Several problems in the middle connector of coal mine cable

The underground space in the coal mine is small and the air is damp. There is a danger of coal dust and gas explosion. Therefore, the requirements for the middle connector of the cable are high. The cold-shrinking intermediate joint has many advantages, and installation does not require a special tool, which is simple and quick, and the production time is short. Do not use an open flame, safe and reliable. We know that the main cause of electric field distortion of the cable connector is: When the connector is made, the copper shield, semiconductor shield, insulation layer, and core of the cable must be stripped. At the cutoff of the cable connector core and shield layer, The phenomenon of electric stress concentration will occur and the electric field strength will be the greatest, which is the weak link of the entire joint. At the same time, poor site conditions will inevitably invade dust, gas, moisture, and other impurities. We know that impurities, air gaps, and moisture are the main causes of creeping discharge of the solid insulating medium. Therefore, the causes of insulation breakdown of the cold-shrinkable joint may be as follows:

(1) When stripping the semiconductor shielding layer of cable, the tool marks are too deep, so that the surface of the main insulation layer is flawed and air gaps are likely to exist.

(2) After the semiconductor layer of the cable is stripped, it is not removed. The semiconductor is left on the main insulating layer, or it does not follow the process requirements during cleaning, scrubbing back and forth, leaving hidden dangers and flashover discharge.

(3) After the cable core is crimped, the connecting pipe is deformed by the tip and corner to cause distortion of the electric field, local field concentration, and tip discharge.

(4) Cold-shrinkable silicone rubber bushings are prefabricated accessories that must be matched to the cable cross-section.

(5) When the cold shrinkable head was made, after the silicone rubber insulating sleeve was shrunk, the two ports were not subjected to any sealing treatment, which was an important reason for the intrusion of moisture.

(6) When making cold shrink fittings, the three-phase cold shrinkable insulating sleeves are in the center position. Due to unevenness, there will be wrinkles in the enveloping waterproof tapes, causing wraps to be tight, resulting in moisture in the joints.

(7) The improper size of the semiconductor shield and the failure to recover copper shields are the major causes of short-circuit faults.

(8) The underground environment is humid, and the main road often flushes with water and dust.

(3) The cable connector becomes blisters during dropping of the ground.

Based on the above analysis, it can be concluded that the cable middle box may be damaged due to the cable's landing, relocation, and movement. Therefore, in the production of joints, it must be installed in accordance with the standard and accurate specification.