Bài giảng An toàn điện - Chương 6: Bảo vệ nối đất

The safety of electrical systems and personnel is paramount, necessitating robust protective measures. Among these, earthing, or grounding, plays a critical role by intentionally connecting specific parts of electrical equipment to an earthing system. This foundational practice is essential not only for mitigating electrical hazards to human life but also for ensuring the reliable operation and longevity of electrical installations. It directly contributes to reducing potentially dangerous fault currents through individuals and facilitating the timely activation of overcurrent protection devices (like circuit breakers and fuses) during phase-to-casing faults. Understanding the principles, purpose, and proper implementation of earthing systems is therefore crucial for anyone involved in electrical engineering and safety.

Electrical engineers, technicians, safety officers, and students involved in the design, installation, maintenance, and inspection of electrical systems and safety protocols.

This document provides a comprehensive overview of earthing (nối đất) in electrical systems, detailing its fundamental purpose, significance, and practical implementation. The primary objectives of earthing are twofold: to significantly reduce the current flowing through a person to a safe threshold, thereby preventing electric shock, and to enhance fault current magnitude to ensure rapid activation of traditional overcurrent protection devices (như CC, ATM, BVRL) during phase-to-casing faults. This swift disconnection safeguards both personnel and equipment. The text further categorizes earthing into working earthing (nối đất làm việc) for network operation, safety earthing (nối đất an toàn) for human protection against insulation failures, and lightning protection earthing (nối đất chống sét) to secure systems from atmospheric discharges. A structured methodology for the design and installation of earthing systems is presented, encompassing data collection, determination of required earthing resistance (Ryc), selection of appropriate electrodes, and calculation of actual resistance. A critical comparison between calculated and required resistance guides further design adjustments. Practical steps include drawing layouts, detailing installation procedures, and emphasizing subsequent inspection. The document also delineates the broad application scope of earthing across high and low-voltage networks, alongside specific considerations for hazardous environments or outdoor equipment. Crucially, it addresses challenges posed by high soil resistivity, offering solutions such as utilizing natural electrodes, soil replacement, or employing specialized chemical compounds like GEM, EEC, or San-Earth to optimize earthing performance. The importance of equipotential bonding and regular inspections (every 6 months) for maintaining system integrity is also highlighted, reinforcing the practical value and implications of proper earthing for overall electrical safety.