Disassembly of the transformer

Disassembly of the transformer

  1. Preparations before the hoist body
    (1) The hoist body should be carried out in good weather where the relative humidity of the air is not greater than 75%, and there is no ash, smoke, dust, and moisture. Do not hoist the body in rainy, foggy or humid weather. If the maintenance task is urgent and the lifting must be carried out when the relative humidity is greater than 75%, measures should be taken to make the temperature of the transformer core (calculated according to the temperature of the upper layer of the transformer oil) higher than the air temperature by more than 10°C, or to keep the indoor temperature higher than the atmospheric temperature 10℃ high and the temperature of the iron core is not lower than the indoor temperature, which can prevent the insulation of the body from attracting lakes and reduce its insulation.

(2) Before lifting, the lifting capacity of the lifting equipment should be checked in detail and proofread. The tools, guide chains, wire ropes, hooks, etc. used for lifting must be strictly checked and have a certain safety factor. When hoisting, serious accidents should be strictly prevented due to insufficient steel wire rope strength. The angle between the wire rope and the plumb line should not be greater than 30°, so as to avoid excessive tension on the wire rope or bending of the hanging plate (box cover), as shown in Figure 1. When the angle is too large, the steel wire rope should be appropriately lengthened or wooden bracing should be added, and the lifting method shown in Figure 1(a) should be adopted. Auxiliary hanger can be used when the hoisting rope sleeve touches the parts of the body. When the temporary hanger shown in Figure 1(b) is used, the stability of the hanger and the quality of the draw rope should be checked in detail, and the height of the hanger should be checked whether the height of the hanger can meet the lifting requirements. When using a car to lift, pay attention to the extension angle of the boom and the safe distance between the rotation angle and nearby live equipment during the lifting process.

Disassembly of the transformer
Figure 1 Schematic diagram of the hoist body

(3) The relative humidity of the air should be monitored in the process of hoisting the body, and the time that the transformer body is exposed to the air should be controlled. The time the body is exposed to the air shall be in accordance with the provisions of DL/T 573-2010 “Guidelines for Inspection and Repair of Power Transformers” The following values ​​should not be exceeded: 16h when the relative humidity of the air is less than or equal to 65%; 12h when the relative humidity of the air is less than or equal to 75%.

(4) Special personnel must be assigned to command when lifting, and the four corners of the fuel tank must be monitored and supported to keep the body (or bell) stable. Prevent the iron core, windings and insulating parts from colliding with the fuel tank from damage. When lifting the bell jar of the bell-shaped transformer, strictly prevent the bell from swinging in the air, otherwise the body will be damaged. For this reason, a few positioning rods can be temporarily installed on the base of the fuel tank to control the bell in the range of the lifting height. Vertical lifting. In addition, some special requirements of the manufacturer must also be paid attention to.

(5) Power plants and substations should go through work ticket procedures before on-site maintenance.

  1. Process procedure of the hoist body
    After completing the lifting preparations, the body can be lifted according to the following procedures.

(1) After the transformer is powered off, remove the high and low voltage bushing leads of the transformer: disconnect the power supply of the fan, thermometer, gas relay, etc., and wrap the thread ends with tape, and make a mark for assembly after maintenance. Remove the transformer grounding wire and the shim under the transformer wheel, and mark the location of the transformer track to make the transformer easy to be in place after maintenance.

(2) A special person will take the unified command to transport the transformer to the overhaul site. For on-site transformers, sheds, hangers and work frames should be set up in front of the crane body.

(3) According to the conditions of the site equipment, in accordance with the test regulations: conduct various tests on the transformer before overhauling, and make test records. If the test results are unqualified according to the requirements of DL/T 596-1996 “Preventive Test Regulations for Power Equipment”, or are significantly inferior to the results of the previous test, the unqualified items shall be listed as the maintenance plan.

(4) Discharge the transformer oil. For the oil tank transformer with fixed heat pipe, put the oil level slightly below the tank edge. For transformers with removable radiators, when you need to remove the radiator, close the butterfly valves at both ends of the radiator, and then drain the oil in the radiator from the oil drain plug at the lower end of the radiator. If the oil in the radiator cannot be discharged completely, it means that the butterfly valve is not closed tightly. At this time, the transformer oil should be put under the connecting pipe at the lower end of the radiator. For bell-type transformers, drain all the oil.

(5) Disassemble parts that can be lifted, such as bushings, oil pillows, explosion-proof tubes, fan motors, radiators, tap changer operating mechanisms, oil purifiers, thermometers and tank cover bolts. After the cooler, explosion-proof tube, oil purifier and oil pillow are removed, they should be sealed with a cover plate. The disassembled bolts and parts should be cleaned with detergent. If damaged, they should be repaired or replaced, and then sorted and stored properly to prevent loss or damage. When removing a bushing with a voltage of 60kV and above, the connecting wire between the bushing and the winding should be removed first. The round pin can be pulled out for the open type casing, the nut can be unscrewed for the closed type casing, and then the fixing screw between the raised flange and the body is removed, and the outer insulating cylinder of the lower part of the casing (some casing lower part) Without insulation tube), tie and adjust the rope, as shown in Figure 2(a). When lifting, the porcelain sleeve and glass oil cup should be wrapped in linen to prevent the wire rope from being worn or bruised. When lifting, pay attention to the two ends of the conductive tube without external force and prevent collision. After the casing is hoisted from the cover, the oil-filled casing should be removed from the raised flange, and then placed upside down on a rack truck. After being transported to the inspection site, it should be placed vertically and securely on the pipe rack to prevent damage. As shown in Figure 2(b).

Disassembly of the transformer
Figure 2 Schematic diagram of casing removal and maintenance operations

When disassembling the operating lever of the no-load tap-changer, remember and mark the position of the tap-changer. When disassembling the on-load tap-changer, it must be placed in the middle position or in accordance with the manufacturer’s regulations.

(6) When hoisting the body, for distribution transformers with a capacity of 3200kVA and below, the box cover and the body can be hoisted out, as shown in Figure 3(a). For transformers with a transformer capacity greater than 4000kVA, since the body is heavier and longer, and the cover is also long, in order to avoid deformation of the cover after being lifted, the connection between the body and the top cover should be removed first and the cover should be lifted out. Hang the body again, as shown in Figure 3(b). When hoisting, the wire rope should be hung on the special hoisting ring on the top cover of the transformer. Just after separation, check the suspension and tying conditions again, and continue hoisting after confirming that it is reliable. During the lifting process, the speed should not be too fast, and the center of gravity should be controlled to prevent tilting.

After lifting the device, use sleepers to padded it on the edge of the fuel tank and keep the sling under a slight stress. It is strictly forbidden to hang the device in the air for maintenance. If you still need to work in the fuel tank, the body should be hung on a clean plastic cloth and stabilized with sleepers. The heavy body can move the lifting equipment, hoist the body to the designated place for inspection and repair. If the lifting equipment cannot be moved, pull the fuel tank away after lifting the body, and then lower the body. When the device body falls to the ground 200~300mm, stop for a period of time, and place an oil collecting pan under the body to connect the residual oil to reduce the loss field of transformer oil and keep it clean. After the residual oil has dripped off, remove the oil collecting pan, put the sleepers on it, and put the body on the sleepers for maintenance.

For bell-shaped transformers, only need to lift the bell-shaped box cover, as shown in Figure 3(c). After the bell is hoisted, it should be moved to the vicinity. It is strictly forbidden to hang the bell on the body for maintenance.

Disassembly of the transformer
Figure 3 Transformer hoist body

(7) Carefully record the disassembly of the transformer.