1. Introduction to DC High-Voltage Generators

DC high-voltage generators are specialized electrical devices designed to convert input AC voltage into precise, stable DC high-voltage output for various testing and industrial applications. These sophisticated instruments play a critical role in power system maintenance, manufacturing quality control, and research activities across multiple industries. According to industry standards, these devices are formally defined as "high voltage DC generators" - complete成套 systems that transform input AC power into controlled DC high-voltage output.

The fundamental purpose of these systems is to provide reliable high-voltage DC power for insulation testing of electrical equipment, dielectric strength verification, and specialized industrial processes. Modern DC high-voltage generators incorporate advanced power electronics, precision measurement systems, and comprehensive safety features to ensure accurate results while protecting both operators and valuable equipment under test.

2. Technical Standards and Specifications

The design, manufacturing, and application of DC high-voltage generators are governed by international and industry-specific technical standards. The DL/T 848.1-2019 standard serves as the primary technical specification for these devices in the power industry, outlining detailed requirements for technical parameters, testing methods, inspection rules, labeling, documentation, packaging, transportation, and storage.

Key technical parameters defined by industry standards include:

• Voltage stability: Random fluctuations must remain within strict limits, with voltage stability ≤0.5% when source voltage changes ±10%

• Ripple factor: Periodic deviation from the DC voltage arithmetic mean, with modern PWM-based systems achieving ≤3% and high-performance models reaching ≤0.5%

• Voltage adjustment rate: Defined as the maximum output voltage variation when input voltage changes ±1%, expressed as a ratio to the average output voltage

• Short-time stability: The maximum output voltage change relative to the arithmetic mean when input voltage and external load remain constant over a specified time interval

These stringent requirements ensure that DC high-voltage generators provide the precision necessary for reliable insulation assessment and accurate measurement of leakage currents in various electrical apparatus.

3. Working Principles and Circuit Topologies

DC high-voltage generators employ several circuit topologies to achieve the required voltage levels and stability characteristics. The most common configurations include:

3.1 Basic Rectifier Circuits

The foundation of DC high-voltage generation begins with basic rectifier circuits, including half-wave rectifiers, full-wave rectifiers, and voltage multiplier configurations. In unloaded conditions, half-wave rectifiers produce output voltage equal to the transformer's peak AC output (Um), while voltage doubler circuits achieve twice this value (2Um). Under load conditions, output voltage decreases somewhat and exhibits characteristic ripple that must be controlled within acceptable limits.

3.2 Cascade DC High-Voltage Generators

For higher voltage requirements, cascade (or串级) configurations connect multiple voltage multiplier stages in series. In theory, an n-stage cascade generator can produce output voltages up to 2nUm under no-load conditions. However, in practice, voltage drop and ripple increase significantly with additional stages, limiting practical implementations to typically 5 stages or fewer. Some advanced designs employ symmetrical or three-phase circuits to extend these limitations and achieve higher output currents.

3.3 High-Frequency PWM-Based Generators

Modern digital and intelligent DC high-voltage generators have embraced high-frequency power conversion techniques using Pulse Width Modulation (PWM). By operating at frequencies between 30-100kHz, these systems achieve superior voltage stability, reduced ripple (often ≤1%), and significantly smaller physical size compared to traditional designs. The incorporation of AIPWM technology (Artificial Intelligence Pulse Width Modulation) further enhances linearity and control precision in advanced models.

4. Types of DC High-Voltage Generators

4.1 Cascade DC High-Voltage Generators

Cascade DC high-voltage generators employ multiple stages of voltage multiplier circuits connected in series to achieve high output voltages. These systems typically utilize microcontroller-based control systems (such as MCS-8098 microcontroller systems) to manage silicon-controlled rectifier (SCR) voltage regulation circuits. Key features include programmable voltage ramp rates (typically 0.5-9.9 kV/s adjustable in 0.1 kV/s increments), real-time voltage and leakage current display (0-600 kV and 0-800 μA ranges, respectively), and automatic overvoltage or breakdown detection.

