Can anyone explain to me the function of the commutating reactor and basic principles of the operation?

 

Commutating reactors are often used for thyristor / SCR controlled circuits such as DC choppers. Normally they would be used in collaboration with a commutation capacitor to generate a sinusoidal 'ring-around' commutation current.

I'd suggest a web search for typical SCR chopper commutation circuits. Most power electronic books which still treat SCR circuits would cover the subject in adequate detail. Try Google books in the power electronics section for instance.

 

Look at post #19 here.... http://forum.allaboutcircuits.com/showthread.php?t=7478&highlight="commutation+capacitor"&page=2