The parameters of power transformers and transmission lines, as a rule, are determined by reference data, but during the operation, it might vary essentially from the actual data. There are noted the reasons for the parameters’ modification. This paper explains the opportu-nity of parameter identification based on the synchronized measurements during the operation of the studied object. The methods of parameter identification can be based on one, two or more measurements. Two-winding power trans-formers and transmission lines can be represented in the form of quadripole, so, applying only the current and volt-age synchronized measurement on both terminals it is pos-sible to obtain parameters of the Г-, Т- and П-forms equiva-lent schemes. There are presented a final and intermediate formula for transformer parameters. Also, there are ob-tained a similar formula for transmission lines. Besides, for transmission lines, there are obtained expressions for the method of the current balance, then for power balance. The last-mentioned methods are based on two samples of meas-urements and haven’t been previously described in any other source. All proposed methods were verified with the models of real transformers and transmission lines. The obtained results show the high accuracy of parameter iden-tification for the proposed methods. For power transform-ers, the influence of load factor upon the values of parame-ters was analyzed. It is worth noting that the most reliable results are obtained from measurements at the load factor β=0.55..0.85. For the model of the transmission line, there were compared the results of all proposed methods: the relative errors of calculation for all mentioned methods are less than 1%. The main contribution of this paper lies in the explanation of the novel method of quadripole (based on one measurement) for parameter identification of transformers and electric lines. That represents a good advantage over other methods with multiple measurements.