Abstract: GB/T 3048.13-2007, as an important part of the national standard series for electrical performance test methods of electric cables and wires in China, specifies the technical requirements, test procedures and evaluation criteria for impulse voltage tests. This standard, which modifies and adopts relevant international standards, plays a crucial role in ensuring the quality of cables and wires, safeguarding the safe and stable operation of power systems. This article elaborates on the core content of GB/T 3048.13-2007, including its scope of application, key terms and definitions, requirements for test equipment, sample preparation, test procedures, result evaluation, and discusses its practical significance and application prospects in the cable industry.

1. Introduction

Electric cables and wires are the core components of power transmission and distribution systems. Their insulation performance directly affects the reliability and safety of the entire power system. In actual operation, cables may be subjected to transient overvoltages such as lightning strikes and operational overvoltages, which pose severe challenges to the insulation layer. The impulse voltage test is an effective means to evaluate the insulation’s ability to withstand such transient high voltages. GB/T 3048.13-2007 “Test methods for electrical properties of electric cables and wires – Part 13: Impulse voltage test” was issued on December 3, 2007, and implemented on May 1, 2008, replacing the previous GB/T 3048.13-1992 . This standard unifies the test methods and technical requirements for impulse voltage tests in the industry, providing authoritative technical support for cable production, testing, and application .

GB/T 3048.13-2007 modifies and adopts IEC 60230:1966 “Impulse test on cables and accessories” and IEC 60060-1:1989 “High-voltage test techniques – Part 1: General definition and test requirements”, combining with the actual situation of China’s cable industry to form a localized technical specification . It is worth noting that a revised draft of this standard (GB/T 3048.13-XXXX) is currently in the consultation stage, which will further improve the technical content and adapt to the development needs of the industry .

2. Scope of Application and Key Terms

2.1 Scope of Application

GB/T 3048.13-2007 specifies the terms and definitions, test equipment, sample preparation, test procedures, result evaluation, precautions and test records for impulse voltage tests of cables and their accessories . This standard is applicable to impulse voltage tests of various types of power cables and their accessories with a maximum rated voltage Um of 1 kV and above, covering common cable types in the medium and high voltage fields, such as power cables and overhead insulated cables . A common doubt in the industry is whether shielded cables are applicable to this standard. The answer is that the basic test process of shielded cables follows this standard, but the influence of the shielding layer should be considered during the test, and the operation should be carried out in accordance with the relevant supplementary provisions in the standard to ensure that the test results can truly reflect the insulation performance of the cables .

2.2 Key Terms and Definitions

To ensure the uniformity of test operation and result judgment, GB/T 3048.13-2007 defines a series of key terms related to impulse voltage tests . The core terms include:

• Impulse voltage: A transient voltage with an extremely short duration, which is the core test parameter in the impulse voltage test .
• Lightning impulse voltage: An impulse voltage that simulates the characteristics of natural lightning, with a fast rise time and high peak value .
• Operational impulse voltage: An impulse voltage generated by operations in the power system (such as switch closing and opening), with a longer duration compared to lightning impulse voltage .
• Breakdown voltage: The minimum impulse voltage value that causes the breakdown of the cable insulation, which is an important index to evaluate the insulation performance .
• Withstand voltage: The maximum impulse voltage value that the cable insulation can withstand without breakdown under specified test conditions .

3. Requirements for Test Equipment

The accuracy and reliability of test equipment are the prerequisites for ensuring the validity of impulse voltage test results. GB/T 3048.13-2007 puts forward clear requirements for the core components of the test equipment, including impulse voltage generators and voltage measurement systems .

3.1 Impulse Voltage Generator

The impulse voltage generator is the core equipment to generate the required voltage waveform and amplitude. Its working principle is based on capacitor energy storage and rapid discharge, generating high-voltage impulses through multi-stage capacitor series charging and parallel discharge . The standard requires that the generator can produce impulse voltages that meet the specified waveforms, and the parameters of the output waveform must be within the allowable deviation range. For example, the output waveform of the lightning impulse voltage generator is 1.2/50 μs, the allowable deviation of the front time is ±30%, and the allowable deviation of the half-peak time is ±20% . In addition, the rated voltage of the generator must meet different test requirements to ensure the accuracy and stability of the output voltage . Compared with the 1992 version, the 2007 version of the standard has improved the special requirements for components when generating operational impulse voltage .

3.2 Voltage Measurement System

The voltage measurement system is used to accurately measure the peak value, waveform parameters and other indicators of the impulse voltage, which is crucial to the accuracy of the test results . The measurement system generally consists of a voltage divider and measuring instruments. The voltage divider reduces the high voltage in proportion to facilitate the detection of the measuring instruments . The standard requires that the measuring instruments have high precision and fast response speed, because the voltage changes rapidly during the impulse voltage test. Only a high-precision and fast-response measurement system can capture accurate voltage data and provide a reliable basis for evaluating the insulation performance of cables .

4. Sample Preparation

Sample preparation is a key link affecting the representativeness and accuracy of test results. GB/T 3048.13-2007 clearly specifies the selection, cutting and preprocessing of samples .

