Feature of Voltage Transformers Operation in the Direct Current Schemes of Ice Melting on Overhead Transmission Lines

Abstract

It is well known that electromagnetic voltage transformers (VT), included in the direct current scheme of ice melting (SIM) on overhead transmission lines (OTL), must be switched off when the SIM is assembling and turned on during disassembling. This action increases the time of the power line output from work and reduces the reliability of the power system. It is noted that capacitance VTs used in the electrical networks of 110-500 kV are not subject to the dangerous influence of DC voltage. Three variants of capacitors installation for electromagnetic VT protection from direct voltage at which it is not required to switch off VTs are considered. A conclusion was made on the conditions of applicability of each variant based on the analysis of basic SIM. The article includes the necessary for practical use equivalent circuits and the values of constant voltages on the VTs in the basic direct current schemes of ice melting on overhead transmission lines. The method and an example of parameters calculation of the capacitors` block and additional resistor, providing the required accuracy class of VT at its constant inclusion as in the normal scheme, and in the scheme of ice melting, are given.