Fundamentals of HV Test Transformers

High-voltage test transformers serve as the primary equipment for generating power-frequency high voltage in insulation testing applications. These devices simulate both continuous operating voltages and transient overvoltages to verify the dielectric integrity of electrical apparatus in power systems.

Key Applications

• Power-frequency withstand voltage tests on electrical equipment

• Research on gas insulation gaps and corona effects

• Flashover voltage testing of insulator strings

• Generation of long-wavefront switching impulse voltages

• Power supply for DC and impulse voltage generators

Modern test transformers can reach 2,250kV, meeting UHV testing requirements in China and other industrialized nations.

Technical Characteristics

Series Resonant Test Systems

For ultra-high voltage testing, cascaded transformer configurations address size/weight limitations:

1. Utilizes multiple transformer units in series

2. Reduces individual unit insulation requirements

3. Increases total system impedance

4. Requires specialized voltage measurement windings

Test Circuit Configuration

Standard test setup includes:

• Grounded test object (C_x)

• Protective resistor (R) with 0.1-100kΩ range

• Metal-wound or water resistors (for >0°C environments)

Protective resistors serve three critical functions:

1. Prevent voltage chopping waves during breakdown

2. Suppress recovery overvoltages

3. Limit fault currents

Operational Considerations

Typical operational constraints:

• 500kV units: 30min continuous operation at rated voltage

• 330kV units: Continuous operation possible at derated capacity

• Special units: As little as 5min operation at full rating