Reason and Analysis of Operation Noise of Dry-type Transformer
Writer： Hengfeng you electric Time：2023-04-12 views：times
With the rapid development of the power industry, various transformers are used more and more widely, among which the use of dry-type distribution transformers is particularly significant. Because of its safety, flame retardant, easy maintenance and other characteristics, this product is widely used in commercial buildings. , because the iron core is exposed in the air, the problem that is easy to bring is noise. Transformer noise is an inherent characteristic of transformers during operation, and the relevant national standards have strict sound level limits for them. However, with the improvement of users' awareness of environmental protection, complaints that reflect the excessive noise on the transformer site have gradually increased, and the reflected noise level has also increased. It is also often larger than the factory test data. Based on some on-site processing experience, I have analyzed the following reasons for reference and mutual learning.
1. Voltage problem
Reason: The high voltage will make the transformer overexcited, and the noise will increase and sharpen, which will directly and seriously affect the noise of the transformer. Judgment method: first look at the low-voltage output voltage, not the voltmeter on the low-voltage cabinet. The voltmeter only serves as an indicator, and a more accurate multimeter should be used for measurement.
Solution: The 10kV voltage in the city is generally on the high side. According to the output voltage of the low-voltage side, the tap gear should be placed in the appropriate gear. On the premise of ensuring the quality of low-voltage power supply, try to increase the high-voltage tap (low-voltage output voltage is reduced), so as to eliminate the over-excitation phenomenon of the transformer and reduce the noise of the transformer at the same time.
2. Resonance problems of fans, casings and other components
Reason: The resonance of the fan, casing, and other components will generate noise, which is generally mistaken for the noise of the transformer.
Judgment method:
1) Shell: Press the aluminum plate (or steel plate) of the shell with your hand to see if the noise changes. If there is a change, it means that the shell is resonating.
2) Fan: Use a dry long wooden stick to top the casing of each fan to see if the noise changes. If there is a change, it means that the fan is resonating.
3) Other parts: Use a dry long stick to top each part of the transformer (such as wheels, fan brackets, etc.) to see if the noise changes. If there is a change, it means that the parts are resonating.
Solution:
1) Check whether the aluminum plate (or steel plate) of the shell is loose, it may be deformed during installation, you need to tighten the screws of the shell, fix the aluminum plate of the shell, and correct the deformed part.
2) To see if the fan is loose, you need to tighten the fastening bolts of the fan, and put a small piece of rubber between the fan and the fan bracket, which can solve the vibration problem of the fan.
3) If the transformer parts are loose, they need to be fixed.
3. Installation problems
Reason: Poor installation will aggravate the vibration of the transformer and amplify the noise of the transformer.
Judgment method:
1) The foundation of the transformer is not firm or flat (one corner is floating), or the bottom plate is too thin.
2) Putting up the transformer with channel steel will increase the noise.
Solution:
1) The original installation method shall be modified by the installation unit.
2) The anti-vibration rubber pad is added under the transformer trolley to solve some noise.
4. The influence of the installation environment
Reason: The operating environment affects the noise of the transformer, and the unfavorable environment increases the noise of the transformer by 3dB to 7dB.
Judgment method:
1) The transformer room is very large and empty, there is no other equipment, and there is an echo.
2) The transformer is too close to the wall, less than 1 meter. The transformer is placed at the corner, and the reflected noise from the wall is superimposed with the transformer noise, which increases the noise.
3) The oil transformer was originally used, and the noise of the transformer will be affected after the dry transformer is replaced. The reason is that the crude oil transformer room is relatively small, and there is an oil leakage chamber and an oil leakage hole, and the transformer is like being placed on a speaker.
Solution: Some sound-absorbing materials can be properly installed indoors.
5. The problem of the vibration of the busbar bridge
Reason: Due to the large current passing through the side-by-side busbar, the busbar vibrates due to the leakage magnetic field. The vibration of the busbar bridge will seriously affect the noise of the transformer, which will increase the noise of the transformer by more than 15dB, which is difficult to judge. Generally, users and installation units will mistake it for the noise of the transformer.
