I. Selection of Transformer Neutral Grounding Methods: Safety and Applicability Analysis
The choice of grounding method requires comprehensive evaluation of power supply continuity, personnel safety risks, equipment insulation levels, overvoltage suppression capabilities, and fault detection needs. Three primary systems are employed:
TN-S System (Protective Earthing System)
Core Features: The transformer neutral is directly grounded. The protective earthing conductor (PE) and neutral conductor (N) are independently routed from the power source to the terminal. Equipment metal enclosures are connected to the PE conductor.
Safety Mechanism: In the event of a single-phase enclosure fault, a metallic short-circuit loop forms, generating high short-circuit current (Id) that triggers instantaneous circuit breaker tripping to cut off the power supply. The PE conductor remains de-energized during normal operation, ensuring stable potential and superior electromagnetic compatibility.
Typical Applications: Civil buildings (residential, commercial, offices), hospitals, data centers, and other spaces requiring high electric shock protection [citation: User Document]. It is the mainstream grounding solution for modern structures.
IT System (Isolated Grounding System)
Safety Mechanism: During the first single-phase earth fault, the fault current is limited to the system's distributed capacitive current to earth (typically <10 A). Line-to-line voltages remain balanced, allowing continued equipment operation. An Insulation Monitoring Device (IMD) must provide real-time alarms to prevent secondary faults causing phase-to-phase short circuits.
Key Value: Ensures power continuity in high-risk areas and significantly reduces explosion/fire risks from electric sparks.
Typical Applications: Underground mines (preventing methane explosions), hospital operating rooms/ICUs (maintaining life-support equipment), and petrochemical explosion-proof zones [citation: User Document].
TN-C-S System (Composite Grounding System)
Core Features: The power supply inlet uses TN-C (combined PEN conductor), which splits into independent PE and N conductors after entering the building. The subsequent system is equivalent to TN-S.
System Characteristics Comparison:
TN-S: Ensures personnel safety through rapid fault clearance but risks power interruptions.
IT: Maximizes supply continuity with minimal fault current but demands stringent insulation monitoring.
TN-C-S: Balances cost efficiency and downstream safety; PEN conductor breakage risks require mitigation.
II. Lightning Protection Grounding Design: Key Parameters and Reinforcement Measures
Lightning overvoltage poses a major threat to power equipment. The core objectives of lightning protection grounding systems are low-impedance lightning current dissipation and potential equalization.
Core Grounding Resistance Standards
impulse grounding resistance for independent lightning rods (air terminals), overhead ground wires, and roof-mounted air termination networks shall be ≤10 Ω (per GB 50057 Code for Design of Lightning Protection of Buildings), preventing "backflashover" hazards.
Enhanced Requirement (≤4 Ω): Applicable to:
High/strong lightning activity areas (annual thunderstorm days >90);
Critical facilities (data centers, communication hubs, control rooms);
High soil resistivity zones (ρ >500 Ω·m);
Power system neutral grounding points (specific codes may require ≤4 Ω).
Clause 6 of GB 50057 regarding ring grounding networks, emphasizing their necessity in high-risk zones.
Reinforcement Measures for High-Risk Areas
Ring Grounding Network: A closed-loop horizontal grounding conductor (galvanized flat steel ≥40mm×4mm or copper strand ≥95mm²) buried >0.5m deep around critical facilities. Functions include:
Reducing grounding resistance (expanding dissipation area);
Equalizing earth potential (minimizing step/touch voltages);
Integrating building foundation grounding into a composite network.
Comprehensive Resistance-Reduction Techniques:
Deep-well Grounding: Drilling to underground aquifers (20–100m depth) to install vertical electrodes;
Resistivity-Reducing Compounds: Backfilling bentonite or chemical agents around electrodes to enhance soil conductivity;
Extended Grounding: Expanding the network to low-resistivity areas (e.g., ponds, moist soil);
≤4 Ω + ring grounding networks in high-risk zones. Rigorous adherence to GB 50057, GB/T 50065, and other standards-combined with soil surveys and simulation-builds reliable electrical safety barriers.