Transformer casing common fault and overhaul skills

The lead of the transformer winding relies on the casing lead-out box. The casing plays the role of insulating, fixing and delivering current to the outside of the tank. It needs to adapt to various environmental conditions and has certain mechanical strength, Is a major component in the transformer.

 

Sleeves need to have different voltage and current levels, most of the outer insulation is porcelain. Sleeve pure porcelain casing, oil-filled casing, inflatable casing, casing and other forms of capacitance.

 

Capacitive bushing is a capacitor core-based insulation casing, there are two kinds of plastic film capacitors and oil-paper capacitance casing, machine transformer below will analyze the transformer casing failure, and put forward maintenance measures and attention matter.

 

First, the transformer casing failure

 

1, winding the main insulation and turn insulation failure

 

Transformer winding the main insulation and turn insulation is prone to failure of the site. The main reason is:

 

Due to long-term overload operation, or poor cooling conditions, or long service life, the transformer winding insulation aging brittle, greatly reduced the dielectric strength; Transformer by short-circuit impact, the stress deformation of the winding, hidden insulation defects, in the event of Voltage fluctuations may break the insulation;

 

Transformer oil into the water, so that the insulation strength is greatly reduced and can not withstand the allowable voltage, resulting in insulation breakdown; in the high-voltage winding reinforcement section or low-voltage winding parts, due to the insulation expansion package.

 

So that blocking the oil passage, affecting heat dissipation, so that the winding insulation due to overheating and aging, breakdown breakdown occurs; due to imperfect lightning protection facilities, the role of atmospheric over-voltage insulation breakdown occurs.

 

2, lead insulation failure

 

Transformer leads through the transformer casing lumen leads to the external circuit, the leads are supported and insulated by the bushing.

 

Due to the tight closure of the top cap (general hat) of the casing, the main insulation of the lead penetrates through the damp and the transformer is severely short of oil, exposing the lead in the fuel tank to the air, resulting in internal flashover and failure of the lead wire .

 

3, core insulation failure

 

Transformer core made of silicon steel stacked from silicon steel sheet insulation film. As the silicon steel fastening is not good, so that the vortex vortex damage and local overheating.

 

Similarly, the core of the core clamp screw, iron and other components, if the insulation damage, overheating will occur. In addition, if the transformer remains in the iron or welding slag, the core of two or more points to the ground, will cause the core failure.

 

4, transformer casing flashover and explosion

 

Transformer high-voltage side (110kV and above) the general use of capacitor bushings, due to porcelain poor trachoma or cracks; manufacturing defects in the core, the internal free discharge; casing seal is not good, there is oil leakage phenomenon; casing Serious scale deposition, etc., may occur flashover and explosion.

 

5, tap switch failure

 

Transformer tap changer is one of the common fault parts of the transformer. There are two types of tap-changer and no-load tap-changer. The reasons for common faults are as follows:

 

1), no-load tap-changer: due to prolonged pressure contact, there will be insufficient spring pressure, roller uneven pressure, so that the effective contact area of ​​the tap changer connection part is reduced, and the contact part of the junction of silver-plated wear and tear, Caused by the tap changer in operation heat damage;

 

Tap changer poor contact, leads to poor connection and welding, can not withstand the impact of short-circuit current caused by the tap-changer is burned out short-circuit current and failure; due to poor management, or tampered with the tap caused by the work of the tripping switch ACCIDENT.

 

2), on-load tap-changer: transformer with on-load tap-changer, tap-changer tank and transformer tank are generally unrelated to each other. If there is a serious shortage of fuel in the on-load tap-changer, the tap changer will short-circuit while switching, which will make the tap-changer burn out.

 

In the casing overhaul, the vacuum is not exhausted, so that the air trapped between the screen, after running under the action of a high electric field, partial discharge occurs, and even lead to insulation breakdown, resulting in accidents.

 

Second, the transformer casing failure measures

 

According to the above failure analysis, summed up some measures to deal with;

 

1, for the casing oil failed, containing acetylene gas and other defects. Measures taken are: to conduct rigorous testing of casing, all kinds of tests before they can be put into operation to avoid human factors caused the failure.

