From August 26 to 27, 2025, SCOTECH welcomed a delegation from its South African client and successfully completed the factory acceptance of a 20 (22) MVA 132/11kV oil-immersed power transformer at its production base. This acceptance strictly followed the dedicated test procedure, conducting a comprehensive inspection of the transformer’s various performance indicators. Ultimately, the transformer obtained high recognition from the client with excellent test results, laying a solid foundation for further cooperation between the two parties and the expansion of the product into the South African power market.
The oil-immersed power transformer accepted this time is a core equipment customized by SCOTECH to meet the needs of the South African power system. With the model clearly marked as 20/22 MVA 132/11kV and the contract number JSSKT25080, it fully meets the client’s dual requirements for voltage level and capacity. This transformer features flexible capacity adjustment capability: under the ONAN (Oil Natural Air Natural) cooling mode, the maximum operating capacity can reach 20 MVA; when switched to the ONAF (Oil Natural Air Forced) cooling mode, the capacity can be increased to 22 MVA. It can adapt to changes in power load in different regions and periods in South Africa, providing reliable support for the stable operation of the local power grid. Meanwhile, the transformer adopts the YNyn0 vector group, has a rated frequency of 50 Hz, and uses an on-load tap changer (OLTC) with ±8×1.25% voltage regulation, ensuring the accuracy and stability of voltage output and further meeting the client’s strict standards for power supply quality.
During the acceptance period, SCOTECH and the South African client jointly followed the 18 routine test standards specified in the test procedure, covering key dimensions such as insulation performance, electrical parameters, and mechanical performance. Each test strictly complied with the IEC 60076 series of international standards (including IEC 60076-1, IEC 60076-3, etc.), ensuring the authority and fairness of the test results.
In the insulation performance testing phase, the two parties focused on conducting a number of core tests. Among them, the measurement of dissolved gases in the insulating liquid of each independent oil compartment (excluding the diverter switch compartment) was particularly crucial. Gas chromatographic analysis was performed on the transformer oil both before and after the test. The results showed that the hydrogen (H₂) content was < 10 ppm, the acetylene (C₂H₂) content was 0, the total hydrocarbon (C₁~C₂) content was < 20 ppm, the moisture content was ≤ 20 ppm, the dielectric strength was ≥ 60 kV, the tangent of the dielectric loss angle tgδ (at 90℃) was ≤ 1%, and the oil appeared transparent without suspended matter or mechanical impurities. These results fully met the relevant standards and technical agreement requirements for new oil test items, proving that the new oil injected into the transformer was qualified and free from potential fault risks. Additionally, the measurement of DC insulation resistance between windings and to earth was conducted using a 5000V megohmmeter, with an absorption ratio ≥ 1.3 and a polarization index ≥ 1.5. In the insulation inspection of the core and clamping parts, the insulation resistance was ≥ 500 MΩ, further verifying the reliability of the transformer’s insulation system and laying a solid foundation for the long-term safe operation of the equipment.
In terms of electrical parameter verification, the voltage ratio measurement and phase displacement check covered all tapping positions. The high-voltage winding voltage was adjusted in 17 gears ranging from 118,800 V to 145,200 V, and the rated voltage of the low-voltage winding was 11,000 V. The measured voltage ratio error was less than ±0.5% of the specified voltage ratio and also less than 1/10 of the actual rated tapping impedance percentage. The vector group met the agreement requirement of YNyn0, ensuring the accuracy of the transformer’s voltage conversion. The short-circuit impedance and load loss measurement were carried out with voltage applied to the high-voltage side and the low-voltage side short-circuited. The impedance value of the main tapping (at 75℃) from high voltage to low voltage was 18.79%, and the load loss was ≤ 120 kW. The no-load loss and current measurement were conducted at 90%, 100%, and 110% of the rated voltage. At 100% rated voltage, the no-load loss was ≤ 15 kW and the no-load current was ≤ +30% of the specified value. All parameters met the design standards, demonstrating the transformer’s excellent energy conversion efficiency and energy-saving performance. Furthermore, tests such as the check of the ratio and polarity of the built-in current transformers and the measurement of winding resistance were also successfully completed. The ratio and polarity of the current transformers met the requirements of the drawings, the DC resistance of the secondary side showed no significant difference from the factory value, and the winding resistance unbalance rate was < 1% between lines and < 2% between phases. These results fully verified the integrity and stability of the equipment’s electrical structure.
In the mechanical and voltage withstand performance tests, the on-load tap changer operation test was strictly carried out in accordance with the procedure: 8 complete operation cycles were completed when the transformer was de-energized; 1 cycle was completed when the operating voltage was reduced to 85% of its rated value; 1 cycle was completed when the transformer was energized at rated frequency and voltage under no-load conditions; and 10 tap change operations were completed with one winding short-circuited and the rated current passed through the tapped winding as much as possible. No faults occurred throughout the process, proving the reliable mechanical performance of the on-load tap changer. For the full-wave lightning impulse test on the line terminals, the 132 kV winding was subjected to 1 impulse at 50% voltage and 3 impulses at 100% voltage, with no significant difference between the voltage waveforms at 50% and 100%. In the applied voltage test, line terminal AC withstand voltage test, and induced voltage withstand test with partial discharge (PD) measurement, there was no sudden drop in the test voltage. During the one-hour PD measurement, the PD level was ≤ 250 pC without an upward trend, and there was no sudden and continuous increase in the last 20 minutes. The background PD level was ≤ 50 pC, fully verifying the transformer’s ability to withstand lightning impulses and AC voltage, as well as the reliability of its longitudinal insulation. Finally, in the pressure tightness test, a pressure of 30 kPa higher than the normal liquid pressure was applied and maintained for 24 hours, and no leakage was found during the visual inspection, ensuring that the transformer would not have oil leakage risks during actual operation.
Throughout the two-day acceptance process, the South African client witnessed the conduct of all tests on-site and highly praised SCOTECH’s strict quality control system, professional technical team, and the excellent performance of the transformer. The client representative stated that SCOTECH not only completed the tests in strict accordance with international standards and contract requirements but also demonstrated an ultimate pursuit of product quality in details. The transformer accepted this time fully meets the operation needs of the South African power grid, and they look forward to conducting in-depth cooperation with SCOTECH on more power equipment projects in the future.
As an enterprise focusing on the R&D and manufacturing of oil-immersed power transformers, SCOTECH has always taken the “IEC 60076 series standards” as its technical benchmark and customer needs as its orientation. The success of this acceptance is not only a reaffirmation of the company’s product quality but also an important milestone for the company to expand into the African power market. In the future, SCOTECH will continue to deepen its presence in the power equipment field, continuously optimize product performance and test procedures, and provide more reliable and efficient power solutions for global customers, contributing to the high-quality development of the global energy industry.
