The Results of Power Grid Research Modes in Case of 6-10 kV Overhead Lines Phase Wire Breakage

Broken wire overhead lines 6-10 kV, supplying electrical networks 6-10 / 0.38 kV, cause a reduction in the quality of the resulting electric energy consumers, creating a fire hazard in an overhead line fault zone and increasing the probability of a passer-by's electrocution, which is lethal in most cases. For the construction of an overhead line protection of 6-10 kV in case of phase wire breakage, the information on the negative sequence voltage that appears at the side of a low voltage power transformer with 6-10 / 0.4 kV voltage can be used. These methods were used for the analysis of the negative sequence voltage changes: the method of symmetrical components; computer and physical modeling; experimental studies in mains voltage of 10 / 0.38 kV. It was established that there are various kinds of asymmetric modes of the mains voltage of 0.38 kV under a normal 6-10 kV airline causing minor changes of the negative sequence voltage, not exceeding 0.02 per unit of the line voltage. In case of the 6-10 kV overhead line phase wire breakdown and an unbalance change of consumers phase loads with voltage 0.38 kV in a wide range, the value of the negative sequence voltage varies within 0.2-1.0 per unit of the line voltage. The studies have allowed the authors to define the limit values set point for the negative sequence voltage protection in case of the 6-10 kV overhead line phase wire breakage.