How are power transformers repaired? Electrical Machinery and Occupational Safety Maintenance with dry cooling

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Ministry of Fuel and Energy of the Russian Federation

Guiding normative document

TYPICAL TECHNOLOGICAL INSTRUCTION.
TRANSFORMERS WITH VOLTAGE 110-1150 kV,
POWER 80 MW×A AND MORE.
MAJOR REPAIR

RDI 34-38-058-91

UDC 621.314.222.6.004.67(083.96)

DEVELOPED by TsKB Energoremont

PERFORMERS B.G. KNYAZEV, V.L. RASKIN, L.L. FEDOSOV

AGREED with PP "Mosenergoremont" 10.04.91 Chief Engineer A.M. KUZNETSOV,
VNIIE 04/11/91 Deputy engineer L.G. MAMIKONYANTS,
plant RETO 15.04.91 Chief engineer G.M.MINASHKIN

APPROVED by Glavremtekhenergo on April 18, 1991. Chief Engineer G.A. ULANOV

1. INTRODUCTION

This manual has been developed for overhaul power transformers(autotransformers and reactors) general purpose voltage 110-1150 kV, power 80 MV×A and more domestic production performed under operating conditions.
The instruction was developed in accordance with the requirements of standards for repair documentation, as well as taking into account the experience of operating and repairing new types of transformers with voltage up to 1150 kV inclusive and taking into account changes in the governing documents.
The instruction establishes the requirements for the materials used in the repair and the requirements for the conduct of repairs.
The instruction is intended for personnel of power plants, enterprises electrical networks, repair enterprises and organizations of the USSR Ministry of Energy involved in the operation and repair of transformers, as well as for representatives of transformer manufacturing plants involved in the overhaul of transformers under operating conditions.
With release of this Instruction the "Guidelines for the overhaul of transformers with a voltage of 110-750 kV, a capacity of 80 MB × A and more" (M .: SPO Soyuztekhenergo, 1982) are cancelled.

2. GENERAL PROVISIONS

2.1. The sequence of work during the overhaul of the transformer is determined by the network model of a typical technological process (Fig. 1).

Rice. 1. Network model of a typical technological process of transformer overhaul:
1 - preparation for repair; 2 - shutdown (disconnection of tires, drops); 3 - dismantling of the cooling system; 4 - repair of the cooling system; 5 - delivery of the transformer to the repair site; 6 - heating of the transformer; 7 - dismantling of inputs and fittings; 8 - transformer opening; 9 - repair and testing of bushings; 10 - repair of fittings; 11 - tank repair; 12 - repair and testing of the active part; 13 - transformer assembly; 14 - fill transformer oil; 15 - repair of the switching device; 16 - heating and testing of the transformer; 17 - moving the transformer to the installation site; 18 - installation of the transformer on the foundation; 19 - final work

Preparation for the repair of the transformer should include checking the completeness of the technical documentation, preparing the repair site, checking the performance technological equipment, equipment and tools, as well as the availability of the necessary materials.
2.2. The set of technical documentation for the overhaul of the transformer should include:
technical documentation of the manufacturer;
network chart;
an act on the readiness of the railway track;
route technological process;
list of technological equipment, tooling and tools;
list of materials needed for repair.
2.3. The repair site should provide protection of the active part and bushings from dust and moisture, as well as placement and communication between technological sections in accordance with the diagram shown in Fig. 2.
The repair site must have:
railway input of at least 20 m with an anchor to secure the chain hoist;
electrical assembly for simultaneous connection of the transformer drying circuit, welding and soldering equipment, and other power tools;
compressed air supply for 0.5-0.6 MPa (5-6 kg/cm2);
locksmith workbenches;
oil pipeline coming from the oil facilities;
efficient ventilation system; necessary funds firefighting, posters.
2.4. Before starting the repair, the equipment should be checked for operability and the availability of materials according to the relevant lists of equipment and materials of the technological process.
2.5. Annexes 1 and 2 give lists of the main technological equipment and materials used in the overhaul.
When determining the nomenclature and quantity of materials for the overhaul of a particular transformer, it is necessary to use the "Consumption rates for materials for repairs" NM 34-Z8-103-88 (M .: SPO Soyuztekhenergo, 1989).

Rice. 2. Scheme of connections between technological sections during overhaul:
1 - place of installation of the transformer (dismantling and installation); 2 - site for repair of the active part; 3 - manufacturing area small parts and nodes; 4 - area for repair of the cooling system; 5 - area for the repair of fittings and small units; 6 - area for repair and testing of bushings; 7 - tank and lid repair area; 8 - area for repair of expander and exhaust pipe; 9 - area for repair and testing of protection and control devices

The range and quantity of technological equipment should be determined according to the technological process for the repair of the transformer.

