It is a specialized high-voltage testing equipment used in power systems for DC withstand voltage tests and leakage current measurements.
It is mainly used to detect the insulation strength of power equipment (especially cables, arresters, generators) under high voltage, and can sensitively detect concentrated defects (such as bubbles, cracks in insulation) that are difficult to detect in AC withstand voltage tests.
The following is a detailed analysis combined with industry standards and technology trends for 2025-2026:
1. Core Application Scenarios
DC high voltage generator is the “standard equipment” for preventive tests of the following devices:
Zinc oxide arrester (MOA): Measure DC reference voltage and leakage current at 0.75 times the reference voltage. This is the most critical indicator for judging whether the arrester is damp, aged, or valve plates are degraded.
Power cables: Especially high-voltage cross-linked polyethylene (XLPE) cables.
Note: Although DC withstand voltage is traditionally used, modern standards (such as GB/T 3048) recommend using series resonance AC withstand voltage for XLPE cables. DC withstand voltage easily causes “space charge” accumulation in XLPE insulation, which can damage the insulation. However, in old standard implementation, oil-paper insulated cable testing, or fault location, DC high voltage source is still widely used.
Large generators/motors: DC withstand voltage and leakage current tests of stator windings, used to detect end insulation defects.
Transformers: DC leakage current tests of bushings, windings together with bushings.
Others: DC withstand voltage tests for insulators, circuit breaker gaps, GIS components, etc.
2. Working Principle and Technical Characteristics
Voltage doubling rectifier circuit: Internally uses high-frequency PWM pulse width modulation technology, through multi-stage voltage doubling rectifier circuits, to boost lower input voltage (220V/380V) to tens of kilovolts or even hundreds of kilovolts of DC high voltage.
High stability: Modern models use closed-loop feedback control. When the load changes (such as flashover), the output voltage can be quickly stabilized, with extremely low ripple factor (usually < 1%).
Microammeter integration: Built-in high-precision digital microammeter (resolution up to 0.1μA), directly connected in series on the high-voltage side, eliminating stray current effects, and accurately measuring leakage current.
3. New Technology Trends for 2025-2026
Medium-frequency inverter technology:
Completely replaces old-fashioned power frequency transformers, reducing volume by 60% and weight by 50%. A 60kV/5mA device now typically weighs only 5-8kg, and can be carried by one person to mountains or into narrow switchgear rooms.
Intelligent protection and automatic discharge:
Zero start: The output is zero by default when powered on to prevent misoperation.
Overvoltage/overcurrent protection: Response time <10ms. Once the test object breaks down, the high voltage is immediately cut off and locked.
Automatic discharge: After the test ends or a trip occurs, the instrument automatically discharges the test object and its own capacitance through internal resistors, eliminating the need for manual discharge rods and long waits (but manual re-check of discharge is still recommended).
Wireless remote control and Bluetooth transmission:
Standard wireless remote control box (distance >30 meters) allows operators to control voltage increase, decrease, and emergency stop from a safe distance.
Supports Bluetooth connection to mobile phone App, real-time plotting of “voltage-current” curves, automatic generation of test reports, and upload to the cloud.
Multiple gears and wide range:
A single device covers a wider range of voltage levels (such as 60kV/120kV/200kV universal), with range switching via DIP switches or software.
Anti-interference capability:
Optimized shielding design for strong electromagnetic environments in substations, ensuring stable microampere-level leakage current readings without fluctuation.
4. Key Selection Parameters
When purchasing, the following indicators need to be clarified:
Table
Parameter Description Typical Specifications
Rated Voltage Select based on the highest test voltage of the test object, with a 20% margin. 60kV, 120kV, 200kV, 300kV, 400kV
Rated Current Determines load capacity. Testing arresters only requires 1-2mA; testing long cables or generators requires 5mA-10mA or higher. 2mA, 5mA, 10mA, 20mA
Power P=U×I. High-power models require higher heat dissipation. 100W - 2000W
Accuracy Voltage error ≤1.0%, current error ≤1.0%. 0.5 class / 1.0 class
Structure Split type (control box + voltage doubling cylinder, mainstream, lightweight); integrated type (old, bulky, obsolete). Split type
5. Operation Procedure and Safety Warnings (Crucial)
DC high voltage has a “memory effect” (residual charge). Improper operation can easily cause electric shock. The following steps must be strictly followed:
Wiring:
Reliable grounding: The control box, voltage doubling cylinder, and test object enclosure must be grounded together.
High-voltage wire connection: Use dedicated shielded high-voltage wires, suspended overhead, avoid dragging on the ground.
Microammeter connection: If an external microammeter is used, it must be placed inside a high-voltage shielding cover.
Check: Confirm the voltage regulator is at zero position, and all personnel evacuate to a safe area.
Voltage increase:
Turn on the power, start high voltage.
Increase voltage at a uniform rate (about 1-2kV/s), closely monitor the voltmeter and microammeter.
For arrester testing: Increase to
record the leakage current.
Voltage decrease and shutdown: After the test is completed, first reduce the voltage to zero, then cut off the high-voltage switch, and finally cut off the main power.
Discharge (life-and-death step):
It is strictly forbidden to directly touch the high-voltage terminal or the test object!
Must first use a discharge rod with a resistor to contact the high-voltage terminal for discharge (hear the “crackling” sound). After the sound disappears, use a grounding wire to directly short-circuit and discharge.
For long cables or large capacitance equipment, the discharge time may take several minutes.
Disassembly: Only after confirming no residual charge can the wiring be removed.
6. Common Fault Troubleshooting
Cannot increase voltage/excessive current: Test object insulation breakdown, high-voltage wire flashover to ground, high air humidity causing surface leakage (need to add shielding ring).
Microammeter reading jumps: High-voltage wire not suspended, strong electromagnetic interference on site, dirty surface of test object (need to wipe or add shielding).
Display “overload”: Output current exceeds the set protection value. Check whether flashover occurs or the setting value is too small.
7. Mainstream Brands and Market
Wuhan UHV, Wuhan Huayi, Guodian Mingke: High market share, complete product lines, with mature products from 60kV to 500kV.
Shanghai Siyuan, Baoding Tianwei: Stable quality, commonly used in power grid company centralized procurement.
Imported brands: Such as Haefely (Switzerland), Megger (UK), expensive, mainly used for scientific research or special UHV testing.
