What are the tests needed to be conducted on a power transformer?

2025,07,21

As the core equipment of the power grid system, the stable performance of the Power Transformer is directly related to the safe operation of the entire power system.

In order to ensure the long-term reliable operation of the transformer, comprehensive testing and diagnosis must be carried out. In this article, Hubei Jutai will introduce in detail the various test items and test methods required for the transformer, and recommend professional Transformer Testing Equipment solutions.

8 key tests that must be performed on Power Transformers

1. Insulation resistance test (IR Test)

Test purpose: evaluate the overall insulation condition of the transformer and detect moisture or contamination problems

Test method:

Use Transformer Measurement Instruments such as insulation resistance testers to apply 500V or 1000V DC voltage between the winding and the ground, and between the windings, and measure the insulation resistance value after 1 minute. The insulation resistance of a new transformer should usually be >1000MΩ. The value of a transformer in operation will decrease but must meet industry standards.

2. Winding DC resistance test (DCR Test)

Test purpose: detect problems such as poor winding connection, increased contact resistance, and inter-turn short circuits

Test method:

Use precision Transformer Inspection Tools such as micro-ohmmeters to measure the DC resistance of the winding at each tap position of the transformer. The three-phase resistance unbalance rate should be <2% (Distribution transformer) or <1% (power transformer). The JT-700 series DC resistance tester produced by Hubei Jutai performs well in this type of test.

3. Turns Ratio Test

Test Purpose: Verify whether the winding turns ratio meets the design and detect inter-turn short circuit

Test Method:

Use a ratio tester to measure the voltage ratio of the high-voltage and low-voltage windings at the rated tap and all tap positions. The deviation between the measured value and the nameplate value should be <0.5%. Modern Transformer Testing Equipment such as the JT-3000 ratio group tester can automatically calculate the error and determine whether it is qualified.

4. Dielectric loss factor test (Tanδ Test)

Test Purpose: Evaluate the aging condition of the insulation material and detect moisture or contamination

Test Method:

Use a dielectric loss tester to measure the tanδ value at 10kV power frequency voltage. The tanδ of a new Oil-immersed Transformer is usually <0.5%, and that of a running transformer should be <2%. Hubei Jutai's JT-6000 series intelligent dielectric loss tester is an ideal choice for this test.

5. Partial Discharge Test (PD Test)

Test Purpose: Detect local defects in the insulation system and prevent sudden failures

Test Method:

Use professional Transformer Diagnostic Equipment to monitor partial discharge at rated voltage. The partial discharge of new transformers should be <10pC, and that of operating transformers should be <100pC. The JT-PD800 partial discharge detection system has high sensitivity and anti-interference capabilities.

6. Frequency Response Analysis (FRA Test)

Test Purpose: Detect winding deformation and displacement and evaluate mechanical stability

Test Method:

Use a frequency response analyzer to scan the winding response characteristics in the range of 20Hz-2MHz. Determine the change in winding status by comparing with historical data. The JT-FRA900 frequency response analysis system provides automatic analysis and diagnosis functions.

7. Dissolved Gas Analysis (DGA Test)

Test purpose: To determine the type and severity of internal faults by the gas composition in the oil

Test method:

After sampling, use a gas chromatograph to analyze the content of characteristic gases such as H₂, CH₄, C₂H₂. The JT-DGA600 online monitoring system can realize real-time gas analysis.

8. Load loss and no-load loss test

Test purpose: To evaluate the energy efficiency of the transformer and detect magnetic circuit and circuit anomalies

Test method:

Use Transformer Measurement Instruments such as power analyzers to measure the loss value under rated conditions. The measured value should not exceed +15% of the nameplate value.

Faced with numerous Transformer Testing Equipment on the market, power companies should pay attention to the following key factors:

Measurement accuracy: Only high-precision instruments can detect small changes.

Automation degree: Automatic testing, calculation and report generation can improve efficiency.

Data management: Support historical data storage and trend analysis.

Safety: Comply with high-voltage test safety standards.

Portability: Field test equipment should be easy to carry and operate.

As a professional power transformer manufacturer, Hubei Jutai can also provide Transformer Inspection Tools solutions. Its products enjoy a high reputation in the industry for high precision, high reliability and excellent after-sales service.

Author:

Mr. jiawenhan

E-mail:

JT13797437282@gmail.com

Phone/WhatsApp:

+86 13797437282