HV System Earthing Design – A Case Study
Published 27 Mar 2020
- Republished with Permission of Matthew Taylor – Principal Engineer & Managing Director at Earthing Risk Management Ltd
HV System Earthing Design – A Case Study
An effective earthing system is vital for large installations such as power stations.
ERM was asked to verify the proposed earthing design against UK standards, including ERM’s previous experience designing the earthing system for the new 400kV connection substation and verifying the designs for the existing 400kV and 275kV substations.
The scale of the site, its varying elevation and the proposed use of a backfill material made this a challenging project.
Sheer size; with a site almost a kilometre across, the amount of electrode involved in calculations is taxing for even modern computing with the latest CDEGS software.
Varying surface elevation presented a technical challenge and required the use of specialised functions within CDEGS as well as top-end hardware to process the model and keep calculation times to an acceptable level.
Lateral variation in soil resistivity and significant depths of imported backfill material to be represented in the model. Staged construction of the earthing system in the vicinity of live 400kV and 275kV substations and the provision of 11kV construction supplies present particular safety hazards. ERM was asked to analyse the construction programme and design out any safety hazards associated with the 11kV power network.
Working with multiple companies to progress the project, including international involvement
The size of the power station earthing system, along with the adjacent interconnected sites and requirement to represent a multi layer soil model including backfill representation made the construction and processing of a CDEGS model difficult.
ERM built a bespoke top-end PC to give sufficient processing power to run this model in a timely manner.
Regular liaison with the client throughout the project allowed ERM to understand the breadth of the project including associated areas such as construction techniques and installation methods proposed.
The range of practical and technical experience at ERM allowed us to not only deliver the customer’s requirements but to provide advice value engineering advice, which subsequently provided significant safety improvements and savings in excess of £1M.
PROJECT OUTCOME / DELIVERABLES
The earthing design was approved from a safety viewpoint and significant cost savings were identified during value engineering both for the design itself and for its construction. The saving exceeded £1M.
Safety hazards with 11kV construction supplies were identified and designed out with a pragmatic solution that required little ongoing management.
The finished product was a detailed model with the functionality required to examine, calculate and draw the above conclusions.
meet the company – erm ltd
Earthing Risk Management Ltd (ERM) was established in 2002 to address the needs of the Electricity Supply Industry to manage safety hazards associated with HV earthing systems.
Since then, the company has grown to be an established, well respected consultancy serving a broad range of clients.
Employing an experienced engineering team as well as full time site testing teams, they are able to manage, assess and evaluate safety hazards associated with all aspects of HV earthing and lightning protection systems.
ERM’s experts from around the world provide their clients with the highest quality services in earthing design and verification, earth testing and measurements, earthing/lightening protection systems commissioning and test pit reconfiguration, pipeline interference studies, high frequency and transient studies, lightening protection design and upgrade, industry training, quantified risk assessment and fault investigation.
Earthing Risk Management has many years of experience in working with many companies throughout the electricity, gas, rail, and renewables industries trust ERM to deliver solutions for critical infrastructure such as National Grid, DNOs, Mitsubishi and Siemens.
Other Case Studies from ERM Ltd
Fall of Potential Measurement
➡An onshore substation which was constructed as a part of the new extension for an offshore wind farm project, located in the Irish Sea has a capacity of approximately 750MW.
The power from the offshore wind farm is to be exported by undersea high voltage cables to the 400kV onshore substation where the power is fed into the transmission network.
ERM was asked to test the new, onshore substation earthing system to verify the earthing installation and the CDEGS (Current Distribution, Electromagnetic Interference, Grounding and Soil Structure Analysis) model.
Lightning Risk Assessment
➡ ERM was asked by Uniper Energy to carry out a lightning protection site survey and risk assessment for one of their sites.
Their approach was to attend the site to obtain all relevant information needed to complete the lightning protection risk assessments (LP RA). This information was then passed over to the engineer who could then check that all of the required information was obtained.
This information was entered into specialist software to calculate the lightning risks in accordance with BS EN 62305. Any structures that were above the risk limits were then reassessed with additional lightning protection to reduce the risks to tolerable levels.
The client was provided with a report which detailed the results of these risk assessments and any improvements that they should make to bring the lightning risk levels down.
Accurate lightning risk assessment results were obtained for each of the structures, taking account of existing lightning and surge protection.
Soil Resistivity Measurement
➡ A new overhead line (OHL) was being built between two EHV substations.
The new planned route was in a difficult location compared to the existing route with Earth Potential Rise (EPR) impacts being likely along the strings. As there is potential for significant impacts ERM were brought in to examine the impact of EPR on towers along the routes.
Their experience and information gathering expertise allowed for the identification of Often Frequented Towers (OFT’s) as points of interest along a significant number of tower spans.
This prioritisation allowed for the planning of Soil Resistivity test routes in proximity to these points of interest only and therefore reduce the number of tests that had to be carried out. This allowed for savings on project costs and time taken to produce results.
The project was delivered to the customer outlining the findings of the study in a timely manner. The report made recommendations to the customer for not only the results but for the possible improvement of this, and any subsequent, studies with regards to the information used and alternative approaches to the study.
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