Revision of a power transformer type tm technological map. We repair power transformers. Protective equipment, devices, tools, fixtures and materials
) on open switchgears, in the preparation of projects for the organization of construction (POS) and projects for the production of electrical work (PPER).
Current transformers of the TFZM and TFRM series (single-phase, electromagnetic, oil, outdoor installation, reference type) are designed to transmit information signals measuring instruments, protection and control devices in AC installations.
Current transformers (hereinafter referred to as "transformers”) TFZM 500 B and TFRM 750 A are made in the form of two stages (lower and upper), the rest are single-stage. Transformers 220 - 750 kV have a screen on the expander, and two-stage transformers, in addition, have an additional screen that closes the joint of the steps.
The technological map contains instructions for organizinginstallations and installation technologies, a list of mechanisms, tools, information on the cost of materials, labor costing and work schedules.
It is assumed in the map that the work associated with the installation of transformers is carried out directly at the installation site, at the place of their installation.
All calculated indicators in the map are given for the installation of one group (three phases) of transformers.
Labor costs for adjustment work, installation schedules andcalculations are not taken into account.
The technological map was developed in accordance with the "Guidelines for the development of standard technological maps in construction." M., TsNIIOMTP Gosstroy of the USSR, 1987.
Forbids to open transformers and take oil samples.
Installation should be carried out with the participation of the chief engineer of the manufacturer.
Technical criteria and controls for operations and processes are given in Table. . Acceptance control of mounted transformers is carried out in accordance with SNiP 3.05.06-85. Upon acceptance of work, documentation is presented in accordance with the list of appendices. .
TYPICAL TECHNOLOGICAL CARD
INSTALLATION OF POWER TRANSFORMERS WITH NATURAL OIL COOLING, VOLTAGE UP TO 35 kV, POWER UP TO 2500 kVA
1 AREA OF USE
Typical routing designed for the installation of power transformers.
Requirements for transportation, storage, as well as installation and commissioning of power transformers are defined by the instruction "Transportation, storage, installation and commissioning of power transformers with voltage up to 35 kV inclusive without revision of their active parts" and guidelines technical guidelines"Power transformers, transportation, unloading, storage, installation and commissioning".
The power transformer, which arrived from the equipment supplier (manufacturer, intermediate base), is subjected to external inspection. During the inspection, they check the presence of all places according to the railway bill, the condition of the packaging, the absence of oil leaks at the joints of the radiators with the tank and in places of seals, the integrity of the seals, etc.
The packaging of dry transformers must ensure their safety from mechanical damage and direct exposure to moisture.
If a malfunction or damage is detected, an act is drawn up, which is sent to the plant or intermediate base.
After the inspection and acceptance of the transformer, they begin to unload it.
It is recommended to unload the transformer with a bridge or mobile crane or a stationary winch of the appropriate carrying capacity. In the absence of lifting means, it is allowed to unload the transformer onto the sleeper stand using hydraulic jacks. Unloading of transformer units (coolers, radiators, filters, etc.) is carried out by a crane with a lifting capacity of 3 to 5 tons. .
To lift the transformer, special hooks are provided on the walls of its tank, and eyelets (lifting rings) are provided on the roof of the tank. Slinging of cables for large transformers is carried out only by hooks, for small and medium ones - by hooks or eyelets. The poles and lifting ropes used for lifting must be made of a steel rope of a certain diameter, corresponding to the weight of the transformer. To avoid cable breaks, wooden linings are placed under all sharp edges of the bends.
The heavy-weight transformer arriving disassembled is unloaded using a heavy-duty railway crane. In the absence of such a crane, unloading is carried out using winches and jacks. To do this, the transformer tank installed on the railway platform is first lifted with two jacks by the lifting brackets welded to the bottom and walls of the tank, then a trolley supplied separately from the tank is brought under the tank, and with the help of winches the tank is rolled off the platform onto a specially prepared sleeper stand. Rolling is carried out along steel strips placed under the trolley rollers. The remaining components of the transformer (expansion tank, outlets, etc.) are unloaded with conventional cranes.
The unloaded transformer is transported to the installation site or to the workshop for revision. Depending on the mass of the transformer, transportation is carried out by car or on a heavy trailer. Carriage by dragging or on steel sheet is prohibited.
Vehicles used for the transportation of transformers must have a horizontal cargo platform that allows free installation of a transformer on it. When the transformer is located on the vehicle, the major axis of the transformer must coincide with the direction of travel. When installing a transformer on a vehicle, it is necessary to take into account the location of the inputs on the transformer in order to prevent a subsequent turn before installation at a substation.
Dismantled components and parts can be transported together with the transformer, if the carrying capacity allows vehicle and if at the same time the requirements for transportation of the transformer itself and its components are not violated.
The carrying capacity of the vehicle must not be less than the mass of the transformer and its elements in case of their transportation together with the transformer. It is not allowed to apply traction, braking or any other types of forces to the structural elements of the transformer during their transportation.
Figure 1 shows a diagram of the installation of a transformer on a car.
Fig.1. Scheme of installation and fastening of the transformer on the car
In some cases, prior to installation, transformers are stored for a long time in on-site warehouses. Storage must be organized and carried out in such a way as to exclude the possibility of mechanical damage to transformers and dampening of the insulation of their windings. These requirements are met by certain storage conditions. Depending on the design and method of shipment of transformers, their storage conditions will be different. In all cases, it is necessary that the duration of storage of transformers does not exceed the maximum allowable established by the instructions mentioned above.
