On the basis of ensuring safety, the state has formulated certain indicators for wires and cables. Only when relevant indicators are met can they be called national standard wires. As for the allowable long-term working temperature of wires and cables, rubber insulation is usually 65 ℃, PVC insulation is 70 ℃ and cross-linked polyethylene insulation is 90 ℃; The maximum allowable temperature of conductor during short circuit (the maximum duration shall not exceed 5S): 160 ℃ for PVC insulation and 250 ℃ for XLPE insulation.
1. Low voltage cross-linked (XLPE) cable has developed rapidly since it was put into use in the mid-1990s. At present, it has accounted for half of the market share with polyvinyl chloride (PVC) cable. Compared with PVC cable, cross-linked cable has higher current carrying capacity, stronger overload capacity and longer service life (the thermal life of PVC cable is generally 20 years when the environment is good, while that of XLPE cable is generally 40 years); PVC will decompose and release a large amount of black smoke and toxic gas when burning, while XLPE will not produce halogen toxic gas when burning. The advantages of cross-linked cable are increasingly recognized by the design and use departments.
2. Ordinary PVC wires and cables (insulation and sheath) burn quickly and contribute to the fire. The power supply capacity will be lost in 1 ~ 2min. The black smoke released by combustion and decomposition can reach the extent that you can’t see your fingers, resulting in difficulty in breathing and evacuation. More seriously, PVC will decompose and release highly toxic and corrosive halogen gases such as hydrogen chloride (HCl) and dioxin during combustion, which is the main cause of human death in the fire (accounting for 80% of the fire death factors), and form a dilute hydrochloric acid conductive film attached to the electrical equipment, which seriously reduces the insulation performance of the equipment and forms a secondary disaster that is difficult to remove.
PVC: low working temperature, short thermal aging life, small transmission capacity, low overload capacity, and great harm of smoke and acid gas in fire. It is a general product in the wire and cable industry, with good physical and mechanical properties, good processing performance and low cost and price. However, it contains halogen, and the amount of sheath is the largest.
XLPE: almost as excellent as the electrical performance of PE. At the same time, the long-term working temperature is relatively higher than PE, the mechanical performance is better than PE, and the aging resistance is better. New environmental protection products with high temperature resistance and good environmental resistance, thermosetting plastics. It is often used in electronic wires and places with high environmental resistance requirements.
The model of XLPE insulated power cable is YJV, and the model of PVC insulated power cable is vv. YJV cable is preferred for general indoor permanent projects. VV cables are generally used in low-voltage systems, while YJV cables are mostly used in high-voltage systems. YJV cables are better than VV cables in temperature resistance, pressure resistance and corrosion resistance. It’s just more expensive.
VV cable is PVC insulated and PVC sheathed, which is made of thermoplastic materials
YJV cable is a cross-linked PVC insulated PVC sheathed cable made of thermosetting materials
Due to different materials, VV and YJV cables allow long-term operation * high temperature is different,
1. VV cable (VLV) cable conductor operation * high rated temperature is 70 ℃. In case of short circuit (duration less than 5 seconds) * high temperature does not exceed 160 ℃.
2. YJV cable (yjlv) cable conductor operation * high rated temperature is 90 ℃. In case of short circuit (duration less than 5 seconds) * high temperature does not exceed 250 ℃.
Therefore, the current carrying capacity of the two cables is different, and YJV is larger.