Abstract
Single-phase earth faults are the predominant type of damage in distribution 6-10 kV cable networks, and are often the root cause of power failures to consumers, accompanied by significant economic damage. Therefore, reliability for about 50% of consumers of industrial and urban power supply systems depends on the technical perfection of protection against earth faults. The currently used approach to the design of protection and signaling of earth faults, based on the application of the existing concept of selectivity of considered protection, does not always ensure the achievement of the main goal – increasing the reliability of power supply to consumers. To improve the reliability of power supply, new technical solutions are needed that provide not only selective detection of the damaged connection for all types of single-phase earth faults, but also the recognition of the most dangerous for the network and the protected connection faults types for automatic selection the most effective protection action (signal or shutdown). Within the framework of the existing approach, the design of protection against earth faults with the specified properties is possible only on the basis different methods of its implementation in networks with different neutral grounding modes, which is associated with the complication of protection circuit, its design and exploitation. A new approach has been proposed that provides universal technical solutions for protection and signaling of earth faults for 6–10 kV cable networks with various neutral grounding modes. To implement the proposed approach, universal adaptive current protection and universal admittance protection based on the control of the capacitance of zero sequence loop of the protected connection have been developed.
Highlights
About 50% of electricity in Russia is distributed to consumers of industrial and urban power supply systems through 6–10 kV cable networks
Accidents in 6–10 kV cable networks account for about 70% of all power supply failures to consumers, and the root cause of most of the emergency shutdowns of cable lines and other elements is single-phase earth faults, accounting for 75–90% of the total number of electrical faults in the indicated networks [1, etc.]
The reliability of power supply to consumers depends on the speed of identifying and disconnecting the damaged element, i.e. technical excellence protection against earth faults
Summary
About 50% of electricity in Russia is distributed to consumers of industrial and urban power supply systems through 6–10 kV cable networks. From the above it follows that in order to obtain a comprehensive solution to the problem of selective protection against earth faults in medium voltage cable networks with different neutral grounding modes, the developers of modern microprocessor terminals as part of relay protection and automation functions are forced to provide several functions of protection against earth faults on various principles designed for use in various neutral grounding modes or action in various types of single-phase earth faults. This leads to the complexity of the earth fault protection, its design and operation. The method of action and principles of implementation of these protections are discussed below
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