6 Questions and Answers about Transformers, Do You Know?

Transformers are one of the most critical components in power systems, widely used in power transmission and distribution, industrial manufacturing, and building electrical systems. How much do you really know about transformers? Let's explore six common questions and their answers to help you understand the basics of transformers.

1. What is a transformer and how does it work?

A transformer is an electrical device that transfers energy between two or more circuits through electromagnetic induction. It consists of a core made of magnetic material and two windings — the primary winding (input side) and the secondary winding (output side). When alternating current flows through the primary winding, it creates a varying magnetic field in the core, which induces a voltage in the secondary winding, allowing for voltage transformation.

2. What types of transformers are there and how are they classified?

Transformers can be categorized based on various criteria:

• By Application: Power transformers, instrument transformers, test transformers, special-purpose transformers;
• By Cooling Method: Dry-type transformers (air-cooled), oil-immersed transformers (oil-cooled);
• By Phase Number: Single-phase transformers, three-phase transformers;
• By Voltage Regulation Method: On-load tap changing (OLTC) transformers, off-circuit tap changers;
• By Structure: Two-winding transformers, three-winding transformers, auto-transformers.

3. How is the capacity of a transformer calculated? What factors should be considered?

Transformer capacity selection should meet load requirements with some margin. The general steps include:

1. Total Load Calculation: Sum up the apparent power (kVA) of all connected equipment;
2. Consider Power Factor: If total active power $P$ and power factor $\cos \phi$ are known:
   $$S=\frac{P}{\cos \phi }$$
3. Apply Safety Factor: Usually 1.2–1.3 to account for unexpected loads or future expansion;
4. Motor Starting Impact: Large motors can cause high inrush currents;
5. Reserve for Future Growth: At least 20% extra capacity is recommended.

4. What is the difference between dry-type and oil-immersed transformers?

Selection depends on installation location, fire safety, heat dissipation, and budget.

5. What key parameters should be considered when selecting a transformer?

In addition to capacity, important technical parameters include:

• Rated Voltage: Must match system voltage levels;
• Short-Circuit Impedance: Affects fault current magnitude and must coordinate with protection devices;
• No-Load and Load Losses: Determines efficiency; energy-efficient models like S11, S13, or amorphous alloy transformers are recommended;
• Insulation Class: F-class (155°C) or H-class (180°C) commonly used;
• Protection Rating (IP): e.g., IP20, IP54 for different environments;
• Voltage Regulation Type: Whether OLTC is needed depends on voltage stability requirements.

6. What maintenance tasks should be performed during transformer operation?

To ensure long-term stable operation, regular maintenance includes:

• Routine Inspection: Check sounds, temperature, and terminal connections;
• Cleaning Dust: Prevent overheating due to dust accumulation;
• Insulation Testing: Measure insulation resistance to assess aging;
• Oil Quality Testing (for oil-immersed only): Monitor moisture content and acidity;
• Ventilation and Heat Management: Ensure proper airflow to avoid thermal stress;
• Operation Data Logging: Maintain records for analysis and preventive maintenance.

Conclusion

As a core component in power systems, the performance of transformers directly affects the safety and economy of the entire system. Through these six questions and answers, we gain a deeper understanding of the basic principles, selection methods, and maintenance practices of transformers. Whether you're a design engineer or a maintenance technician, mastering this foundational knowledge will help improve system reliability and sustainability.