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Protection Study for Incident Energy Mitigation

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Background & Challenge

Following an IEEE 1584-based arc flash assessment conducted at NovaSource’s utility-scale solar site, high incident energy (I.E.) values were identified on the LV side of inverter transformers—particularly in areas protected by legacy HV fuses. These slow-clearing devices contributed to elevated I.E. levels beyond safe working thresholds.
NovaSource sought a technical solution to reduce the risk to site personnel without undertaking extensive hardware upgrades. The LV cubicles, provided by SMA, were confirmed to comply with IEC 62109-1 and IEC 60664-1. However, RelyOn advised that compliance with AS/NZS 61439:2021 (now mandated under AS/NZS 3000) should also be verified to align with Australian regulatory requirements.

Scope of Work

RelyOn Australia was engaged to review the protection configuration and propose mitigation options through a protection-focused lens. Our work included:

• Evaluation of LV cubicle insulation coordination and construction standards
• Clarification of applicable design standards: IEC 62109-1, IEC 60664-1, AS/NZS 61439
• Assessment of fault clearing time implications on arc flash energy
• Modelling of fault current limiting device (FCL) integration within ETAP
• Guidance on relay coordination improvement strategies
• High-level review of manufacturer data and integration feasibility

Key Recommendations

• Replace HV Fuses with High-Speed Circuit Breakers
  • Introduced CBs with faster clearing times and adjustable protection curves to lower arc duration
  • Improved protection selectivity and compliance with modern design principles
• Implement Fault Current Limiters (FCLs)
  • Modelled fault current limiting upstream of LV cubicles to reduce prospective fault current
  • Reduced I.E. without requiring relay or breaker changes
• Integrate Arc Flash Detection Systems
  • Advised consideration of optical arc flash sensors to achieve sub-cycle clearing times when paired with fast-acting relays
• Verify Compliance with AS/NZS 61439
  • While the LV cubicle was built to IEC standards, RelyOn highlighted the requirement for AS/NZS 61439 compliance under AS/NZS 3000
  • Advised checking form of separation within cubicles and its influence on arc containment and mitigation

Deliverables

• LV Cubicle Compliance & Risk Memo: Highlighting current standards and suggested validation steps
• Incident Energy Mitigation Options Report: With comparative analysis of fuses, circuit breakers, FCLs, and arc flash sensors
• ETAP Modelling Outputs: Estimated reductions in I.E. under each proposed method
• Site Advisory & Manufacturer Liaison Guidance: Assisted client in engaging with SMA to obtain relevant documentation for further validation

Results & Client Benefit

• Enabled a multi-path mitigation roadmap for reducing I.E. from >12 cal/cm² to below 8 cal/cm²
• Highlighted regulatory gaps in cubicle design for future procurement
• Empowered the client with cost-effective and staged upgrade options
• Strengthened compliance position under AS/NZS 61439 and AS/NZS 3000
• Supported risk mitigation strategy with a clear technical basis and forward implementation plan

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Project Details

• Client: NovaSource
• Location: Utility-Scale Solar Facility, Australia
• Project Type: Arc Flash Follow-On Study and Protection System Enhancement Options
• Completion Date: December 2024
• Prepared By: RelyOn Australia

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