Distribution transformer is one of the important equipment in the power supply and distribution system of industrial and mining enterprises and civil buildings. Oil-immersed transformer uses transformer oil as insulation and cooling medium.
Distribution transformer is one of the important equipment in the power supply and distribution system of industrial and mining enterprises and civil buildings. Oil-immersed transformer uses transformer oil as insulation and cooling medium.
1) The insulation performance is good, which can reduce the insulation distance and reduce the cost.
2) Transformer oil has low viscosity and good heat transfer performance.
3) It can well protect the iron core (silicon steel sheet) and windings from the influence of moisture in the air.
4) Protect insulating paper and insulating cardboard from oxygen, reduce the aging of insulating materials, and prolong the life of transformers.
Structural classification
Oil-immersed power transformer is mainly composed of iron core, winding, oil tank, oil conservator, insulating bushing, tap changer and gas relay.
1. Iron core
The iron core is the magnetic circuit part of the transformer. In order to reduce heat loss and reduce volume and weight, the iron core is made of cold-rolled grain-oriented silicon steel sheet with high magnetic permeability.
2. Winding
Windings and cores are the core components of a transformer. The main faults of transformer windings are inter-turn short circuit and short circuit to shell. Turn-to-turn short circuit is mainly due to insulation aging, or due to the overload of the transformer and the mechanical damage of the insulation during the short circuit. The oil level in the transformer drops, so that when the winding is exposed to the oil level, an inter-turn short circuit can also occur; in addition, when there is a through-circuit short circuit, the winding is deformed due to the overcurrent action, causing the insulation to be mechanically damaged, and an inter-turn short circuit will also occur. When inter-turn short circuit occurs, the current in the short-circuit winding may exceed the rated value, but the current of the entire winding may not exceed the rated value, in which case the gas protection will operate. The reason for the short circuit to the shell is also due to insulation aging or oil damp, oil level drop, or due to lightning and operating overvoltage. In addition, when a through short circuit occurs, the winding is deformed due to overcurrent, and a short circuit to the casing will also occur. When the shell is short-circuited, the gas protection device and the grounding protection are generally activated.
3. Fuel tank
The body (winding and iron core) of the oil-immersed transformer is installed in an oil tank filled with transformer oil, and the oil tank is welded with steel plates. The oil tank of medium and small transformers is composed of a tank shell and a tank cover. The body of the transformer is placed in the tank shell, and the tank cover can be lifted out for maintenance.
Features
a. The low-voltage windings of oil-immersed transformers generally adopt a cylindrical structure with copper foil around the shaft, except for small-capacity copper wires; the high-voltage windings adopt a multi-layer cylindrical structure to balance the ampere-turn distribution of the winding and prevent magnetic flux leakage Small, high mechanical strength, strong short circuit resistance.
b. The iron core and the winding have adopted fastening measures respectively. The fastening parts such as the height of the device and the low-voltage lead wire are all equipped with self-locking locknuts. The non-hanging core structure is adopted, which can withstand the vibration of transportation.
c. The coil and iron core are vacuum-dried, and the transformer oil is vacuum-filtered and oil-filled to minimize the moisture inside the transformer.
d. The oil tank adopts corrugated sheet, which has a breathing function to compensate the volume change of oil caused by temperature changes, so this product does not have an oil storage tank, which obviously reduces the height of the transformer.
e. Since the corrugated sheet replaces the oil conservator, the transformer oil is isolated from the outside world, which effectively prevents the entry of oxygen and water and leads to the decline of insulation performance.
f. According to the above five points of performance, it is guaranteed that the oil-immersed transformer does not need to change oil during normal operation, which greatly reduces the maintenance cost of the transformer and prolongs the service life of the transformer.
Installation points
The distribution transformer is an important component of the substation, and the oil-immersed transformer is generally installed in a separate transformer room. Oil-immersed transformers are fully oil-filled and sealed. The corrugated oil tank shell adapts to the expansion of oil with its own elasticity and is a permanently sealed oil tank. Oil-immersed transformers have been widely used in various power distribution equipment.
