Abstract
In the latest research, it has been proven that from the point of view of losses in a cable distribution line, the most advantageous operation is to work with two or one phase of metallic cable screen ungrounded. However, such an operation may cause changes in the network characteristics and thus the occurrence of undesirable phenomena. One of those characteristics is the overvoltages in those cable screens, which can lead to cable line damage. The simulation tests presented in this article are closely related to the unusual method of operation of the MV cable screens and their performance, and they address the question of whether in a given system ground fault overvoltages may be a significant threat to the operation of the cable. The research methods used to verify these risks are related to the simulation of the cable line operating states using the DIgSILENT PowerFactory program (DIgSILENT GmbH, Gomaringen, Germany). Overvoltage simulations were performed, taking into account changes in the network configuration, such as the method of cable screens grounding, the length of cable lines, the cross-section of the conductor and cable screen, or the method of operation of the neutral point. The results for the cable line modeled as a part of the MV network with the variables considered during the tests indicate the possible impact of the one-sidedly cable screen ungrounding on overvoltages in this cable screen. The obtained results at the level of a few kV in one-sidedly ungrounded cable screens show that the change of the configuration of the operation of these cable screens may affect the safety of the network operation.
Highlights
Many years of adaptation and the multitude of possible uses of cable in the power industry result in a huge selection of cable constructions and the elements they comprise.Among the conductive elements, conductors, shields, sheaths, and metallic screens can be distinguished
To determine the magnitude of overvoltages that may occur in MV cable lines in the event of specific operating conditions, a cable model created with the use of the Power Factory program will be used
Summarizing the results for the overvoltages in the cable screens obtained as a result of computer simulations and taking into account the dependencies described in the Discussion section, conclusions can be drawn about the influence of the parameters of the variables selected for consideration in the described model
Summary
Conductors, shields, sheaths, and metallic screens can be distinguished. Except for conductors, other components, in most cases, need to be grounded in sleeves or at cable heads [1]. According to the latest research [2], the cable screen may, under certain conditions, be an exception. Ungrounding cable screens were originally associated with a positive phenomenon [3], which is a decrease in transmission losses. In the course of research related to methods of reducing these losses, the negative effects of such a solution were discovered [4]. Crucial to the new solution are problems such as changing the longitudinal parameters of the cable line or the appearance of dangerous overvoltages at the end of cable runs
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