Transformers are the backbone of modern power systems. In China, they are widely applied in urban distribution networks, subway systems, factories, and data centers. While many users think of a transformer as a single 'iron box' for stepping voltage up or down, it is in fact an assembly of precisely engineered components. Each part is essential for efficiency, safety, and long-term reliability.
At TAILI ELECTRIC, we combine practical Chinese manufacturing experience with international IEC standards. Here is a comprehensive guide to the major transformer components, organized in a way that aligns with both domestic practice and global buyer expectations.
1. Core
In The transformer core provides the magnetic path and largely determines no-load losses and efficiency class.
-CRGO (Cold Rolled Grain-Oriented Steel):
Widely used in China and worldwide, CRGO steel features a grain structure aligned in one direction, which significantly reduces hysteresis loss and improves efficiency.
Advantages: low core loss, high efficiency, mature supply chain.
-Amorphous Alloy Core:
Made of metallic glass with a disordered atomic structure.
No grain boundaries, leading to extremely low hysteresis loss.
Core loss can be 30–40% lower than CRGO under the same conditions.
Advantages: excellent energy-saving performance, ideal for data centers, metro systems, and green energy projects.
Limitation: higher cost, more brittle material, requiring careful handling.
At TAILI ELECTRIC, we primarily use high-grade CRGO steel for most distribution transformers, and we also offer amorphous alloy core transformers for customers who prioritize ultra-low losses and energy efficiency.s.
2. Windings
Windings form the electrical circuit of the transformer.
- Copper: higher conductivity, lower loss.
- Aluminum: cost-effective, widely used in rural and urban projects.
The winding insulation method (enameled wire, paper-covered conductor, etc.) affects long-term safety and durability.
3. Insulation System
The insulation system prevents dielectric breakdown and ensures safe operation.
- Oil-immersed transformers: use mineral oil or ester oil, combined with solid insulation such as pressboard and paper.
- Dry-type transformers: use epoxy resin or Nomex paper.
Insulation guarantees phase-to-phase, phase-to-ground, and turn-to-turn protection, directly impacting transformer lifespan.
4. Bushings & Terminals
Bushings provide an insulated path for conductors to pass through the transformer tank, while terminals are the external connection points.
- Low-voltage side: epoxy resin or silicone rubber bushings.
- High-voltage side: porcelain bushings remain dominant, with composite bushings becoming popular.
High-quality bushings and terminals prevent creepage, flashover, and oil leakage.
5. Tap Changer & Winding Taps
Tap changers adjust the number of turns in the winding to regulate output voltage.
- On-Load Tap Changer (OLTC): used in 110 kV, 220 kV transformers, adjustable under load.
- Off-Circuit Tap Changer (NLTC): used in M/V distribution transformers, adjustable only when de-energized.
- Winding taps provide fixed adjustment points, typically ±2×2.5% or ±5%.
This ensures stable voltage supply under varying grid conditions.
6. Cooling System
Cooling maintains safe operating temperatures.
- ONAN (Oil Natural, Air Natural): natural convection cooling.
- ONAF (Oil Natural, Air Forced): forced-air cooling with fans for large-capacity units.
Radiators, tubes, and fans are common cooling elements. In China's hot summers, fan reliability is a key factor.
7. Oil Tank & Enclosure
The oil tank contains the core and windings, filled with insulating oil for cooling and dielectric strength. The enclosure also provides mechanical protection.
- Painted or powder-coated steel is standard.
- For coastal or humid regions, hot-dip galvanizing or multi-layer anti-corrosion coatings are recommended.
Buyers often focus on whether the enclosure can resist corrosion and leakage for 20+ years.
8. Conservator Tank
A conservator tank is mounted above the main tank in larger transformers (≥ 2500 kVA).
- It balances oil volume changes due to temperature.
- It allows connection of monitoring devices such as oil level indicators and Buchholz relays.
Smaller distribution transformers in China often use hermetically sealed corrugated tanks instead, for maintenance-free operation.
9. Breather (Silica Gel Breather)
The breather dries incoming air using silica gel, preventing moisture from entering the oil. It is a critical accessory for maintaining oil quality in conservator-type transformers.
10. Protection Devices
- Pressure Relief Valve / Explosion Vent: releases pressure during internal faults, preventing tank rupture.
- Buchholz Relay: detects internal faults by monitoring gas accumulation between the main tank and conservator.
These are standard in IEC specifications and in Chinese utility tenders.
11. Accessories & Monitoring Devices
Common accessories include:
- Oil level indicators.
- Temperature gauges (top oil, winding temperature).
- Gas detectors and monitoring relays.
These devices help operators maintain safe and efficient operation.
Conclusion
A transformer is far more than a metal box—it is the integration of specialized components working together to ensure safe and efficient power delivery. By understanding each part, project owners and engineers can make informed decisions when selecting the right solution.
At TAILI ELECTRIC, we deliver oil-immersed and dry-type transformers engineered to meet both domestic requirements and international IEC standards, providing customers with reliability, safety, and long-term performance.
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