Bài giảng Hệ thống cung cấp điện: Chương 7 - TS. Lê Thị Minh Châu

The reliable and efficient operation of electrical power systems hinges critically on the appropriate selection of electrical equipment. This document delves into the fundamental principles and practical methodologies for choosing such equipment, emphasizing aspects crucial for system stability and longevity. Special attention is given to the calculation of short-circuit currents in low-voltage grids, a prerequisite for ensuring the thermal and electrodynamic withstand capabilities of components. Furthermore, it provides a comprehensive guide to conductor cross-section selection, a vital step in minimizing energy losses and optimizing investment costs. The discussion covers criteria based on long-term heating conditions, coordination with protective devices, and the concept of economic current density, all aligned with established standards.

Sinh viên, kỹ sư điện, nhà thiết kế hệ thống điện và các chuyên gia trong lĩnh vực điện lực.

This academic content comprehensively explores the principles and methodologies for selecting electrical equipment in power systems, with a particular focus on low-voltage grids. It begins by outlining the general concepts of equipment operation under various conditions, including normal, overload, and short-circuit states, stressing the importance of dynamic and thermal stability. A significant portion is dedicated to the calculation of short-circuit currents, providing formulas and examples to determine the stresses components must withstand. The document then transitions into detailed guidance on conductor cross-section selection, presenting two primary approaches: selection based on long-term heating conditions and selection based on economic current density. For long-term heating, the text elaborates on the criteria for permissible current, incorporating various correction factors dependent on installation environment, ambient temperature, and soil resistivity, referencing the IEC 60364 standard. Crucially, it details the coordination requirements between conductor cross-sections and overcurrent protection devices, such as fuses and circuit breakers, to ensure both system safety and operational continuity. The economic current density method is also presented, offering a way to balance initial investment costs with operational efficiency by minimizing energy losses over the equipment's lifespan. An illustrative exercise demonstrates the practical application of these selection criteria for aluminum-steel core conductors in a 110kV system, emphasizing how to choose appropriate standard cross-sections. This systematic approach ensures the design of robust, safe, and cost-effective electrical installations.