The storage conditions of power transformers with natural oil cooling are accepted according to the group of storage conditions of the OZHZ, i.e. in open areas.
Storage conditions for dry non-sealed transformers must comply with the conditions of group L, transformers with a non-combustible liquid dielectric - group OZH4. Storage conditions for spare parts (relays, fasteners, etc.) for all types of transformers must comply with condition group C.
Dry-type transformers must be stored in their own enclosures or original packaging and must be protected from direct exposure to atmospheric precipitation. Oil transformers and transformers with non-combustible liquid dielectric must be stored in their own tanks, hermetically sealed with temporary (during transportation and storage) plugs and filled with oil or liquid dielectric.
When storing transformers up to 35 kV inclusive, transported with oil without expanders, the installation of the expander and adding oil must be done as soon as possible. short term but not later than 6 months. When storing transformers with a voltage of 110 kV and above, transported without an expander with oil and without oil, the installation of the expander, topping up and filling with oil should be carried out as soon as possible, but no later than 3 months from the date of arrival of the transformer. The oil must comply with the requirements of the PUE. The oil level must be periodically monitored (when the level drops, it is necessary to add oil), at least once every 3 months it is necessary to take an oil sample for a reduced analysis. The absence of oil leakage from the transformer tank is checked periodically by traces on the tank and fittings. Sealed oil transformers and transformers with non-flammable liquid dielectric must be stored in the manufacturer's packaging and protected from direct precipitation.
2. ORGANIZATION AND TECHNOLOGY OF WORK PERFORMANCE
INSTALLATION OF POWER TRANSFORMERS WITH NATURAL OIL COOLING
The facilities mainly use power transformers with natural oil cooling, voltage up to 35 kV, power up to 2500 kVA. The scope of work for the installation of a power transformer with natural oil cooling depends on whether it comes from the factory - assembled or partially disassembled. Regardless of the type of delivery, the sequence of installation operations will be the same.
When installing a power transformer, it is necessary to perform the following operations in sequence:
Accept a room (installation site) and a transformer for installation;
Inspect the transformer;
Dry the windings (if necessary);
Assemble and install the transformer in place.
Acceptance for installation of a room (installation site) and a transformer
The room (open area) for the installation of the transformer must be completely completed by construction. Lifting devices or portals must be installed and tested prior to installation of the transformer.
As you know, the supply of power transformers and their delivery to the installation area must be carried out by the customer. When accepting transformers for installation and determining the possibility of further work, the whole range of issues related to transportation and storage, the condition of transformers for external inspection and determination of insulation characteristics, readiness and equipment of the room or installation site are considered.
The customer must submit the following required information and documents:
Date of dispatch of transformers from the manufacturer;
Conditions of transportation from the manufacturer (by rail or other transport, with or without oil, with or without expander);
The act of acceptance of the transformer and components from the railway;
Scheme of unloading and transportation from the railway to the installation site;
Storage conditions for transformers and component parts (oil level in the transformer, period for filling and topping up oil, characteristics of filled or topped-up oil, results of transformer insulation assessment, oil sample tests, leak tests, etc.).
At the same time, the condition of the transformer is assessed by external inspection, the results of the transformer tightness test and the condition of indicator silica gel.
During an external examination, they check for dents, the safety of the seals on the taps and plugs of the transformer.
The tightness of the transformer is checked before installation, before topping up or pouring oil. The seals must not be tightened before the tightness test. The tightness of transformers transported with an expander is determined within the limits of the oil indicator marks.
The tightness test of transformers transported with oil and a dismantled expander is carried out by pressure of an oil column 1.5 m high from the level of the cover for 3 hours. transformer. It is allowed to check the tightness of the transformer by creating an excess pressure of 0.15 kgf/cm (15 kPa) in the tank. The transformer is considered sealed if, after 3 hours, the pressure drops to no more than 0.13 kgf/cm (13 kPa). Checking the tightness of transformers transported without oil, filled with dry air or inert gas, is carried out by creating an excess pressure of 0.25 kgf / cm (25 kPa) in the tank. The transformer is considered sealed if the pressure drops after 6 hours to no more than 0.21 kgf / cm (21 kPa) at a temperature environment 10-15 °С. The creation of excess pressure in the transformer tank is carried out by pumping dry air through a silica gel dryer with a compressor or by supplying dry inert gas (nitrogen) from cylinders to the tank.
Acceptance of transformers for installation is documented by an act of the established form. Representatives of the customer, assembly and commissioning (for transformers of size IV and above) organizations participate in the acceptance.
revision
An audit of power transformers is carried out before installation in order to check their condition, identify and timely eliminate possible defects and damage. The audit can be carried out without inspection of the removable (active) part or with its inspection. All transformers subject to installation are subject to audits without inspection of the removable part. An audit with an inspection of the withdrawable part is carried out in cases of detection of damage to the transformer, which cause assumptions about the presence of internal faults.
Transformers currently produced have additional devices that protect their removable part from damage during transportation. This makes it possible, under certain conditions of storage and transportation, not to carry out a laborious and expensive operation - an audit with a lift of the removable part. The decision to install transformers without revision of the withdrawable part should be made on the basis of the requirements of the instructions "Transportation, storage, installation and commissioning of power transformers for voltage up to 35 kV inclusive without revision of their active parts" and "Power transformers. Transportation, unloading, storage, installation and commissioning. At the same time, a comprehensive assessment of the fulfillment of the requirements of the instructions is carried out with the execution of the relevant protocols. If the requirements of the instructions are not met or faults are detected during external inspection that cannot be eliminated without opening the tank, the transformer is subject to revision with an inspection of the removable part.
