The resistance and leakage reactance of high-voltage (HV) and low-voltage (LV) windings are critical parameters that strongly impact the performance, efficiency, and stability, and therefore must be carefully monitored in power transformers. The real part of the transformer’s impedance, winding resistance, is dependent on the factors of conductor material (usually copper or aluminum), cross-sectional geometry, operating temperature, and frequency. Other influences, such as skin and proximity effects at higher frequencies, increase effective resistance and must be corrected for using correction factors.