Introduction to DC High-Voltage Generators

DC high-voltage generators are specialized testing devices designed to produce direct current high voltages for various industrial and research applications. These systems serve as crucial tools for investigating the insulation strength of DC transmission and converter station equipment, as well as insulating materials under high DC voltage conditions. Additionally, they are extensively used for performing leakage current tests on power equipment and for studying corona effects and ion flow phenomena in DC transmission lines.

Technical Principles and Operation

In high-voltage laboratories, DC high voltage is typically generated by rectifying AC high voltage. The most common rectifier circuits include simple rectifier circuits and cascade rectifier circuits. These systems must meet two fundamental requirements: First, the output voltage ripple coefficient should not exceed 3%. Second, in case of a flashover on the test object, the power supply must be able to maintain the arc to prevent extinction.

The characteristics of a DC high-voltage generator are defined by its rated DC current (average value) Id, corresponding output voltage (average value) Ud, and voltage ripple coefficient S, where S = (Umax - Umin)%/(2Ud). In this formula, Umax and Umin represent the maximum and minimum output voltages respectively.

Circuit Configurations and Technologies

Basic Rectifier Circuits

The most widely used basic rectifier circuits in high-voltage laboratories include half-wave rectifiers and voltage multiplier circuits. Under no-load conditions, a half-wave rectifier circuit produces an output voltage equal to the maximum value Um of the transformer's AC output voltage. Voltage multiplier circuits, on the other hand, can generate an output voltage of 2Um, effectively doubling the input voltage.

Cascade DC High-Voltage Generators

Cascade DC high-voltage generators consist of multiple stages of voltage multiplier circuits connected in series :cite[1]. When unloaded, a cascade generator with n stages can achieve an output voltage of 2nUm. However, these systems require specially manufactured insulated core transformers for charging operations.

While cascade configurations can deliver higher output currents, both voltage drop and ripple increase dramatically as more stages are added. Consequently, the number of stages in practical cascade generators typically does not exceed five. To achieve larger output currents while managing these limitations, engineers often employ symmetrical circuits, three-phase circuits, or increased power supply frequencies in cascade DC high-voltage generators.

Key Components and Specifications

High-Voltage Silicon Stacks

High-voltage silicon stacks, composed of multiple silicon diodes connected in series, serve as the critical components in high-voltage rectifier circuits that convert AC to DC. These components are characterized by their rated rectifier current, forward voltage drop, and peak inverse voltage. Silicon stacks offer significant advantages including compact size, light weight, long service life, ease of use, and absence of radiation.

Modern Control Systems

Contemporary DC high-voltage generators incorporate advanced control systems for enhanced precision and functionality. Modern systems utilize microcontroller-based controls, such as MCS-8098 microcontroller systems, which enable features including:

• Adjustable voltage rise rates between 0.5-9.9 kV/s with 0.1 kV/s intervals

• Voltage stabilization accuracy not less than 1%

• Real-time display of DC output voltage (0-600 kV) and leakage current (0-800 μA)

• Automatic detection of overvoltage or breakdown conditions

Applications in Electrical Testing

DC high-voltage generators play a vital role in various electrical testing applications:

Insulation Testing of Capacitive Equipment

Electrical equipment with significant capacitance, such as power cables and capacitors, often undergoes insulation testing using DC high-voltage generators. This approach reduces the capacity requirements for test equipment compared to AC testing methods. According to IEC and national standards, DC withstand voltage tests serve as a key method for insulation detection of capacitive test objects :cite[1]. These tests must apply voltage at a specific rate and maintain the test voltage stably and continuously.

Specialized Testing Applications

Beyond standard insulation tests, DC high-voltage generators are employed in specialized scenarios including:

• Insulation pollution tests where test objects demonstrate strong non-linear characteristics

• As power sources for other high-voltage test equipment such as impulse voltage generators, impulse current generators, and oscillation circuits

• Research applications across various scientific and technological fields

Standards Compliance and Testing Requirements

DC high-voltage testing must adhere to strict international and national standards. For DC withstand voltage tests, the standards specify that:

• For test durations under 60 seconds, the allowable voltage deviation is ±1%

• For tests exceeding 60 seconds, the allowable voltage deviation expands to ±3%

During DC withstand voltage tests, the test object exhibits non-linear resistance characteristics, potentially resulting in significant current fluctuations. Therefore, maintaining voltage stability within the specified tolerances is essential for conducting tests accurately.

Recent updates to high-voltage testing standards include GB/T 16896.1-2024, which specifies requirements for instruments used in impulse tests, and DL/T 846.17—2025, which covers technical requirements for high-voltage dielectric loss testers :cite[6]:cite[9]. These evolving standards reflect the continuous advancement of high-voltage testing technology and methodologies.

Anti-Interference Measures in Control Systems

High-voltage environments present significant challenges for control systems. The intense corona discharge at hundreds of kilovolts and strong electromagnetic interference during flashover events can disrupt computer operations. To address these issues, modern DC high-voltage generators implement multiple protective measures:

• Signal acquisition components utilize photoelectric isolation technology to separate sampling circuits from microcomputers

• Shielded enclosures and properly grounded cables provide electromagnetic shielding

• Careful circuit design separates digital and analog grounds, connecting them at a single point

• Floating power supply methods and isolation transformers implement ground potential isolation

Conclusion

DC high-voltage generators represent sophisticated testing systems essential for evaluating electrical insulation and conducting research in high-voltage environments. From basic rectifier circuits to advanced cascade systems with microcontroller-based controls, these devices have evolved to meet increasingly demanding testing requirements across various industries. With ongoing standardization efforts and technological advancements, DC high-voltage generators continue to provide reliable, precise testing solutions while incorporating enhanced safety and interference protection features for accurate measurements in challenging electromagnetic environments.

As high-voltage testing technology progresses, we can anticipate further refinements in measurement accuracy, control system sophistication, and compliance with international standards, ensuring these critical testing devices continue to meet the evolving needs of the electrical power industry and research communities.