A tertiary winding is an additional winding on a power transformer used for several purposes. It can provide a path for zero sequence currents to balance unbalanced loads, support connection of auxiliary loads, supply station service or feed harmonic filters. In some designs, a delta connected tertiary helps stabilize the system by absorbing third harmonic currents and improving voltage waveform. Tertiary windings can also be used to connect reactive compensation equipment or link different voltage levels without adding separate transformers.