Abstract: GB/T 3048.8-2007, as an important part of the national recommended standards for electrical performance test methods of wires and cables in China, specifies the technical requirements and implementation procedures for AC voltage tests. This standard is of great significance for ensuring the insulation performance and operational safety of wires and cables. This article elaborates on the core content of GB/T 3048.8-2007, including its scope of application, key technical provisions, differences from relevant international and previous standards, and its application value in the industry, providing a comprehensive technical reference for professionals in the field of wires and cables worldwide.

1. Introduction

Wires and cables are the core medium for power transmission and signal transmission, and their insulation performance directly determines the safety and stability of the entire power system. The AC voltage test is a key means to detect potential defects in the insulation layer of wires and cables, such as pinholes, impurities, and poor bonding, which can effectively avoid accidents such as leakage and short circuits during operation. Issued on December 3, 2007 and implemented on May 1, 2008, GB/T 3048.8-2007 “Test Methods for Electrical Properties of Electric Cables and Wires – Part 8: AC Voltage Test” replaces the previous GB/T 3048.8-1994 standard. It is revised in accordance with GB/T 1.1-2000 “Directives for Standardization – Part 1: Rules for the Structure and Drafting of Standards”, optimizing the standard structure and improving technical requirements to adapt to the development of the wire and cable industry. This standard is classified under China National Standard Classification (CCS) K13 and International Standard Classification (ICS) 29.060, which is in line with the international classification system for electrical engineering and wire and cable fields.

2. Scope of Application

GB/T 3048.8-2007 specifies the terms and definitions, test equipment, sample preparation, test procedures, test results and evaluation, precautions, and test records for AC voltage tests of wires and cables. It is applicable to the AC voltage withstand test of various wire and cable products, including common power cables such as polyvinyl chloride insulated cables and cross-linked polyethylene insulated cables with a rated voltage of 1kV and below, as well as control cables and communication cables that require insulation performance testing. These cables must undergo AC voltage tests in accordance with this standard during factory inspection and type testing.

It should be emphasized that this standard is not applicable to winding wire products. Meanwhile, GB/T 3048.8-2007 must be used in conjunction with GB/T 3048.1 “Test Methods for Electrical Properties of Electric Cables and Wires – Part 1: General Principles” to ensure the completeness and accuracy of the test process. In special scenarios such as high-temperature and high-humidity environments, adjustments can be made on the premise of not deviating from the core requirements of the standard, such as appropriately extending the preprocessing time of samples or increasing drying steps to ensure the stability of sample status.

3. Core Technical Provisions

3.1 Terms and Definitions

GB/T 3048.8-2007 adopts the terms and definitions established in GB/T 2900.19 “Electrotechnical Terminology – High-Voltage Test Technology and Insulation Coordination” and supplements key definitions related to AC voltage tests. For example, “peak value” refers to the maximum value of AC voltage, excluding minor high-frequency oscillations caused by non-destructive discharge; “root-mean-square (effective) value” is the effective value of AC voltage, which is an important parameter for determining the test voltage level. Accurate understanding of these terms is crucial to avoid misinterpretation of test data.

3.2 Requirements for Test Equipment

The standard puts forward strict requirements on the performance parameters of test equipment to ensure the accuracy and reliability of test results. The output voltage accuracy of the test transformer must be within ±3% to ensure that the applied voltage meets the standard requirements. The range of current measuring equipment must cover the possible leakage current range, with a resolution of not less than 1μA, and the equipment must be equipped with an overcurrent protection function to avoid equipment damage when the sample breaks down.

For the series resonance circuit, the standard has revised the relevant provisions and supplemented Appendix A “Inductance-Tunable Series Resonance Test Circuit and Parameter Selection” as a normative appendix. In terms of test voltage measurement, the standard has improved the relevant regulations and added three direct measurement methods from the high-voltage end for routine tests, which effectively improves the accuracy of voltage measurement.

In addition, the standard requires regular calibration of test equipment: the voltage measurement part should be calibrated every 6 months, and the current measurement part should be calibrated every 12 months. Calibration must be carried out by qualified institutions, and the calibration records should be properly kept.

3.3 Sample Preparation

Sample preparation is a key link affecting the representativeness of test results. GB/T 3048.8-2007 stipulates that samples should be randomly selected from the same batch and specification of cables, with a length of not less than 1m. During selection, the appearance of the cable should be checked to ensure no obvious damage or deformation.