Judgment method:
1) The noise varies with the size of the load.
2) Use a wooden stick to push the busbar bridge hard, if the noise changes, it is considered that the busbar bridge is resonating.
3) The busbar vibrates in the bridge, and it is useless to top it with a wooden stick. It is necessary to open the busbar bridge cover to check whether the busbar is fixed.
Solution:
1) It is mainly to destroy the condition of the resonance of the busbar bridge, and tighten or loosen the boom screws.
2) Open the busbar bridge cover and fix the busbar.
3) The low-voltage outlet adopts a soft connection.
4) Please ask the manufacturer of the busbar bridge to solve it.
6. Transformer core self-resonance
Reason: There is an electromagnetic attraction between the joints of the silicon steel sheets and the laminations due to magnetic flux leakage.
Judgment method:
1) The noise of the transformer is too large, and other noises are mixed with the normal noise.
2) Transformer noise is wavy.
Solution:
1) Tighten the screws on the transformer, including the screws at both ends of the clip, the through-hole screws, and the spacer screw.
2) Add anti-vibration pads under the transformer trolley to solve some noise.
7. Transformer coil self-resonance
Reason: When a load current passes through the winding, the magnetic leakage generated by the load current causes the vibration of the winding
Judgment method:
1) The noise of the transformer is too large, and the noise is relatively low.
2) When the load of the transformer reaches a certain level, noise starts to appear, sometimes it occurs and sometimes no phenomenon.
Solution:
1) Tighten all the screws of the spacer to increase the axial compression force of the coil.
2) Loosen all the screws of the spacer, loosen all the bolts on the outgoing copper bar and the neutral copper bar, shake the low-voltage coil, move the high-voltage coil by 3-5 mm, and then tighten all the bolts.
8. The problem of the nature of the load
Reason: The voltage waveform of the transformer is distorted (such as resonance phenomenon), resulting in noise.
Judgment method:
1) In addition to the noise of the transformer itself, the noise is also mixed with "cluck, cluck" noise.
2) During the operation, the noise of the transformer will suddenly increase sharply, and it will return to normal soon.
3) Check whether the load has rectifier equipment and frequency conversion equipment.
Solution: The user may consider installing a device to reduce harmonics.
9. The problem of transformer phase loss
Reason: The transformer can not be excited normally, resulting in noise.
Solution:
1) Transformer power failure, check whether the power supply lacks one phase;
2) Check whether the high-voltage fuse of the transformer has blown one phase;
10. The problem of poor contact
Reasons: First, due to poor contact in the high-voltage cabinet. Second, the knife switch is not in place
Judgment method: The transformer emits intermittent and abnormal noise.
Solution:
1) Check the contacts and fuses of the high-voltage cabinet and the entire high-voltage circuit.
2) Ask someone from the manufacturer of the high-voltage cabinet to check.
11. The problem of floating potential
Reason: The clip channel steel, pressure nail bolts, pull plates and other parts of the transformer are all sprayed with blue paint, and the contact between the parts is not very good. Under the action of the leakage magnetic field, a floating potential discharge is generated between the parts and makes a sound. .
Judgment method: The floating potential discharge emits a very slight "squeak, squeak" sound, which can be heard only by listening carefully. Users often mistakenly believe that the transformer is discharging high voltage or low voltage.
Solution:
1) This discharge will not affect the normal operation of the transformer.
2) The paint can be scraped off from the places with poor contact during power outage maintenance, so that all parts of the transformer are in good contact.
12. The low-voltage line is grounded or short-circuited
When the low-voltage line is grounded or a short-circuit accident occurs, the transformer will make a roaring sound; the closer the short-circuit point is to the transformer, the louder the sound; if the short-circuit point is close to the transformer, the transformer will make a louder and more obvious sound.
13. Comparison of transformers with each other
It is generally believed that transformers of different manufacturers, different types of transformers, different use environments, and improper installation will make the noise of the transformers different.
