MODAL TRANSFORM FEATURES OF CABLE LINE ELECTRICAL VALUES IN A TRAVELING WAVE FAULT LOCATOR

Abstract

It is known that during a short circuit on an overhead line, the traveling waves in the phases contain components of two aerial and one ground modes. Due to the different propagation velocity along the line of these components at the locator installation place they arrive at different times. This leads to the fact that the traveling wave front in the phases becomes less pronounced, and, consequently, the accuracy of determining their arrival time and accuracy of the fault location decrease. To divide the phase values ​​of an overhead line into independent components of modes, invariant transformations – Clark transformation, Karrenbauer transformation, or Wedepohl transformation – are used. However, these transformations in their classical form cannot be applied to the electrical values of a cable line, since its design differs from that of an overhead power line. The purpose of the article is to illustrate the use of modal transformation on a cable line. As a result of the study, the following conclusions were obtained: currents in the cable line cores do not affect each other, therefore, in the wave fault locator that measures current waves, it is necessary to use directly the phase currents of the cores without modal transformation; if the wave fault locator measures the currents or voltages of the cable screens, the modal transformation should be performed, and it must be taken into account that the three modes formed by the screens are similar to the three modes of the overhead line; if a power transformer is adjacent to the cable line, the current traveling waves in the cores will be completely reflected from the measurement place, in this case in the wave fault locator it is necessary to use voltage traveling waves in the mode between the core and the screen of each cable of the three-phase group.