The power transformer serves as a central node in the transmission and distribution of electrical energy, making it a critical component of the power grid. Its reliable operation directly affects the quality of power supplied to users and the overall security of the system. The reliability of a power transformer is not only determined by its design, manufacturing, and material quality, but also significantly influenced by maintenance practices. This document discusses strategies for improving the short-circuit resistance of transformers within power systems.
**I. Overview of Power Transformers**
Electronic power transformers are primarily implemented using power electronics technology. The basic principle involves converting the power frequency signal on the primary side into a high-frequency signal through a power electronic circuit, which is then coupled to the secondary side via an intermediate high-frequency isolation transformer. The signal is subsequently converted back to the original frequency, enabling the transformation of voltage, frequency, and waveform. By controlling the operation of power electronic devices with an appropriate control scheme, the transformer can efficiently convert one form of electrical energy into another. Since the size of the intermediate isolating transformer depends on the core's saturation flux density and temperature limits, increasing the operating frequency improves core utilization, reduces the transformer’s size, and enhances its overall efficiency.
**II. Measures to Improve the Short-Circuit Resistance of Power Transformers**
Ensuring the safe, economical, and reliable operation of a transformer relies on its manufacturing quality, operating environment, and maintenance standards. This chapter explores practical measures to prevent sudden failures during operation and maintenance. Power grids often experience short circuits due to lightning strikes, relay protection malfunctions, or human errors. These events can cause severe damage to transformers. Therefore, efforts should be made to enhance the transformer’s short-circuit resistance from multiple angles.
Statistical data on transformer short-circuit incidents indicate that 80% of cases are due to manufacturing defects, while only about 10% result from operational and maintenance issues. While Chapter 2 focused on design and manufacturing improvements, this chapter emphasizes measures taken during operation and maintenance. During these processes, minimizing short-circuit faults reduces the number of impacts on the transformer, and timely detection of winding deformation helps prevent serious issues.
**(1) Standardized Design and Attention to Coil Manufacturing**
During the design phase, manufacturers must consider not only reducing losses and improving insulation levels but also enhancing mechanical strength and short-circuit resistance. In manufacturing, the use of insulating press plates and shared press plates for high- and low-voltage coils requires advanced techniques. The padding must be compacted, and after processing, each coil undergoes constant pressure drying and height measurement. Coils under the same press plate are adjusted to the same height, and during assembly, hydraulic devices apply the required pressure to meet design specifications. Special attention must be given to the compression of low-voltage coils.
**(2) Conducting Short-Circuit Tests**
The reliability of large transformers depends on their structural design and manufacturing quality. Regular testing during operation helps monitor equipment conditions. Performing short-circuit tests allows identification of weak points and ensures the transformer’s structural strength is carefully designed.
**(3) Using Reliable Relay Protection and Automatic Reclosing Systems**
Short-circuit accidents are inevitable, especially due to misoperations, small animals, or external forces. To minimize damage, reliable DC power supplies for protection systems must be in place. Automatic reclosing after a short-circuit trip can sometimes worsen the situation, so some operators have stopped using it for nearby lines or extended intervals to reduce risks. Testing short-circuit tripped transformers is essential to avoid further damage.
**(4) Active Deformation Testing and Diagnosis**
After experiencing a short-circuit current, windings may deform, even if no immediate damage occurs. This can lead to insulation issues, partial discharges, and potential breakdowns. Active diagnosis of winding deformation helps identify problems early, saving resources and preventing major accidents.
**(5) Strengthening On-Site Inspection and Maintenance**
During installation, strict adherence to manufacturer guidelines is crucial. Operation and maintenance teams must ensure the transformer remains in good condition and take steps to reduce the likelihood of short-circuit faults. Equipping the transformer with a reliable protection system and conducting frequency response tests after a short-circuit trip can help avoid major failures.
In conclusion, a transformer’s ability to withstand short-circuit currents largely depends on its design, manufacturing, and operational management. Transformer short-circuit accidents pose significant risks to the power grid, and effective control measures must be implemented across all aspects to ensure safe and stable operation.
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