14. The problem of understanding dry change
Reason: Some users have used oil transformers before, and they have a deep understanding of oil transformers. When they contact dry-type transformers for the first time, they think that the noise of dry transformers and oil transformers should be the same.
Solution: In fact, the noise of the oil change is also very loud, but it is filled with oil and a sealed iron shell is added on the outside, so the sound cannot be transmitted. The dry iron core is exposed, and a little sound will come out. Noise is an inherent characteristic of transformers, and the size of noise will not affect the quality of transformers.
Judging faults and solutions from the sound of the transformer
1. The sound when the phase is missing
When the transformer is out of phase, if the second phase is blocked, there is still no sound when the second phase is sent, and there is a sound when the third phase is sent; if the third phase is blocked, the sound does not change, the same as when the second phase is connected. There are generally three reasons for the lack of phase:
①The power supply lacks one phase of electricity;
②The transformer high voltage fuse blows one phase;
③Due to careless transportation of the transformer and the thin high-voltage lead wire, the vibration disconnection (but not grounded) is caused.
2. The pressure regulating tap changer is not in place or has poor contact
When the transformer is put into operation, if the tap changer is not in place, it will make a loud "chirp" sound, which will cause the high-voltage fuse to blow in severe cases; if the tap changer is not in good contact, it will produce a slight "squeak" spark discharge sound , once the load increases, it is possible to burn out the contacts of the tap changer. In this case, the power outage should be promptly repaired.
3. Falling foreign objects and looseness of the threading screw
When the through-core screw that clamps the iron core of the transformer is loose, there are nut parts left on the iron core or small metal objects are dropped into the transformer, the transformer will make a "ding-ding-dong" percussion sound or a "hu...hu..." blowing sound And the "squeaky" sound like a magnet pulling a small gasket, but the voltage, current and temperature of the transformer are normal. This kind of situation generally does not affect the normal operation of the transformer, and can be dealt with when the power is cut off.
4. Dirty and cracked transformer high-voltage bushings
When the high-voltage bushing of the transformer is dirty, the surface enamel is peeled off or cracked, surface flashover will occur, a "hissing" or "chirp" sound will be heard, and sparks can be seen at night.
5. The iron core of the transformer is grounded and disconnected
When the iron core of the transformer is grounded and disconnected, the transformer will produce a slight discharge sound of "beep peeling beep peeling".
6. Internal discharge
When you hear a crisp "crackling" sound of hitting the iron during power transmission, it is the discharge sound of the conductive lead to the transformer shell through the air; if you hear a dull "crackling" sound through the liquid, it means that the conductor faces the shell through the transformer oil. discharge sound. If the insulation distance is not enough, the power should be cut off and the core should be checked, and the insulation should be strengthened or an insulation partition should be added.
7. External circuit disconnection or short circuit
When the line is disconnected at the connection of the wire or at the T connection, it is disconnected from time to time when the wind blows, and arcs or sparks occur when contacting, then the transformer will make a frog's "wow, wow, wow" sound; when the low-voltage When the line is grounded or a short-circuit accident occurs, the transformer will make a "boom" sound; if the short-circuit point is close, the transformer will make a roaring sound like a tiger.
8. Transformer overload
When the transformer is seriously overloaded, it emits a low "hum" sound like a heavy-duty aircraft.
9. The voltage is too high
When the power supply voltage is too high, the transformer will be overexcited, and the sound will increase and become sharp.
10. The winding is short-circuited
When the transformer winding is burnt out due to short-circuit between layers or turns, the transformer will make a "gumbling" sound of boiling water.
There are many abnormal noise factors in transformers, and the fault locations are not the same. Only by continuously accumulating experience can an accurate judgment be made.
Noise from Transformer External Structure and Solutions
(1) Dry-type transformers generally have a fan cooling system, and the abnormal noise of dry-type transformers is often caused by the failure of the fan system. Fans mainly have the following three types of faults:
①When the fan is put into use, it makes a "crackling" sound of metal hitting. This means that there is a foreign body in the fan, and the foreign body needs to be cleaned at this time.
