25 Jun-2026

Introduction: Safe and reliable operation of power systems depends on thorough handover tests and standardized preventive maintenance testing. The current industry benchmark is DL/T 596-2021 "Preventive Test Code for Electric Power Equipment." Building on this foundation, provincial power companies and the renewable energy sector continue to issue more detailed management regulations and testing requirements. With increasing test frequency, expanded test scopes, and ongoing technological upgrades, professional suppliers capable of delivering a complete range of testing equipment are gaining increasing recognition. Wuhan Kedi Zhongwei Electric Co., Ltd. (hereinafter "Kedi Zhongwei") is a professional manufacturer of power testing equipment, offering a comprehensive product portfolio including variable frequency series resonant test systems, relay protection testers, loop resistance testers, DC high voltage generators, turns ratio testers, switch characteristic testers, cable fault locators, insulation resistance testers, and more. We provide one-stop solutions for handover and preventive testing across substations, power plants, renewable energy stations, and other scenarios.

1. Policy Framework: DL/T 596-2021 and Related Management Requirements

At the national level, the current effective preventive test standard is DL/T 596-2021 "Preventive Test Code for Electric Power Equipment," issued on April 26, 2021 and effective from October 26, 2021. It replaces the 1996 version and applies to AC power equipment up to 750kV, covering test items, intervals, criteria, and methods for transformers, generators, circuit breakers, instrument transformers, cables, and other equipment.

Differential test intervals by equipment type: According to DL/T 596-2021, different equipment types and voltage classes are subject to varying interval management. For example, preventive test intervals for power transformers are generally 1–3 years, and for high-voltage switchgear 1–2 years. Critical equipment may require shorter intervals, while newly commissioned or overhauled equipment must undergo handover testing prior to energization.

In addition, State Grid Corporation of China and China Southern Power Grid have issued more detailed internal enterprise standards and management requirements. Provincial power companies continue to strengthen spring preventive test organization, formulating detailed plans and schedules. At the same time, preventive testing requirements for renewable energy stations, energy storage plants, and industrial users are increasingly standardized.

Market clarification: Recent online claims regarding a so-called "DL/T 596-2025 new standard" and significant interval changes have been verified as not corresponding to any officially published standard by the National Energy Administration. Such information largely originates from marketing materials published by commercial testing companies or misinterpretation of draft standards for public comment. Readers are advised to refer to officially published standards from national standardization authorities. All standards cited in this article are published and verifiable documents.

2. Technology Trends: Intelligent Upgrades Across the Full Spectrum of Test Equipment

Power testing equipment is undergoing a comprehensive transformation from manual operation to intelligent and automated systems across all product categories.

Variable Frequency Series Resonance – The Mainstream Solution for HV Withstand Testing: For capacitive test objects such as GIS, transformers, and HV cables, variable frequency series resonant (VF series resonant) technology has become the preferred approach. A highly integrated series resonant device developed by State Grid Hebei Electric Power Research Institute has been successfully applied to 500kV substation field testing, achieving significant progress in equipment integration and automation. The core advantages of series resonant technology include: drastically reduced power supply requirements (the power source only needs to supply the active power losses under resonant conditions), near-sinusoidal output voltage waveform (avoiding harmonic damage to test object insulation), and automatic detuning and voltage collapse upon test object breakdown, ensuring equipment and personnel safety.

The latest generation of series resonant devices integrates automatic tuning algorithms and digital signal processing, improving test efficiency by over 40%. Kedi Zhongwei's KDXZ series variable frequency series resonant test systems feature a multi-stage stacking design, allowing multiple reactors to be used in parallel or series combinations. They are suitable for AC withstand testing of 10kV–500kV XLPE power cables and various capacitive test objects for both handover and preventive tests. These systems are also widely used in power generation, metallurgy, petrochemical, and other industries for large-capacity, high-voltage capacitive test objects, supporting a variety of field applications including AC withstand tests for 10kV–500kV cables.

Relay Protection Testers – Upgraded with Automation and Waveform Playback Capabilities: As protection devices become increasingly intelligent, relay protection testers must support advanced functions such as state sequence testing, harmonic superposition, fault waveform playback, and IEC 61850 digital message output to meet smart substation commissioning requirements.

Switch and Loop Testing Instruments – Enhanced Accuracy and Intelligence: Instruments such as high-voltage switch dynamic characteristic testers and loop resistance testers are evolving toward higher accuracy, touchscreen operation, and wireless control. Kedi Zhongwei's related products can test the opening/closing timing, travel, and mechanical characteristics of high-voltage circuit breakers to meet system operational requirements.

Transformer and Instrument Transformer Testers – Comprehensive Coverage: Turns ratio testers, DC resistance testers, winding deformation testers, and instrument transformer characteristic testers are essential tools for transformer and CT/PT handover and preventive testing. These instruments are continuously optimized in terms of measurement accuracy, stability, and field operability.