During the operation of the transformer in the electrical installation, it gradually loses its original properties, and without proper maintenance it will simply fail. It comes from constant negative impact electrodynamic, thermal and mechanical loads. In order to prevent the failure of any transformer, it is necessary to carry out, in addition to daily external inspection, the following types of repairs:

  1. Current;
  2. Capital.

They are scheduled preventive maintenance. There is one more special kind repair - extraordinary. It is carried out in case of detection of a defect, if it can lead to a failure in work. This decision is not accepted by simple electrical personnel, this must be done either by the head of the Consumer, or by the person responsible for the electrical facilities of this workshop or section. The staff only informs their management about malfunctions in the work.

One of the most common types of transformers in production has the abbreviation TMG (oil sealed transformer) and is used in almost all types of substations and switchgears. Winding repair and maintenance is a very difficult task, since only to inspect them you need to drain all the oil and disassemble the hermetically clamped case.

Who sets the frequency of current repairs of transformers

Depending on the local conditions operation, as well as the condition of the transformer, current repairs are carried out as necessary. Their frequency is established by the technical manager or the person responsible for the electrical facilities. Most often, these works are performed at least once a year. Sometimes this period can be extended up to 1 time in three years. Major renovations are a different story. Overhaul is carried out according to the standard range of works and should be carried out:

  1. For transformers of 110 kV and above, whose power is from 125 MVA and more, no later than 12 years after its commissioning. This is done taking into account the result of diagnostic control. Further repairs are made as needed;
  2. All others are less powerful transformers(TMG) are subject to major repairs in accordance with their condition and based on the results of diagnostic control.

Conclusion to the repair of a power transformer sequence

During operation, any transformer, step-down or step-up, is taken out of service in an emergency in the following cases:

  1. Internal crackling, which is characteristic of an electrical discharge between two conductors of opposite polarity;
  2. Abnormal or uneven noise that appears both with and without load;
  3. With unreasonable heating, which increases even at rated load and good cooling;
  4. With oil emissions, which can be both from the expander and from the destroyed exhaust pipe diaphragm;
  5. With a strong oil leak, as well as when the minimum allowable level is reached;
  6. After receiving bad results from a chemical analysis of the oil from the laboratory.

The sequence of actions of personnel when decommissioning a transformer for repair is clearly regulated against a signature. Depending on local conditions and the connection scheme of the transformers, these switchings may differ slightly from each other, but the main logical chain still remains unchanged. Most importantly, they must be carried out without consequences for the powered equipment and for sources that consume electricity, and also safely, that is, using both basic and additional funds personal protection.

Here is the sequence of shutdowns and switchings in the circuit of a step-down three-phase oil or dry transformer of a substation, to bring it into repair:

  1. If there is a sectional disconnector and an oil switch on the low side, then to ensure uninterrupted power supply to the supplied consumers. in this case, first of all, the disconnector is turned on and only then the sectional oil switch;
  2. The low side oil switch is turned off. Now both sections are powered by one transformer, which, during the repair of the other, will feed both sections. Naturally, this is if there are only two of them, like transformers;
  3. The introductory oil switch is turned off, that is, from the high side;
  4. Now it is already possible to provide a visible break to the power buses of the transformer being taken out for repair by disconnecting the line or bus disconnectors;
  5. From the low and from the high side, portable grounding should be installed, of course, after a direct check of the absence of voltage and posting safety posters.

After that, a team is allowed to the repaired transformer, in compliance with all organizational and technical measures.

Current repair of power transformers

The scope of work performed during the current repair includes:

  • Thorough external examination;
  • Reading the case, wiping insulators;
  • Tightening of all bolted connections, special attention should be paid to current-carrying connections, in case of their oxidation, it is necessary to unwind, clean and re-tighten;
  • Checking the cooling system and operation of the oil indicator device;
  • Operation of gas protection and cleaning of auxiliary contacts in it;
  • If there automatic devices cooling, it is necessary to check their operation and performance;
  • The descent of the wag and condensate from the sump of the expander;
  • Checking the degree of humidity of silica gel. Particles color pink must be replaced with new ones;
  • Adding oil to the expansion tank if necessary;
  • Measurement of insulation resistance, this procedure is performed with a megger rated for a voltage of 2500 volts. The instrument error should not exceed 10–15%.

If between the current repairs during operation minor faults were noticed, they must be eliminated by the repair personnel. At the same time, the number of units and parts that must be replaced with new ones should be minimal.

During current repairs of dry-type transformers, it is necessary to remove the casing and make sure that there are no electric heating and mechanical damage to all its parts. After tightening, be sure to blow compressed air, only after that put back the casing. Repair pulse transformer due to its small size, it can be performed even at home.

Overhaul of power transformers

During a major overhaul, the cover must be opened, and a thorough check of all components. Then it is tested according to normative documents. Repair of large power oil transformers (TMG) is carried out directly at the installation site using prefabricated structures, without sending it to the repair shop. If there are transformer towers built near switchgears or repair sites for machine rooms with access roads, then they will also be used. Repair of oil transformers (TMG) should include complete replacement old oil to new.

