The grounding resistance of power equipment is a critical factor in ensuring the safety and reliability of electrical systems. For effectively grounded systems, the grounding resistance must meet specific criteria to ensure proper operation during fault conditions. The standard cycle for testing is generally no more than six years, but this can be adjusted based on the results of grounding network excavation inspections.
The required grounding resistance (R) should typically be less than or equal to 2000/I or 0.5Ω when the short-circuit current (I) exceeds 4000A. This ensures that the system remains safe and functional under various conditions. When measuring grounding resistance, if the soil resistivity is relatively uniform, compensation methods can be used. Otherwise, the transport method should be applied. In areas with high soil resistivity, it may be acceptable to exceed the standard value if the technical and economic justification is strong, provided that certain safety measures are in place. These include ensuring that contact and step voltages remain within allowable limits, avoiding high potential differences outside the grounding network, and preventing unnecessary operation of valve arresters.
For non-effectively grounded systems, the requirements differ slightly. When the grounding grid is connected to equipment rated at 1kV or below, the grounding resistance should not exceed 120/I. If the connection is above 1kV, the limit is 250/I. In all cases, the resistance should generally not exceed 10Ω. These values take into account seasonal variations and ensure that the system remains stable during faults.
For overhead line towers equipped with ground wires, the grounding resistance requirements depend on the tower height and soil resistivity. Towers within 1–2 km of a power plant or substation should be tested every 1–2 years, while other towers should be tested no more than once every five years. For towers under 40 meters tall, the grounding resistance should be as follows: up to 10Ω for soil resistivity below 100Ω·m, 15Ω for 100–500Ω·m, 20Ω for 500–1000Ω·m, 25Ω for 1000–2000Ω·m, and 30Ω for over 2000Ω·m. If the soil resistivity is higher than 2000Ω·m, the resistance can be increased to 20Ω, provided that additional grounding methods such as radial or elongated grounding bodies are used. For towers 40 meters or taller, the resistance should not exceed 20Ω regardless of soil conditions.
Composite Insulators
The Composite Insulator are made of glassfiber epoxy core rod, silicone rubber shed and metal fittings.
The silicon rubber shed adopt the whole packing pressure technique, can solve the key problem – interface electric spark puncture, which would affect the reliability of composite insulator.
Connection of the glassfiber rod and metal fittings adopts the pressure welding technique of the international advanced level, and have the full automatic sound wave detection of defects system, high intension, beautiful outline, small volume, light weight, and the metal fitting of galvanization can corrosion prevention and exchange used with porcelain insulator.
Composite Insulators,Insulation Resistance,Transmission Lines Insulator,Line Post Type Insulator
Jilin Nengxing Electrical Equipment Co. Ltd. , https://www.nengxingelectric.com