The value of the cable sheath grounding box

For the high-voltage single-core cable system, the appropriate cable sheath grounding method should be adopted according to the actual situation. In engineering applications, one end of the metal sheath is generally grounded, and the other end is grounded through the sheath protector; for long cable lines, the cable sheath cross-connection is generally used. When lightning waves or operating waves flow along the wire core, overvoltage will occur at the ungrounded end of the metal shielding layer of the cable joint, which is easy to cause insulation damage to the sheath, resulting in multi-point grounding and a large annular induced current. For this reason, a cable sheath protector should be installed at the ungrounded point of the metal sheath at the cable joint. In order to prevent the accelerated aging of the insulation of the outer sheath of the cable under the condition of single-phase short circuit, the long cable line should be protected by complete cross-connection. When the metal shielding layer adopts the hybrid connection method, the return line should be added to the cable section of the single-point grounding protection method to select the length of the cable reasonably.

Construction of the cable grounding box

     There are three main types, namely ZJJD cable sheathing direct grounding box, BHJD cable sheathing protective grounding box, JXJD cable sheathing cross-connection box

     The cable sheath direct grounding box contains connecting copper bars, copper terminals, etc., which are used for direct grounding of the cable sheath, and there is no need to install a cable sheath protector inside.

     Cable sheath protective grounding box and cable sheath cross-connection protective grounding box contains cable sheath protectors, connecting copper bars, copper terminals, etc., which are used for the protective grounding of cable sheathing.

Cable Sheath Protector

The cable sheath protector uses ZnO varistor as the protection element, has no series gap, has good protection characteristics, and has an excellent nonlinear volt-ampere characteristic curve. It not only has the advantages of porcelain sleeve type metal oxide arrester, but also has good electrical insulation performance, high dielectric strength, anti-leakage, anti-electric corrosion, heat resistance, cold resistance, aging resistance, explosion-proof and other excellent chemical stability, hydrophobicity, tightness. When the long-line high-voltage single-core cable is running, due to electromagnetic induction or equipment failure, overvoltage is generated, and it is very easy to break down the outer sheath of the cable, resulting in a multi-point grounding fault of the single-core cable. The cable sheath protector can effectively limit the metal of the cable. The shielding layer (metal sheath) induces voltage and equipment fault overvoltage to better protect the normal operation of the cable. The cable sheath protector is mainly used for the cable sheath protection grounding box and the cable sheathing cross-connection grounding box.

The characteristics of the cable sheath protector are as follows:

1. Excellent protection characteristics, effectively limit the induced overvoltage and fault overvoltage of the metal shielding layer (metal sheath) of the cable.

2. The volt-ampere characteristic curve is flat, the current capacity is large, and the protection characteristics are good.

3. The silicone rubber jacket adopts the unique interface bonding technology and the overall one-time molding process, which has good sealing performance, safety and anti-riot and maintenance-free.

Main Specifications

1. Normal use conditions Ambient temperature -40 ℃ ~ 40 ℃ can be installed outdoors or in cable trenches.

2. Main technical performance after disconnecting the grounding or protector link

3. DC withstand voltage test: 20kV/min without flashover and breakdown;

4. Impulse voltage test: 40kV ± 10 times, no flashover, no breakdown;

5. After installation, the main insulation part test of the grounding box

6. The insulation resistance value measured by a 5kV megohmmeter should be greater than 5MΩ;

7. 10kV DC withstand voltage test for 1min, no flashover and no breakdown.

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