Talking about lightning protection of natural gas station
Lightning is a frequent atmospheric phenomenon that involves the release of immense energy, causing various physical effects such as strong electric currents, high temperatures, powerful shock waves, dramatic electrostatic fields, and intense electromagnetic radiation. These effects can lead to significant damage to people and infrastructure. In China, long-distance natural gas pipelines stretch across the country from east to west and north to south, passing through numerous stations and valve rooms. Due to the diverse geographical locations, some areas are prone to frequent thunderstorms, making them particularly vulnerable to lightning strikes. If lightning strikes these facilities, the resulting damage can be unpredictable and severe. Therefore, it is crucial to implement effective lightning protection measures at natural gas stations, valve rooms, and other critical infrastructure along the pipeline.
**1. Impact of Lightning on Natural Gas Stations**
**1.1 Influence of Lightning on Instrument Control Systems**
Lightning can occur in two main forms: direct strikes and induced strikes. Each can pose different risks to instrument control systems:
- **Direct Lightning Strikes**: When lightning hits field instruments or connected piping, it can damage sensors and control boards. The lightning current creates a strong magnetic field along the instrument bracket, which may couple with control room equipment via signal lines, potentially damaging control devices.
- **Inductive Lightning Strikes**: This includes electrostatic induction, where charged objects (especially conductors) build up large amounts of charge before discharging into the system, and electromagnetic pulse radiation, where lightning generates an electromagnetic field that couples with control equipment and metal conductors, causing interference or damage.
- **Lightning Overvoltage Intrusion**: Direct or induced lightning can cause overvoltages in wires or pipes, introducing high potentials into the control system through metal pipes, cable trays, and cables, leading to interference or failure.
- **Counterattack**: When a lightning protection device is activated, a large current flows through the grounding system, raising the local ground potential. If the grounding of the control system is not sufficiently isolated, this can result in a counter-current, damaging insulation and causing system failures.
**1.2 Impact of Lightning on Pipelines**
The above-ground sections of process piping and spanning pipelines act as natural lightning receptors. When lightning occurs nearby, an electrostatic field forms beneath the buried pipeline, inducing opposite charges on its surface. Once the charge accumulates enough, a discharge occurs, creating a strong current inside the pipe. For pipes with poor insulation, the current may leak through the insulation, causing minimal damage. However, for well-insulated pipes, the surge may generate high voltage, leading to secondary discharges and damaging equipment. Metal pipes, being good conductors, are especially vulnerable to direct lightning strikes.
Additionally, cathodic protection equipment and anti-corrosion power supplies are also susceptible to lightning damage. Components like discharge tubes, capacitors, and integrated circuits may be damaged, with severe cases burning out circuit boards. Since these systems are directly connected to the pipeline, they serve as easy pathways for lightning currents, increasing the risk of damage.
**2. Lightning Protection Measures for Natural Gas Stations**
A comprehensive lightning protection system should include three key components:
1. **External Lightning Protection**: This involves lightning rods, down conductors, and grounding systems to intercept and safely discharge most of the lightning current.
2. **Surge and Electromagnetic Protection**: Using equipotential bonding, shielding, and surge protective devices (SPDs) to block lightning waves from entering through wires or electromagnetic fields.
3. **Surge Protection Devices (SPDs)**: These nonlinear components are used to divert overvoltages and overcurrents from power and signal lines to the ground.
For the instrument control system, additional measures such as lightning diversion, voltage equalization, grounding, and shielding are essential. These must be implemented together to ensure effective protection.
**2.1 Lightning Diversion**
Protecting against direct lightning strikes typically involves using building lightning protection systems. Field instruments should also be integrated with the lightning protection of surrounding gas transmission equipment to ensure full coverage.
**2.2 Voltage Equalization**
During a lightning strike, a transient potential rise occurs along the path of the lightning current, creating a potential difference between the path and surrounding metal objects. This can lead to breakdown discharge, damaging equipment or generating electromagnetic pulses that interfere with operations. To prevent this, all metal components—such as instrument casings, frames, and control room equipment—should be bonded together and connected to the lightning protection grounding system, forming an equipotential network.
**2.3 Grounding**
There are two main grounding methods for instrumentation systems: floating ground and multi-point grounding. While floating ground isolates the system from building grounding, it may still allow dangerous voltage differences during lightning events. Multi-point grounding, though more effective, can introduce risks if lightning enters through the protective ground. A combined approach—connecting both working and protective grounds to the lightning protection system—is often recommended for better safety.
**2.4 Shielding**
Given the sensitivity of semiconductor devices and signal cables, shielding is crucial. Control rooms should have closed structures with reinforced walls and grounded rings to protect against electromagnetic pulses. Field instruments can use shielded enclosures, while signal and power lines should use metal-shielded cables, grounded at multiple points to reduce interference.
**2.5 Diversion**
Diversion is a key method for protecting against surges. Surge protectors (SPDs) are installed in critical parts of the system to limit overvoltages and surges. They should be strategically placed in power and signal loops to provide optimal protection.
**2.6 Strengthening Lightning Protection Management**
Regular inspection and maintenance of lightning protection devices are essential. Grounding resistance should be kept below 0.03 Ω for valves and flanges, and grounding resistance should not exceed 100 Ω. All jumpers removed for testing must be restored. Additionally, equipment should be maintained regularly, and safety standards strictly followed to minimize risks. Electrical devices should be selected based on their safety and explosion-proof ratings, and all protective systems—including leakage, short-circuit, and insulation protection—must remain functional at all times. Regular verification of detection and alarm systems is also necessary to ensure reliability.
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