Earthing System Condition Assessment

Project Brief

The site is a 400kV substation with two L2 double-circuit overhead lines and four 400/132kV transformers that feed an adjacent 132kV substation. The existing perimeter fence and security system were to be upgraded as part of the security upgrade works. ERM was engaged to provide an earthing design for the new fence and security systems and ensure the site earthing system was in good condition prior to work commencement. On completion of the survey, a report and CAD drawing were provided, detailing the investigation, remedial action / repairs for the earthing system and the fence earthing design.

Our Approach

ERM’s expertise and experience of earthing condition surveys at large sites was instrumental in providing a detailed report on the condition of the earthing system and an earthing design for the new fence line. ERM was able to liaise effectively with the client, providing detailed methods statements and risk assessments and managing high levels of on-site safety. The survey required minimal client planning input. Where possible ERM will carry out further investigations to pinpoint the cause of any problems or issues found, to enable a swift and cost effective solution.

Challenges

Earthing condition assessments on live high voltage sites can be challenging.
The factors below were important in successfully completing the project:

• Detailed analysis of dated earthing drawings to determine the existing earthing system layout and specification and a programme of tests to give a full condition assessment.
• Carrying out several weeks of testing in a live substation environment.
• Impressed voltage management.
• Combining on-site tests with CDEGS calculations to verify the test and measurement results, provide calculated potential hazard analysis and the new fence earthing design.
• Obtaining accurate records of buried services (pipelines and cables) and overhead transmission lines and finding off-site test routes that would avoid them.
• Managing contractor and public access to test areas to maintain high levels of safety.
• Computer analysis of overall impedance measurement results to remove test lead coupling from raw results.
• Condensing a large amount of test data and computer simulation results into a concise report.

Project Outcome / Deliverables

• A detailed fence and associated security equipment earthing design was provided.
• A report was provided detailing earthing defects found with remedial action required. Risks were prioritised to draw attention to those requiring immediate attention.
• Safety maintained throughout the test. No environmental footprint left.
• Accurate earth impedance measurement result achieved, which confirmed the CDEGS model and validated the EPR calculations, earthing design and safety recommendations.
• Client requirements met with delivery of the report in a timely manner.
• Positive feedback received from client.