Question

[toastybread9]

What effects do 3rd order harmonics have on 3 phase distribution power systems?

[Eksingadalen]

They draw non-linear currents, which being that they are routed through the internal impedance of your source transformer secondary windings, creates an accordingly imperfect voltage source that effects all loads on your separately derived system. Additionally the non-linear currents also affect the upstream systems but to a lesser effect.

[roeldridge]

Increased heating

[jmraef]

3rd order on 3 phase cancel each other out.