To this end, Section 2 of the article develops the following novelties in the technical literature:  
* The expressions of the short-circuit resistances specific to each harmonic (\(R_{cc,h}\)) according to IEEE Standard C57.110-2018, and their condition as characteristic parameters of each transformer;
* The expressions of the effective short-circuit resistances of each phase (\(R_{cc,z}\)) as a function of those of each harmonic (\(R_{cc,h}\));
* The expressions for the combined effective short-circuit resistances of all non-fundamental frequency harmonics (\(R_{cc,Hz}\)) as a function of \(R_{cc,z}\) and the short-circuit resistances inherent to the fundamental frequency harmonics of each phase (\(R_{cc,1}\));
* The phase load losses (\(P_{cc,}(h_{z})\), \(P_{cc,z}\), \(P_{cc,Hz}\)) characterized by these short-circuit resistances;* The harmonic loss factors of each phase (\(HL_{F_{2}}\%\)), which are the parameters that determine the relative importance of the load losses caused by the non-fundamental harmonic currents in each phase of the three-phase transformers. In the Section 3 of the article (Results), the values of the short-circuit resistances calculated for the 630 kVA Dyn11 distribution transformer, immersed in oil, of an actual residential network are used to calculate the load losses and the harmonic loss factors of each phase of that transformer, using the measurements made by a Fluke 435 Series II analyzer at 6:55 a.m. and 8:55 p.m. on 10 November 2022. Furthermore, in this section, it is verified that the values of the load losses calculated with the short-circuit resistances developed in Section 2 are the same as those obtained with IEEE Standard C57.110-2018. In the Section 4 (Discussion), the values of the load losses calculated every hour on 10 November 2022, using the short-circuit resistances of our approach, based on the IEEE Standard C57.110-2018, are compared with the obtained with the use of the nominal short-circuit resistance (\(R_{ccN}\)) of the traditional method. As a result of the comparison, it is found that the traditional procedure underestimates the effect of harmonics in determining load losses. Finally, in the article's Section 5, the main conclusions are summarized. Load Losses According to the Institute of Electric and Electronics Engineers (IEEE) Standard C57.110-2018  
IEEE Standard C57.110 establishes that the following three power phenomena affect the value of load losses (\(P_{cc}\)) of three-phase transformers: the resistance of the material of the windings, in direct current (\(P_{DCN}\)), the Skin effect (\(P_{EC}\)) and the phenomenon of electromagnetic induction in other metallic parts of the transformer other than the core (\(P_{OSL}\)), which satisfy the following equation:  
\[P_{cc}=P_{DCN}+P_{EC}+P_{OSL}=P_{DCN}+P_{AC} \tag{3}\]  
In the previous equation, direct current losses (\(P_{DCN}\)) are constant. In contrast, the phenomena that cause alternating current losses (\(P_{AC}=P_{EC}+P_{OSL}\)) depend on the frequencies (\(f_{h}\)) or the order (\(h=f_{h}/f_{1}\)) of the harmonic currents, with \(f_{1}=50-60\) Hz being the fundamental frequency. Substituting the expressions of the load loss components (\(P_{DCN},\ P_{EC},\ P_{OSL}\)) included in the standard in Equation (3), the total load losses of the three-phase transformers can be expressed as follows:  
\[P_{cc}=\sum_{h=1}^{h_{max}}\Big{(}P_{DCN}+P_{ECN}\cdot h^{2}+P_{OSLN}\cdot h^{ 0.8}\Big{)}\cdot\bigg{(}\frac{I_{sh}}{I_{SR}}\bigg{)}^{2} \tag{4}\]  
where \(P_{DCN}\), \(P_{ECN}\), and \(P_{OSLN}\) are the load losses corresponding to the three phenomena defined by IEEE Standard C57.110-2018, for the nominal conditions and at the fundamental frequency (\(f_{1}=50-60\) Hz). These losses satisfy the following equation:  
\[P_{ccN}=P_{DCN}+P_{ECN}+P_{OSLN}=P_{DCN}+P_{ACN} \tag{5}\]  
where \(P_{ccN}\) are the nominal load losses of the transformer, provided by the manufacturer in their catalogs or obtained after carrying out a nominal short-circuit test.