With the rapid development of the global power industry, various transformers have been widely used, among which dry-type distribution transformers are particularly prominent. Due to their advantages of safety, flame retardancy and easy maintenance, products such as dry power transformer and 2500 kva dry type transformer are widely applied in commercial residential buildings. However, since the iron core is exposed to the air, noise has become a common problem. With the improvement of users' environmental awareness, complaints about excessive noise of transformers on site have gradually increased, and the noise level is often much higher than the factory test data of the manufacturer. Based on rich on-site handling experience, JINSHANMEN TECHNOLOGY CO., LTD summarizes and analyzes the causes of dry-type transformer noise, hoping to provide valuable references for the industry. The company mainly produces oil immersed power transformers, dry-type power transformers, oil immersed three-dimensional coiled power transformers, dry-type three-dimensional coiled power transformers, mining explosion-proof dry-type transformers, mining explosion-proof mobile substations, amorphous alloy power transformers, on load capacity regulating power transformers, locomotive dry-type transformers, as well as prefabricated substations, modular substations, wind energy box type substations, high and low voltage switchgear and other transmission and distribution equipment.
1. Noise Sources
Specifically, the noise of transformers comes from three main sources: the iron core, the winding, and the cooler. That is to say, the total noise is caused by no-load operation, load operation and the cooling system. For dry power transformer, especially 2500 kva dry type transformer, the noise generation mechanism is basically the same, but the noise amplitude may vary with the capacity and structure.
The reason for the noise generated by the iron core is that the silicon steel sheets composing the iron core will undergo slight changes, namely magnetostriction, under the action of the alternating magnetic field. Magnetostriction makes the iron core vibrate periodically with the change of the excitation frequency. The noise of the iron core is caused by the magnetostrictive deformation of the iron core and the electromagnetic force in the winding, oil tank and magnetic shield.
The reason for the vibration of the winding is that the current in the winding generates electromagnetic force, and the leakage magnetic field can also cause the vibration of structural parts. The electromagnetic noise is caused by the longitudinal vibration of the iron core laminations induced by the magnetic field. The amplitude of this vibration is related to the magnetic flux density in the iron core laminations and the magnetic properties of the iron core material, but has little to do with the load current. The electromagnetic force (and vibration amplitude) is proportional to the square of the current, while the emitted sound power is proportional to the square of the vibration amplitude.
2. Causes and Solutions
2.1 Voltage Issues
Cause: High voltage will cause over-excitation of the transformer, making the noise louder and sharper, which directly and seriously affects the noise of the transformer. For 2500 kva dry type transformer, over-excitation caused by high voltage is more likely to lead to obvious noise increase due to its large capacity.
Judgment method: First, check the low-voltage output voltage. Do not rely on the voltmeter on the low-voltage cabinet, as it only serves as an indicator. A more accurate multimeter should be used for measurement.
Solution: At present, the 10kV voltage in cities is generally on the high side. According to the low-voltage side output voltage, the tap position should be adjusted to the appropriate gear. On the premise of ensuring the quality of low-voltage power supply, try to adjust the high-voltage tap upward (to reduce the low-voltage output voltage), so as to eliminate the over-excitation phenomenon of the dry power transformer and reduce its noise at the same time.
2.2 Resonance of Fans, Enclosures and Other Components
Cause: Resonance of fans, enclosures, and other components will generate noise, which is generally mistaken for transformer noise. This problem is also common in dry power transformer operation.
Judgment method: 1) Enclosure: Press the aluminum plate (or steel plate) of the enclosure with your hand to see if the noise changes. If it changes, it indicates that the enclosure is resonating. 2) Fans: Use a dry long wooden stick to prop up the enclosure of each fan to see if the noise changes. If it changes, it indicates that the fan is resonating. 3) Other components: Use a dry long wooden stick to prop up each component of the transformer (such as wheels, fan brackets, etc.) to see if the noise changes. If it changes, it indicates that the component is resonating.
Solution: 1) Check if the aluminum plate (or steel plate) of the enclosure is loose. It may be deformed by stepping during installation. It is necessary to tighten the screws of the enclosure, fix the aluminum plate of the enclosure, and correct the deformed parts. 2) Check if the fan is loose. It is necessary to tighten the fixing bolts of the fan, and place a small piece of rubber between the fan and the fan bracket, which can solve the fan vibration problem. 3) If the transformer components are loose, they need to be fixed.
2.3 Installation Issues
Cause: Poor installation will aggravate transformer vibration and amplify transformer noise. For large-capacity transformers such as 2500 kva dry type transformer, installation quality has a more significant impact on noise.
Judgment method: 1) The transformer foundation is not firm or flat (one corner is suspended), or the bottom plate is too thin. 2) Erecting the transformer with channel steel will increase noise.
Solution: 1) The installation unit shall transform the original installation method. 2) Install shock-absorbing rubber pads under the transformer trolley, which can solve part of the noise problem.
2.4 Impact of Installation Environment
Cause: The operating environment affects the noise of the transformer. An unfavorable environment can increase the noise of the dry power transformer by 3dB ~ 7dB.
Judgment method: 1) The transformer room is large and empty, with no other equipment, resulting in echo. 2) The transformer is too close to the wall, less than 1 meter. If the transformer is placed at a corner, the noise reflected by the wall overlaps with the transformer noise, increasing the noise. 3) If an oil-immersed transformer was originally used and then replaced with a dry-type transformer, the noise of the dry-type transformer will be affected. The reason is that the original oil-immersed transformer room is relatively narrow, with an oil leakage room and an oil leakage hole, making the transformer seem to be placed on a speaker.
Solution: Properly install some sound-absorbing materials indoors.
2.5 Vibration of Busbar Bridge
Cause: Due to the large current passing through the parallel busbars, the busbars vibrate due to the leakage magnetic field. The vibration of the busbar bridge will seriously affect the noise of the dry power transformer, increasing the noise by more than 15dB. This problem is difficult to judge, and general users and installation units will mistakenly think it is the noise of the transformer itself, even for 2500 kva dry type transformer.
Judgment method: 1) The noise changes with the load. 2) Use a wooden stick to firmly prop up the busbar bridge. If the noise changes, it is considered that the busbar bridge is resonating. 3) If the busbars vibrate inside the bridge, propping with a wooden stick will not work. It is necessary to open the cover plate of the busbar bridge and check whether the busbars are fixed properly.
Solution: 1) The main way is to destroy the resonance conditions of the busbar bridge, either tightening or loosening the hanger screws. 2) Open the cover plate of the busbar bridge and fix the busbars properly. 3) Use flexible connections for low-voltage outgoing lines. 4) Invite the manufacturer of the busbar bridge to solve the problem.
Conclusion
The noise problem of dry-type transformers such as dry power transformer and 2500 kva dry type transformer is closely related to voltage, installation, environment and other multiple factors. Correctly identifying the causes and taking targeted solutions can effectively reduce noise and improve the operating environment. JINSHANMEN TECHNOLOGY CO., LTD has rich experience in the research, development and production of dry-type transformers. If you have more questions about transformer operation and maintenance, you can consult us at any time.