②When the fan is started, the sound of friction is continuous and continuous. This is a quality problem of the fan itself. The fan must be replaced to ensure the normal operation of the fan system.
(2) The transformer with the protection level of IP20 or IP40 has a casing device, and the casing is also the source of transformer noise. The transformer will vibrate during operation. If the casing is not fixed, it will cause the casing to vibrate, thus Noise is generated, so when installing the casing, it is best to add rubber pads between the casing and the ground and between the casing and the transformer base to reduce the transmission of vibration sound.
(3) After entering the electric room, a high and low "hum" sound can be heard in a certain direction of the transformer. This is the result of the superposition of the sound waves generated by the vibration of the transformer through the reflection of the wall. The space of the electric room is related to the placement of the transformer. At this time, the position of the transformer can be adjusted to reduce the sound, and some sound-absorbing materials can be appropriately installed on the walls of the electric room.
(4) The poor floor or bracket of the transformer installation position will aggravate the vibration of the transformer and increase the noise of the transformer. Some transformers are placed on the ground that is not strong. At this time, you will find that the ground will vibrate. If you stand next to it, you will feel the vibration. In severe cases, you will see cracks on the ground. If this is the case, the placement of the transformer must be reinforced to reduce noise. .
Control method from transformer design
The iron core of the transformer itself emits excessive noise, which is the main source of noise of the transformer. The material used for the dry-transformation iron core is mainly silicon steel sheet at present. Magnetostriction of silicon steel sheets. The so-called magnetostriction of silicon steel sheet means that when the iron core is excited, the size of the silicon steel sheet along the direction of the magnetic force line increases, while the size of the silicon steel sheet perpendicular to the direction of the magnetic force line decreases.
When the magnetic flux density in the iron core reaches a certain value, the magnetostrictive size of the silicon steel sheet per meter of length is generally 10 -7 to 10 -5 mm. Magnetostriction causes the core to vibrate periodically as the excitation frequency changes. The iron core silicon steel sheet will have 100 times of magnetostriction with the excitation power frequency voltage. Therefore, the methods to reduce the noise caused by the magnetostriction of silicon steel sheets are as follows:
1. Use high-quality silicon steel sheets. High-quality silicon steel sheet has high silicon content and good magnetostriction. Magnetostriction is usually expressed by ε, which is equal to the ratio of the change in the length of the silicon steel sheet to the length of the sheet during excitation: ε = ΔL/L. The size of ε depends on the rotation of the silicon steel sheet during excitation, and the cold-rolled oriented silicon steel sheet can make 97% of the grains in the silicon steel sheet have the best direction, so the value of ε is small, which is beneficial to reduce the noise of the transformer.
2. Reduce the magnetic flux density B of the iron core. Experiments show that the general magnetic flux density B is in the range of 1.5~1.8T. If the magnetic flux density B in the iron core is reduced by 0.1T, the noise of the iron core can be reduced by 2~3 dB(W), but this will increase the manufacturing cost of the transformer.
3. Change the structure. At present, most of the iron cores used are laminated, and the noise of the iron core will be increased if the lap joint is not good. The newly developed three-dimensional dry-type transformer has changed the traditional plane structure.
Hengfengyou Electric focuses on the manufacture and export of various distribution transformers, rectifier transformers, electric furnace transformers, mining transformers, and has been exported to Uzbekistan, Kazakhstan, Pakistan, Kuwait, Iraq, United Arab Emirates, Zimbabwe, Tanzania, South Africa, the United States, Spain and other more than 30 countries and regions around the world. Thirty years of experience in power transformer manufacturing and sales, Hengfengyou Electric will provide you with the best electrical product solutions, www.hengfengyou.com ; info@hengfengyou.com; WhatsApp: +86158 5325 2696 (Jack) +86158 5326 5269 (Alisa)
