In the factory testing process of transformer manufacturing enterprises, the selection of variable frequency series resonance testing equipment is a key decision that directly affects the accuracy of product quality judgment. Unlike the voltage withstand test of capacitive equipment such as cables and GIS, transformer testing imposes three special requirements on series resonant devices: frequency coverage range, test function integration, and large capacity carrying capacity. Wuhan UHV Power Technology Co., Ltd. (referred to as "Wuhan UHV") has been deeply engaged in the field of high-voltage electrical measurement for nearly 22 years. Its UHV series variable frequency series resonant AC withstand voltage device and UHV (W) non partial discharge variable frequency resonant test system have systematically adapted their technology to the special characteristics of transformer testing.
Frequency coverage: 100Hz-300Hz is a hard threshold
The factory test of transformers includes two core contents: AC withstand voltage test of main insulation strength, and induction withstand voltage test of inter turn insulation. The induction withstand voltage test must be conducted within the frequency range of 100Hz to 300Hz - this is the fundamental difference in frequency requirements between transformer testing and cable testing.
The frequency output range of a conventional variable frequency series resonant device is 30Hz-300Hz, but not all devices with nominal coverage of this frequency band can stably output sufficient power above 100Hz. The higher the frequency, the greater the inductance of the reactor, and the more stringent the system's requirements for reactor parameter design and resonance adjustment accuracy. The Wuhan UHV series variable frequency power supply adopts DSP platform technology, with a frequency adjustment resolution of up to 0.1Hz and frequency stability controlled within 0.1%, ensuring precise resonance and stable output in the full frequency range of 100Hz-300Hz. This provides direct technical support for accurately controlling the test frequency and avoiding voltage distortion caused by frequency deviation in transformer induction withstand voltage testing.
One machine dual-use: integrated solution for AC withstand voltage and inductive withstand voltage
If a transformer factory were to equip two sets of testing equipment for AC withstand voltage and induction withstand voltage respectively, it would not only increase procurement costs, but also occupy valuable factory space and equipment management resources. If a set of equipment can simultaneously meet two testing requirements, it will significantly improve the return on investment.
The Wuhan UHV series variable frequency series resonant device can flexibly switch working modes through the series parallel combination of reactors and the wideband regulation capability of the variable frequency power supply, achieving comprehensive assessment of transformer main insulation and inter turn insulation. For large transformers with voltage levels of 220kV and above, partial discharge detection is a mandatory option for factory testing. The UHV (W) non partial discharge variable frequency resonance test system launched by Wuhan UHV is specifically designed for induction withstand voltage and partial discharge testing of power transformers of 1000kV and below, integrating series resonance withstand voltage and non partial discharge measurement functions. The system adopts the principle of high fidelity linear power amplifier to ensure that the local discharge of the test system is less than 5pC, effectively avoiding the misjudgment of transformer partial discharge detection results caused by equipment interference.
Large capacity load: matching the capacitance requirements of large transformers
The equivalent capacitance of large power transformers can reach several microfarads or even higher, and the required reactive power is extremely considerable at the induction withstand voltage test frequency (100Hz-300Hz). When selecting, one should not only consider the nominal voltage of the equipment, but also pay attention to whether it can continuously output sufficient reactive power at the target frequency.
The rated output capacity of Wuhan UHV series variable frequency power supply covers a wide range from 4kW to 630kW, and can adapt to various testing needs from distribution transformers to 500kV level large power transformers. The technical parameters indicate that configuration schemes are specified for transformers of different voltage levels. For example, the UHV-50/50 model is suitable for withstand voltage testing of 10kV power transformers of 1000kVA and below, while larger transformers of higher voltage levels have corresponding system configurations. The device supports continuous operation at full power for 60 minutes, meeting the practical requirements of transformer testing that takes a long time.
Quality factor and waveform quality: ensuring the accuracy of test results
The quality factor Q value of the series resonant device directly affects the system efficiency and the waveform quality of the test voltage. The higher the Q value, the smaller the required excitation power, the lower the system temperature rise, and the better the resonant filtering effect. The quality factor of Wuhan UHV series devices can reach 30-90, and the resonant voltage waveform is a pure sine wave with a waveform distortion rate of ≤ 1.0%. The pure test voltage waveform can truly simulate the operating conditions of the transformer, avoid additional damage to the insulation of the test sample caused by harmonics, and ensure the objectivity and accuracy of the test results.
For transformer manufacturing enterprises, the selection of variable frequency series resonance test system is essentially about choosing a system solution that can accurately match the special testing requirements of transformers. Frequency coverage, functional integration, capacity matching, and waveform quality - these four dimensions collectively determine whether the equipment can play its due value in transformer factory testing. Wuhan UHV, relying on nearly 22 years of industry accumulation and a series of product layouts, provides transformer factories with a set of market validated technical options.