110KV oil-immersed transformer overhaul and overhaul, what exactly is \"repairing\"?

Transformer is an extremely important electrical equipment in the power transmission and distribution system, but due to various reasons, it sometimes fails during operation. According to the nature of the maintenance work, transformer maintenance is divided into overhaul and minor repair. It is customary that oil-immersed transformers that require oil-releasing hanging cores (or hanging bell covers) for maintenance are called overhauls; if they do not need oil-releasing, they do not hang the cores (hanging bell covers) and only perform external maintenance or refueling Performing oil treatment is called minor repair.

First, the conventional transformer maintenance process

1. Clean the casing and check the porcelain sleeve for signs of discharge and damage;

2. Check whether the fastening bolts on the top of the casing are loose. Whether overheating

3.Clean the transformer oil tank and oil storage tank, safety air channel and pressure regulating device and other accessories;

4. Check the dust and other debris deposited in the valve cover of the pressure release valve;

5. Check whether the oil level of the oil storage tank is normal, whether the oil level gauge is intact and clean, and drain the oil in the sewage collection basin;

6. Check the respirator and replace the desiccant that has failed to change color;

7. Supplement the insulation oil of the transformer body and the oil-filled bushing;

8. Check the radiator for oil leakage and whether the cooling fan is normal;

9. Check the thermometer that measures the upper oil temperature;

10. Check the gas relay for oil leakage, whether the valve is flexible and reliable to open and close, and whether the control cable insulation is good;

11. Check and handle the ground wire of the transformer shell and the neutral point grounding device;

12. Check the operation of the on-load tap-changer operation control circuit, the transmission part and its contacts, and clean the inside of the operation box;

13. Take oil samples from the transformer body and oil-filled casing for simplified analysis, and take oil samples from the transformer body and capacitor casing for chromatographic analysis;

14. Handle defects that can be eliminated on the spot, such as seepage and oil leakage;

15. Carry out electrical tests on specified items.

When the electrical test and oil test show that the results are unsatisfactory, it is necessary to carry out overhaul. According to the site conditions, determine whether the transformer has the conditions for hanging core inspection, and then perform related maintenance operations.

In addition to this reason, the hood inspection is required in the following three cases:

1. Generally, the transformer should be inspected within 5 years after being put into operation.

2. After the main transformer running in the power system is subjected to a short circuit at the outlet, after comprehensive diagnosis and analysis, overhaul can be considered in advance.

3. During the operation of the transformer, when abnormal conditions are found or internal faults are found through testing, overhaul should be carried out in advance.

Transformer overhaul project

1. Lift the bell cover or lifter for maintenance.
2. Maintenance of coils, leads and magnetic (electrical) shielding devices.
3. Inspection of iron cores, iron core fasteners (through-hole screws, clamps, drawstrings, straps, etc.), nails, connecting pieces and grounding pieces.
4. Overhaul of fuel tank and accessories, including casing, moisture absorber, etc.
5. Maintenance of auxiliary equipment such as coolers, oil pumps, water pumps, fans, valves and pipes.
6. Maintenance of safety protection device.
7. Calibration of temperature measuring device and calibration of gas relay.
8. Maintenance and test of operation control box.
9. Maintenance of non-excitation tap-changer or on-load tap-changer.

10. Replace all sealing rubber pads and test leakage of components.
11. If necessary, dry the body insulation.
12. Transformer oil treatment or oil change.
13. Test and trial operation after overhaul.
14. Technical transformation projects that can be carried out in conjunction with transformer overhaul (such as strengthening the mechanical strength of the fuel tank, changing the internal grounding device of the body to external grounding, improving the oil level gauge, and installing a sealing device in the oil storage tank)