When carrying out an audit without inspecting the removable part, a thorough external examination of the transformer is carried out, an oil sample is taken for testing for dielectric strength and carrying out chemical analysis; measure the insulation resistance of the windings.
During the inspection, they check the condition of the insulators, make sure that there are no oil leaks at the seals and through the welds, in the presence required level oil in the expander.
The electric strength of the oil, determined in a standard vessel, should not be less than 25 kV for devices with higher voltage up to 15 kV inclusive, 30 kV for devices up to 35 kV and 40 kV for devices with voltage from 110 to 220 kV inclusive.
Chemical analysis of transformer oil is carried out in a special laboratory, and the compliance of the chemical composition of the oil with the requirements of GOST is determined.
The insulation resistance of the windings is measured with a megaohmmeter for a voltage of 2500 V. The insulation resistance is measured between the windings of higher and lower voltages, between each of the windings and the housing. For oil transformers with higher voltage up to 35 kV inclusive and power up to 6300 kVA inclusive, insulation resistance values measured at the sixtieth second () must be at least 450 MΩ at +10 °C, 300 MΩ at +20 °C, 200 MΩ at +30 °C, 130 MΩ at +40 °C. The value of the absorption coefficient must be at least 1.3 for transformers with a power of up to 6300 kVA inclusive.
The physical essence of the absorption coefficient is as follows. The nature of the change in the measured value of the winding insulation resistance over time depends on its condition, in particular, on the degree of moisture. To understand the essence of this phenomenon, we use the equivalent circuit of the winding insulation.
Figure 2 shows the insulation resistance measurement circuit and the equivalent circuit. In the process of measuring the insulation resistance with a megohmmeter, a DC voltage is applied to the insulation of the winding. The drier the winding insulation, the greater the capacitance of the capacitor formed by the winding conductors and the transformer case, and therefore, the greater the charge current of this capacitor will flow in the initial measurement period (at the fifteenth second from the moment the voltage is applied) and the megohmmeter readings will be smaller ( ).
In the next measurement period (at the sixtieth second), the capacitor charge ends, the charge current decreases, and the megohmmeter reading increases () .
The drier the insulation of the windings, the greater the difference in the readings of the megohmmeter in the initial () and final () periods of measurement and, conversely, the wetter the insulation of the transformer windings, the smaller the difference in these readings. 
6. TECHNICAL AND ECONOMIC INDICATORS
State budget standards.
Federal unit prices for equipment installation.
Part 8. Electrical installations
FERM 81-03-08-2001
Order of the Ministry of Regional Development of Russia dated 04.08.2009 N 321
Table 08-01-001. Power transformers and autotransformers
Meter: pcs.
| Price code | Name and technical specifications equipment or types of mounting | Direct costs, rub. | Including, rub. | Labor costs of workers - installers, man-hour |
|||
| Wages of workers installers | machine operation | mate- rials | |||||
| Total | including the wages of the workers who operate the machine | ||||||
| Three-phase transformer: |
|||||||
| 08-01-001-06 | 35 kV with a capacity of 2500 kVA | 7018,51 | 2635,88 | 3748,71 | 360,72 | 633,92 | 274 |
BIBLIOGRAPHY
SNiP 3.03.01-87. Bearing and enclosing structures.
SNiP 12-03-2001. Labor safety in construction. Part 1. General requirements.
SNiP 12-04-2002. Labor safety in construction. Part 2. Construction production.
GOST 12.2.003-91. SSBT. Production equipment. General safety requirements.
GOST 12.3.009-76. SSBT. Loading and unloading works. General safety requirements.
GOST 12.3.033-84. SSBT. Construction vehicles. General safety requirements for operation.
GOST 24258-88. Scaffolding tools. General specifications.
PPB 01-03. Rules fire safety in Russian Federation.
The electronic text of the document was prepared by CJSC "Kodeks"
and verified according to the author's material.
Author: Demyanov A.A. - Ph.D., teacher
Military Engineering and Technical University,
St. Petersburg, 2009
Current repairs of transformers are carried out in the following terms:
- transformers of central distribution substations - according to local instructions, but at least once a year;
- all others - as needed, but at least once every 3 years.
The first overhaul of substation transformers is carried out no later than 6 years after commissioning, and subsequent repairs are carried out as necessary, depending on the measurement results and the condition of the transformer.
The scope of the current repair includes the following works:
- external inspection and repair of damages,
- cleaning of insulators and tank,
- descent of dirt from the expander,
- adding oil and checking the oil gauge,
- checking thermosyphon filters and, if necessary, replacing the sorbent,
- checking the condition of the blow-out fuse, circulation pipes, welds, flange seals,
- security check,
- taking and checking oil samples,
- carrying out preventive tests and measurements.
The scope of the overhaul includes all the work provided for current repairs, as well as repair of windings, magnetic circuit, checking the condition of the contact connections of the windings to the voltage switch and outputs, checking switching devices, repairing their contacts and the switching mechanism, checking the condition of the transformer tank, expanders and pipelines, repairing inputs.
The transformer is taken out of operation for repairs under the following conditions:
- strong internal crackling characteristic of an electrical discharge, or uneven noise,
- abnormal and constantly increasing heating during normal load and cooling,
- ejection of oil from the expander or destruction of the exhaust pipe diaphragm,
- oil leaks and lowering its level below the permissible limit,
- upon receipt of unsatisfactory results of the chemical analysis of the oil.