Small power transformers (welding, pulse, etc.) are repaired in specially equipped workshops or repair shops. These rooms must reliably protect the disassembled transformers from dust and various atmospheric precipitation on their parts. Species especially important works, which should be performed only by highly specialized workers with skills and knowledge:

  • Delivery of TMG to the repair site. Its loading, unloading and transportation;
  • Removal of contact conclusions;
  • Repair of the active part of the transformer;
  • Moving and installing individual components and assemblies.

Moreover, employees must be able to perform not only electrical work, but also rigging. Having passed the appropriate training with passing exams, as well as receiving a supporting document. Technological process repair of the transformer must be carried out with high quality and strictly according to the schedule, then this unpretentious equipment will last for decades. Testing the transformer after repair is reduced to:

  • determination of the transformation ratio. It is determined for all existing windings and branches;
  • measurement of winding insulation resistance;
  • applying high voltage to the primary winding. Each winding is subjected to this test. The technology of this process is carried out using a step-up autotransformer. It is he who makes it possible to increase and decrease the test voltage smoothly

Repair of welding transformers

Before proceeding directly to the repair of the welding transformer, it is worth making sure that the terminals for connection are not burned. power wire. Terminal block, to which the ends of the welding wires are connected, the most weakness this device. Phase winding short circuits are rare, most often these are short circuits to a grounded case, and if they nevertheless occur, strong heating will be observed. That is, when repairing welding transformers special attention must be paid to all bolted connections, since the welding process is still associated with the constant operation of the transformer in the short circuit mode. Also, this repair is aimed at revision of the mechanism connecting the core, and reliable fastening of the windings on the magnetic core. Repair of windings is a very rare procedure and it comes down to applying a special varnish to its damaged areas or completely replacing it with a new one.

High-quality maintenance and overhaul of transformers, performed in in full, often becomes the main component of its long-term trouble-free operation.

Transformer Overhaul Video

Transformer power type is a complex piece of equipment that requires periodic maintenance. This ensures its stable operation. long time. Capital and "current repairs of power transformers" are carried out with a certain frequency and according to established scheme. Also, "between overhaul tests of the power transformer" are carried out. Features of the maintenance and repair of the presented units will be discussed further.

Varieties

There are several types of repair of power equipment. If service is required for the instrument high power, for example, 1600 kVA, 2500 kVA, 6300 kVA, etc., special skills are indispensable. Special equipment may only be inspected and repaired by a qualified professional.

There are the following types of repairs:

  1. Maintenance. It is produced according to the schedule established by the standards. In this case, the operation of the equipment does not stop.
  2. Maintenance power transformer. Requires disconnection of the device from the network. Refers to preventive action.
  3. Overhaul of transformers. Measures are taken to eliminate malfunctions that occurred during the operation of the unit, as well as in case of obsolescence, wear and tear of the system. After 10-15 years of operation of the installation, it must be reconstructed.

In addition to the presented actions, inter-repair and “post-repair tests” are carried out. For devices with a power of more than 110 kV, the first major maintenance is required 12 years after the start of operation. For other varieties, similar actions are performed according to test results and general condition.

Inspection of "power oil transformers" and units with an oil cooling system of the type "TSZM", "TSZN" and other varieties that incorporate adjusting elements (OLTC) is required once a year. For devices without an on-load tap-changer, the type of service presented is carried out every two years.

For other types of maintenance, it is required at least once every four years. There are also special instructions. They are used in areas of high pollution.

Interrepair tests are carried out in accordance with the rules established by the PPR (project for the production of works).

Maintenance

The maintenance process is carried out at regular intervals. The procedure is clearly regulated. It includes several required steps:

  • Inspection of the "transformer" device from the outside, definition possible faults and hull damage.
  • Cleaning the tank, insulators.
  • Elimination of mud deposits in the expander.
  • “Oil” is added (if necessary), the state of the coolant level indicator is studied.
  • Thermosyphon type filters are inspected. If necessary, they change the sorbent.
  • The condition of the circulation pipes, fuse, seals, welds is assessed.
  • For a device with an oil cooling system, samples of the internal fluid are taken.
  • "Power transformer tests" and measurements of the main indicators of their work are carried out.

According to a certain technology, the state of the installation is assessed after maintenance.

