The application of tertiary and stabilizing windings in liquid-immersed power transformers, as covered by IEEE Std C57.12.00™, as well as recommendations to evaluate the need or convenience of having such windings, are addressed in this guide. The primary application of this guide is for transformers and autotransformers with wye-wye-connected windings, with or without a delta-connected tertiary or stabilizing winding. Tertiary windings in conventional delta-wye and delta-delta–connected transformers are not addressed by this guide.