Static Excitation Pt. 2: Reactors 1

[n1mr0d]

Question 1: How can a reactor (inductor) limit short circuit current?

Question 2: How can i do a QnD measurement of the inductance of the reactor without use of expensive DMMs?

 

[vic3fan]

Answer to Q1: By mounting the reactor in series.

Answer to Q2: Consulting the documentation provided by the manufacturer/distributor, or checking out the nameplate of the reactor.

 

[ScottyUK]

A reactor has impedance at AC. They are preferable over resistors because they have (almost!) zero power loss. Fault limiting reactors are usually of low ohmic value and are basically intended to reduce very high fault levels to a more manageable value within the rating of switchgear.

I'm not sure what would make this question specific to a static excitation system, although reactors are often found within the large semiconductor rectifiers used in static AVR's if several diodes or thyristors have been paralleled to increase current rating. The reactors are primarily to improve current sharing between devices and to calm down very high di/dt edges caused by thyristor switching. The reactor slows the rising edge of the current allowing time for the full silicon die to reach a conducting state and thus avoid current crowding and thermal runaway in local hotspots which can occur if the die is partially conducting.

Guessing reactor impedance is a tough question - it depends on the construction of the reactor. Air cored types are harder to predict than those with an iron core. The presence or absence of an airgap in a iron cored type makes a difference too. You should refer to a high school physics textbook for some calculation methods for inductance of various coils. You will gain some useful understanding of the principles too.

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I don't suffer from insanity. I enjoy it...

 

[powerjunx]

I agree to scottyUk, serves as a current limiting device for abnormal condition of a system. It also installed usually between neutral to ground of power transformers and generators.
On static excitation application, probably your referring to SATURABLE CORE REACTORS.. It was also used on static stepless motor control, brush generator static excitation system, though obsolete(i think).