Power system relay protection
Abstract
The material provides information on the design and calculation of relay protection settings in the power system. The selection of basic technical parameters of current and voltage measuring transformers is presented, observed from the aspect of relay device connection. A brief overview of the dynamic behavior of a current transformer (class P) when transmitting a maximum asymmetrical short-circuit current is given. The calculation of the settings of the relay protection system of a distribution network is treated in detail with regard to the grounding method and configuration (radial or loop network, parallel lines, etc.). Low-adjustable and high-adjustable overcurrent protection, directional and non-directional homopolar overcurrent protection, including sensitivity, selectivity, backup protection, etc. are considered. The principle of operation and the selection of settings of the differential protection parameters of two-winding and three-winding power transformers are presented in detail. The blocking of the operation of the aforementioned protection when the transformer is switched to no-load, overexcitation, and stabilization when the current transformer is saturated are discussed, as well as the influence of errors and various characteristics of current transformers on the operation of (stabilized) differential protection. The implementation of distance protection on single lines in the transmission network is presented in detail. The method of calculating the range settings of distance protection zones, coordination with other protections in the network, backup protection, etc. are analyzed. Different designs of operating characteristics are considered, their advantages and disadvantages, and the influence of transition resistances on the measured impedance of distance protection. The method of blocking distance protection when power fluctuations occur in the network is presented, as well as various ways of implementing communication schemes for distance protection. The basics of working with the DIGSI and SIGRA software packages from Siemens for working with numerical relay devices are presented.
