In the power system, the grounding system is an important part to ensure safe and stable operation. The grounding resistance refers to the resistance value between the grounding device and the earth, which is usually required not to exceed 4Ω.
1 Safety
First of all, the main purpose of the grounding resistance is to ensure personal safety. In the power system, the fault current or lightning current needs to be quickly introduced into the ground through the grounding device to reduce the risk of electric shock and fire. Low grounding resistance can provide a lower current path resistance, ensure the fault current discharge speed, and avoid voltage accumulation on the equipment casing or other accessible parts, thereby reducing the risk of electric shock. For example, if the casing of a certain device is accidentally charged, low grounding resistance can quickly introduce the current into the ground by providing a low-resistance path to avoid electric shock accidents caused by personnel contacting the charged casing.
2 Protecting equipment
Electrical equipment may encounter overvoltage and overcurrent caused by lightning strikes or internal faults during operation. Low grounding resistance can quickly discharge these overvoltage and overcurrent to the ground, thereby protecting the equipment from damage. Especially in thunderstorms, electrical equipment in thunder-prone areas needs a good grounding system to prevent lightning damage to the equipment. High grounding resistance may cause lightning current or fault current to be unable to be effectively discharged, thus causing damage to the equipment.
3 Electromagnetic compatibility
Electromagnetic compatibility (EMC): refers to the fact that electrical equipment should not generate too much electromagnetic interference during operation, and should also be able to work normally in a certain electromagnetic environment.
Low grounding resistance helps to reduce the conduction and radiation of electromagnetic interference and improve the electromagnetic compatibility of the power system. If the grounding resistance is too high, the electromagnetic interference in the system may affect the normal operation of other electronic equipment, causing equipment failure or performance degradation. Ensuring that the grounding resistance is within a reasonable range can effectively reduce the impact of electromagnetic interference.
4 Stability of the power system
The stability of the power system: refers to the ability of the system to maintain or return to a stable state when it is disturbed (such as faults, load fluctuations).
Low grounding resistance can ensure the good performance of the grounding grid in the power system, thereby improving the stability of the system. Too high grounding resistance may cause the system to be unable to quickly return to a stable state when a fault occurs, thereby affecting the normal operation of the power system. For example, in the event of a short circuit fault, low grounding resistance can ensure that the fault current is quickly introduced into the ground, thereby quickly restoring the normal operation of the system.
5 Standards for grounding resistance
The specific standards for grounding resistance are determined according to the electrical safety specifications and standards of the country or region. For ordinary residential and commercial buildings, the grounding resistance is usually required to be no more than 4Ω, in order to ensure adequate safety and protection in most cases. However, in some special occasions, such as hospitals, data centers, and areas prone to lightning, the grounding resistance requirements may be more stringent, and may even require no more than 1Ω.
These standards are switched according to different application scenarios to ensure optimal safety and stability.
6 Design and maintenance of grounding system
To achieve the requirements of low grounding resistance, the design and maintenance of the grounding system is very important. Common grounding measures include:
1) Use grounding conductors of sufficient length and cross-sectional area,
2) Reasonable arrangement of grounding bodies,
3) Select grounding materials with good conductivity (such as copper, galvanized steel), etc. 4
4) Regularly inspect and maintain the grounding system. (For example, corrosion of the grounding body, looseness or damage of the grounding conductor may lead to increased grounding resistance, so regular inspection and maintenance are required).
7 Conclusion
In summary, there are many reasons why the grounding resistance usually does not exceed 4Ω, including:
1) Personal safety
2) Equipment protection
3) Electromagnetic compatibility
4) Power system stability
and other considerations. The design and maintenance of the grounding system plays a vital role in ensuring the safe and reliable operation of the power system. By deeply understanding these principles and requirements, we can better design and maintain the grounding system to ensure the efficient and safe operation of the power system.