Discussion on the insulation performance of LSZH flame-retardant polyolefin insulating materials

Insulating material electrical insulation properties are generally expressed in volume resistivity, volume resistivity of insulating materials to determine the volume resistivity, is made of wire or cable, can meet the wire or cable insulation resistance of the index requirements as a prerequisite, and can leave a certain margin.

The volume resistivity of the insulating material and the insulation resistance of the wire or cable exists in the following conversion relationship:

At present, the use of halogen-free low-smoke flame-retardant materials as insulation wire or cable have some of the following standards, the standards have a clear requirement for the insulation resistance of the wire or cable, accordingly, can be converted to the volume resistivity of the insulating material requirements:

① EN50525 and IEC62821 standards, its wire for 450/750V voltage level, the assessment of insulation resistance at 70 ℃, converted to volume resistivity at 70 ℃ is about 3.0 × 108Ω-m;

② JB/T10491-2004 standard, its wire for the 450/750V voltage level, the assessment of its insulation resistance at operating temperature, converted to volume resistivity of 1.0 × 108Ω-m or so;

③ EN50264 locomotive cable standard, according to the wire insulation resistance requirements of the value, converted to 20 ℃ volume resistivity requirements for 2.0 × 1011Ω-m;

④ 2PfG1169 photovoltaic cable standard, the required 20 ℃ volume resistivity of 1.0 × 1012Ω-m;

⑤ In the IEC60092-360:2004 standard for marine cables, the electrical properties of halogen-free low-smoke flame retardant insulating material HF90 are required as follows:

So the volume resistivity of the LSZH flame retardant insulating material used can be determined according to different standard requirements.

It should be noted that the LSZH flame-retardant insulating material, due to the addition of a large number of inorganic flame retardants, its volume resistivity is difficult to reach the level of 1.0 × 1014Ω-m of pure PE materials and EPR materials.

Currently, some wire and cable manufacturers use LSZH flame-retardant insulating material as insulation to manufacture 0.6/1kV LSZH flame-retardant low-voltage power cables, which may be aimed at cables with higher flame retardant level. In fact, as long as the use of reasonable cable structure, the use of excellent quality of halogen-free low-smoke flame-retardant sheath materials, XLPE as insulation, can produce a high level of flame retardant LSZH flame-retardant low-voltage power cables.

Of course, if we must use LSZH flame-retardant materials as insulation to manufacture 0.6/1kV low-voltage power cables, although the physical and mechanical properties of the insulating material can be based on the requirements of the GB/T 19666-2005 standard, but there is no standard for its insulation performance, because in the GB/T 19666-2005 standard can not be found in the halogen-free low-smoke flame-retardant cables if the insulation using LSZH insulation materials, the insulation resistance of the flame-retardant cable. insulation materials, the insulation resistance requirements, which brings problems.

One method is that the insulation layer adopts double-layer insulation structure, the inner insulation layer adopts XLPE, and the outer layer adopts LSZH flame retardant materials. Its insulation resistance constant according to the same assessment of XLPE, that is, at 20 ℃ for a minimum of 3670MΩ - km, the minimum operating temperature of 3.67MΩ - km.

Another method is to establish a LSZH flame retardant insulating material for 0.6/1kV power cable insulation performance requirements. This is because the IEC 60092-360:2014 standard for marine cables has a more reasonable index for HF90, which can be used as a reference. This eliminates the need for a double-layer insulation structure and meets the insulation resistance requirements.