06112 Halle (Saale)