Challenges

• Rising short-circuit levels due to added generation and network expansion, exceeding equipment ratings.
• Need to limit fault current without the drawbacks of traditional reactors (voltage drop, losses, space).
• Precisely calculating tripping values for Is-limiters, which depend on:
  • Fault location
  • Network impedance
  • Operating configuration (generators / ties in or out)
• Ensuring that in every operating scenario, for any short-circuit location, at least one Is-limiter operates fast enough to protect the system.
• Performing all studies according to IEC 60909 and internal ABB standards.

ABB is-limiter technology (Why FCL instead of reactors or breakers?)

• A fault current limiter (FCL) is required when calculated fault levels exceed equipment withstand ratings.
• Traditional reactors limit current but cause continuous voltage drop, losses and occupy valuable space.
• A standard circuit breaker typically clears faults in 45–120 ms (relay + breaking time), long enough for the first current peak to reach the destructive zone.
• ABB’s Is-limiter detects faults in microseconds and interrupts in roughly 5–10 ms, so the first peak never reaches the destructive zone.
• Internally, it acts like an intelligent fuse: a hollow conductor with a charge element and a parallel fuse. When the control unit decides to trip, the charge opens the conductor and the current transfers to the fuse, which then melts and isolates the phase.

Selected applications

• Full digital twin of the plant from high-voltage grid to low-voltage loads
• Short-circuit duties at all buses, with and without Is-limiters in service

Scenario & study wizard

• Automation of 26 operating scenarios (different generator combinations, tie-switch states, etc.) and multiple fault locations
• Rapid identification of which buses exceed their fault-current withstand ratings in which scenarios

Configuration manager

• Visualization of which Is-limiter is in service in each configuration and how it splits the system (blue / red / grey areas)
• Understanding which Is-limiter can effectively reduce fault current for a given fault location

Custom post-processing (tripping-value calculation)

• For each scenario and fault location, read fault level at the bus and contribution through the Is-limiter
• Apply the proportion method to compute the required tripping value so that resulting current stays within switchgear capability

Determine fault contribution through the limiter path

• Example: for a bus fault, total prospective current is 60 kA, of which 30 kA flows through the Is-limiter → 50% contribution.

Consider downstream impedance

• If cable impedance reduces total fault to 40 kA, contribution through Is-limiter is still ~50% → 20 kA.

Use ETAP results to populate the equation

• Scenario 18, fault at a 31.5 kA / 80 kA peak bus:
  • Total fault level: 46.276 kA
  • Contribution via Is-limiter 1: 28.366 kA
  • Equipment withstand: 31.5 kA
  → Calculated tripping value ≈ 19.3 kA
  

• Scenario 14, same fault location, different generators in service:
  • Total fault: 31.778 kA
  • Contribution via Is-limiter: 12.722 kA
  → Tripping value ≈ 12.6 kA

Repeat for all scenarios and all buses

• For every operating configuration and every potential fault location, ABB computed the required tripping value.

Choose the smallest tripping value

• The final setting for each Is-limiter is the minimum of all calculated values → guarantees safe operation in any configuration.

Main customer benefits

• Safe fault levels: short-circuit currents are limited below the 31.5 kA / 40 kA equipment rating and 80–100 kA peak withstand limits
• High selectivity and speed: Is-limiters clear faults in 5–10 ms, avoiding destructive peaks while leaving normal operation unaffected
• Comprehensive coverage: protection is valid for all 26 operating scenarios and every bus, thanks to ETAP’s automated studies
• Efficient engineering process: ETAP’s Scenario & Study Wizard and Configuration Manager drastically reduced manual work for ABB engineers
• Future-proof approach: lessons learned are being used to develop an ETAP library component for ABB fault current limiters, which will simplify planning and protection studies for future projects

Customer perspective

Fault current limiter application engineering is a complex task that depends heavily on operating scenarios and fault locations. ETAP’s automation allowed us to handle 26 operating scenarios, calculate tripping values for each Is-limiter and each bus, and ultimately choose safe settings that keep DG Cement’s equipment protected in every case.