Challenges

Model the actual electrical system

• Build a unified ETAP model of the plant (brownfield + greenfield), all transformers, busbars, lines, cables, relays and breakers with their actual parameters.

Understand the existing protection strategy

• Reconstruct protection curves, time grading and arc-flash levels from legacy settings to know where the plant currently stood.

Define new protection for the expansion

• Set relays for new motors and transformers, then check interaction with existing upstream devices to guarantee selectivity.

Arc-flash mitigation at 10 kV

• Initial ETAP analysis showed incident energy of ~10 cal/cm² at a critical 10 kV bus, which was above the 8 cal/cm² limit requested by the customer.

Prove the solution to stakeholders

• Deliver a new protection & coordination recommendation that is technically sound, traceable and easily explained with both graphical and tabular evidence.

Selected applications

1. Digital Twin & TCC Diagrams

• Built a detailed electrical digital twin to simulate the entire SS4 area
• Created TCC (time-current characteristic) diagrams including:
  • Transformer and cable full-load currents and ampacities
  • Withstand curves and short-circuit ratings
  • Minimum / maximum short-circuit currents at MV and LV
  • Existing relay curves for incomers, feeders and bus ties

Result: confirmation that the existing system was generally well protected and well coordinated, but with excessive arc-flash incident energy.

2. Motor starting & protection coordination

• Ran motor acceleration studies using the ETAP motor starting model.
• Automatically overlaid real starting current and time on the TCC diagrams, ensuring:
  • Motors start safely under true plant conditions
  • Protection settings do not trip during acceleration, yet still provide good fault protection.

3. Transformer & feeder protection optimization

• Compared brownfield and greenfield philosophies:
  • Existing feeders used two stages: an inverse-time stage plus a definite-time stage
  • For greenfield transformers, Selecty added an extra definite-time stage, dedicated to clearing secondary faults and arc-flash situations faster

• Performed detailed Arc-Flash studies at 10 kV.
• Used C-Area Plot Editor to:
  • Target 8 cal/cm² incident energy on the line side
  • Explore combinations of fault current and clearing time, including tolerances in short-circuit level, working distance and electrode configuration

• Developed a company rule book (coordination margins, thermal limits, grading criteria).
• Used ETAP’s auto-evaluation to automatically:
  • Compare tripping characteristics against cable & transformer withstand curves
  • Check motor starting curves vs relay settings
  • Verify coordination between upstream and downstream devices

• Leveraged automatic zone detection so ETAP could:
  • Identify which protection devices belong to which transformer, motor or feeder
  • Evaluate both micro-zones (single motor / cable) and macro-zones (entire bus sections, brownfield + greenfield)

Main customer benefits

Arc-flash level successfully mitigated

• At the critical 10 kV bus, incident energy was reduced from about 10 cal/cm² to ~6 cal/cm², comfortably below the 8 cal/cm² limit.
• This was achieved even though the greenfield arcing current was >1.5× the brownfield value, thanks to significantly faster clearing times.

Coordinated brownfield and greenfield protection

• New transformer and motor protections are fully coordinated with upstream brownfield incomers, bus-ties and feeders.
• Where small grading compromises were intentional (to keep clearing times short and arc-flash low), they are clearly documented and accepted.

Single multi-purpose analysis platform

• Short-circuit, motor starting, arc-flash, coordination and Auto-Evaluation all run from the same ETAP model, saving engineering time and avoiding data inconsistencies.

Objective verification for the client

• Auto-Evaluation + Rule Book gave a traceable, repeatable proof that protection and coordination criteria are met.
• High-quality reports with combined tabular and graphical views made it easy to communicate the new philosophy to stakeholders.

Future-ready Digital Twin

• The ETAP model is now a living Digital Twin: it can be reused for future expansions, case studies and “what-if” scenarios without rebuilding the model from scratch.

Customer perspectives

So, what I really love about the ETAP is that we can combine modern calculations and properties together to quickly evaluate motor starting based on the actual conditions at the client’s facility. 

ETAP Auto-Evaluation and the flexibility provided by the Rule Book helps us to validate various projects. It makes it very easy to compare the tripping characteristic, the withstand characteristic against the rules that have been defined.