Abstract: GB/T 18890.3-2015 is an important national standard in China that specifies the technical requirements, test methods, and application conditions for accessories of 220 kV (Um=252 kV) cross-linked polyethylene (XLPE) insulated power cables. This standard, which replaced the previous GB/Z 18890.3-2002, has been upgraded from a guiding technical document to a recommended standard, incorporating more comprehensive and stringent technical provisions. This article elaborates on the core content of GB/T 18890.3-2015, including its scope of application, key definitions, operating conditions, product classification and model specifications, technical requirements for materials and components, test methods, and main technical changes from the previous version. It aims to provide technical reference for engineers, manufacturers, and relevant practitioners in the power cable industry.

1. Introduction

With the rapid development of China’s power grid construction, 220 kV power transmission and distribution systems play a crucial role in ensuring the stable and efficient operation of the power grid. As an integral part of the power cable system, cable accessories (such as terminations and joints) are responsible for connecting cables, insulating, and protecting the cable ends and connection points. Their performance directly affects the overall reliability and safety of the power cable system. To standardize the design, production, and application of accessories for 220 kV XLPE insulated power cables, the Standardization Administration of the People’s Republic of China issued GB/T 18890.3-2015 on October 9, 2015, which has been in effect since its release. This standard is part of the GB/T 18890 series, which is divided into three parts: Part 1 (Test Methods and Requirements), Part 2 (Cables), and Part 3 (Accessories).

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 220 kV (Um=252 kV) XLPE insulated power cables that meet the requirements of GB/T 18890.1-2015 under normal installation conditions. It should be noted that this standard does not apply to taped insulation joints, transition joints for connecting XLPE insulated cables and paper-insulated cables, and separable cable terminations. The clear definition of the scope of application helps to ensure the targeted and effective implementation of the standard in practical engineering.

3. Key Terms and Definitions

To facilitate the correct understanding and application of the standard, GB/T 18890.3-2015 defines a series of key terms, incorporating relevant definitions from GB/T 18890.1-2015 and GB/T 2900.10-2013, and adding new terms to adapt to the development of cable accessory technology. 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.
• Termination with porcelain insulator: An (outdoor) cable termination with porcelain insulator as the external insulation.
• Termination with composite insulator: An (outdoor) cable termination with a composite insulator as the external insulation, which consists of a glass fiber-reinforced epoxy tube as the core and a weather-resistant, pollution-resistant elastomer material (such as silicone rubber) coated on the outside.
• GIS termination: A cable termination installed inside gas-insulated metal-enclosed switchgear (GIS) equipment, with sulfur hexafluoride (SF6) gas as the 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, with insulating oil as the external insulation for the liquid-insulated part.
• Straight joint: An accessory that connects two cables to form a continuous circuit. Specifically in this standard, it refers to a joint where the metal shell of the joint is electrically continuous with the metal shield and insulation shield of the connected cables.
• Insulated joint: A joint that keeps the metal sheath, metal shield, and insulation shield of the connected cables electrically disconnected (discontinuous).
• Pre-fabricated accessories: Cable accessories that use pre-fabricated rubber components (and pre-fabricated epoxy insulation components) with electric field stress control function as the main insulation components, including pre-fabricated terminations and pre-fabricated joints.

4. Operating Conditions

GB/T 18890.3-2015 specifies the operating conditions for cable accessories, which are consistent with the relevant provisions for cables in GB/T 18890.2-2015. The main requirements include:

1. Rated voltage and conductor operating temperature: The rated voltage of the accessories, the maximum operating temperature during normal operation, and the short-circuit temperature shall be consistent with the requirements for cables specified in Chapter 4 of GB/T 18890.2-2015. This ensures the matching performance between the accessories and the cables during operation.
2. External insulation environment classification: The standard modifies the classification of external insulation environment and pollution types, and adds the expression of on-site pollution severity (SPS) levels. This helps to select appropriate cable accessories according to different environmental conditions and improve the adaptability of the accessories to the environment.
3. Special environmental conditions: The standard adds explanations for special environmental conditions, providing technical guidance for the application of cable accessories in harsh environments such as high altitude, high humidity, and high pollution.
4. System category: The accessories covered by this standard are suitable for the same system category as specified in 4.1 of GB/T 18890.2-2015, ensuring the compatibility of the accessories with the power system.

5. Product Classification and Model Specifications

GB/T 18890.3-2015 classifies cable accessories according to their structure, insulation type, and application scenario, and specifies the model composition and product names. The model of the cable accessory is composed of a series code, an accessory code, an internal insulation code, and a code for the external insulation of the termination or the external protective box and external protective layer of the joint (as shown in Figure 1). The standard lists the product models and names in Table 2, covering various types of terminations and joints, such as:

• YJZWY series: Liquid-filled insulated porcelain sleeve terminations for XLPE insulated power cables, with different external insulation pollution levels (a, b, c, d, e grades).
• YJZWQ series: SF6 gas-insulated porcelain sleeve terminations for XLPE insulated power cables, with different external insulation pollution levels.
• YJZWFY series: Liquid-filled insulated composite sleeve terminations for XLPE insulated power cables, suitable for c, d, e grade external insulation pollution levels.
• YJZGY series: Liquid-filled insulated GIS terminations for XLPE insulated power cables.
• YJZYY series: Liquid-filled insulated (transformer) oil-immersed terminations for XLPE insulated power cables.
• YJJTI series: Integral pre-fabricated rubber insulation straight joints for XLPE insulated power cables, without protective boxes.

