In general, there are three sound sources for transformer noise, one is the iron core, the other is the winding, and the third is the cooler, that is, the sum of the noise caused by no-load, load and cooling system. The reason for the noise of the iron core is that under the action of the alternating magnetic field of the silicon steel sheet forming the iron core, there will be a slight change, namely magnetostriction. Magnetostriction causes the iron core to periodically vibrate with the change of the excitation frequency, the iron core magnetostrictive deformation and winding, fuel tank and magnetic shield Caused by internal electromagnetic force.
The reason for the vibration of the winding is the electromagnetic force generated in the current winding, and the leakage magnetic field can also cause the structural parts to vibrate. The cause of electromagnetic noise is that the magnetic field induces the longitudinal vibration of the iron core laminations to produce noise. The amplitude of the 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, and the emitted sound power is proportional to the square of the vibration amplitude.
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Listen to good or bad
The external distribution transformer will make different sounds during normal operation or failure. If the operation of the transformer can be judged by judging the sound inside the transformer, it saves time and effort. Today I will share with you "Listen to the sound of good or bad".
Sound of normal operation
"Buzzing" uniform electromagnetic sound
It shows that the transformer is operating normally, and the current passing through the iron core produces alternating magnetic flux, and a uniform electromagnetic sound of "buzzing" will be emitted. The strength of the sound is proportional to the size of the load current.
Sound of abnormal operation
"Squeak"
Divided into two situations:
(1) After the tap changer is adjusted, the noise is aggravated. The DC resistance value of the double-arm bridge test is more than 2% of the original factory data. It is caused by poor contact and dirt on the contacts.
Solution: Unscrew the weather cover of the tap changer, remove the locking screw, and use the handle to rotate the axis of the tap changer back and forth 10-15 times to eliminate this phenomenon. After repairing, install and restore it immediately.
(2) The down conductor from the terminal rod to the drop-out fuse adopts bare aluminum or bare copper stranded wire, but the tension is not enough, and the porcelain bottle tie wire is loose. At dusk and dawn, small sparks can make a "squeaking" sound, which is obviously different from the "squeaking" sound made inside the transformer.
Solution: Use the holidays to arrange power outages and repairs to eliminate the fault.
"Cracking" a clear iron strike
This is the lead of the high-voltage porcelain bushing, and the discharge sound of the transformer shell through the air is caused by the lack of oil in the upper part of the transformer tank.
Treatment method: insert a clean and dry funnel into the oil pillow from the oiler hole, add transformer oil of the same size that has passed the test (cannot be mixed with oil), add the oil supplement to the oil surface temperature + 20 ℃, and then add Good oiler. Otherwise, the oil will expand due to heat and will cause oil spills. If conditions permit, vacuum oil injection should be used to eliminate air bubbles in the coil.
"Zhi La" is like the sound of a small shim being attracted by a magnet
This kind of sound is emitted, and the indication values of the transformer monitoring device, voltmeter, ammeter, and thermometer are all normal. This is often due to negligence during the new assembly or the maintenance of the hanging core, and the screws or iron pads are not tightened or dropped into the small iron parts, which are caused by electromagnetic force.
Treatment method: remove it when the transformer is overhauled.
"Chip-wow" sound like a frog's croak
When the wind blows, it is switched on and off, arcs and sparks occur when in contact, but the sound is uneven, strong and weak, and the sound is transmitted to the transformer through the wire. It can be judged with the indicated value of the voltmeter. If phase B lacks power, the voltage is roughly: u1-2=230V, u1-3=400V u2-3=230V, u1-0=230V u2-0=0V, u3 -0=230V
Solution: Arrange for power outage maintenance immediately. Generally, it occurs on high-voltage overhead lines, such as the connection between the wire and the isolating switch, the joint in the tensile section, the contact point of the drop-out fuse, and the T-shaped joint are broken or loose, causing oxidation and overheating. After the fault is eliminated, it is allowed to be put into operation.
Faint hiss
When the capacity of the transformer is small (below 100kVA), it is impacted by the starting current of individual electrical equipment, for example, the arc starting of a 26kW DC arc welding machine, or the driving of a 22kW250kg air hammer, etc., are transmitted to the transformer through the wire and the weak output Hiss.
Treatment method: If the protection, monitoring device, and other electrical components have no abnormal signs, this should be a normal phenomenon.
"Tiger Roar"
When the low-voltage line is short-circuited, it will cause the short-circuit current to suddenly increase and cause this "tiger roar" sound.
Treatment method: The inspection and testing of the transformer body starts from the visual inspection, see the treatment method of "Sound Reduction".
"Grumbling" like the sound of boiling water
There is a short circuit between layers or turns in the transformer coil, the short-circuit current increases sharply, or the iron core generates strong heat, causing fire and burning, causing the insulation to be burned, causing oil injection, smoke and fire.
Treatment method: first disconnect the low-voltage load switch to make the transformer in a no-load state, then cut off the high-voltage power supply, and disconnect the drop-out fuse. Remove the operating system and arrange for the overhaul of the lifting core.
