Numerical evaluation of the effects of phase admittances asymmetry at HVAC overhead lines

摘要

The paper offers an answer to the question: a high voltage overhead line, operating in no load conditions, “generates” active power (energy)? In order to justify the answer, a case study on an untransposed 110 kV single circuit overhead line was used, for which the no load operating condition has been studied using phase amounts. For this goal, applying the modified Carson's equations and the Kron's method of reduction, were determined the equivalent phase impedances and admittances matrices. Numerical analysis of stationary no load operating conditions, demonstrates that on two of the phases the overhead line takes active power from the network, that delivers back to the network on the third phase. On the whole three phases the sum of the active powers at the beginning of the line results of a value much smaller than the phase active power being actually consumed power, corresponding to line losses. Actually the line doesn't generate active power, but its measurement system indicates a negative value for the sum of the active powers redistributed by the line between the network phases, due to the asymmetry of the measurement errors of the elements installed on different phases. Of these elements, the most presumably are the current transformers, known that at low values of the currents have large measurement errors for both rms and angle.