Also known as high-voltage test transformer or power frequency withstand voltage test device. It is a special type of transformer specifically used for AC withstand voltage tests and leakage current tests on electrical equipment (such as power transformers, cables, switchgear, insulators, etc.).
Since the keywords you provided are relatively brief, I have compiled core information about test transformers, including their uses, characteristics, classifications, and working principles:
1. Main Uses
The core function of a test transformer is to generate high voltage to check whether the insulation strength of electrical equipment meets the requirements for safe operation. Specific applications include:
Power frequency withstand voltage test: Simulates overvoltage conditions that may occur during grid operation to assess the main insulation's withstand capability.
Leakage current test: Measures the leakage current of the test object under high voltage to judge insulation condition.
Partial discharge test: Works with other equipment to detect partial discharge inside the insulation.
2. Differences from Ordinary Power Transformers
Table
Characteristic Ordinary Power Transformer Test Transformer
Operating State Long-term continuous operation with load Short-time duty (usually a few minutes), no-load or micro-capacitive load
Voltage Waveform Requires extremely low sine wave distortion Allows certain waveform distortion, but must meet standards
Impedance Voltage Small (4%-10%) to ensure voltage stability Large (usually 5%-15% or even higher) to limit short-circuit current
Insulation Margin Designed according to rated voltage Designed according to maximum test voltage, with large insulation margin
Capacity Designed based on load requirements Usually small (a few kVA to several hundred kVA) because only capacitive current needs to be supplied
3. Common Classifications
Based on different structures and media, test transformers are mainly divided into the following categories:
Oil-immersed test transformer:
Features: Uses transformer oil as insulation and cooling medium.
Advantages: Low cost, large capacity, suitable for on-site testing of large equipment.
Disadvantages: Large volume, heavy weight, risk of oil leakage, not suitable for frequent movement.
Dry-type test transformer:
Features: Uses epoxy resin casting or gas (such as SF6) insulation.
Advantages: Small size, light weight, no oil contamination, simple maintenance, suitable for laboratory or indoor use.
Disadvantages: Difficult to manufacture in large capacities, relatively high cost.
Cascade test transformer:
Features: Multiple transformers connected in series to obtain higher output voltage (such as 300kV, 500kV and above).
Applications: Used for withstand voltage tests on ultra-high voltage equipment.
4. Typical Test Wiring
When conducting a transformer withstand voltage test, the following components are usually included:
Voltage regulator: Adjusts the input voltage to smoothly increase the output voltage of the test transformer.
Test transformer: Raises the voltage to the high voltage required for the test.
Protective resistor: Connected in series on the high-voltage side to limit short-circuit current during breakdown and protect the transformer.
Voltage divider/measuring sphere gap: Used to accurately measure the actual voltage value on the high-voltage side.
Test object: The power transformer or other equipment to be tested.
5. Precautions
Grounding safety: The casing, base, and non-energized windings of the test transformer must be reliably grounded.
Voltage rise speed: The voltage must be raised uniformly; impact closing or rapid voltage rise is strictly prohibited to avoid overvoltage damaging the test object.
Environmental requirements: The test site should be clean and dry; excessive air humidity may cause surface flashover.
Discharge: After the test, the test object and the high-voltage terminal of the transformer must be fully discharged using a discharge rod before disconnecting wires.
