Noise in operation of 10kV dry-type transformer

 

With the rapid development of power industry, the use of all kinds of transformer is more and more widely, including 10 kv the use of dry type transformer is particularly significant, because of its safety, flame retardant, easy to maintenance etc., the product is widely used in commercial buildings, bare in the air, because of its core is easy to bring the problem of noise, it will bring serious problems to the residents, along with the people environmental protection consciousness enhancement, the noise of the transformer problem has been the power department and the transformer manufacturer and user common focus of reform in rural power grid in recent years, the electric power department puts forward a new control for transformer noise level requirements. I have been responsible for the inspection and after-sales service of power transformer products of the company for a long time, and have accumulated some practical experience in the operation noise of 10kV dry-type transformer. This paper discusses the operation noise of 10kV dry-type transformer for mutual learning.

 

 

 

Types of noise generation and solutions

 

2.1 Noise types and solutions of transformer body

 

(1) the transformer issued a harsh "motor" sound, which is caused by the transformer phase loss or overload operation. At this time, measures should be taken immediately. First of all, check whether the power transfer switch shows a lack of electricity. If it is a power failure, check whether the high voltage fuse of the transformer fuses a phase, and then measure whether the transformer is intact. If the operation is overloaded, then you should first check the electricity meter, see how much load, and then reduce to the appropriate load.

 

(2) around the transformer in a direction appeared "dangdang" small abnormal sound, this is due to the long-term operation of the transformer vibration, so that some fastening parts loose and caused by the sound, so the solution should be power failure to check the fasteners, tighten the screws loose.

 

(3) the transformer core appear uneven sound field around a certain direction, this is caused by the unbalance of three-phase transformer load and three-phase unbalanced load can cause a large secondary side of zero sequence current, flux produced large zero sequence in the core, so core can appear uneven sound field, the three phase power should be adjusted at this time, try to keep the relative balance.

 

"Waves" discharge (4) transformers, electrical response is closed room lights, observed discharge area in darker electric room, generally speaking, there are two parts: one is the coil between high and low pressure discharge, if the insulation between the high and low voltage is provided by the barrel aging is punctured, at this time should be a power outage, replace the insulation tube or repair the insulation of the discharge area, the second is the coil end up and down in the face of a discharge, if is that coil insulation aging or have conductive stuff out there, at this time should be a power outage, the need to change the transformer coil insulation aging, a conductive sundry clean up in time.

 

(5) the core of the transformer itself makes too much noise, which is the main noise source of the transformer. At present, the materials used in the dry core are mainly silicon steel sheets. Different types of silicon steel sheets have different qualities, and the magnetic core will cause magnetostriction of the silicon steel sheets in the process of magnetic conductivity. Magnetostriction of silicon steel sheet means that when the core is excited, the size of the silicon steel sheet should increase along the direction of the magnetic field line, while the size of the silicon steel sheet should decrease perpendicular to the direction of the magnetic field line. When the magnetic flux density in the core reaches a certain value, the magnetostrictive size of the silicon steel sheet per meter length is generally 10-7 ~ 10-5 mm. Magneostriction causes the core to vibrate periodically with varying excitation frequencies. The core silicon steel sheet will undergo 100 times of magnetostriction with the excitation power frequency voltage. Therefore, the methods to reduce the noise caused by magnetostriction of silicon steel sheet are as follows:

 

① Use high quality silicon steel sheet. High quality silicon steel sheet of the silicon content is higher, has good magnetostriction, magnetostriction is usually expressed in epsilon, silicon steel sheet when it is equal to the excitation running time variation and the ratio of running time: epsilon = Δ L/L. The size of the ε depends on the rotation of the silicon steel sheet during excitation, and the cold-rolled oriented silicon steel sheet can make the grain in 97% of the silicon steel sheet have the best direction, so the small ε value is beneficial to reduce the noise of the transformer.

 

② Reduce the magnetic flux density of the core B. The experiment shows that the general magnetic flux density B is within the range of 1.5-1.8T. If the magnetic flux density B in the core is reduced by 0.1T, the noise of the core can be reduced by 2-3 dB (W), but this will increase the manufacturing cost of the transformer.

 

③ Change the structure. Most of today's core is fold type, bad lap place also increases the noise from the core, and the newly developed a multiple-layered dry type transformer has changed the traditional flat structure, the core adopts three-phase symmetric vertical structure, the winding way without overlapping, make the iron circuit of three-phase, perfectly balanced three-phase voltage, excitation current no-load loss significantly reduced, so that the running noise is lower.

 

2.2 Noise caused by the external structure of the transformer and its solutions

 

(1) dry transformers are generally with fan cooling system, the abnormal noise of dry transformers is often caused by the failure of the fan system. The fan mainly has the following three types of fault phenomena:

 

① When the fan is put into use, it makes a "crackling" sound of metal impact. This is the fan inside the foreign body, then need to clean up the foreign body.

 

The sound of friction and continuous when the fan is just started is the quality problem of the fan itself. The fan must be replaced to ensure the normal operation of the fan system.

 

(2) the degree of protection for transformer IP20, it with a shell, the shell will be transformer noise source, the transformer produces vibration in the operation, if there is no fixed shell, will cause the vibration of the shell, so as to produce noise, so the device shell, had better be in between the shell and the shell and the transformer with the ground base to add rubber gasket, to weaken vibration transmission of sound.

 

(3) into the house, in a certain direction of the transformer can be heard when the "buzzing" sound of high low, this is the transformer vibration produced by the result of sound waves through the reflex of the wall to produce this kind of situation is special, associated with electric room space and the transformer is placed, then the position of the adjustable transformer to reduce the noise, can also be in some electric wall inside the room equipped with appropriate sound-absorbing material.

 

(4) the floor or bracket of the transformer installation position is not good, which will aggravate the transformer vibration and increase the noise of the transformer. Some transformers placed on the ground is not strong, then you will find that the ground will vibrate, stand to the side will feel the vibration, serious will see the ground cracks, if this is the case to the transformer placement position reinforcement, so as to reduce noise.

 

 

 

Strengthen the daily maintenance of transformer in operation

 

(1) strengthen the transformer daily inspection, once found abnormal, timely maintenance, to ensure the normal operation of the transformer.

 

(2) often observe the temperature of the temperature controller display changes, observe whether the three-phase temperature balance, such as a phase of the temperature display is abnormal, the temperature rise of the transformer is not normal, to find out the reason in time.

 

(3) strengthen the regular inspection of transformers, the inspection items are:

 

(1) Check whether all fastening connectors are loose;

 

(2) check whether the connecting piece of the connecting file is loose;

 

(3) Check whether the fan, temperature controller device and other auxiliary devices can operate normally;

 

(4) check the shell, iron core grounding is good grounding;

 

⑤ clean the dust and stolen goods on the transformer;

 

Timely replacement of aging rubber pad, to prevent the noise caused by aging rubber pad.

 

 

 

4 conclusion

 

The noise of the 10kV dry-type transformer is mainly produced by the iron core. The reason for the noise is related to the raw material of the iron core, electromagnetic design, structural design, operating conditions, load conditions and installation environment of the product. At present, the noise of SCB11 type or SGB11 type transformer can meet the requirements, so in order to adapt to the development of society, promote energy saving and environmental protection products, require the selection of high quality core materials, to ensure that the noise of the transformer meets the requirements of users.