Study on the measurement of power-transmission-line parameters with induced voltage

Parameters of the power transmission line are the gist of the power system load flow calculation as well as the protection setting value, which are important in the proper arrangement of power system operation mode, the reliability and sensitivity improvement of the relay protection, etc. However, the measurement of the power transmission line parameters will be affected easily by the induced voltage when the traditional meter-method or the non-power frequency method is employed, and the measurement methods mentioned above are also limited by the additional power supply. Due to the induced voltage, the open circuit voltage and the short circuit current of the power transmission line can be measured, furthermore, the sequence parameters of the linear transmission lines are independent when the lines have the symmetrical parameters of the triple-phase, i.e. the certain sequence current (voltage) will only bring the same sequence voltage (current). As a result, the sequence impedance of the power transmission line can be solved by decomposing the induced voltage (current) into positive, negative and zero sequence respectively. By simulating the sequence impedance of the transmission line with lumped parameters in the PSCAD, the results indicate that the error between the induction-method and the meter-method is less than 10%. Sequence impedance simulation of quadruple circuit lines on same tower by induction-method was also carried out, it reveals that the sequence impedance of the transmission lines can be accurately calculated by the induction-method. A sequence impedance measuring instrument was also developed based on the induction-method, sequence impedance of the analog lines as well as the quadruple circuit lines on same tower was measured, and the result shows that the instrument is fit for the measurement of the transmission lines. Effect of the voltage amplitude dispersion on the induction-method-measurement is also discussed in this paper, results reveal th- t the error of the zero sequence impedance will be reduced under the large voltage amplitude dispersion.