Aging of the winding insulation and moistening of the oil can lead to ground faults and phase-to-phase faults in the transformer windings, resulting in abnormal operating noise of the transformer.
A “steel fire” failure, which occurs due to a violation of the interlayer insulation of the core or the insulation of the tie bolts, leads to an increase in the heating of the case and oil under normal load, humming and characteristic crackling inside the transformer.
Increased “humming” in the transformer can occur due to the weakening of the magnetic circuit pressing, significant phase load asymmetry, and when the transformer is operating at increased voltage. A crackle inside the transformer indicates a flashover (but not a flashover) between the winding or case taps, or an open ground that could cause electrical discharges from the winding or case taps.
| Loosening the bolts securing the transformer cover and other parts (expander, exhaust pipe, etc.) | Check and tighten all bolts |
| Transformer operates at high voltage | Set the voltage switch to the appropriate position. |
| The pressing of the joints in the magnetic circuit is broken | The tightening of the vertical studs tightening the rods with yokes has loosened. Repress the magnetic circuit, replacing the gaskets in the upper and lower joints of the magnetic circuit |
| The weakening of the pressing of the laminated magnetic circuit | Check all pressure bolts and studs and tighten loose ones. |
| Vibration of the outer sheets of the magnetic circuit | Wedged the sheets of the magnetic circuit |
| Transformer overload | Reduce load | Reduce load unbalance |
| Short circuits between phases, between turns of windings | Repair or replace winding |
Breaks in the windings are a consequence of the poor quality of the contact connections in the windings.
An open in the primary winding of a transformer connected in delta-star, delta-delta and star-star circuits leads to a change in the secondary voltage.
To determine the scope of the forthcoming repair, a transformer fault detection is carried out, which is a set of works to identify the nature and degree of damage to its parts. Based on fault detection, the causes, extent of damage and the necessary amount of repair of the transformer are determined. At the same time, the needs for materials, tools, fixtures for the repair are determined.
| Symptoms | Possible causes of malfunction | Troubleshooting |
| Overheating of transformers | Transformer overloaded | Set overload on instruments or by removing the daily current graph. Eliminate overload by switching on another transformer or disconnect less critical consumers |
| High air temperature in the transformer room | If the air temperature is exceeded by 8 - 10 ° C at a distance of 1.5 - 2 m from the transformer in the middle of its height - improve the ventilation of the room | |
| Reduced oil level in the transformer | Add oil to normal level | |
| Damage inside the transformer (turn circuit, short-circuited circuits due to damage to the insulation of the tie bolts and studs, etc.) | With the rapid development of these damages, an increase in oil temperature will occur, the release of gases and the operation of the gas protection on a signal or shutdown | Eliminate overload or reduce load unbalance in phases |
| Breakdown of windings on the case, between HV and LV windings or between phases | Deterioration of oil quality or lowering of its level | Insulation is tested with a megohmmeter or increased voltage |
| Deterioration of insulation quality due to its aging | If necessary, the winding is repaired, and the oil is topped up or completely changed. | |
| Crackling inside the transformer | Overlapping between windings or taps on the housing | Open the transformer and repair the taps of the windings and grounding |
| Ground break | ||
| Break in the windings | Badly soldered windings | Often a break occurs at the bend of the wire ring under the bolt |
| Damage in taps from windings to terminals | Replaced with a flexible connection in the form of a damper | |
| The contact surfaces of the switching device are melted or burnt out | The switch is poorly assembled or there are short circuits | Repair or replace switch |
| Oil leakage from taps, flanges, welded joints | The valve plug is badly ground, the gaskets of the flange connections are damaged, the tightness of the welded seam of the transformer tank is broken | Grind the valve, replace the gaskets or tighten the bolts on the flanges, weld the seams with acetylene welding. After welding, test the tank with water for 1 - 2 hours with a water column pressure of 1.5 m above the oil level in the expander |
Disassembly of transformers
The disassembly of the transformer during the overhaul is carried out in the following order. Oil is drained from the expander, the gas relay, safety pipe and expander are removed; put plugs on the holes in the tank lid. With the help of lifting mechanisms, slings lift the cover with the active part of the transformer by lifting rings. Raising it by 10 - 15 cm, inspect the condition and position of the sealing gasket, separate it from the tank frame with a knife and, if possible, save it for reuse. After that, the active part is removed from the tank in sections convenient for removing oil sludge, washing the windings and the core with a jet of heated oil and fault detection. Then the active part is installed on a pre-prepared platform with a pallet. Having raised the active part of the transformer 20 cm above the level of the tank, they move the tank to the side, and the active part is installed on a solid platform for ease of inspection and repair. The windings are cleaned of dirt and washed with a stream of transformer oil heated to 35 - 40 ° C.
If the transformer inputs are located on the walls of the tank, then first remove the cover, drain the oil from the tank 10 cm below the input insulators and, having disconnected the inputs, remove the insulators, and then remove the active part from the tank.
Dismantling, inspection and repair of the transformer is carried out in a dry, closed and adapted room for the production of these works.
After removing the active part, the state of the magnetic circuit is checked - the density of the assembly and the quality of the lamination, the strength of the fastenings of the yoke beams, the condition of the insulating sleeves, washers and gaskets, the degree of tightening of nuts, studs, tie bolts, the state of grounding. draw Special attention on the condition of the windings - the wedging on the rods of the magnetic circuit and the strength of the fit of the windings, the absence of traces of damage, the condition of the insulating parts, the strength of the connections of the leads, dampers.
