Key Factors for Purchasing Transformer Testing Instruments

Power transformers are critical in power transmission systems, ensuring reliable electricity distribution. Given their complex structure, transformers are susceptible to faults, making routine inspection and testing essential. Regular testing helps to identify faults early, reduce maintenance costs, extend service life, and prevent failures, thus playing a significant role in transformer maintenance.

Below is an overview of the routine inspection items, testing methods, and key factors to consider when selecting testing instruments for power transformers.

1. Measurement of Transformer Insulation Resistance Absorption Ratio
Purpose: Measure the main insulation resistance of the transformer to assess insulation integrity.
Method: Use a 2500V or 5000V insulation resistance tester to measure the resistance, which should be at least 1000MΩ. Calculate the absorption ratio as kr = (R60/R15), where R60 and R15 are the resistance values at 60 and 15 seconds, respectively.
Instrument Selection: Choose an insulation resistance tester with adjustable voltage settings (e.g., 2500V and 5000V) and high sensitivity for accurate readings in high-resistance environments.
2. DC Leakage Current Test of Transformer Winding
Purpose: Identify insulation defects that may not be detectable by resistance tests.
Method: Using a DC high-voltage generator, connect a microampere meter in series with the generator's high-voltage side. Gradually increase the voltage to the test level and read the leakage current after one minute.
Instrument Selection: Select a high-voltage generator compatible with microampere meters for precise current readings. Ensure it has over-voltage protection for safety.
3. Transformer Dielectric Loss Tangent Value Test (TG)
Purpose: Detect moisture and degradation in insulation.
Method: Use an automatic anti-interference dielectric tester to apply high voltage and measure the dielectric loss tangent value (TG).
Instrument Selection: Opt for an automatic dielectric loss tester with anti-interference capabilities, as power transformer environments may have electrical noise that could impact test accuracy.
4. DC Resistance Measurement of Transformer Winding
Purpose: Verify the quality of internal connections and identify potential short circuits within windings.
Method: Use a DC resistance tester, typically the bridge method, to measure the DC resistance of each phase winding.
Instrument Selection: A DC resistance tester with a high degree of precision is essential. Look for models that allow individual phase testing and are stable under various testing conditions.
5. Transformer Transformation Ratio Measurement
Purpose: Confirm the transformer’s ratio accuracy and detect any winding or core anomalies.
Method: Measure the transformer’s transformation ratio using either the differential method or bridge method.
Instrument Selection: A high-accuracy transformation ratio tester is recommended, with features for testing under different load conditions and providing fast, repeatable results.
6. AC Withstand Voltage Test of Transformer
Purpose: Detect insulation moisture and pinpoint any concentration of defects.
Method: Use a power frequency withstand voltage test device or series resonance test device, selecting based on the voltage level and capacity of the transformer.
Instrument Selection: Choose a test device with adjustable voltage capabilities for different transformer classes. A series resonance test device is beneficial for larger transformers, as it provides efficient testing at reduced power requirements.
7. Transformer Induction Withstand Voltage and Partial Discharge Test
Purpose: Verify the integrity of the longitudinal insulation and detect internal defects.
Method: The induction withstand voltage test uses a triple-frequency power generator, applying double-frequency power from the low voltage side. The partial discharge test detects the discharge propagation from faults.
Instrument Selection: For induction withstand testing, use a frequency-variable power generator. A partial discharge detector with sensitivity to small discharges and accurate localization capability is essential for effective fault detection.
Key Considerations for Selecting Testing Instruments
When selecting testing instruments for transformers, consider the following:

Instrument Compatibility: Ensure that instruments are suited for the specific transformer types and voltage ratings.
Precision and Sensitivity: Accurate measurements require instruments with high precision, especially for insulation resistance and partial discharge tests.
Environmental Suitability: Some transformers operate in high-interference or harsh conditions. Choose instruments with anti-interference features or rugged builds for outdoor use.
Safety Features: High-voltage testing equipment should include features like over-voltage protection and automatic shutdown to prevent accidental damage or injury.
Ease of Use: Instruments should be straightforward to opera