4.1 Selection and Cutting of Samples

Samples should be randomly selected from the same batch and specification of electric cables to ensure that they can represent the quality of the batch . When cutting, special tools should be used to avoid damaging the insulation layer, which may lead to deviations in test results . The length of the sample should meet the standard requirements, generally 1-3 meters. For some special cables, the sample length should include key parts such as the cable body and joints to simulate the actual use scenario . The standard stipulates that the number of test samples per batch is usually not less than 3 to ensure that the test results can reflect the overall insulation performance of the batch of cables .

4.2 Preprocessing of Samples

The preprocessing of samples mainly includes cleaning and end treatment. The cleaning step is to remove impurities, oil stains and other substances on the surface of the sample to prevent local discharge during the test, which may interfere with the test results . When cleaning, appropriate cleaning agents and tools should be selected according to the cable material to ensure the cleaning effect without damaging the cable . The end treatment involves stripping an appropriate length of insulation layer at both ends of the sample to expose the conductor, which is convenient for connecting with the test equipment . In addition, for some tests, shielding treatment is required for the samples to reduce external electromagnetic interference and ensure that the test is carried out in a stable environment .

5. Test Procedures

The test procedure of GB/T 3048.13-2007 is strictly standardized, which mainly includes pre-test preparation, impulse voltage application and test process monitoring .

5.1 Pre-test Preparation

Before the test, it is necessary to comprehensively check the state of the test equipment, confirm that there is no fault and the parameters are normal . At the same time, the sample information should be verified to ensure that it is consistent with the test requirements . Then, the test circuit is built, the sample is correctly connected to the equipment, and the firmness and correctness of the circuit wiring are checked . In addition, safety protection measures should be taken, such as setting warning signs and checking the grounding system, to ensure the safety of the test process .

5.2 Application of Impulse Voltage

The application of impulse voltage should follow the principle of gradually increasing the voltage from low to high. First, a low-voltage pre-test is carried out to check the reliability of the test circuit and the connection state of the sample . Then, the voltage is gradually increased to the specified test voltage, and the number of applications is carried out in accordance with the standard requirements. For some cables, it is necessary to apply impulse voltages of positive and negative polarities for a certain number of times, because different polarities of voltage impulses may expose defects in different parts of the cable insulation, and multiple applications can more comprehensively detect the insulation performance .

5.3 Test Process Monitoring

During the test, the test state should be monitored in real time, including the waveform and amplitude of the impulse voltage, and the response of the sample . If abnormal phenomena such as insulation breakdown or flashover occur in the sample, the test should be stopped immediately, and the relevant parameters at the time of the abnormality should be recorded .

6. Evaluation of Test Results

The evaluation of test results is based on whether the sample has insulation breakdown, flashover and other phenomena during the test, and whether the test voltage parameters meet the standard requirements .

6.1 Key Evaluation Indicators

Insulation breakdown and flashover are the key indicators for evaluating test results . Insulation breakdown means that the insulation layer of the cable is damaged under the action of impulse voltage, leading to current passing through, which indicates that the insulation performance is seriously invalid . Flashover is a discharge phenomenon occurring on the surface of the insulation. Although it does not necessarily lead to the complete damage of the insulation immediately, it is also a signal of the decline of insulation performance .

6.2 Evaluation Criteria

According to the standard, if the cable does not have insulation breakdown or flashover during the specified number of impulse voltage applications, and all voltage parameters are within the allowable range of the standard, the test result is judged as qualified . If insulation breakdown, flashover or other abnormal phenomena occur, the sample is judged as unqualified, and the relevant reasons should be analyzed to provide a basis for improving product quality .

7. Practical Significance and Application Prospects

7.1 Practical Significance

GB/T 3048.13-2007 provides a unified technical standard for the impulse voltage test of electric cables and wires in China, which is of great significance for ensuring product quality, safeguarding the safe operation of power systems and promoting the healthy development of the industry . By carrying out impulse voltage tests in accordance with this standard, manufacturers can find insulation defects in cables in a timely manner, improve production processes and product quality . For the power industry, the application of qualified cables that have passed the test can reduce the probability of power failures caused by insulation problems, improve the reliability and stability of the power system .

7.2 Application Prospects

With the development of the power industry, especially the continuous advancement of ultra-high voltage power transmission and deep-sea cable laying technologies, the application environment of cables is becoming more and more complex, and higher requirements are put forward for their insulation performance . In the future, the test equipment specified in GB/T 3048.13-2007 needs to develop towards higher precision, intelligence and scalability . Higher precision can meet the more stringent detection requirements for cable insulation performance; intelligence can realize automatic control, data collection and analysis, improve test efficiency and accuracy; scalability can adapt to the needs of different types, specifications of cables and new test methods . At the same time, the revised version of the standard (GB/T 3048.13-XXXX) will further improve the technical content, add test types such as superimposed impulse voltage test, and better adapt to the development needs of the industry .

GB/T 3048.13-2007 is an important technical specification in the field of electrical performance testing of electric cables and wires in China. It systematically specifies the technical requirements and operation procedures for impulse voltage tests, providing authoritative guidance for the production, testing and application of cables. By strictly implementing this standard, the quality of cable products can be effectively guaranteed, and the safe and stable operation of the power system can be safeguarded. With the continuous development of the industry, the standard will also be continuously revised and improved to adapt to new application scenarios and technical requirements. It is of great significance for relevant enterprises and testing institutions to accurately grasp and implement the requirements of this standard to promote the high-quality development of the cable industry.