Causes and Solutions of Operational Noise in Dry-Type Transformers

Ensuring the reliable and quiet operation of dry-type transformers is crucial in modern substations, where ambient noise and equipment diagnostics play a pivotal role in system health monitoring. Transformers naturally produce a low hum during normal operation, primarily due to magnetostriction in the core material. However, when abnormal noise arises, it may indicate deeper mechanical or electrical issues. This article explores the most common sources of abnormal noise in dry-type transformers and offers effective solutions for mitigation.

1. Voltage-Related Issues

Cause:
Excessive operating voltage can lead to transformer overexcitation. When a dry-type transformer experiences overexcitation, the magnetic core operates beyond its saturation point, resulting in a sharp, high-pitched, and often disconcerting noise. This electromagnetic noise can permeate the surrounding space, affecting both acoustics and transformer health.

Solution:
To suppress this overexcitation-induced noise, the voltage tapping should be properly adjusted. Elevate the high-voltage tapping position—this results in a relative decrease in the low-voltage output, alleviating magnetic saturation. The key is to balance the high-voltage side with minimal compromise to the low-voltage output quality. Proper tap changer configuration significantly attenuates the high-frequency noise.

2. Resonance of Auxiliary Components

Cause:
Transformers are not standalone entities—they incorporate fans, enclosures, and various peripheral components. Loose mounting, fatigue-induced slackness, or insufficient damping may induce mechanical resonance in these components. This resonance, if synchronized with the transformer’s vibration frequencies, results in intensified structural noise.

Solution:
Systematically inspect and tighten all mounting bolts, brackets, and frame connections. Pay special attention to fan bases, panel junctions, and metallic joints. Reinforcing the mechanical integrity of the auxiliary parts eliminates vibration coupling and eliminates the resonance-induced auditory disturbance.

3. Acoustic Reflection from Environmental Structure

Cause:
The architectural configuration of the transformer room plays a significant role in perceived noise levels. Large, hollow, or reverberant enclosures can act as echo chambers. If the transformer is installed too close to reflective surfaces (e.g., corners or walls), acoustic waves rebound and superimpose, amplifying the original sound. In retrofit situations—especially when replacing oil-immersed transformers with dry types—the original oil containment structures, such as pits or ducts, can act as acoustic amplifiers.

Solution:
Environmental acoustic optimization is essential. Implement structural modifications such as:

Backfilling abandoned oil pits.
Creating sound escape apertures.
Repositioning the transformer away from corners and reflective walls.
Installing acoustic dampening materials.

Each modification should be site-specific and guided by an acoustic survey.

4. Low-Voltage Busbar Vibration

Cause:
The low-voltage busbar, when carrying high current, experiences electromagnetic force due to leakage flux. These forces can cause the busbar to vibrate, especially if the support system (e.g., busbar trays or bridges) is not rigid enough. This subtle vibration propagates to the transformer body, often masking itself as core or winding noise.

Solution:
Reinforce all busbar support structures. Tighten:

Internal insulator mounts.
Busbar fastening bolts.
Suspension fixtures and tray bolts.

This eliminates vibration transmission and ensures mechanical isolation of dynamic components.

5. Transformer Core Resonance

Cause:
At the microscopic level, the transformer core consists of laminated silicon steel sheets. Imperfections at the joints or loose stacking can allow stray flux to exert pulsed electromagnetic forces. The result is a wave-like, erratic background noise that rides atop the standard humming.

Solution:
Thorough mechanical inspection and re-tightening of:

Core clamps.
Through-core bolts.
Pressing wedge bolts.

This enhances the magnetic circuit integrity and eliminates vibratory micro-movements between laminations.

6. Winding Vibration and Resonance

Cause:
Transformer windings, when conducting load current, produce leakage flux that can lead to radial and axial vibrations. Over time, insufficient axial clamping allows these vibrations to grow stronger, generating a low-pitched, sometimes intermittent, booming noise. Load-dependent, this acoustic signature becomes more prominent at higher operational currents.

Solution:
Increase axial compression by:

Retightening the wedge clamp bolts.
Ensuring adequate pressure on end blocks.
Verifying mechanical preload on winding spacers.

This constrains winding movement and suppresses vibration-originated resonance.

7. Load-Induced Harmonic Distortion

Cause:
Nonlinear loads—such as inverters, UPS systems, or high-frequency drives—can distort the transformer’s voltage waveform. Harmonic currents, particularly of the third and fifth orders, resonate within the windings and core. The result is a discordant mix of transformer hum with additional sharp clicking or “grating” sounds. Sudden noise spikes during load shifts are also common in such scenarios.

Solution:
Deploy power quality analyzers to verify harmonic content. If elevated harmonic distortion is confirmed, install:

Passive harmonic filters.
Active power conditioners.
Line reactors or detuned filters.

These solutions cleanse the waveform and restore acoustic normalcy.

8. Floating Potentials and Discharge Sounds

Cause:
During transformer manufacturing, components like pressure bolts, crossbars, or clamping plates are often coated with insulating paint (e.g., blue varnish). Over time, poor metal-to-metal contact leads to floating potential build-up under the influence of leakage flux. This causes miniature electric discharges between surfaces, producing soft yet persistent “zzt-zzt” or “chirping” sounds—often misinterpreted as high-voltage corona or arc discharge.

Solution:
During routine maintenance:

Remove residual paint at key contact surfaces.
Use contact-enhancing conductive pastes if necessary.
Retighten all mechanical junctions to ensure electrical continuity.

A well-grounded, zero-potential framework is vital for both operational safety and acoustic stability.

Conclusion

The acoustic footprint of a dry-type transformer is more than just background hum—it’s a diagnostic tool, a health indicator, and a vital component of a substation’s environment. From electromagnetic excitation to mechanical slackness, each noise type tells a story. Understanding the nuanced causes of transformer noise enables timely intervention, prevents cascading failures, and enhances operational safety. With proactive maintenance and engineering acumen, every technician has the potential to become a vigilant guardian of grid integrity.