In power equipment acceptance testing, accurate and comprehensive testing of the electrical performance of the secondary windings of current transformers is a crucial step in ensuring metering accuracy and relay protection reliability. Recently, the QLD-120P instrument transformer comprehensive tester, developed and manufactured by Baoding Qilida Electric Technology Co., Ltd., successfully diagnosed an internal winding wiring error in a bushing-type current transformer during on-site acceptance testing at the CFE 35kV substation SVG project in Mexico. This provided strong technical support for the safe commissioning of the project and once again demonstrated the superior performance and reliability of our equipment in complex field environments.
Case Background: Instrument Transformer Acceptance Challenges in Multinational Projects
Date: January 15, 2026 Source: Baoding Qilida Electric Technology Co., Ltd.
This project, located at the CFE 35kV substation SVG project site in Mexico, involved the acceptance testing of a bushing-type current transformer, model FCRG-L-40.5/3150. This bushing-type current transformer has a rated voltage of 40.5kV, a rated current of 3150A, a current ratio of 3150/5, an accuracy class of 5P20/5P20/5P20/5P20, and a rated capacity of 50VA/winding. The field testing team used the QLD-120P comprehensive transformer tester provided by Baoding Qilida Electric Technology Co., Ltd. to conduct comprehensive electrical performance tests on the four secondary windings (1S, 2S, 3S, and 4S) of the current transformer.
Testing Process and Anomalies Found
During the test, the testers sequentially tested the turns ratio, polarity, volt-ampere characteristics, and DC resistance of each winding. The results showed:
1S and 2S windings: The instrument could not normally measure the turns ratio, polarity, volt-ampere characteristics, and DC resistance data. The test interface displayed “communication abnormality” or “test failed,” indicating that there might be an electrical connection interruption or internal wiring error in these two windings.
4S and 5S windings: All tests were successfully completed. Measured data are as follows:
DC resistance: 630mΩ (compliant with specifications) Polarity: Same polarity (correct) Turning ratio: 3150/5 (consistent with nameplate) Voltage-ampere characteristic: Qualified (meets 5P20 accuracy class requirements)
Test results indicate that the electrical performance of the 4S and 5S windings fully complies with technical specifications.
This anomaly immediately attracted the attention of on-site technicians. Because the QLD-120P instrument transformer comprehensive tester possesses high-precision measurement and intelligent diagnostic functions, it can quickly identify wiring abnormalities or internal faults. A preliminary judgment was made that there was a serious electrical connection problem in the 1S and 2S windings.
Problem Analysis and Manufacturer Verification
The on-site testing team immediately contacted the after-sales personnel of the bushing-type current transformer manufacturer and described the test phenomenon in detail. Based on experience, the manufacturer’s technicians judged that it was likely due to incorrect internal wiring or an open circuit in the windings, causing the instrument to be unable to collect signals normally. Under the manufacturer’s guidance, on-site personnel disassembled and inspected the faulty transformer. The results confirmed a serious wiring error in the internal wiring of windings 1S and 2S, preventing the secondary circuit from forming a valid electrical path and resulting in a “no response” during testing.
The Value of Technical Support from Baoding Qilida Electric Technology Co., Ltd.
In this case study, the QLD-120P instrument transformer comprehensive tester demonstrated its three core capabilities in complex field environments:
1. High-precision diagnostic capability: The instrument can quickly identify winding anomalies and accurately distinguish between “normal windings” and “faulty windings,” providing a reliable basis for on-site judgment.
2. Intelligent prompts and anti-interference design: Even in multinational engineering sites, the instrument can still operate stably, intelligently prompting the test status and avoiding misjudgments.
3. Strong field adaptability: The equipment is lightweight, easy to operate, and supports multilingual interfaces, making it suitable for international engineering projects.
Baoding Qilida’s Core Commitment
Baoding Qilida Electric Technology Co., Ltd. is committed to providing the global power industry with highly reliable, intelligent, and easy-to-operate electrical testing solutions. Our series of instrument transformer comprehensive testers not only possess comprehensive testing functions but also integrate rich on-site diagnostic logic and intelligent prompting systems to help users quickly locate problems and improve testing efficiency. Whether for domestic power grid projects or international energy projects, Baoding Qilida is committed to safeguarding your equipment safety and system stability with professional products and attentive service.
About Baoding Qilida Electric Technology Co., Ltd. Baoding Qilida Electric Technology Co., Ltd. is a high-tech enterprise specializing in the R&D, production, sales, and technical services of high-end electrical measurement and testing instruments. The company’s products cover a range of series including dielectric loss testers, instrument transformer comprehensive testers, high-voltage testing equipment, and relay protection testers, widely used in power systems, new energy, rail transportation, industrial manufacturing, and scientific research and education, committed to providing customers with comprehensive, high-value testing solutions.
