Client Background & Needs
Following the acquisition of a hydrocarbon processing plant by a large multinational corporation, the site’s 11kV high voltage switchgear and low voltage distribution boards required recommissioning after being dormant for several years.
To ensure a safe and compliant electrical system, the client engaged us to perform a fault and grading study across the entire network. This study was crucial for:
- Verifying equipment ratings
- Ensuring correct protection device grading
- Identifying necessary adjustments before the protection testing phase of recommissioning.
Challenges & Approach
The project presented several challenges:
- Outdated System Information: The plant’s electrical documentation was incomplete, requiring extensive on-site data collection.
- Potential Safety Risks: Incorrect protection settings could jeopardise critical systems like the fire pumps.
- Complex Grading Issues: Ensuring effective coordination between transformer feeders, incomers, and DNO protection required detailed analysis.
Our team conducted a comprehensive site visit to gather key data, including:
- Protection devices and settings
- CT ratios
- Transformer characteristics
- Cable lengths and sizes
- Equipment make, manufacturer, and rating
This detailed data set allowed us to build an accurate electrical model for the site.
Implementation & Solution
The collected information was input into the latest edition of ETAP, where we produced:
- A single line diagram mapping the site’s electrical network
- A protection setting schedule showing existing grading characteristics
During the analysis, several issues were identified:
- Fire Pump Protection: Protection settings were too low, risking the fire pumps tripping on start-up.
- Transformer Feeder Grading: The transformer feeder settings did not align with either the incomer settings or the DNO protection settings.
- Low Voltage Incomer Grading: The LV incomer settings did not properly grade across the transformer during a single-phase-to-ground fault.
To resolve these issues, we re-calculated and designed revised protection settings to improve coordination and ensure system stability. We supplied these new settings to the principal contractor for implementation during the protection testing phase.
Additionally, we provided:
- Detailed grading charts for the entire network
- A comprehensive protection settings report for use during routine maintenance and future upgrades
Results & Impact
Our fault and grading study successfully ensured:
- Improved network protection and system stability
- Enhanced fire pump protection, reducing the risk of nuisance trips
- Protection settings that comply with Electricity at Work Regulations 1989
- Clear documentation for future testing and maintenance
By identifying and addressing critical protection issues before commissioning, we helped the client mitigate potential risks and achieve a safer, more efficient electrical network.
Compliance with the Electricity at Work Regulations 1989
Our study ensured compliance with key regulations, including:
- Regulation 4 (1): Ensuring the system’s construction prevents danger where reasonably practicable.
- Regulation 5: Ensuring no electrical equipment is used beyond its capacity, reducing the risk of overload and failure.
- Regulation 11: Ensuring efficient protection devices are correctly graded to prevent excessive current without compromising system coordination.
Our comprehensive approach ensured the site’s electrical infrastructure met all relevant safety and regulatory standards.
Conclusion & Key Takeaways
This project demonstrated our expertise in conducting detailed fault and grading studies, ensuring protection settings are optimised for both safety and system efficiency. By providing accurate calculations, revised protection settings, and detailed documentation, we helped the client successfully recommission their electrical network with confidence.
Our proactive approach ensured compliance, minimised risk, and provided a clear framework for future testing and maintenance — delivering a robust and future-proof solution for the site’s electrical safety.