Special noise
Due to changes in the load and ambient temperature, the oil level of the oil pillow changes. Therefore, water vapor is sucked into the oil pillow along with the air and condenses into water droplets, which promotes internal oxidation and rust. As the accumulation degree intensifies, Will fall to the bottom of the oil pillow. The rust accumulates on part of the yoke through the connecting pipe between the oil pillow and the oil cap, so that it vibrates and emits special noise under the action of electromagnetic force. This will also lead to increased mechanical impurities in the transformer operating oil, which will deteriorate the oil quality.
Treatment method: The cleaning of the oil pillow and the mud collector is carried out at the same time, which should be determined according to the load condition and temperature rise of the transformer. Experience has proved that it is better to clean once every two years.
three
Testing standard
Article 61 of the "Law of the People's Republic of China on the Prevention and Control of Environmental Noise Pollution" stipulates that units and individuals that have been harmed by environmental noise pollution have the right to request the perpetrator to eliminate the harm; if losses are caused, they shall be compensated in accordance with the law.
The national "Code for Residential Design" stipulates that boilers, transformers and other equipment rooms with noise and vibration sources should not be arranged in residential buildings. If it is required to be arranged due to conditions, it shall comply with the current building fire protection, building sound insulation and related regulations. The "Code for Sound Insulation Design of Civil Buildings" stipulates that when conditions permit, it is easy to set the noise source underground, but it is not advisable to set it next to the theme building or under the main building. If it cannot be avoided, reliable vibration and sound insulation measures must be taken.
In 2008, the mandatory standard "GB 3096-2008 Acoustic Environment Quality Standard" issued by the Ministry of Environmental Protection of my country stipulates that the acoustic environment is divided into the following five types according to the functional characteristics and environmental quality requirements of the area:
Various acoustic environment functional areas are applicable to the environmental noise equivalent sound level limits specified in Table 1.
Table 1 Limits of equivalent sound level of environmental noise in various acoustic environment functional areas
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For sudden noise at night in various acoustic environment function areas, the maximum sound level exceeding the environmental noise limit shall not be higher than 15dB (A).
In addition, the Ministry of Environmental Protection implemented stricter regulations on indoor noise emission limits in the "GB22337-2008 Social and Living Environment Noise Emission Standards" implemented on October 1, 2008. The regulations on structure-borne noise are as follows:
In the case where the social life noise emission source is located in a noise-sensitive building, when the noise is transmitted to the noise-sensitive building through the structure of the building, the indoor equivalent sound level of the noise-sensitive building shall not exceed the prescribed limit.
In the case of non-steady-state noise (such as elevator noise, water pump noise) during the noise measurement period, the maximum sound level exceeding the limit shall not be higher than 10dB (A).
In addition to the two standards on noise emissions issued by the Ministry of Environmental Protection, the mandatory standard "GB 50368-2005 Residential Building Code" implemented by the Ministry of Construction on March 1, 2006 has the following requirements for residential noise and sound insulation:
Houses should adopt noise prevention measures in the layout and building structure. The allowable noise level during the daytime of the bedroom and living room with the windows closed is 50dB (A sound level), and the allowable noise level at night is 40dB (A sound level). The elevator should not be arranged next to the bedroom and living room. When it is necessary to arrange in close proximity due to conditions, effective sound insulation and vibration reduction measures must be taken. Effective sound insulation measures should be taken for pipeline wells, water pump rooms, transformer rooms, and fan rooms, and vibration reduction measures should be taken for water pumps, transformers, and fans.
In addition, Article 3.1.1 of the "GBJ 118-1988 Code for Sound Insulation Design of Civil Buildings" issued by the Ministry of Urban and Rural Construction and Environmental Protection of China stipulates that the allowable noise level of bedrooms, studies and living rooms in residences should meet the normative limits.
Now that there are so many national standards to regulate transformer noise, why do we still have frequent disputes about transformer noise between owners and developers around our lives? A large part of the reason should be attributed to the imperfect construction acceptance. We can find from the building acceptance record that many buildings only accept the construction part in the acceptance certificate, and the remarks of some acceptance certificates clearly indicate that water supply and power supply are not included in the acceptance. It is precisely because there are some irregularities and imperfections in the construction and acceptance of the building that will cause the transformer noise dispute after the house is delivered.
In the British Standard BS 661 (terms related to acoustics), standard definitions have been used to emphasize the subjectivity of noise. That is, for the receiver of noise, noise is annoying. Therefore, it is easy to understand why people feel that music and noise are a kind of enjoyment at the dance, and when people want to fall asleep, even the same sound will feel a kind of interference and annoyance. Transformer noise is not only continuous, but most of it belongs to medium audio frequency. The harm to human hearing is minimal, and there is no inherent harmfulness. This means that the degree of annoyance caused by transformer noise is probably related to the apparent volume of the transformer. The best way to solve this problem is to determine the apparent loudness emitted by transformers of various types and specifications.
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