Introduction
Anyone who has ever come closer to a power transformer will hear a strange buzzing sound, known as a hum. The sound is heard when the power transformer is in operation. Is this sound normal or a malfunction that we should be aware of?
In this brief post, we will discuss what the hum is and what causes it. Additionally, some emerging technologies for noise reduction in power transformers are also being explored.
Why do Power Transformers Hum?
The humming sound in power transformers is primarily caused by a physical phenomenon known as magnetostriction. This is a property of ferromagnetic materials, such as steel, used in transformer cores. The core and windings (either copper or aluminum) are key components of the power transformer. The core is typically made of a stack of laminations of high-permeability grain-oriented steel sheets.
But what is Magnetostriction in a Power Transformer?
Whenever current flows through the winding, a magnetic field is created around the core. When a magnetic material is subjected to a magnetic field, its dimensions change slightly. This effect is referred to as magnetostriction. In transformers, the alternating magnetic field causes the core to expand and contract twice every cycle (once for each half-cycle).
Frequency of Hum (f_hum):
f_hum = 2 x f
So, at f = 50 Hz → f_hum is 100 Hz
And for f = 60 Hz → f_hum is 120 Hz
This physical vibration leads to mechanical oscillations, which generate audible sound waves perceived as a hum. The humming sound of power transformers is commonly heard near large transformers, particularly during quiet periods, such as nighttime, or even in substation enclosures or indoors.
Figure 1 and 2 shows how humming occurs and the measurement of the displacement of the core by micrometer, respectively.
How Harmful Could a Hum Be?
Generally, the humming sound is harmless by itself, except in some scenarios. The hum may not pose a health hazard under normal operating conditions. However, the sound could be annoying or disruptive in proximity to the neighborhood due to its persistent humming. It is common to consider the humming sound as a pollutant in industrial settings due to the discomfort to workers. This effect has the potential to reduce workers’ productivity.
While the hum itself is not dangerous, any unusual increase in sound magnitude or changes in the sound may suggest issues such as loose structural components, deteriorating insulation, or other mechanical wear, which should be inspected to prevent further complications.
As such, manufacturers and designers of power transformers need to consider noise reduction, as well as any relevant regulations, when installing the power in the area where it may be used. There is a need to comply with the strict industrial standards, national codes, or regulations of the authority having jurisdiction.
How do Engineers Reduce the Humming of Power Transformers?
Since the impacts of humming power transformers have been identified, the next important concern is how to minimize this effect.
We can achieve a reduction in humming through mechanical (such as the use of vibration-absorbing mounts or pads), electrical (such as the use of grain-oriented steel that produces less vibration, ensuring a balanced magnetic field, and reduction of flux leakage), and routine maintenance checks (like tightening loose bolts and correcting misalignment of parts).
Sophisticated software such as Simcenter MAGNET is used to perform electromagnetic field simulations and predict the magnetostriction of the core.
Emerging Technologies for Power Transformer Noise Reduction
As the world of power transformers continues to evolve, challenges are primarily addressed by engineers, researchers, industrial players, and manufacturing R&D teams. To understand the fundamentals of the grid and identify potential areas for improvement, explore power engineering here.
Advanced Noise Canceling Systems
This concept represents one of the most innovative approaches to reducing transformer noise, utilizing active noise cancellation technology. It is similar to the approach used in noise-canceling headphones. This method employs microphones to detect the transformer hum in real-time. Then, speakers emit sound waves that are the exact opposite (anti-phase) of the detected hum. When these waves interact, they cancel each other out, significantly reducing the audible noise. This technology (Sonobex NoiseTrap Active) is still being refined for industrial use, but it holds great promise for environments where noise reduction is critical, such as near residential areas, hospitals, or schools.
Advanced Materials Under Development
Grain-oriented silicon steel is the traditional material for making the transformer’s core. This material, despite being widely used, poses the losses and audible sounds during operations. However, recent research into new core materials has led to the development of transformer cores made from amorphous metals and nanocrystalline alloys.
These materials exhibit very low magnetostriction, which means they undergo much less physical deformation when exposed to a magnetic field. As a result, they vibrate significantly less, producing a much lower hum.
Additionally, these materials have lower core losses, making transformers more energy-efficient. Though they are more expensive than traditional silicon steel, the long-term benefits in noise reduction and energy savings make them a compelling choice for new transformer designs.
Artificial Intelligence, Acoustic Design, and Monitoring
Artificial intelligence is revolutionizing the way transformers are monitored and maintained. With the help of acoustic sensors, engineers can continuously record and analyze the sound profile of a transformer in real-time.
AI algorithms then detect subtle changes in the hum’s frequency, intensity, or pattern, which can indicate wear, mechanical looseness, or other potential issues before they become serious.
This predictive maintenance approach helps utilities avoid unexpected failures and costly downtime while also ensuring that noise remains within acceptable limits.
Digital Design Tools
Leading engineering firms now use advanced simulation software to design quieter and more efficient transformers from the start. Through 3D modeling and Finite Element Analysis (FEA), they can accurately predict how different core shapes and material choices will behave under electrical load.
These tools enable designers to identify and minimize vibration hotspots, thereby optimizing the magnetic flux path to achieve a uniform distribution of forces.
By refining the transformer’s geometry and mechanical layout during the design stage, it has become significantly possible to reduce vibration resulting in hum, making these tools essential in modern transformer engineering.
Summary
Power transformers are critical equipment in our grid, and without them, it is practically impossible to transmit electricity over longer distances. Electricity utilization is on the perpetual rise, and so is the demand for power transformers. However, the humming noise of the power transformer causes discomfort to populations in urban and industrial areas.
In this post, we have looked at the cause of humming in power transformers (magnetostriction). Moreover, some modern advancements have been made in resolving or attenuating the nuisance sounds. Watch the insightful video below that summarizes this post.
2 Responses
Why frequency at Both ends of transformer remains the same? If it is 50 we receive 50 or if it is 60 we receive 60.
Under which mechanism this is happening?
Hello Muhammad, thanks for your questions.
As you may be aware, the working principle of the power transformer is based on Faraday’s Law of Electromagnetic Induction. The voltage supplied at the primary winding induces alternating magnetic flux in the core. This same core links the secondary winding.
As such, the frequency at both ends of a transformer windings remains the same because the induced electromotive force (EMF) in the secondary winding is produced by the same time-varying magnetic flux created by the primary, as governed by Faraday’s Law of electromagnetic induction.
This is one of the best features of transformers that makes them very easy to transport power at different voltages across the grid while maintaining the same grid frequency. If the frequencies were different, converter stations would be needed.
For instance, if you want to interconnect a 50Hz grid to a 60Hz system, there must be a frequency-converting substation (commonly referred to as a frequency-conversion interface) to integrate the dissimilar power networks (in terms of frequency). A back-to-back High-Voltage Direct Current (HVDC) system is implemented, where 50Hz AC is converted to DC via rectifiers, and then the DC is inverted to 60Hz AC on the other side.
Kindly let me know if this helps. Thank you, again for the question.