The standard also puts forward clear requirements for sample pretreatment: samples should be placed in a standard environment (temperature 23℃±5℃, relative humidity 45%-75%) for not less than 24h to stabilize their state; the surface should be cleaned with absolute ethanol to remove oil stains and dust, and the test should be carried out as soon as possible after pretreatment. For special cables, the standard adds sample preparation methods for cross-linked polyethylene insulated cables and mineral insulated cables, which fills the gap in the previous standard.

3.4 Test Procedures

The test procedure specified in GB/T 3048.8-2007 includes pre-test preparation, voltage application, and voltage maintenance. Before the test, it is necessary to check that the test equipment has no external damage, the connection lines are firm, the sample is correctly installed between the electrodes, and the test parameters (such as voltage value and duration) are set in accordance with the standard requirements.

During voltage application, the voltage rise rate should be controlled within 1kV/s to avoid local damage to the insulation layer caused by rapid voltage rise. After reaching the specified voltage, the voltage should be kept stable, with a fluctuation range not exceeding ±2%. The standard specifies different test voltage levels and durations for different types of cables, with common durations of 1min and 5min. In addition, the standard supplements the step-by-step breakdown test, which provides a more comprehensive evaluation method for the insulation performance of cables.

3.5 Test Results and Evaluation

The standard clarifies the criteria for judging test results: if there is no breakdown phenomenon and the leakage current is stable within the specified limit during the test, the sample is judged as qualified; if breakdown occurs or the leakage current exceeds the limit, it is judged as unqualified. For suspected false breakdown phenomena, the standard adds relevant judgment methods to avoid misjudgment of test results.

4. Differences from Relevant Standards

4.1 Differences from International Standard IEC 60060-1:1989

GB/T 3048.8-2007 corresponds to Chapter 5 “AC Voltage Test” of IEC 60060-1:1989 “High-Voltage Test Techniques – Part 1: General Definitions and Test Requirements”, with a consistency degree of non-equivalent (NEQ). The main differences are as follows: (1) The “frequency of AC voltage” is modified according to product standards; (2) The “requirements for transformer test circuits” are deleted; (3) The “series resonance circuit” is revised, and Appendix A is added; (4) The “measurement of test voltage” is revised, and three direct measurement methods from the high-voltage end for routine tests are supplemented; (5) The “test procedure” is greatly modified, detailed regulations on sample wiring are supplemented, and “destructive discharge voltage test” is deleted.

4.2 Differences from Previous Standard GB/T 3048.8-1994

Compared with GB/T 3048.8-1994, the main changes of GB/T 3048.8-2007 include: (1) The English name of the standard is revised to “Test Methods for Electrical Properties of Electric Cables and Wires – Part 8: AC Voltage Test”; (2) The overall structure is adjusted in accordance with GB/T 1.1-2000, adding Chapter 3 “Terms and Definitions” and Chapter 9 “Test Records”; (3) The requirements for “allowable deviation” in test equipment are improved, and the expression of “series resonance circuit” is refined; (4) The sample preparation methods for special cables are added; (5) The requirements for test area safety in “precautions” are modified.

5. Industry Application and Significance

GB/T 3048.8-2007 provides a unified technical standard for the AC voltage test of wires and cables in China, which plays an important role in standardizing the production and testing processes of enterprises, improving product quality, and ensuring the safety of power transmission. In practical applications, this standard is widely used in factory inspection, type testing, and quality supervision of wires and cables, helping enterprises to timely find quality problems in the production process and avoid unqualified products entering the market.

With the development of new energy, high-speed rail and other fields, the demand for wires and cables in harsh environments is increasing. GB/T 3048.8-2007 provides a basic test basis for the adaptability testing of cables in these fields. In the future, with the intelligence of test technology, the AC voltage test based on this standard will be more efficient and accurate, and will continue to play an important role in promoting the high-quality development of the wire and cable industry.

GB/T 3048.8-2007 is a core standard for the AC voltage test of wires and cables in China, which has the characteristics of comprehensive content, strict requirements, and strong applicability. It not only ensures the insulation performance and operational safety of wires and cables, but also promotes the standardized development of the industry. By understanding and implementing this standard, enterprises can improve their product competitiveness, and relevant institutions can carry out more accurate and effective quality supervision. In the context of global electrical industry integration, the technical content and implementation experience of GB/T 3048.8-2007 also provide valuable reference for the international exchange and cooperation of wire and cable testing technology.

References: GB/T 3048.8-2007, Test Methods for Electrical Properties of Electric Cables and Wires – Part 8: AC Voltage Test; IEC 60060-1:1989, High-Voltage Test Techniques – Part 1: General Definitions and Test Requirements; GB/T 3048.1-2007, Test Methods for Electrical Properties of Electric Cables and Wires – Part 1: General Principles.