The 33rd China International Exhibition on Electric Power Equipment and Technology
Shanghai International Energy Storage Technology Application Expo / Hydrogen Energy Expo
A power transformer is a static electrical device that transfers electrical energy between two or more circuits through electromagnetic induction, stepping voltage up (for transmission) or down (for distribution and end use) while maintaining approximately constant power. Power transformers are the workhorses of the electricity grid, present at every voltage level from generation step-up transformers (stepping generator output from 10–25 kV to 110–1,000 kV for transmission) to distribution transformers (stepping down to 10–35 kV for distribution) to service transformers (stepping down to 220/380 V for end users). China is the world's largest transformer market, with domestic manufacturers including TBEA, CHINT, and Baoding Tianwei supplying both domestic and international markets. Transformer technology is evolving with the development of smart transformers incorporating sensors, communication, and power electronics.
5 Key Questions About Power Transformer
Power transformers are classified by several criteria: by voltage level (distribution transformers below 35 kV, power transformers 35–750 kV, UHV transformers above 750 kV); by cooling method (oil-immersed with ONAN/ONAF/OFAF cooling, or dry-type with AN/AF cooling); by winding configuration (two-winding, three-winding, or autotransformer); by application (generator step-up, transmission, distribution, traction, furnace, rectifier); and by phase (single-phase or three-phase). Oil-immersed transformers dominate at medium and high voltage, while dry-type transformers are preferred for indoor, fire-sensitive, or environmentally sensitive applications.
Modern power transformers are among the most efficient electrical machines, with efficiencies of 98–99.7% at rated load. Losses consist of no-load losses (core losses due to hysteresis and eddy currents in the magnetic core, constant regardless of load) and load losses (copper losses in the windings, proportional to the square of current). Energy-efficient transformer designs use amorphous metal cores (reducing no-load losses by 70–80% compared to conventional silicon steel) or high-grade grain-oriented silicon steel with optimised core geometry. China's GB 20052 efficiency standard mandates minimum efficiency levels for distribution transformers, driving adoption of energy-efficient designs.
A smart transformer (also called a solid-state transformer or power electronic transformer) replaces the traditional electromagnetic transformer with a combination of high-frequency transformers and power electronics, enabling active voltage regulation, power quality control, and bidirectional power flow management. Smart transformers can provide DC outputs for data centres and EV charging, integrate distributed energy resources, and provide reactive power compensation — functions impossible with conventional transformers. While still more expensive than conventional transformers, smart transformers are being deployed in demonstration projects and are expected to become commercially competitive as power electronics costs decline.
The main causes of transformer failure are: insulation degradation due to thermal ageing, moisture ingress, or partial discharge; overloading causing excessive temperature rise; short-circuit forces damaging windings; lightning and switching surges; and oil contamination or leakage. Preventive measures include dissolved gas analysis (DGA) of transformer oil to detect incipient faults, thermal monitoring, partial discharge measurement, oil quality testing, and load management to avoid sustained overloading. Modern smart transformer monitoring systems continuously analyse multiple parameters to provide early warning of developing faults, enabling planned maintenance rather than emergency replacement.
The integration of large-scale renewable energy is changing transformer requirements in several ways: offshore wind and remote solar farms require large step-up transformers with high reliability and low maintenance requirements; the growth of distributed rooftop solar creates bidirectional power flows in distribution transformers designed for unidirectional flow; EV charging creates new load patterns with high harmonic content; and the replacement of synchronous generators with inverter-based resources reduces system inertia, increasing the rate of change of frequency (RoCoF) and imposing new dynamic requirements on transformer designs. Smart transformers and transformer monitoring systems are key enablers of the energy transition.
Key Takeaways
Power transformers are the backbone of electrical power systems, enabling efficient voltage conversion for transmission and distribution. As China's grid expands and incorporates more renewable energy, demand for advanced transformers with higher efficiency and smart monitoring capabilities continues to grow. EP Shanghai showcases transformer innovations from leading domestic and international manufacturers.
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