Selection of power cable accessories below 35kV

1. Terminology
1.1 Cable line
The entire system composed of cables, accessories, ancillary equipment and ancillary facilities.
1.2 Cable accessories
Cable terminals, joints and oil-filled cable pressure boxes are collectively referred to as cable accessories;

1.3 Cable accessory equipment
The collective name of the cable circuit components such as the cross interconnection box, the grounding box, the protective layer protector, and the monitoring system;
1.4 Cable ancillary facilities
The general term for the components of cable lines such as cable ducts, brackets, bridges and structures.
1.5 armor layer
A coating composed of metal tape or wire. Usually used to protect the cable from external mechanical forces.
1.6 Cable termination
Also known as a cable head, it is a device installed at the end of a cable to connect the cable with other electrical equipment or overhead transmission lines and maintain insulation until the connection point.

1.7 Cable connector
A device that connects the conductor, insulation, shielding layer and protective layer of a cable to the cable to make the cable line continuous.
1.8 Metal shield
It is composed of one or more metal belts, metal braids, concentric layers of metal wires, or a combined structure of metal wires and metal belts.
2. Selection of cable accessories
2.1 Cable head composition
From the perspective of three-core cables, cable accessories mainly include 3 cold-shrinkable terminal heads, 1 cold-shrinkable three-finger sleeve, 3 cold-shrinkable sheaths (or cold-shrinkable insulating tubes), 3 cold-shrinkable sealing tubes, and grounding 1 ground wire.

2.2 Classification of cable heads
According to the working voltage, it is divided into: 1kV, 10kV cable head, 35kV cable head;
According to the conditions of use, it is divided into: outdoor terminals, indoor terminals, and intermediate connectors;
According to the number of cable cores, it is divided into: single-core terminal, three-core terminal, four-core terminal, and five-core terminal.
According to the installation materials, it is divided into: heat shrinkable cable terminal head and cold shrinkable cable terminal head;

2.3.2 Applicable scope of cable cross section

2.3.3 Cable plug connector 1) It is widely used in the connection of box transformers, ring network boxes, branch boxes, buried transformers and other equipment. It is a fully insulated and fully sealed plug-in terminal.

2) Classification:
A. Divided into 10kV plug head, 20kV plug head, 35kV plug head according to the voltage level; B. Divided into European plug head and American plug head. European-style plug-in heads are divided into: European-style front connector, European-style rear connector, and rear-connected lightning arrester; widely used in the connection of ring network boxes, European-style box transformers, and European-style branch box equipment. They are fully insulated and fully sealed plug-in terminal heads. The cable and the equipment are connected by a bolted connection type cable joint. American plug heads are divided into: 200A American elbow head, 600A American III-generation T-shaped head. It is widely used in the connection of American ring net boxes, American box transformers, and American branch boxes. It is a fully insulated and fully sealed plug-in terminal. A plug-in connection is adopted between the cable and the device.
Third, the choice of the area of ​​the metal shielding layer of the cross-linked polyethylene cable
3.1 Grounding the metal shield
According to Article 4.1.10～4.1.11 of GB 50217-2018 Power Engineering Cable Design Standard: 4.1.10 The metal sleeve of power cable should be directly grounded. The metal sheath of the 3-core cable in the AC system should be directly grounded at the two terminals and joints of the cable line.
4.1.11 The metal sheath of the AC single-core power cable shall be directly grounded at least at one end, and the maximum value of the normal induced potential at any non-directly grounded end shall meet the following requirements:
1. When safety measures that can effectively prevent personnel from arbitrarily contacting the metal sleeve are not taken, the voltage shall not exceed 50V;
2. Except for the circumstances specified in paragraph 1 of this article, it shall not exceed 300V;
3. The normal induced potential of the metal sheath of the single-core cable of the AC system should be calculated according to the formula in Appendix F of this standard.
4.1.13 If the metal sheath of single-core power cables below 35kV is directly grounded at a single point, and there is a need for reinforced sheath insulation protection, a sheath voltage limiter can be installed at the ungrounded terminal of the line.

3.2 Selection of the cross-sectional area of the metal shielding layer
According to Article 6.3.1 of DL/T401-2002 High-Voltage Cable Selection Guidelines: For the extruded insulated metal shielding layer without metal sleeve, when the conductor cross-section is 240mm² and below, the copper tape can be used for shielding, but when the conductor cross-section is larger than 240mm² should be shielded with copper wire. The cross-section of the metal shield should meet the short-term requirements when a single-phase ground fault or two simultaneous faults occur in different locations.