15. Finally, clean the fuel tank and spray paint.

3. Overhaul site conditions

1. The bell jar (or body) should generally be carried out indoors to keep the body clean. If it is carried out in the open air, it should be carried out on a sunny day. The time when the body is exposed to the air is specified as follows: relative air humidity When it is not more than 65%, it does not exceed 16h; when the relative humidity of the air is not more than 75%, it does not exceed 12h; the exposure time of the device is calculated from the time when the transformer discharges oil until the vacuum is started.
2. In order to prevent condensation on the body, the temperature of the body should not be lower than the ambient temperature. Otherwise, a vacuum oil filter should be used to circulate heating oil and heat the transformer to make the body temperature higher than the ambient temperature by 5 ° C.
3. The inspection of the body should be performed by a special person, and the dress conforms to the regulations. Lighting should be at a safe voltage. Do not lean the ladder on the coils or leads, and workers must not step on the coils or leads.
4. The tools used for body inspection should be kept and registered by a special person to prevent them from being left in the fuel tank or the body; ventilation should be considered when working in the tank.
5. The dismantled parts should be cleaned and kept in proper classification. If damaged, they should be repaired or replaced.
6. Disassembly sequence: first remove the small instrument and casing, and then remove the large components; the sequence is reversed during assembly.
7. After the components such as cooler, pressure relief valve (or safety air passage), oil purifier and oil storage tank are removed, the cover plate should be used for sealing. The rising seat with current transformer should be filled with qualified transformer oil (or Take other moisture-proof sealing measures).
8, casing, oil level gauge, thermometer and other vulnerable parts should be properly stored after disassembly to prevent damage and moisture.
9. Check the cooler, oil purifier and gas relay valve after assembly, and open or close according to regulations.
10. For the casing raising seat, the upper vent holes of the upper pipe hole cover, cooler and oil purifier, etc., should be exhausted repeatedly until it is exhausted, and reseal and wipe the oil marks.
11. When disassembling the non-excitation tap-changer operating lever, the position of the tap-changer should be recorded and marked; when the on-load tap-changer is disassembled, the tap should be adjusted to the rated position (or according to the manufacturer's regulations) .
12. Each component of the assembled transformer should be intact.

Fourth, overhaul process

Remove the lead wire → electrical, oil preparation test, insulation judgment → remove some oil and remove the accessories and overhaul → drain the oil and dispose of it, remove the tap changer connection → check the bell body (body), inspect and repair the insulation → damp Then dry treatment → fill oil according to the prescribed oil filling method → ​​install accessories such as bushings and coolers → seal test → oil level adjustment → electrical and oil testing → end

V. Overhaul of transformers

1, winding maintenance

a) Check the phase spacers and enclosures (the first phase should be disassembled). The enclosures should be clean and undamaged, the bindings should be tight and tight, the outlet of the tap leads should be well closed, and the enclosures should be free of deformation, heat and tree-like discharge. If abnormality is found, the other two-phase enclosures should be opened for inspection, and the phase spacers should be complete and firmly fixed.
b) Check that the winding surface is free of grease and deformation, that the entire winding is free of inclination and displacement, that there is no obvious protrusion of the conductor radial, and that the insulation of the turns is not damaged.
c) Check whether the pads of each winding are loose. The pads should be arranged neatly, the radial spacing is equal, and the support is properly pressed.
d) Check whether the winding insulation is damaged, and whether the oil passage is blocked by insulating paper, grease or debris. If necessary, wipe it gently with a soft brush (or use silk cloth or foam plastic). If it is damaged and exposed, it should be wrapped.
e) Press the surface of the winding with your finger to check its insulation status, and give a rating judgment as to whether it is available.

2, lead and insulation support maintenance

a) Check whether the insulation of the lead and the stress cone is deformed, brittle, damaged, whether the lead is broken or twisted, whether the lead and the lead joint are in good welding condition, and whether there is overheating.
b) Check the length of the lead from the winding to the tap changer, the thickness of the insulation band, the welding (or connection) of the lead joint, the insulation distance of the lead to various parts, and the fixation of the lead.
c) Check the insulation support for looseness, damage, and displacement. Check the fixing of the leads in the insulation support. The fixing bolts should have anti-loosening measures. The inside of the clips holding the leads should be padded with additional insulation to prevent the lead insulation from being damaged.
d) Check whether the insulation distance between the lead and each part meets the requirements. The distance between the high-current lead (copper bar or aluminum bar) and the box wall should not be less than 100mm to prevent magnetic leakage and heating.