Abstract: GB/T 18890.3-2015 is an important national recommended standard in China, which specifies the technical requirements, test methods, acceptance criteria, packaging, transportation and storage for accessories of cross-linked polyethylene (XLPE) insulated power cables with rated voltage of 220kV (Um=252kV). This article elaborates on the core content of the standard, including its scope of application, key terms and definitions, main technical requirements, test and acceptance regulations, aiming to provide a comprehensive technical reference for relevant engineering and technical personnel in the power industry.

1. Introduction

With the rapid development of the power industry, high-voltage power transmission and distribution systems have increasingly high requirements for the reliability and safety of power cables and their accessories. As a key part of the power cable system, cable accessories play a crucial role in ensuring the stable operation of the entire power transmission network. GB/T 18890.3-2015, titled “Power cables with cross-linked polyethylene insulation and their accessories for rated voltage of 220 kV (Um=252 kV)—Part 3: Accessories”, was issued on October 9, 2015, and implemented on May 1, 2016 . This standard replaces the previous guiding technical document GB/Z 18890.3-2002, and its nature is adjusted from guiding to recommended, which further standardizes the design, production, test and application of 220kV XLPE insulated power cable accessories in China .

2. Scope of Application

GB/T 18890.3-2015 applies to outdoor terminations, GIS terminations, oil-immersed (transformer) terminations, straight joints and insulated joints used with 220kV (Um=252kV) XLPE insulated power cables that meet the requirements of GB/T 18890.1-2015 under general installation conditions . It should be noted that this standard does not apply to taped insulated joints, transition joints used for connecting XLPE insulated cables and paper-insulated cables, and separable cable terminations .

3. Key Terms and Definitions

The standard defines a series of key terms related to cable accessories, which lay the foundation for the unified understanding and application of the standard. The main key terms are as follows :

• Outdoor termination: A cable termination used in conditions where it is directly exposed to sunlight, climatic environment, or both (according to GB/T 2900.10-2013, definition 461-10-14).
• Termination with porcelain insulator: An (outdoor) cable termination with porcelain insulator as external insulation.
• Termination with composite insulator: An (outdoor) cable termination with a composite insulator as external insulation, which takes glass fiber reinforced epoxy tube as the core and is covered with weather-resistant and pollution-resistant elastomer material (such as silicone rubber).
• GIS termination: A cable termination installed inside the gas-insulated metal-enclosed switchgear (GIS) and using sulfur hexafluoride (SF6) gas as its external insulation for the gas-insulated part.
• Oil-immersed termination (transformer termination): A cable termination installed inside the oil tank of oil-immersed transformer equipment and using insulating oil as its external insulation for the liquid-insulated part.
• Straight joint: An accessory that connects two cables to form a continuous circuit. In this part, it specifically refers to the joint where the metal shell of the joint is electrically continuous with the metal screen and insulation screen of the connected cables.
• Sectionalizing joint: A joint that keeps the metal sheath, metal screen and insulation screen of the connected cables electrically disconnected (discontinuous).
• Pre-fabricated accessories: Cable accessories that use prefabricated rubber components (and prefabricated epoxy insulation components) with electric field stress control function as the main insulation components, including prefabricated terminations and prefabricated joints.

4. Main Technical Requirements

GB/T 18890.3-2015 puts forward detailed technical requirements for 220kV XLPE insulated power cable accessories, covering aspects such as conductor connection fittings, semi-conductive shielding, insulation components, external insulation, and metal shielding. The key technical requirements are as follows:

4.1 Conductor Connection Fittings

The conductor connection fittings shall have reliable electrical conductivity and mechanical strength. The standard modifies the requirements for conductor connection fittings compared with the previous version, emphasizing the stability of the connection performance to ensure the safe transmission of electrical energy .

4.2 Semi-conductive Shielding

The standard adds requirements for semi-conductive rubber tape for semi-conductive shielding and specifies the performance of semi-conductive rubber tape (see Appendix A) . The semi-conductive shielding layer shall have uniform conductivity to ensure the uniform distribution of the electric field and avoid local electric field concentration.