Preparation
1. The working hours quota includes: body in place, body inspection, bushing, oil conservator and radiator cleaning, etc., oil column test, accessory installation, production and installation of pad iron and wheel stopper, supplementary column and overall sealing after installation Tests, grounding, touch-ups, etc.
2. Installation site layout: It is best to carry out the overhaul and assembly of power transformers in the maintenance room. If there is no maintenance room, it is necessary to choose a temporary installation site. It is best to choose near the foundation platform of the transformer to make the transformer in place. It can also be installed on the foundation platform. There should be tents on the outdoor site. The temporary installation site must be convenient for transportation, the road should be flat and wide enough, the ground should be solid, flat and dry, away from smokestacks and water towers, and the distance from nearby buildings should meet the fire protection requirements.
3. Specified safety measures: ① Prevent accidents such as personal electric shock and falling. ②Prevent insulation from overheating. ③Prevent fire. ④ Prevent something from falling into the fuel tank. ⑤ Prevent damage to accessories. ⑥ Prevent the transformer from falling over.
4. Formulate technical measures: ① Prevent the transformer core from getting wet. ② How to ensure good contact of each connecting part. ③ All parts should be well sealed without oil leakage. ④ How to ensure transformer insulation and oil insulation.
5. Basic procedures for installation work: ①Preparation (tools, materials, equipment, drawings) ②Insulation inspection and judgment (mainly coils and iron cores) ③Accessories inspection (should be complete and intact) ④Hanging core inspection (to prevent Moisture absorption and tools, parts, etc. falling into the fuel tank) ⑤ Attachment installation (visual inspection, insulation measurement and strict test) ⑥ Finishing work ⑦ Handover test ⑧ Trial run
6. The organization and division of labor of the staff: ①Installation commander and technical person in charge ②Safety officer ③Oil filter group ④Hoisting and transportation personnel ⑤Test personnel ⑥Installation personnel.
7. Requirements for the transformer room: ①First-class fire protection ②Good ventilation ③The safety distance should be sufficient ④The foundation platform should be firm ⑤The hoisting facilities should be in good condition.
8. Preparation of tools and materials:
⑴Installing equipment (such as vacuum pumps, oil pumps, oil tanks, compressed air machines, oil filters, electric welding machines, valves, various wrenches, etc.)
⑵Testing instruments (such as shaking meter, step-up transformer, voltage regulator, ammeter, voltmeter, power meter, thermometer, etc.)
⑶ Lifting equipment (such as cranes, hangers, hanging beams, hoists, wire ropes, pulleys, chain hoists, etc.)
⑷Insulating materials (such as insulating oil, cardboard, cloth tape, bakelite insulating paint, etc.)
⑸ Sealing materials (such as right-resistant rubber gasket, asbestos rope, steel bottom, shellac paint, nylon rope, etc.)
⑹Adhesive materials (such as epoxy resin glue, glue, cement, mortar, etc.)
⑺ Cleaning materials (such as white cloth, alcohol, gasoline, etc.)
⑻Other materials (such as asbestos board, square wood, wire, steel pipe, oil filter paper, Vaseline oil, enamel paint, etc.)
9. External inspection of the transformer:
①No mechanical damage in the content
②The box cover bolts are in good condition
③The gasket is well sealed
④ There is no defect on the casing surface
⑤No oil seepage and oil leakage
⑥ No rust, complete paint
⑦The accessories are intact
⑧ The track of the rollers is consistent with the gauge of the basic rail.
Test run
1. The transformer can only be put into trial operation after all the test items are qualified.
2. Before the trial operation, a comprehensive inspection of the transformer should be carried out.
3. Do 2-3 times of impact test (closing test) on the transformer.
4. The no-load running time is related to the transformer capacity, generally not less than 24 hours.
5. After the no-load running time is completed, the transformer is loaded again