What is the purpose of an inductor?

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)

What is the cost of an 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

What is the lead time to procure an inductor?

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

Inductor: Learn the Purpose, Cost, and Lead Time to Procure

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.

Neutral ground inductor to limit ground fault current

Limit in-rush currents associated with the energization of capacitor banks.

Limit all variations of fault current 3-ph, L-G, L-L-G, etc. when tied in series on a line.

Current limiting series reactor. Image credit: Trench Group

230kV air core reactors shown here. It limits the fault current contribution from one bus section to the other. Because the electro-magnetic field is unconfined, they are strategically installed in a triangle pattern to cancel out the stray magnetic fields. Image credit: WAPA – Mead substation.

On extremely long EHV transmission lines, the Ferranti effect is prominent. An inductor tapped off the t-line negates this effect (the leading vars generated on the long line is consumed by a shunt inductor.)

Filter out harmonics (when used in conjunction with capacitor and resistor). Inductors are also implemented on other Flexible AC Transmission devices.

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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Substation Major Equipment

It’s only stupid-simple, let’s begin.

A transformer develops an internal fault. Which device would you install on the transformer high-side to interrupt fault current?

Either a breaker or a circuit switcher

Circuit switcher

Circuit breaker

Disconnect switch

For which event should a surge arrester operate? Check all that apply.

Switching surge

Lightning strike

Temporary overvoltage

Phase-to-ground short-circuit

What’s the purpose of a conventional power transformer?

Transform power, voltage, and current

Transform voltage only

Transform voltage and current

An industrial facility is plagued with voltage flicker and poor power factor at the service entrance. Which device would you install to fix both issues?

Install capacitor bank

Voltage regulator

Harmonic filter bank

In a distribution substation, the available ground-fault current on the low side of the step-down transformer is excessive, over-dutying the switching equipment. What is your cost-effective solution to reducing the fault current?

Add current limiting fuses in series on the switchgear

Add inductor in the transformer neutral

Add series inductors

Buy new transformer with higher impedance (%Z)

Which combination of devices would you use to implement power line carrier?

Wave trap and line tuner

Wavetrap, capacitor coupled voltage transformer, and line tuner

Wave trap, capacitor voltage transformer and line tuner

You are building an interconnect station, tying wind farm generation to the power grid. At the substation, the sources are tied through a tie-breaker. Which device would you install to make sure the sources are synchronized?

Voltage transformer

Ideal transformer

Power transformer

Current transformer

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