During the overhaul of the transformer, in addition to the above works, if necessary, the yoke of the magnetic circuit is unloaded with the iron being pressed out and the winding coils are removed.
Repair of the transformer magnetic circuit
The most common type of magnetic circuit of power transformers is flat (rod) (Fig. 123, a). The cross section of the yoke 6 and 7 is rectangular in shape, and the rod is in the form of a multi-stage figure 3, close to a circle. The magnetic circuit is pulled together by yoke beams 5 n 8 using through studs 4 and tie rods 2.
Rice. 123. Flat (a) and spatial (b) magnetic cores of the transformer:
1 - axes of the rods; 2 - vertical tie rods: 3 - multi-stage rod figure; 4 - through studs; 5, 8 - yoke beams; 6, 7 - cross sections yoke; 9 - support beam; 10 - bandage; 11 - insulating tube; 12 - insulating gasket; 13 - Belleville spring, 14 - insulating gasket.
Transformers with a power of 250 - 630 kVA are produced with pinless magnetic cores. The pressing of the rod plates in these transformers is carried out by means of strips and wedges driven between the magnetic circuit and the cylinder. Recently, the industry has been manufacturing 160 - 630 kVA power transformers with a spatial magnetic circuit (Fig. 123, b). The magnetic core of such a transformer is a rigid structure, the vertical axes of the rods 1 of which have a spatial arrangement. The steel sheets of the rod are pressed with a bandage 10 of insulating material or a steel tape with a lining of insulating material instead of studs. The upper and lower yokes are pulled together by vertical tie rods 2 by means of nuts, under which belleville springs 13 are placed. Insulating gaskets 14 are used to isolate the studs from the yoke, and insulating tubes 11 are used from the rods. The entire structure of the magnetic circuit is fastened with studs to the support beams 9.
The spatial magnetic circuit is made butt instead of laminated, since the yoke and rods are connected into a magnetic circuit by docking. To avoid shorting between the steel of the yoke and the rod, an insulating gasket 12 is laid between them.
In previously produced transformers, the magnetic cores were pulled together by horizontal studs, insulated from the steel of the magnetic core and passing through holes in the plates.
The disassembly of the magnetic circuit is as follows: unscrew the top nuts of the vertical studs and the nuts of the horizontal studs, remove them from the holes in the yoke, remove the yoke beams and proceed to unload the upper yoke of the magnetic circuit, starting with the outermost packages of two or three plates. The plates are folded in the same sequence in which they are removed from the yoke and tied into packages.
In magnetic cores tied with horizontal studs, the insulation of the studs is often damaged, which leads to short circuits of steel plates and causes strong heating of iron by eddy currents. During the repair of a magnetic circuit of this design, the insulating sleeve is replaced with a new one. In the absence of spares, the sleeve is made from bakelite paper, wound on a hairpin, impregnated with bakelite varnish and baked. Insulating tubes for studs with a diameter of 12 - 25, 25 - 50 and 50 - 70 mm are made with a wall thickness of 2 - 3, 3 - 4 and 5 - 6 mm, respectively. Pressure insulating washers and spacers for studs are made of electrical cardboard with a thickness of 2 mm or more.
Restoration of the broken insulation of the magnetic circuit plates begins with boiling the sheets in a 10% sodium hydroxide solution or in a 20% trisodium phosphate solution, followed by washing the sheets in hot (50 - 60 ° C) running water. After that, a mixture of 90% hot-drying varnish No. 202 and 10% pure filtered kerosene is carefully sprayed onto a steel sheet heated to 120 ° C. Glyptal varnish No. 1154 and benzene and gasoline solvents can be used to isolate the plates. After applying the insulation layer, the plates are dried at 25 C for 7 hours. For large volumes of work, special machines are used for varnishing the plates, and special ovens are used for baking and drying them.
When replacing worn-out plates, new steel plates made according to samples or templates are used. In this case, the sheets are cut in such a way that the busbar side of the plates is along the rolling direction of the steel. Holes for tie rods in the plates are made by stamping, not drilling. After making the plate, I cover it! isolated in one of the above ways.
Laying starts from the central package of the middle rod, laying the plates with the insulated side inside the yoke. Then, the extreme packages are blended, starting with long plates and avoiding overlapping of narrow plates of rods and gaps in the joints. The holes in the yoke plates must exactly match the holes in the rod plates. The plates are leveled by hammer blows on a copper or aluminum bus. A well-stitched yoke has no gaps between the layers of plates, gaps, or damage to the insulation between the plates at the junction.
After leveling the upper yoke, the installation of the upper yoke beams is performed and pressing with their help of the magnetic circuit and windings. The yoke beams in transformers are isolated from the plates with an annular washer made of electric cardboard 2-3 mm thick with pads attached on both sides.
On both sides of the upper yoke, yoke beams are installed into the openings of the beams, four vertical tie rods with insulating tubes are inserted, cardboard and steel washers are put on the ends of the studs and tightened with nuts, Grounding of the vertical yoke beams is carried out with several tinned copper tapes.
Nuts are tightened on the tie rods, pressing the upper yoke, and the nuts of the vertical pressing rods are evenly tightened; the winding is pressed, and then the upper yoke is finally pressed. They measure the insulation resistance on the studs with a megger, unscrew the nuts on the studs so that they do not unscrew themselves during the operation of the transformer.
Repair of transformer windings
Windings of power transformers are the main element of the active part. In practice, windings are damaged much more often than other elements of the transformer.
