In power equipment maintenance and fault handling, transformer ratio testing is a critical procedure to verify correct winding connections and ensure electrical performance meets design requirements after component replacement.
Recently, Datang Sanmenxia Power Plant conducted a comprehensive acceptance test after replacing a faulty transformer bushing. The plant used the QLD-BB Transformer Turns Ratio Tester, developed by Baoding Qilida Electric Technology Co., Ltd., to perform precise ratio and vector group verification.
The test results were accurate and reliable, enabling the transformer to be successfully re-energized. This case once again demonstrates the efficiency and precision of the QLD-BB Transformer Turns Ratio Tester in real maintenance environments.
Background: Post-Bushing Replacement Verification Requirements
Transformer bushings are critical components for current lead-out and insulation isolation. Over time, insulation aging, mechanical stress, or environmental factors may cause failures.
After detecting abnormal conditions in a transformer bushing, the power plant decided to replace the faulty component. According to the Chinese standard Electrical Equipment Installation Engineering Acceptance Test Standard (GB 50150) and preventive testing regulations, a full acceptance test must be conducted after bushing replacement to verify:
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Winding connection correctness
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Transformer turns ratio accuracy
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Three-phase vector group consistency
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Overall electrical condition before re-energization
Transformer ratio testing plays a key role in this verification process.
Test Procedure Using the QLD-BB Transformer Turns Ratio Tester
After the bushing replacement was completed, field engineers used the QLD-BB Transformer Turns Ratio Tester to measure the turns ratio and vector group at each tap position.
Test Standards and Tolerance Requirements
According to regulations:
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Rated tap voltage ratio deviation: ±0.5%
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Other tap positions deviation: ≤ ±1%
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Vector group must match the transformer nameplate
Testing Steps
Engineers followed standard procedures:
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Connected the high-voltage A, B, C terminals of the QLD-BB Transformer Turns Ratio Tester to the transformer’s HV bushings
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Connected the low-voltage a, b, c terminals to the LV bushings
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Entered rated voltage, vector group, and tap position parameters
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Activated automatic testing mode
The instrument automatically measured each tap position and displayed:
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Turns ratio values
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Percentage deviation
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Vector group identification
The automated workflow significantly improved testing efficiency while reducing human error.
Test Results: High Accuracy and Stability
✔ Turns Ratio Deviation
Measured deviations at all tap positions were within ±0.3%, exceeding the required ±0.5% standard tolerance.
✔ Vector Group Verification
The vector group identification fully matched the nameplate, confirming correct winding connections after bushing replacement.
✔ Repeatability Test
Three repeated measurements at the same tap position showed stable and consistent data, proving excellent repeatability and anti-interference performance.
Data Comparison and Trend Analysis
To ensure maximum reliability, engineers compared the new test data with historical transformer records.
The results showed:
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Consistent ratio variation trends
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No abnormal fluctuations
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Stable transformer condition
This further confirmed the quality of the maintenance work and the reliability of the equipment.
Successful Re-Energization
After completing all acceptance tests, the transformer was successfully put back into operation. Since re-energization, all operating parameters have remained normal with no alarms.
The use of the QLD-BB Transformer Turns Ratio Tester provided a reliable technical basis for safe recommissioning and offered valuable experience for similar maintenance scenarios.
Core Advantages of the QLD-BB Transformer Turns Ratio Tester
In this case, the QLD-BB Transformer Turns Ratio Tester demonstrated significant on-site value:
1. High Measurement Accuracy
Accuracy level up to 0.1 class, meeting precision testing requirements for various power transformers.
2. Automatic Testing and Intelligent Judgment
One-button multi-tap measurement with automatic deviation calculation and pass/fail evaluation.
3. Accurate Vector Group Identification
Quick identification of three-phase transformer vector groups to prevent wiring errors.
4. Data Storage and Export
Supports test data storage and export for historical comparison and report generation.
5. Strong Field Adaptability
Portable design and simple operation, ideal for power plants, substations, and transformer manufacturers.
Conclusion
Accurate transformer ratio testing is essential for ensuring safe operation after maintenance. This successful application at Datang Sanmenxia Power Plant highlights the precision, reliability, and efficiency of the QLD-BB Transformer Turns Ratio Tester.
For power plants, substations, and electrical equipment manufacturers seeking a professional solution for transformer ratio testing, the QLD-BB Transformer Turns Ratio Tester delivers dependable performance and high-precision results in demanding field conditions.