4.3 Insulation Components

The insulation components of cable accessories mainly include rubber insulation parts, epoxy insulation parts, etc. The standard modifies the performance requirements of insulation materials and semi-conductive materials for rubber insulation parts compared with the previous version . For example, the epoxy resin cured body used in accessories shall meet the specified electrical and thermal performance indicators, such as the volume resistivity at 23℃ being not less than 1.0×10¹⁴ Ω·m, the short-term power frequency breakdown electric field strength being not less than 20 kV/mm, and the thermal deformation temperature being not less than 105℃ . In addition, the standard also adds requirements for insulation parts used for metal sheath segmentation of insulated joints .

4.4 External Insulation

The standard modifies the external insulation environment classification and pollution type, and adds the expression of on-site pollution degree (SPS) levels . The external insulation of cable terminations shall have sufficient creepage distance to adapt to different pollution environments. The standard changes “minimum creepage distance” to “three-phase system creepage distance” to more accurately reflect the insulation requirements of the three-phase power system . For composite sleeve terminations, the standard adds their codes, model names (see Table 2) and technical requirements .

4.5 Metal Shielding

The standard adds technical requirements for the metal shielding of joints to ensure that the metal shielding layer can effectively play the role of electromagnetic shielding and protect the internal insulation .

5. Test and Acceptance Regulations

The test and acceptance of cable accessories are important links to ensure that their performance meets the standard requirements. GB/T 18890.3-2015 specifies the test classification, requirements and test methods of accessories (see Table 3), including type tests, routine tests, sampling tests, etc. Compared with the previous version, the standard adds the content of sampling tests for accessories and the type tests of cable systems composed of accessories and cables, and also adds pre-qualification extension tests .

In terms of specific tests, the standard modifies the sealing test conditions after terminal assembly . At the same time, it deletes the requirement for the radio interference test of outdoor terminations . Common tests include AC voltage test, partial discharge test, impulse voltage test, etc., which are carried out in accordance with the relevant provisions of GB/T 3048.8-2007, GB/T 3048.12-2007, GB/T 3048.13-2007 and other normative reference documents .

The acceptance of cable accessories shall be carried out in accordance with the acceptance rules specified in the standard. Only the products that pass all the tests can be accepted and put into use.

6. Packaging, Transportation and Storage

GB/T 18890.3-2015 also specifies the requirements for the packaging, transportation and storage of cable accessories. The packaging shall be able to protect the accessories from damage during transportation and storage. During transportation, they shall be protected from moisture, collision and other harmful factors. During storage, they shall be placed in a dry, clean and well-ventilated environment, avoiding direct sunlight and contact with harmful substances.

GB/T 18890.3-2015 provides comprehensive and detailed technical specifications for 220kV XLPE insulated power cable accessories. By standardizing the design, production, test and application of cable accessories, the standard effectively improves the reliability and safety of the 220kV power cable system, and provides strong technical support for the stable operation of the power grid. Relevant enterprises and engineering and technical personnel should strictly abide by the requirements of this standard in practical work to ensure the quality and performance of cable accessories. In the future, with the continuous progress of power technology, the standard may be further revised and improved to adapt to the new development needs of the power industry.

References

• [1] General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China, Standardization Administration of the People’s Republic of China. GB/T 18890.3-2015 Power cables with cross-linked polyethylene insulation and their accessories for rated voltage of 220 kV (Um=252 kV)—Part 3: Accessories[S]. Beijing: Standards Press of China, 2015.
• [2] General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China, Standardization Administration of the People’s Republic of China. GB/T 18890.1-2015 Power cables with cross-linked polyethylene insulation and their accessories for rated voltage of 220 kV (Um=252 kV)—Part 1: Test methods and requirements[S]. Beijing: Standards Press of China, 2015.
• [3] General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China, Standardization Administration of the People’s Republic of China. GB/T 2900.10-2013 Electrical terminology—Cables[S]. Beijing: Standards Press of China, 2013.