Depending on the power and rated voltage in transformers, various designs windings. So, in power transformers with a power of up to 630 kVA at low voltage, mainly single- and double-layer cylindrical windings are used; with a power of up to 630 kV -A at the highest voltage of 6, 10 and 35 kV, multilayer cylindrical windings are used; with a power of 1000 kVA and more, screw windings are used as LV windings. At the helical winding, the rows of wound turns are arranged so that oil channels are formed between them. This improves winding cooling conditions due to cooling oil flows. Helical winding wires are wound on paper-bakelite cylinders or split templates using electrical cardboard strips and spacers, which form vertical channels along the inner surface of the winding, as well as between its turns. Screw windings have high mechanical strength. Repair of windings of power transformers can be carried out without unloading or with unloading of magnetic circuits.
Slight deformation of individual turns, damage to small sections of wire insulation, loosening of windings, etc., are eliminated without dismantling the active part of the transformer.
When repairing the windings without removing them, the deformed turns of the windings are straightened by hammer blows on wood pad superimposed on the coil. When repairing turn insulation without dismantling the windings, oil-resistant varnished cloth (LKhSM brand) is used, which is applied to the bare conductor of the turn. The conductor is pre-wrung out with a wooden wedge for the convenience of working on the insulation of the coil. Lacquered cloth tape is wound overlapping with overlapping of the previous turn of the tape on V2 part of its width. A general bandage of cotton tape is applied to the coil isolated with varnished cloth.
Pre-pressing of weakened windings, the design of which does not provide for pressing rings, is carried out using additional insulating gaskets made of electrical cardboard or getinaks. To do this, a wooden wedge is temporarily hammered into adjacent rows of winding to weaken the density of the gaskets, thus ensuring the entry of the driven pressing gasket in the weakened place. Clog the pressure pad and move on to the next place. This work is carried out along the entire circumference of the winding, clogging the spacers between the yoke and additional insulation.
Significant damage to the windings (turn short circuits, breakdown of the insulation of the windings on the steel of the magnetic circuit or between the HV and LV windings, etc.) is eliminated after the windings are removed.
To dismantle the windings, the magnetic circuit of the transformer is unloaded. Work begins with unscrewing the upper nuts of the vertical studs. Then the nuts of the horizontal studs are unscrewed, the horizontal pressing studs are removed from the hole in the yoke and the yoke beams are removed. One of the yoke beams is pre-marked with a symbol (VN or NN).
The unloading of the plates of the upper yoke of the magnetic circuit begins simultaneously from the side of the HV and LV, taking out 2 - 3 plates alternately from the extreme packages. The plates are laid in the same order in which they were removed from the yoke. and tied into packages. To protect the plates of the cores of the magnetic circuit from damage to the insulation and scattering, they are tied by threading a piece of wire into the hole for the stud.
The dismantling of the windings of transformers of small power is carried out manually, and with a power of 630 kV A and above - using removable devices. Before lifting, the winding is firmly tied with a rope along the entire length and the grips of the device are carefully brought under the winding.
Damaged coils are replaced with new ones. If a new coil during storage could be moistened, then it is dried in a drying chamber or with infrared rays.
The copper wire of the failed coil is reused. To do this, the wire insulation is burned in the furnace, washed in water to remove the remaining insulation, straightened and wound with new insulation. For insulation, cable or telephone paper 15–25 mm wide is used, wound onto the wire in two or three layers. The bottom layer is applied end-to-end, and the top layer is overlapped with overlapping of the previous turn of the tape by ½ or ¼ of its width. Strips of insulating tape are glued together with bakelite varnish.
Often, a new coil is made to replace a failed coil. The method of manufacturing windings depends on their type and design. The most perfect design is a continuous winding, produced without breaks. In the manufacture of a continuous winding, the wires are wound on a template wrapped with a sheet of electrical cardboard 0.5 mm thick. Laths with spacers are laid on the cylinder installed on the winding machine to form channels and the end of the winding wire is fixed with cotton tape. Winding of turns of continuous winding can be done clockwise (right-hand version) and counter-clockwise (left-hand version). Turn on the machine and guide the winding wire evenly along the cylinder. The transitions from one coil to another during winding are determined by the settlement note and are performed in the interval between the same two rails. The places of wire transitions are additionally insulated with boxes of electrical cardboard, fixed with a cotton tape. After winding is completed, bends are made (external and internal), arranging them in accordance with the drawings, and isolating them. At the ends of the coil, insulating support rings are installed and removed from the machine. The coil is pulled together with metal plates by means of tie rods and sent for drying in a drying chamber.
The scheme of the algorithm and the technological map for the manufacture of a multilayer winding of a HV transformer with a power of 160 kV A and a voltage of 10/04 kV are given below.
