How to Improve the Testing Quality of Electrical Products

How to Improve the Testing Quality of Electrical Products

Switching electrical apparatus is a major component of power transmission and distribution lines, and its reliability and safety are closely tied to the safety of people’s lives and property. The quality assurance of switchgear products is achieved mainly through testing. Throughout the entire lifecycle of a product—from new product development and commissioning to maintenance and retirement—three broad categories of tests are generally required: type tests, routine factory tests, and maintenance/periodic tests.

Among these, type tests for the qualification and launch of new products, as well as early-stage research tests, form the fundamental basis for designing and developing high-quality new products. Factory tests (including sampling tests) are necessary overall and sample-based tests conducted to ensure the quality of products released to the market. Maintenance, handover, and periodic tests are essential quality assurance steps during the operational lifecycle of electrical products. Tests at different stages have different focuses and use different methods. For example, type tests are often destructive tests intended to verify the overall performance of a product, while factory tests mainly perform functional verification, and maintenance and periodic tests focus on assessing certain critical parameters during operation.

This shows the important role electrical testing plays in ensuring product quality. However, it must be pointed out that testing itself can also have quality issues—in other words, tests can go wrong. If test quality cannot be guaranteed, then product quality certainly cannot be guaranteed either. Therefore, strictly controlling the quality of the tests themselves is one of the prerequisites for ensuring product quality. So, how can the testing quality of electrical products be controlled in order to improve the quality of the products themselves? The answer lies in several aspects: test methods, measurement methods, and test equipment.

1. Adopt Correct Test Methods

The test methods used for electrical products include test conditions, test circuits, and test parameters. The use of electrical products is subject to specific conditions. For example, indoor and outdoor products, as well as standard and high-altitude products, all have different usage requirements and conditions. Therefore, testing must first be carried out under conditions that meet the applicable requirements. In addition to environmental factors, test conditions also include requirements such as how the specimen is installed and whether maintenance is permitted during the test. These conditions are intended to match the actual operating conditions of the product and simulate real-world operation.

Test circuits strictly define the wiring used in electrical testing, including the main circuit, protective circuit, and control circuit. Different tests require different test circuits, and even the same type of test may allow different circuit configurations. For example, in a three-phase, three-pole making-and-breaking test, several different test circuits may be used: the specimen connected before the load, with both the transformer neutral point and load neutral point grounded; the specimen connected after the load, with both the transformer neutral point and load neutral point grounded; the specimen connected before the load, with the transformer ungrounded and the load grounded; or the specimen connected after the load, with the transformer ungrounded and the load grounded. These different circuits can produce completely different test results, so the correct test circuit must be selected according to the product’s operating conditions.

The parameters of the test circuit determine the level of stress applied to the test specimen. To simulate different testing scenarios, standards specify parameters such as test voltage, current, power factor/time constant, and energization time. Only by conducting the test within the required standard parameters can the testing process be accurate and the results reasonable.

It is also worth noting that as technology continues to develop and evolve, standards for test methods are constantly being refined, revised, and supplemented. Therefore, when designing a test system, one must base it on the currently valid national standards rather than outdated or obsolete standards, books, or literature.

2. Select Appropriate Measurement Methods

The design of the measurement circuit, the location of measurement points, and the design of shielding can all affect measurement results and therefore influence the judgment of test outcomes. If measuring instruments are selected or used improperly, accurate data may not be obtained, which can affect test results and lead to incorrect judgments about product quality. For a long time, test results were limited by available measurement methods and tools, making it difficult to obtain more accurate and effective conclusions. Traditional analog instruments—such as electromagnetic, electrodynamic, and electrostatic meters—introduced considerable uncertainty into test results due to instrument error and reading error. The emergence of high-precision, high-speed digital acquisition cards has greatly improved both the measurement and recording of test data, and they now play a key role in modern test systems.

Data measurement also includes sensor selection and measurement circuit design. For example, in short-circuit tests, the system may need to carry currents ranging from several thousand amperes to hundreds of thousands of amperes. Conventional sensors such as current transformers find it difficult to measure such a wide current range accurately. In these situations, a Rogowski coil, which utilizes electromagnetic induction, is highly suitable, and when used with an integrator, can provide more accurate results. As another example, in temperature-rise tests, thermometers, thermocouples, and resistance temperature detectors are conventional measurement methods. However, because all of these methods require contact with the product being measured, they cannot be used to measure certain locations, such as contacts inside the product. In such cases, technologies developed in recent years—such as thermal imaging and laser temperature measurement—are needed as supplementary methods to achieve more accurate and comprehensive measurement.

During data acquisition and transmission, anti-interference capability is another factor that requires special attention. Generally speaking, current signals are less susceptible to interference during transmission, but they require more conversion steps. Voltage signals may be more vulnerable to external interference, but signal generation and acquisition are relatively simple. It is therefore necessary to comprehensively evaluate and select the appropriate signal transmission method and use suitable shielding measures to reduce external interference. At the same time, special attention must be paid to the potential impact and damage that occasional high-voltage signals may cause to electronic systems.

3. Use Qualified Test Equipment

Test equipment includes power supply equipment, voltage and current regulation equipment, load impedance equipment, and other specialized devices used for testing, all of which are subject to certain quality requirements under test standards. For example, test standards impose strict requirements on the frequency and waveform of AC power supply equipment. This is because if the test equipment itself has quality problems, the test results will inevitably be affected, which in turn will affect the correctness of judgments about product quality. Test equipment is different from ordinary power distribution and control equipment. In order to provide the environment and conditions required for testing, test equipment may need to operate frequently under high-voltage, high-current, overloaded, or even short-circuit conditions, which places much stricter demands on its quality and reliability. Therefore, qualified test equipment should not only meet the requirements of the relevant test standards (which is of course the basic requirement), but should also demonstrate reliability and stability during long-term operation. At the same time, test equipment should be designed and manufactured in accordance with the latest current standards, and the test procedures as well as data acquisition and analysis strategies should be fully considered during the design and manufacturing process. Only in this way can the intended testing effect be truly achieved and the desired goals reached.

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