Calculation of relay currents in active weakly-meshed distribution systems

Abstract

This paper deals with short-circuit calculation, as one of the basic Distribution Management System (DMS) applications. It is common practice in short-circuit calculations to neglect loads, line and transformer shunt parameters as well as influence of the pre-fault state. This paper shows that some of these approximations could lead to incorrect results when calculating currents at relay locations (relay currents) in distribution systems. Consequently, an efficient short-circuit calculation procedure for active weaklymeshed distribution systems is proposed. Procedure is based on back/forward sweep with compensation for loops applied to faulted network models. The proposed procedure is robust and easy for programming and the results are significantly more accurate than those obtained by the oversimplified methods commonly used. Results show that errors made by listed approximations could be as high as 16% for a 20 KV test system, which can seriously affect the setting and coordination of protective equipment.

Integration of renewable energy systems and challenges for dynamics, control, and automation of electrical power systems

“…The distribution systems with the RDGs integrated are referred to as active distribution systems and are significantly more complex for analysis than traditional passive systems. The greater degree of complexity is the result of two main factors (Strezoski & Prica, ): In active distribution systems, the directions of power and current flows could be bidirectional in both normal and contingency operating conditions. The physical structure, operation methods, control schemes, and consequently models of the RDGs differ from the traditional synchronous generators. …”