| No. p / p | Winding manufacturing procedure | Tool, material |
| 1. | Prepare a bakelite cylinder, for which check its condition and dimensions, strengthen it on the machine. If there is no ready-made one, make a cylinder of electric cardboard longer than the length of the winding by 32 mm | Yardstick Electrocardboard EMC 1.5 - 2 mm thick |
| 2. | Prepare insulating material for interlayer insulation. For the manufacture of layered insulation, electric cardboard is used with a thickness equal to the diameter of the wire (or the thickness of the coil); the finished insulation is wrapped with telephone paper. | Scissors, cable paper (0.1 m), EMC electric cardboard (0.5 mm) telephone paper (0.05 mm) |
| 3. | Install the spool of wire on the turntable, adjust the wire tension. | Turntable, PB winding wire with a diameter of 1.45 / 1.75. |
| 4. | Install the end equalizing belt on the cylinder close to the cheek of the template. Bend the wire lead at a right angle. | Ribbons (keeper, lacquer). |
| Isolate the output and fix. | ||
| Pass the tap through the cutout in the template and fix the template on the faceplate of the winding machine. | Hammer, fiber wedge. | |
| Wind one layer of the coil, sealing its turns in the axial direction with a wedge. | Cable paper 0.1 mm. | |
| Wrap the first winding layer with layers of cable paper. | ||
| 5. | Wind the winding layers alternately. Each transition from layer to layer should lag behind by one third of the circle. At the end of each layer (2 - 3 turns before the end), an equalizing belt is installed (as in 4). Between the layers, beech planks are installed in accordance with the settlement note. | Manual scissors for metal. Beech planks with cardboard boxes. |
| When making taps on beech strips, according to the settlement note, the exit points of the taps are marked. | ||
| 6. | Perform withdrawals in accordance with the settlement note. The cross section of the taps must be at least 1.5 - 2 sections of the winding wire with a diameter of up to 1 mm and 1.2-1.25 - with a diameter of more than 1 mm. | |
| Insulate the end of the coil with tape in a semi-overlapping layer. | ||
| Pass the end of the coil through the ribbon loop and tighten it. Cut off the end of the tape. | ||
| Lay the cable paper half-overlapping on the upper layer windings. | ||
| Strip the insulation at the ends of the winding. | ||
| 7. | Remove the winding from the machine. | A hammer. |
| Tie the winding in the axial direction in 3 - 4 places with tape. | ||
| Fasten in connected places with electric cardboard pads. | ||
| 8. | Soak the winding in varnish for at least 15 minutes and allow the varnish to drain (15 - 20 minutes). | Installation for impregnation and drying. Glyftel varnish GF-95. one |
| Dry the winding at 100°C for 5-6 hours. | ||
| Bake the varnish of the winding at a temperature of 85 - 90 ° C for 18 - 20 hours with hot air blowing. | ||
| Remove from the oven and cool the winding. |
The winding is dried at a temperature of about 100 ° C for 15 - 20 hours, depending on the volume of the coil, the degree of insulation moisture, the drying temperature, etc. Then it is pressed, impregnated at a temperature of 60 - 80 ° C with TF-95 varnish and baked at a temperature of 100 ° C for 10-12 hours. The winding is baked in two stages - first, the impregnated winding is dried at a slightly lower temperature to remove solvents remaining in the insulation, and then the temperature is increased to bake the winding. Drying and baking the winding increase the dielectric strength of the insulation and the mechanical strength of the coil, giving it the necessary solidity.
Rice. 124. Machine for winding transformer windings:
1 - electric motor; 2 - body; 3 - belt drive; 4 - counter of turns; 5 - clutch; 6 - spindle; 7 - textolite disk; 8 - nut; 9 - template; 10 - control pedal.
For the manufacture of windings, various machines are used. The console winding machine for winding transformer windings of small and medium power (up to 630 kVA) (Fig. 124) consists of a template with two wooden counter wedges 9, clamped textolite disks 7 and fixed nuts 8. The template is mounted on a spindle 6, which rotates from an electric motor 1 through a belt drive 3. To count the number of turns of wire, the machine has a coil counter 4. The finished winding is removed from the template after unscrewing the nut 8, removing the right disk and spreading the wedges 9 of the template. The machine is controlled by a pedal 10 connected to the clutch 5.
Rice. 125. Insulation of the magnetic circuit (a) and wedging of the windings (c) when installing the transformer windings:
1 - yoke insulation; 2 - a cylinder made of electric cardboard; 3 - round rods; 4 - slats; 5 - extension.
The windings are mounted on the rods of the magnetic circuit, previously tightly pulled together with a keeper tape (Fig. 125). The windings mounted on the magnetic circuit are wedged using beech strips and rods, having previously laid two layers of electric cardboard between the HV and LV windings. The beech strips rubbed with paraffin are first inserted between the wrappers to a depth of 30 - 40 mm, and then they are hammered alternately in opposite pairs (Fig. 125, b). To save cylindrical shape windings, first round rods 3 are hammered, and then strips 4 with a hammer using a wooden extension 5, avoiding splitting the ends of the rods or strips.
In the same way, the LV winding is wedged on the rod with round wooden studs, hammering them around the entire circumference of the winding between the cylinder and the steps of the magnetic circuit rod.
After the end of the wedging of the windings, the upper yoke insulation is installed and the upper yoke of the magnetic circuit is charged.
In transformers of small power, for connecting windings with switch contacts and input rods, the ends of the wires are carefully stripped over a length of 15 - 30 mm (depending on their cross section), superimposed on each other, connected with a bracket of tinned copper tape 0.25 - 0 thick, 4 mm or a bandage of tinned copper wire 0.5 mm thick and soldered with POS-30 solder, using rosin or borax as a flux.
In high-power transformers, copper-phosphorus solder with a melting point of 715 ° C is used to connect the ends of the windings and attach them to the taps. The place of soldering is cleaned, insulated with paper and varnished cloth up to 25 mm wide and coated with GF-95 varnish. Winding taps are made with a damper at the end to protect the wire from breaking. The taps of the HV windings along the entire length are varnished GF-95.
The insulating parts of the transformer core are made of cardboard, paper, wood. These materials are hygroscopic and absorb moisture from the surrounding air, reducing their electrical insulating properties. For high electrical strength of the core insulation, it is dried in ovens in special cabinets, with a blower, etc.
