What is a no-excitation voltage-regulating oil-immersed power transformer

In the power system, transformers, as the core equipment for voltage conversion and power transmission, play an irreplaceable role. Among them, non-excitation voltage-regulated oil-immersed power transformers are widely used in distribution networks, industrial enterprises, and urban and rural power supply systems due to their advantages of simple structure, reliable operation, and moderate cost. This article will comprehensively analyze this type of transformer from the aspects of working principle, structural characteristics, voltage regulation mechanism and application scenarios.

I. What is a non-excitation voltage regulating oil-immersed power transformer?

The non-excitation voltage-regulating oil-immersed power transformer is a transformer that adjusts the output voltage by changing the tap changer position when the power supply is cut off and there is no load. Its windings are immersed in insulating oil, and the oil is used as the insulating medium and cooling medium. The so-called "no excitation" means that the voltage regulation operation must be performed after the transformer exits operation and is powered off.

II. Working principle

This type of transformer works based on the law of electromagnetic induction. When alternating current is supplied to the primary side, alternating magnetic flux is generated in the iron core, thereby inducing an electromotive force on the secondary side. By adjusting the tap position of the primary winding (that is, changing the turns ratio), the secondary side voltage can be fine-tuned to compensate for voltage deviations caused by grid voltage fluctuations or load changes.

III. Main structural components

IV. Voltage regulating method and range

The voltage regulation of the non-excitation voltage regulating transformer is generally set on the main high voltage side. The common voltage regulation range is ±5% or ±2×2.5% of the rated voltage, with a total of 3 or 5 levels. For example, a 10kV/0.4kV transformer can be selected through a tap changer:

• +5% (10500V)

• Rated (10000V)

• -5% (9500V)

Voltage regulating operations must strictly abide by safety regulations such as power outages, power inspections, and grounding wires, and must be performed by professionals.

V. Product Features and Advantages

1. Simple structure, easy maintenance: Compared to on-load tap-changing transformers, excitation-free tap-changing transformers eliminate complex electric mechanisms and control circuits, resulting in lower failure rates.

2. High operational reliability: No risk of arc switching, suitable for applications with low requirements for continuous power supply.

3. Cost-effective: Both manufacturing costs and maintenance expenses are lower than those of on-load tap-changing transformers.

4. Strong adaptability: Suitable for locations where grid voltage is relatively stable and frequent voltage regulation is not needed.

VI. Typical Application Scenarios

• Rural distribution networks: Load variations are minimal, and seasonal voltage regulation can meet needs.

• Medium and small industrial and mining enterprises: Production equipment has moderate requirements for voltage stability.

• Urban residential community substations: Operate in conjunction with substations with fixed voltage levels.

• Temporary construction power supply: Low cost and easy relocation.

VII. Precautions for model selection

1. Capacity matching: Select the appropriate capacity according to the actual load to avoid long-term overload or light-load operation.

2. Voltage level: Confirm whether the rated voltage of the primary side and secondary side meets the local power grid standards.

3. Environmental conditions: Consider the altitude, temperature, humidity and other factors of the installation location, and select a special protection level if necessary.

4. Voltage regulating gears: Determine the required number of gears according to the fluctuation range of the grid voltage.

VIII. Maintenance and Maintenance Points

• Regularly check the withstand voltage value and moisture content of the insulating oil, and filter or replace it if necessary.

• Carry out insulation resistance testing at least once a year.

• Check whether the tap changer contact is good and whether the contacts are ablated.

• Keep the outside of the tank clean to ensure heat dissipation.

• Pay attention to the oil level in the oil conservator and replenish qualified insulating oil in time.

Conclusion

Non-excitation voltage-regulated oil-immersed power transformers occupy an important position in my country's power system with their mature technology, reliable performance and good economy. Although on-load voltage regulation and reactive power compensation technologies have become increasingly popular with the development of smart grids, in a large number of conventional power distribution situations, non-excitation voltage regulation transformers are still a highly cost-effective choice. Correct selection, standardized operation and scientific maintenance will effectively extend its service life and ensure the safe and stable operation of the power system.