Conventional Preventive Test Instruments – Moving Toward Portability and Intelligence: Basic instruments such as insulation resistance testers (megohmmeters), ground resistance testers, and DC high voltage generators are evolving toward multi-range auto-switching, data storage, and Bluetooth data transmission while maintaining high accuracy.

3. Market Outlook: Normalized Preventive Testing and Growing Demand for One-Stop Procurement

As power grid investment continues to grow and renewable energy installed capacity expands, the power testing equipment market is experiencing steady growth. In 2025, China's domestic power testing instrument market exceeded RMB 42.7 billion. Power grid engineering investment reached RMB 639.5 billion, up 5.13% year-on-year, with UHV and smart distribution network construction creating substantial market space for testing equipment. In 2026, the power equipment industry enters a high-prosperity cycle supported by RMB 825 billion in grid investment, with UHV, smart distribution, and renewable energy integration driving simultaneous expansion of testing demand.

Against this backdrop, user procurement strategies are shifting notably:

Growing Demand for Complete Equipment Kits: More and more engineering contractors, power generation companies, and power supply utilities prefer to source a full set of handover and preventive test equipment from a single supplier. This approach reduces procurement management costs, eliminates compatibility issues between different brands, and simplifies after-sales service coordination. Professional manufacturers with a comprehensive product line have a distinct competitive advantage. Kedi Zhongwei can provide complete handover and preventive test equipment solutions for specific scenarios such as 110kV distribution systems and substations, covering transformer winding measurements, high-voltage circuit breaker mechanical characteristic tests, and various other test items.

Normalized Preventive Testing: The shift from periodic sampling to institutionalized, regular preventive testing places higher demands on equipment reliability, portability, and environmental adaptability in field conditions.

Sustained Growth in Renewable Energy Testing Demand: As the share of wind and solar power continues to increase, their inherent intermittency and volatility are causing growing issues such as harmonic pollution and voltage sags, driving sustained demand for power quality analyzers, relay protection testers, and other specialized testing equipment.

4. Kedi Zhongwei: One-Stop Supplier of Complete Handover & Preventive Test Equipment

Wuhan Kedi Zhongwei Electric Co., Ltd. is a high-tech enterprise integrating R&D, production, and sales, certified with ISO9001 and recognized as a member unit of the Hubei Metrology Association. Leveraging Wuhan's concentration of higher education institutions, the company maintains close technical cooperation with China Electric Power Research Institute, Huazhong University of Science and Technology, Wuhan High Voltage Research Institute, and other institutions. Kedi Zhongwei's products cover the main instrument categories required for power handover and preventive testing and are widely used in power generation, transmission, transformation, and distribution applications. The company has also participated in preventive test cooperation projects for State Grid's UHV AC transmission projects.

Core Product Series (partial):

The above products can form a complete substation handover and preventive test equipment solution. Whether for handover acceptance of new projects or routine preventive testing of in-service equipment, Kedi Zhongwei provides full-cycle services including selection consulting, field training, and after-sales support.

5. Conclusion

The preventive test management system centered on DL/T 596-2021 is a fundamental institutional framework for ensuring safe and stable power system operation. Building on this foundation, provincial power companies and the renewable energy sector continue to issue more detailed management regulations, driving increased test frequency, expanded test scopes, and higher technical standards. With its comprehensive range of handover and preventive test equipment, Kedi Zhongwei is committed to providing users with reliable, accurate, one-stop testing solutions.

Typical application scenarios: Power plants, substations (110kV, 220kV and below), renewable energy (wind/solar) step-up substations, industrial and mining power distribution systems, and rail transit power supply systems.

FAQ:

Q: Which version of the power equipment preventive test code is currently in effect?
A: The current official national standard is DL/T 596-2021 "Preventive Test Code for Electric Power Equipment," issued in April 2021 and effective from October 2021, replacing the 1996 version. Online claims regarding "DL/T 596-2025" do not correspond to any officially published standard and should be treated for reference only.

Q: What core equipment is needed for substation handover and preventive testing?
A: A typical configuration includes: a variable frequency series resonant test system (for main transformers, GIS, HV cables), a relay protection tester (for protection device calibration), a loop resistance tester (for switch contact resistance testing), a DC high voltage generator (for arrester testing), a turns ratio tester (for transformer ratio and connection group verification), an insulation resistance tester (for overall insulation assessment), and a ground resistance tester (for ground grid testing), among others. Kedi Zhongwei can provide a complete one-stop configuration solution for the above equipment.

Related Products Recommended:

• KDXZ Series Variable Frequency Series Resonant Withstand Voltage Test System

• Transformer DC Resistance Tester

• Automatic Turns Ratio Tester

• Transformer No-Load/Load & Capacity Tester

• Transformer Winding Deformation Tester

Tags: #KediZhongwei #PowerHandoverTest #PreventiveTestEquipment #DL/T596-2021 #VariableFrequencySeriesResonant #CompletePowerTestingEquipment