Stacked Current Limiting Reactor

[mls1]

Why is the center coil of a stacked air core current limiting reactor reverse wound? Is it to offset the higher mutual inductance of the center coil? It seems that reverse winding the center coil will exacerbate induced currents external to the reactor since the total flux will no longer cancel. Any insight would be greatly appreciated.

 

[scottf]

It's done to reduce the short-circuit current forces on adjacent reactors.

 

[pie314]

When center phase is wound in the reverse direction then the force between the adjacent phases will be compressive. In other words the phases will be forced together during a short circuit. If the reactors are all wound in the same direction the the force will be repulsive. The insulators used to stack the reactors are much stronger in compression than they are in tension.

 

[pie314]

MLS1

I should also mention that when the center phase is wound in the opposite direction then the ohms in the center phase are increased due to the mutual flux between the phases.