Causes of moisture in the cables of XLPE insulated power cables

XLPE insulated power cable causes moisture or moisture to enter the cable insulation during laying, installation and operation, mainly in the following situations.

1) The sealing of the cable end cap is not tight, or the cable end cap is damaged by external force during cable transportation and laying.

2) The cable sheath is damaged by external force during cable transportation or laying.

3) During the cable test or operation, the cable insulation breakdown destroys the cable sheath.

4) The cable accessories (especially the intermediate joints when directly buried laying) are not tightly sealed. Once moisture or moisture enters the cable insulation from the cable end or cable outer sheath, it may penetrate longitudinally from the gap in the copper wire shield outside the insulation or from the gap in the conductor, endangering the entire cable system. After moisture, the cable will produce the phenomenon of "water branches" under the action of high electric field, which will reduce the insulation performance of cross-linked polyethylene, and eventually lead to cable insulation breakdown.

Therefore, the cable after being exposed to moisture must be dehumidified.

Moisture in the cables of XLPE insulated power cables can be caused by cable defects or water ingress, as well as damage to the cable sheath during cable operation. The principle of dehumidification treatment can be done with a compressed gas medium at one end of the cable.

The main reasons for the moisture of the cable caused by XLPE insulated power cable are:

1. Water ingress due to unsealed or poor installation of the splice box or terminal box;

2. The cable is defective, and the metal sheath has small holes or cracks;

3. During cable test or operation, cable insulation breakdown destroys the cable sheath;

4. When the cable is transported or operated, the cable sheath is damaged due to external force;

5. The operating environment is corrosive, and the cable sheath is corroded and damaged.

The operating conditions and places of XLPE insulated cables are very wide.

1. It is suitable for power frequency rated voltage or distribution network or industrial equipment of 1kV and below, such as transformer outlet, etc.

2. The maximum allowable temperature of the cable conductor for long-term operation is 90.

3. When the short circuit is short-circuited (the longest duration is not more than 5s), the maximum allowable temperature of the cable conductor does not exceed 250.

4. The ambient temperature should not be lower than 0 when the cable is laid.

5. The bending radius of the cable shall not be less than 15 times of the outer diameter of the cable.

When laid in air.

1. The center distance of single-core cable when laid in parallel: 185mm and below is twice the diameter of the cable, and 240mm and above is 90mm.

Ambient air temperature: 40

Long-term maximum operating temperature of the conductor: 90

4. Correction coefficient (k) of current carrying capacity at different ambient temperatures

Ambient air temperature.

When directly buried and laid.

1. When the single-core cable is laid without contact, the distance between the center of the cable is twice the diameter of the cable.

2. Soil temperature: 25

3. The long-term maximum working temperature of the conductor: 90

4. Soil temperature coefficient:

5. Direct burial depth:

Soil temperature. Also add a few cable models.

The cross-linked polyethylene insulated cable adopts the method of peroxide cross-linking, so that the polyethylene molecule changes from a linear molecular structure to a three-dimensional network structure, and from a thermoplastic material to a thermosetting material, and the working temperature is increased from 70 to 90, which significantly improves the current carrying capacity of the cable. XLPE insulated cables have the following advantages:

1. Heat resistance: XLPE with mesh three-dimensional structure has excellent heat resistance. It will not decompose and carbonize below 300, the long-term working temperature can reach 90, and the thermal life can reach 40 years.

2. Insulation performance: XLPE maintains the original good insulation characteristics of PE, and the insulation resistance is further increased. The tangent of the dielectric loss is very small and is not greatly affected by temperature.

3. Mechanical characteristics: Due to the establishment of new chemical bonds between macromolecules, the hardness, stiffness, wear resistance and impact resistance of XLPE are improved, thus making up for the shortcomings of PE that are susceptible to cracking due to environmental stress.

4. Chemical resistance: XLPE has strong acid and alkali resistance and oil resistance, and its combustion products are mainly water and carbon dioxide, which is less harmful to the environment and meets the requirements of modern fire safety

It is suitable for fixed laying in the distribution network or industrial equipment below the power frequency rated voltage.

Laying in the air 1. The center distance of the single-core cable when laying in parallel: 185mm and below is twice the diameter of the electric lapping and infiltration cable, and 240mm and above is 90mm. 2. Ambient air temperature:

40 3. The long-term maximum working temperature of the conductor: 90 4. The correction factor of the current carrying capacity of different ambient temperatures (k) The ambient air temperature 20 25 30 35 40 45 The correction factor (k) Direct burial laying 1. When the single-core shouting cable is not in contact with the laying, the distance between the center of the cable is 2 times the diameter of the cable. 2. Soil temperature:

25 3. Long-term maximum operating temperature of the conductor: 90 4. Soil temperature coefficient:

5. Direct burial depth: 6. Correction coefficient of the current carrying capacity of Zhiqin at different soil temperatures Soil temperature 20 25 30 35 40 Correction coefficient (k).