By sion932 
As a crucial national recommended standard in China’s power cable industry, GB/T 18890.1-2015, titled “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”, plays a pivotal role in regulating the quality and performance of 220kV cross-linked polyethylene (XLPE) insulated power cables and their accessories. Issued on October 9, 2015, and implemented on May 1, 2016, this standard replaces the previous guiding technical document GB/Z 18890.1-2002, marking a more standardized and mandatory requirement for the related products in the industry <superscript>1<superscript>3.
1. Scope and Application
GB/T 18890.1-2002 specifies the test methods and requirements for fixedly installed 220kV (Um=252kV) XLPE insulated power cable systems, cable bodies, and their accessory bodies. It is applicable to single-core cables and their accessories used under normal installation and operating conditions. However, it should be noted that this standard does not apply to cables and accessories used under special conditions, such as submarine cables. For such special-purpose products, modifications to the test procedures specified in this standard or the establishment of special test conditions may be required. Additionally, transition joints connecting XLPE insulated cables and paper-insulated cables are not covered by this standard <superscript>3<superscript>6.
2. Key Technical Content
2.1 Core Definitions and Specifications
The standard introduces the definition of nominal electric field strength, which provides a clear basis for the design and performance evaluation of cables and accessories. For the identification of cables and accessories, the standard specifies detailed requirements for the characteristics that need to be clarified or declared. For cables, these include manufacturer information, rated voltage (U0, U, Um values), conductor type and material, nominal cross-sectional area, insulation material and nominal thickness, shielding layer water-blocking measures, metal shielding structure, outer sheath material and thickness, and other key parameters. For accessories, the relevant cable identification, conductor connection fitting information (installation process, tooling requirements, contact surface treatment, etc.), and accessory manufacturer information, rated voltage, and installation instructions must be clearly stated <superscript>7.
2.2 Test Conditions
Unless otherwise specified for specific tests, the standard requires that tests be conducted at an ambient temperature of (20±15)℃. For AC test voltages, the frequency should be within the range of 49Hz to 61Hz, with a substantially sinusoidal waveform, and the voltage value is expressed as the root mean square (r.m.s.). For standard lightning impulse test voltages, the front time should be 1μs to 5μs, and the half-peak time should be (50±10)μs in accordance with GB/T 3048.13 and GB/T 16927.1. The test voltages specified in the standard are expressed as multiples of the rated voltage U0 (127kV for 220kV systems), and specific values are in line with the requirements in Table 4 of the standard <superscript>7.
2.3 Test Classification and Requirements
The standard classifies tests into routine tests, sampling tests, type tests, pre-qualification tests for cable systems, and extended pre-qualification tests, each with clear scopes and requirements.
Routine tests are conducted on each manufactured length of cable and each prefabricated accessory’s main insulation. For cables, the routine tests include partial discharge test, voltage test, and outer sheath electrical test. The partial discharge test should be performed in accordance with GB/T 3048.12, with a detection sensitivity of 10pC or better. The test voltage is gradually raised to 1.75U0 and maintained for 10s, then slowly reduced to 1.5U0, and no detectable discharge exceeding the declared sensitivity is allowed at 1.5U0. The voltage test applies a power frequency AC voltage of 2.5U0 at ambient temperature for 30min without insulation breakdown. The outer sheath electrical test involves applying a DC voltage of 25kV (with the metal sheath connected to the negative electrode) between the metal shield/metal sheath and the outer sheath surface conductive layer for 1min in accordance with IEC 60229:2007, requiring no breakdown <superscript>7.
Sampling tests are carried out on cable samples representing the delivery batch, including conductor inspection, conductor resistance and metal shield/metal sheath resistance measurement, insulation and outer sheath thickness measurement, metal sheath thickness measurement, diameter measurement (when required), XLPE insulation thermal extension test, capacitance measurement, lightning impulse voltage test, water permeability test (when applicable), and tests for cable assemblies with longitudinally wrapped metal tape or foil bonded to the outer sheath. The frequency of sampling tests is clearly specified to ensure the representativeness and reliability of the test results <superscript>7.
Newly added in this standard are type tests for cables and accessories, as well as extended pre-qualification tests for cable systems. These tests further verify the long-term reliability and stability of products under various operating conditions, providing a more comprehensive quality guarantee <superscript>1.
3. Major Technical Changes from Previous Standard
Compared with the replaced GB/Z 18890.1-2002, GB/T 18890.1-2015 has the following significant technical changes: Firstly, the nature of the standard is changed from a guiding technical document to a recommended standard, enhancing its normative role in the industry. Secondly, the standard name is revised to be more concise and accurate, focusing on the core content of test methods and requirements. Thirdly, the definition of nominal electric field strength is added. Fourthly, PVC-based ST1 and PE-based ST3 outer sheath materials are deleted, and the corresponding test items and requirements are removed accordingly. Fifthly, requirements for measuring the resistance of metal shields and/or metal sheaths are added, along with a method for measuring the thickness of the outer sheath on corrugated metal sheaths. Sixthly, the sampling tests for accessories and the pre-qualification tests for cable systems are revised, and extended pre-qualification tests for cable systems are added. Seventhly, type tests for cables and accessories are newly added. Eighthly, a method for determining conductor temperature is added in Appendix A. Ninthly, the sample length for the water permeability test is modified. Tenthly, tests for cable assemblies with longitudinally wrapped metal tape or foil bonded to the outer sheath are added in Appendix F <superscript>1.
4. International Reference and Technical Significance
GB/T 18890.1-2015 is formulated by modifying and adopting IEC 62067:2011 “Power cables with extruded insulation and their accessories for rated voltages above 150 kV (Um=170 kV) up to 500 kV (Um=550 kV) — Test methods and requirements” using the re-drafting method. While aligning with international advanced standards, the standard also makes structural adjustments and technical modifications based on China’s actual industry conditions to adapt to the development needs of China’s power cable industry. Appendix 1 of the standard provides a comparison table of chapter and clause numbers with IEC 62067:2011, and Appendix J details the technical differences and their reasons, facilitating international technical exchange and cooperation <superscript>1<superscript>3.
The implementation of GB/T 18890.1-2015 has important technical significance for China’s power industry. It effectively improves the quality control level of 220kV XLPE insulated power cables and their accessories, ensures the safe and stable operation of the power grid, promotes technological progress and industrial upgrading of related enterprises, and provides strong technical support for the construction and development of China’s high-voltage power transmission and distribution system.
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 18890.1-2015 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]. 2015.
[2] International Electrotechnical Commission. IEC 62067:2011 Power cables with extruded insulation and their accessories for rated voltages above 150 kV (Um=170 kV) up to 500 kV (Um=550 kV) — Test methods and requirements[S]. 2011.