4.2 Digital DC High-Voltage Generators

Digital DC high-voltage generators incorporate modern digital signal processing and measurement technologies to provide enhanced precision and user convenience. These devices typically offer voltage outputs ranging from 60-400 kV with current capabilities of 1-10 mA, all with measurement accuracy of ±1%. Specialized functions include automatic calculation of zinc oxide surge arrester reference voltage (U1mA) and leakage current at 0.75U1mA, timed test sequences, and comprehensive data logging capabilities.

4.3 Intelligent DC High-Voltage Generators

Intelligent systems represent the current state-of-the-art, incorporating comprehensive automation, advanced diagnostics, and enhanced safety features. These generators typically feature large LCD displays for real-time parameter monitoring, RS232 or USB interfaces for data communication, and automated test sequences for specific applications like zinc oxide arrester testing. Sophisticated protection systems include multi-level safeguards: low-voltage overcurrent, high-voltage overvoltage, poor grounding protection, and emergency stop functions with nanosecond-level response times.

5. Key Applications in Power Systems

DC high-voltage generators serve essential functions across multiple aspects of power system testing and maintenance:

5.1 Insulation Strength Testing

These devices are indispensable for DC withstand voltage tests on power cables, power capacitors, and other capacitive test objects. Standards require that these tests apply voltage with specific ramp rates and maintain stable test voltage with strict tolerances: ±1% for durations up to 60 seconds and ±3% for longer periods. The non-linear resistive characteristics of test objects during DC withstand tests make voltage stability particularly important for obtaining accurate, reproducible results.

5.2 Zinc Oxide Surge Arrester Testing

A specialized application of DC high-voltage generators is the testing of zinc oxide surge arresters, which involves measuring the reference voltage (U1mA) at 1mA current and the leakage current at 0.75 times this reference voltage. Modern intelligent generators include dedicated functions for these tests, often with single-button operation (the 0.75UDC-1mA button) that automatically calculates and applies the appropriate test voltages.

5.3 Industrial Applications

Beyond power system testing, DC high-voltage generators find applications in various industrial processes, including electron microscopy, electrostatic painting, precipitation systems, and other specialized equipment requiring stable high-voltage DC power.

6. Safety Considerations

Operating DC high-voltage generators requires strict adherence to safety protocols due to the potentially lethal energy levels involved. Essential safety measures include:

• Qualified personnel: Operators must possess "high-voltage test certification" and thorough understanding of electrical safety procedures

• Proper grounding: Test circuits must employ single-point grounding configurations, and equipment must include comprehensive grounding verification before operation

• Discharge procedures: Capacitive test objects must be discharged through appropriate resistance (typically 100Ω/V discharge resistance rods) using a gradual approach method to prevent destructive discharge transients

• Ion field awareness: At voltages above 200kV, space charge effects can induce different DC potentials on personnel in proximity, potentially causing minor shocks if contact is made between individuals or with grounded structures

Industry standards explicitly require that two clearly visible disconnection points be incorporated in the power supply line before the test equipment when changing test specimens or connections.

7. Conclusion

DC high-voltage generators have evolved significantly from basic rectifier circuits to sophisticated, intelligent test systems incorporating advanced power electronics, precision measurement technology, and comprehensive safety features. These devices remain essential tools for ensuring the reliability and safety of electrical power systems through accurate assessment of insulation integrity and dielectric strength.

The continuing development of DC high-voltage generator technology follows trends toward greater precision, enhanced safety, improved portability, and expanded functionality. Modern standards like DL/T 848.1-2019 establish rigorous requirements for these devices, while technologies such as high-frequency PWM conversion, microcontroller-based control, and sophisticated protection algorithms continue to push performance boundaries. As power systems evolve toward higher voltages and greater complexity, DC high-voltage generators will maintain their critical role in preventive maintenance and quality assurance programs across the electrical industry.