 

2, for poor sealing casing, water or oil leakage phenomenon. The steps to be taken are: To maintain the seal by replacing the good quality rubber pad, tighten the fastening bolts so that the casing does not leak.

 

3, in view of the structure of the casing itself unreasonable head caused by overheating and other defects. Specific measures can be changed copper and aluminum transition to silver-copper contact, thereby reducing the oxidation.

 

4, demolition, access, cited the process, pay attention to check the various parts are well connected, the contact surface should be polished conductive paste coated to reduce the contact resistance. Thus eliminating its overheating phenomenon.

 

Through the above oil and paper capacitance casing failure analysis and some measures can be roughly found in the formation of defects in two ways: The first is the design of the casing itself weak links; The second is the human factor is the installation and maintenance personnel in the operation Caused.

 

Third, the transformer casing should pay attention to the application

 

In the analysis of the main reasons for the common casing failure, I think the casing in the transport, installation, maintenance and other aspects should pay attention to the following questions:

 

1, Crane lifting speed should be slow during lifting, lying down and transportation, to avoid collision with other objects; when lifting upright, the lifting lugs on the flange should be used, and the upper part of the casing should be tied with hemp to prevent dumping ;

 

Be careful not to lift the sleeve porcelain skirt to prevent the rope and porcelain sets collide damage; erected casing, should avoid any part of the floor; casing lying and transport, should be placed in a dedicated box.

 

Installation flange should have two support points, no porcelain skirt at the top of the support points, the tail should also be set at the support point, and the soft point of the support pad. Casing in the box should be fixed, so as to avoid transport injury injury.

 

2, in the casing overhaul of the assembly should pay special attention to the following points: To prevent damp. In addition to the assembly to be clean and dry conditions, the best at 40-50 ℃ temperature assembly.

 

Because the capacitance of the core temperature is higher than the ambient temperature of 10-15 ℃ can reduce the impact of moisture, so the best assembly before the casing parts and capacitor core heating to 70-80 ℃, for 3-4h, so that Eliminate the surface moisture, as far as possible when the temperature has not been reduced assembly finished; top of the casing seal.

 

Casing top of the seal can be divided into the casing itself and the lead wire lead seal. At present most of the substation main transformer oil conservator top is equipped with elastic corrugated plate, which together with the compression spring to adjust the role of temperature changes.

 

When assembling the elastic corrugated board, the sealing ring between the positive and negative compression nuts on the pipe and the gasket on the oil conservator must be properly matched to prevent the corrugated board from cracking, so as to achieve the sealing effect.

 

Casing lead-through cable structure, if the top of the wiring board, the conductive head between the seal is not tight, rain along the casing top of the wiring board, conductive head and cable into the transformer inside the tube. Moisture into the root of the transformer leads, will lead to moisture breakdown, resulting in power outages.

 

3, maintenance and repair personnel should pay attention to the following questions: Test personnel demolition end of the screen when the small casing lead should prevent the guide bar rotation or twist off the ground lead, the test should be restored to its original state.

 

According to my work experience, the end of the test can be used to measure the end of multimeter is grounded, which is to check whether the last screen grounding has been restored after a more reliable way;

 

Take the sample staff work after the junction, should tighten the sampling valve; demolition of the lead staff, up and down the casing should be taken to prevent casing damage; maintenance personnel should observe the casing oil level and timely replenishment.

 

In addition, maintenance personnel should be familiar with the technical requirements of casing. First of all, to be familiar with the technical performance of the casing, such as the main test items when the casing factory dielectric loss measurement, partial discharge measurement, power frequency withstand voltage test, tightness test, and the appearance and size testing.

 

Second, to be familiar with the use of casing conditions, such as casing installed around the ambient temperature of -40 ~ +40 ℃, the mounting angle on the transformer and its vertical axis does not exceed 30 ° and so on.

 

Maintenance personnel should also be done: the use of all blackouts the opportunity to carefully inspect the casing, timely elimination of defects, eliminate hidden dangers; strict quality control, purchased maintenance and repair materials are recognized by the parties concerned; continue to improve their professional and technical level, To ensure the quality of maintenance.