What is the impact of harmonics on an Oil Immersed Power Transformer?

Harmonics have become a significant concern in the operation of electrical power systems, especially when it comes to equipment like oil immersed power transformers. As a leading supplier of Oil Immersed Power Transformer, I have witnessed firsthand the impact that harmonics can have on these critical components. In this blog post, I will delve into the various effects of harmonics on oil immersed power transformers, explore the causes of harmonics, and discuss strategies to mitigate their impact.

Understanding Harmonics

Harmonics are sinusoidal voltages or currents with frequencies that are integer multiples of the fundamental frequency (usually 50 or 60 Hz). In an ideal power system, the voltage and current waveforms are pure sinusoids at the fundamental frequency. However, the increasing use of non - linear loads such as variable - speed drives, power electronics, and fluorescent lighting has introduced harmonics into the power system. These non - linear loads draw current in a non - sinusoidal manner, which distorts the voltage and current waveforms.

Impact of Harmonics on Oil Immersed Power Transformers

1. Increased Core Losses

One of the most significant impacts of harmonics on oil immersed power transformers is the increase in core losses. The core losses in a transformer consist of hysteresis losses and eddy current losses. Hysteresis losses occur due to the reversal of magnetization in the core material, while eddy current losses are caused by the circulating currents induced in the core.

Harmonics increase the core losses because they cause the magnetic flux in the core to vary more rapidly. The higher - frequency harmonics result in a greater number of magnetization reversals, which leads to an increase in hysteresis losses. Additionally, the eddy current losses are proportional to the square of the frequency. As the frequency of the harmonics is higher than the fundamental frequency, the eddy current losses increase significantly. This increase in core losses leads to higher operating temperatures in the transformer, which can reduce the lifespan of the insulation and other components.

2. Increased Copper Losses

Copper losses in a transformer are due to the resistance of the windings. When harmonics are present in the current, the effective resistance of the windings increases. This is because the skin effect and the proximity effect become more pronounced at higher frequencies. The skin effect causes the current to flow near the surface of the conductor, increasing the effective resistance. The proximity effect, on the other hand, is the interaction between adjacent conductors, which also increases the resistance.

As a result of the increased resistance, the copper losses in the transformer windings increase. This not only leads to higher power consumption but also generates more heat, which can further degrade the insulation and other components of the transformer.

3. Voltage Distortion

Harmonics can cause voltage distortion in the power system. When the voltage waveform is distorted, it can affect the performance of other electrical equipment connected to the same system. In the case of oil immersed power transformers, voltage distortion can lead to uneven distribution of the magnetic flux in the core. This can cause local overheating in the core and windings, which can damage the insulation and reduce the efficiency of the transformer.

4. Resonance

Harmonics can also cause resonance in the power system. Resonance occurs when the natural frequency of a circuit matches the frequency of the harmonics. In an oil immersed power transformer, resonance can lead to excessive currents and voltages, which can damage the transformer and other equipment in the system. Resonance can also cause mechanical vibrations in the transformer, which can lead to premature failure of the transformer.

5. Reduced Transformer Capacity

Due to the increased losses and the potential for overheating caused by harmonics, the effective capacity of an oil immersed power transformer is reduced. A transformer that is designed to operate at a certain load under normal conditions may not be able to handle the same load when harmonics are present. This means that additional transformers may be required to meet the power demand, which increases the cost of the power system.

Causes of Harmonics in the Power System

As mentioned earlier, non - linear loads are the primary cause of harmonics in the power system. Some common non - linear loads include:

• Variable - speed Drives (VSDs): VSDs are widely used in industrial applications to control the speed of motors. They use power electronics to convert the AC power to DC and then back to AC at a variable frequency. This process introduces harmonics into the power system.
• Power Electronics: Devices such as rectifiers, inverters, and switch - mode power supplies are all non - linear loads. They draw current in a non - sinusoidal manner, which generates harmonics.
• Fluorescent Lighting: Fluorescent lamps use electronic ballasts, which are non - linear loads. They also contribute to the generation of harmonics in the power system.

Mitigation Strategies

To mitigate the impact of harmonics on oil immersed power transformers, several strategies can be employed:

1. Filtering

Harmonic filters can be used to reduce the level of harmonics in the power system. There are two main types of harmonic filters: passive filters and active filters. Passive filters consist of capacitors, inductors, and resistors and are designed to provide a low - impedance path for the harmonics. Active filters, on the other hand, use power electronics to inject currents that are equal and opposite to the harmonic currents, thereby canceling them out.

2. Transformer Design

Transformers can be designed to be more resistant to harmonics. For example, using a larger core size can help to reduce the core losses caused by harmonics. Additionally, using conductors with a larger cross - sectional area can reduce the copper losses due to the skin effect and the proximity effect.

3. Load Management

By managing the non - linear loads in the power system, the level of harmonics can be reduced. This can be done by using power factor correction devices, limiting the use of non - linear loads during peak demand periods, and ensuring that the non - linear loads are properly sized and installed.

Conclusion

Harmonics have a significant impact on oil immersed power transformers, including increased core and copper losses, voltage distortion, resonance, and reduced transformer capacity. As a supplier of Oil Immersed Power Transformer, we understand the importance of addressing the issue of harmonics to ensure the reliable and efficient operation of our transformers.

If you are in the market for a Three Phase Oil Transformer or a Station Service Transformer, we are here to provide you with high - quality products and solutions. Our team of experts can help you select the right transformer for your application and provide guidance on how to mitigate the impact of harmonics. Contact us today to start a discussion about your transformer needs and to explore the best solutions for your power system.

References

• J. Arrillaga, N. R. Watson, and P. S. Bodger, Power System Harmonics, John Wiley & Sons, 1985.
• C. L. Sullivan, “Harmonics in power systems: causes, effects, and mitigation,” IEEE Power Engineering Review, vol. 20, no. 10, pp. 27 - 31, 2000.
• IEEE Standard 519 - 2014, IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems.