Current limiting inductor

Purpose of inductor

An inductor prevents sudden change in current magnitude. It is installed in substations to:

  • Limit ground fault current entering the power system through transformer neutral. Read more.
  • Limit in-rush currents associated with energization of capacitor banks.
  • Limit all variations of fault current 3-ph, L-G, L-L-G, etc. when tied in series on a feeder.
  • On extremely long EHV transmission lines, the Ferranti effect is prominent. An inductor tapped off the t-line negates this effect (the capacitive vars generated on the long line is consumed by a shunt inductor.)
  • Filter out harmonics (when used in conjunction with capacitor and resistor)
Neutral ground inductor to limit ground fault current
Neutral ground inductor to limit ground fault current
Shunt inductors to negate Ferranti effect
Shunt inductor for each phase at an EHV station. Image credit: Western Area Power – Mead substation.

Cost of inductor:

  • 15kV 800A neutral air core inductor (1 unit): ~$5,000
  • 15kV 450A series air core inductor (3 units): ~$15,000
  • 34kV 1000A series air core inductor (3 units): ~$60,000
  • 138kV 600A series air core inductor (3 units): ~$60,000
  • 345kV 120,000KVAR shunt air core inductor (3 units): ~$150,000

Lead time to procure inductor:

  • ~20 weeks for medium voltage units
  • ~30 weeks for HV & EHV units

Information on cost and lead time is for your general knowledge only. Contact vendor with your equipment specifications for actual figures.

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