The standardized product classification and model specifications facilitate the production, selection, and management of cable accessories, and improve the interchangeability and universality of products.

6. Technical Requirements for Materials and Components

The technical performance of materials and components is the basis for ensuring the quality of cable accessories. GB/T 18890.3-2015 puts forward strict requirements for various materials and components used in cable accessories, including conductor connection fittings, semi-conductive shielding materials, insulation materials, and external insulation components.

For conductor connection fittings, the standard modifies the relevant requirements to ensure good electrical conductivity and mechanical strength of the connection part, and reduce contact resistance. For semi-conductive shielding rubber strips, the standard adds specific requirements and specifies their performance indicators (see Appendix A), ensuring the uniformity of the electric field and the reliability of the shielding effect. For insulation materials, such as rubber insulation parts and epoxy insulation parts, the standard modifies the performance requirements for insulation materials and semi-conductive materials, and specifies the performance indicators of epoxy resin cured products (see Appendix B), such as volume resistivity (≥1.0×10¹⁴ Ω·m at 23℃), dielectric loss tangent (≤5.0×10⁻³ at 23℃), and short-term power frequency breakdown electric field strength (≥20 kV/mm).

In terms of liquid insulation fillers, the standard modifies the performance requirements for silicone oil and adds polyisobutylene as a new type of liquid insulation filler, specifying their performance indicators (see Appendix C). For external insulation components, such as porcelain sleeves and composite sleeves, the standard modifies the technical requirements for porcelain sleeves and adds technical requirements for composite sleeves, ensuring their weather resistance, pollution resistance, and mechanical performance.

7. Test Methods

To verify whether cable accessories meet the technical requirements of the standard, GB/T 18890.3-2015 specifies a complete set of test methods, including type tests, routine tests, sampling tests, and pre-qualification extension tests. The test items cover electrical performance, mechanical performance, sealing performance, and environmental adaptability.

The standard adds the content of sampling tests for accessories (see 8.3) and the type test of the cable system composed of accessories and cables (see 8.5), which helps to comprehensively evaluate the performance of accessories in practical applications. For the sealing test of assembled terminations, the standard modifies the test conditions to ensure the sealing reliability of the terminations in different environments. It should be noted that the standard deletes the requirement for the radio interference test of outdoor terminations, which is adjusted according to the development of technology and practical application needs.

8. Main Technical Changes from GB/Z 18890.3-2002

Compared with the previous version GB/Z 18890.3-2002, GB/T 18890.3-2015 has undergone significant technical changes, mainly including the following aspects:

• The nature of the standard is changed from a guiding technical document to a recommended standard, enhancing the mandatory and guiding role of the standard in the industry.
• The standard name is simplified, making it more concise and accurate.
• New terms are added, such as porcelain sleeve terminations, composite sleeve terminations, GIS termination connection enclosures, design pressure, and minimum functional pressure, adapting to the development of cable accessory technology.
• The “accessory characteristics” are changed to “operating conditions”, making the standard more closely combined with practical application scenarios.
• The pressure requirement for GIS terminations is modified to ensure the safety and reliability of GIS terminations in operation.
• The classification of external insulation environment and pollution types is modified, and the expression of on-site pollution severity (SPS) levels is added, improving the adaptability of the standard to different environmental conditions.
• The “minimum creepage distance” is modified to “three-phase system creepage distance”, making the requirement more scientific and reasonable.
• The naming of oil-immersed (transformer) terminations is modified, and the code for composite sleeve terminations, model names, and their technical requirements are added.
• The code for liquid-filled insulation is modified, and the requirement for insulation parts used for metal sheath segmentation of insulated joints is added.
• The technical requirement for the metal shield of joints is added, ensuring the reliability of the shielding effect.
• The content of sampling tests for accessories is added, and the type test of the cable system composed of accessories and cables is added.
• Pre-qualification extension tests are added to expand the scope of application of pre-qualification test results.
• References are added to provide a basis for further research and application of the standard.

GB/T 18890.3-2015 is a comprehensive and systematic technical standard for 220 kV (Um=252 kV) XLPE insulated power cable accessories. By specifying strict technical requirements, test methods, and application conditions, the standard provides important technical support for the design, production, testing, and application of cable accessories, helping to improve the overall level and reliability of the power cable industry in China. Compared with the previous version, the standard has been significantly upgraded and improved, adapting to the development needs of the power grid and cable technology. In practical engineering applications, relevant enterprises and institutions should strictly implement the requirements of the standard, strengthen quality control and test verification, and ensure the safe and stable operation of the power cable system.

References

[1] 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] 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] Standardization Administration of the People’s Republic of China. GB/T 18890.2-2015, Power cables with cross-linked polyethylene insulation and their accessories for rated voltage of 220 kV (Um=252 kV)—Part 2: Cables[S]. Beijing: Standards Press of China, 2015.

[4] Standardization Administration of the People’s Republic of China. GB/T 2900.10-2013, Electrical terminology—Power cables[S]. Beijing: Standards Press of China, 2013.