The most commonly used in practice is the method of drying in its own heated tank: when an alternating current passes through a special winding superimposed on the insulated surface of the tank, a strong magnetic field is formed, which closes through the steel of the tank and heats it.
Dry the transformers in a tank without oil (to speed up the drying process of the active part and preserve the quality of the oil and winding insulation). The magnetizing winding placed on the tank heats the tank. The winding turns are placed on the tank in such a way that at least 60% of the winding is in the lower part of the tank. During warm-up, the tank lid is also insulated. The increase in temperature is controlled by changing the number of turns of the winding, while not allowing the temperature of the windings to rise above 100°C, and the temperature of the tank above 110-120°C.
The indicator of the end of drying is the steady value of the insulation resistance of the windings for 6 hours at a constant temperature not lower than 80°C. After drying is completed and the temperature of the windings decreases to 75-80 °C, the transformer tank is filled with dry oil.
Transformer tank repair
The inner surface of the tank is cleaned with a metal scraper and washed with used transformer oil. Dents are heated by a flame gas burner and straighten with hammer blows. Cracks on the edge and the wall of the body are welded by gas welding, and in the pipe - by electric welding. To check the quality of welding, the outer side of the seam is cleaned and covered with chalk, and moistened with kerosene from the inside (if there are cracks, the chalk is wetted with kerosene and darkens). The tightness of the body is checked by filling the tank with used oil for 1 hour at a temperature not lower than 10°C.
Before welding, cracks at its ends are drilled through holes with a diameter of several millimeters. The edges of the crack are chamfered and welded by electric welding. The density of the seam is controlled using kerosene. Loose seams are cut out and welded again.
Extender repair
When repairing the expander, check the integrity of the glass tube of the oil indicator, the condition of the seals. The defective flat glass or glass tube of the oil indicator is replaced. Rubber gaskets and seals that have lost elasticity are replaced with new ones made of oil-resistant rubber. The sediment is removed from the bottom of the expander and washed with clean oil. The cork is rubbed with a fine abrasive powder. The gland packing is replaced with a new one, which is prepared from an asbestos cord soaked in a mixture of fat, paraffin and graphite powder.
Check the strength and tightness of the fastening of the glass diaphragm at the safety pipe; inner part pipes are cleaned of dirt and washed with clean transformer oil.
When repairing transformers, special attention is paid to the safety of insulators and the reinforcement of the bushings. Chips up to 3 cm² or scratches up to 0.5 mm deep are washed with acetone and covered with two layers of bakelite varnish, drying each layer in drying cabinet at a temperature of 50 -60°C.
Repair of reinforcing seams
Reinforcement joints are repaired as follows: the damaged section of the joint is cleaned with a chisel and filled with a new cementing composition. If the reinforcing seam is destroyed by more than 30%, the bushing is completely replaced. The cementing composition per serving of one input is prepared from a mixture consisting (by weight) of 140 parts of magnesite, 70 parts of porcelain powder and 170 parts of magnesium chloride solution. This composition is used for 20 minutes. After the putty has cured, the seam is cleaned and coated with 624C nitro enamel.
Cleaning the thermosyphon filter
The thermosyphon filter is cleaned from the old sorbent, the internal cavity is washed with transformer oil, filled with a new absorbent and attached to the transformer tank on flanges.
Switch repair
Repair of the switch consists in the elimination of defects in the contact connections, insulating tubes of the cylinders and sealing devices. The contacts are cleaned, washed with acetone and transformer oil. Burnt and melted contacts are filed with a file. Broken and burnt contacts are replaced with new ones. Minor damage to the insulation of the tube or cylinder is restored with two layers of bakelite varnish. The weakened points of connection of the winding taps are soldered with POS-30 solder.
The repaired switch is assembled, the installation site is wiped with a rag, the gland seal is inspected, the switch handle is replaced and the studs are tightened. The quality of the switch is checked by switching its positions. Switching should be clear, and the locking pins in all positions should fully enter their sockets.
Checking the operation of a switching device for voltage regulation under load consists in determining the correct operation of the moving contacts in series. a and b switch and contactors K1 and K2. Violation of the sequence of operation of these elements of the switching device can lead to serious damage to the transformer and an accident in the electrical network.
Transformer Assembly
The assembly of a transformer without an expander, the inputs of which are located on the walls of the tank, begins with lowering the active part into the tank, then the inputs are installed, the taps from the windings are connected to them and the switch, and the tank cover is installed. Small power transformer covers are installed on the lifting studs of the active part, complete necessary details, and in more powerful ones - assembled separately. During assembly, the correct installation of sealing gaskets and the tightening of the fixing nuts are monitored. The length of the lifting studs is adjusted so that the removable part of the magnetic circuit and the cover are correctly positioned in their places. Pre-determine the required length of the lifting studs wooden lath. The length of the studs is adjusted by moving the nut.
The active part of the transformer with the help of lifting devices is lowered into the tank with a sealing gasket made of oil-resistant sheet rubber (Fig. 126).
Rice. 126. Gasket joint (a) and methods of installing the gasket (s) when sealing the tank with an oil-resistant rubber gasket:
1 - tank wall; 2 - limiter; 3 - tank cover; 4 - gasket; 5 - tank frame.
Brackets are installed on the tank cover for attaching an expander with an oil indicator, a safety pipe, a switch actuator, a gas relay and a blowout fuse.
The transformer is filled with dry transformer oil to the required level according to the oil indicator of the expander, the tightness of the fittings and parts is checked, as well as the absence of oil leakage from joints and seams.