Maintenance with dry cooling

Dry-cooled equipment has cast insulation. It is easy to use, not fussy. Maintenance of such a device is carried out according to the established regulations. Its items depend on the environmental and operating conditions. The process is carried out according to the following scheme:

  1. The cooling system should be checked every six months. If fans are installed in the structure ( forced ventilation), the quality of their work must be assessed. It is important to determine the performance of the temperature controller.
  2. The surface of the device is cleaned of various pollution. This procedure is carried out once a quarter or six months. If a Environment It has high level contamination, cleaning is carried out more often.
  3. Once a year, the hull is examined for cracks. If necessary, they should be removed immediately.
  4. The integrity of the insulation, protection is checked metal elements designs. The inspection is carried out once a year.
  5. The fixation of the winding must be strong. It is checked during inspection. If damage is found in the cast winding, it is completely changed.

Caring for a dry type of device requires less effort and time. This is due to the absence of fluid in the system, the state of which must be constantly monitored. Oil varieties need to be investigated more carefully.

Current repair with oil type cooling

The complexity of the current troubleshooting of an oil-cooled instrument depends on the complexity of its design and operating characteristics. Includes a tank filled with oil. This structural element requires special attention. Maintenance is carried out according to the following scheme:

  1. The process is carried out without transporting the unit, at the place of its installation.
  2. The body is inspected, external defects are detected.
  3. Minor malfunctions in the fittings, cooling system and attachments are eliminated.
  4. Fasteners tighten up. If there is a leak, it must be sealed. Oil is added.
  5. Silica gel is changed in the thermosyphon filter.
  6. The housing is free of contaminants.
  7. Resistance is measured insulating material on windings.

Video: Maintenance of a 35 kV power transformer

The above actions are performed within 1-2 days. In this case, the working part of the transformer is not affected.

Overhaul

Overhauls of power transformers include the entire list of routine maintenance work, as well as the elimination of possible malfunctions of the "windings", core, switches. During this procedure, the winding connections at the terminals and points of contact with the voltage switch are inspected. The condition of the oil tank, pipelines, expanders, conclusions are being investigated.

In Russia major view maintenance can be deep or involves opening the oil tank. This is a complex procedure that must be performed by trained professionals.

Video: Overhaul of a 110 kV transformer

Deep overhaul

When conducting capital restoration equipment is disconnected from the network. If deep maintenance is required, a series of sequential actions are taken:

  1. The installation case opens.
  2. The active part rises.
  3. The windings are disconnected from the magnetic drive.
  4. Coils are rewound in accordance with the design features.
  5. The main insulation is restored or completely replaced.
  6. The functioning of the magnetic system is adjusted.
  7. Branches, inputs, coolers and switches, fans, oil pumps and its shutoff valves are subject to replacement or restoration.

This is difficult process, requiring high qualification of the master, regardless of the type of device. In some cases, it will be necessary to open the oil tank. To do this, after carrying out the above steps, it is necessary to dry the working part. The tank is examined on a special site. In this case, the power must be completely turned off.

Preventive testing

Testing the operation of equipment after prevention also goes through a series of successive stages. First of all, the conditions for turning on the device are studied. Winding resistances are measured. Next, the deviation of the dielectric losses of the coil insulation is measured.

At the next stage, the correct operation of the equipment is determined when connected to an industrial frequency. increased power. The resistance of the windings at direct current is investigated. The transformation ratio is checked.

If the unit is of the three-phase type, its connection group is checked. When testing single-phase devices, their polarity is measured. Current indicators, idle losses are investigated.

Then the switch, tank and radiators, cooling devices, indicator are checked. Inputs and built-in currents are tested.

emergency situations

In some cases, the inspection may be carried out in emergency. It can occur when a strong crackling or uneven noise is detected inside the case. The equipment requires an unscheduled inspection if the heat level is abnormal. It may gradually increase.

In some cases, oil is ejected, it leaks (the liquid level drops below the permissible value), the diaphragms of the expansion pipes are destroyed. In this case, the unit cannot function normally. You need to perform a disaster recovery.

Oil samples may be taken after maintenance or during testing. If the quality of the substance is unsatisfactory, the power is turned off. An emergency fluid change is in progress.

Abnormal hum

If an abnormal buzz is detected inside the case, there may be several reasons for this condition. It is caused by loose cover bolts or other parts. They need to be pulled up.

If the mains voltage is too high, noise may occur. To fix it, you need to move the switch to correct position. If the pressing is broken at the joints inside the magnetic circuit, a buzz appears. The core will need to be repressed. If the outer sheets of the magnetic circuit begin to vibrate, noise can be heard. They need to be split.

The buzz also causes overload of the equipment (it must be reduced), uneven loading of the phases or a short circuit between them or the turns of the windings.

In addition to the above malfunctions, breaks may appear in the turns of the coils when they are of poor quality connection. If a similar situation is determined in the primary winding, there will be a change in the secondary voltage.

To determine the scope of work in an emergency, the process of fault detection of the transformer is carried out. This allows you to determine the severity and nature of damage. Based on the analysis, the need for materials, fixtures and tools necessary for troubleshooting is established.

Power transformers, like any equipment, need periodic maintenance. To avoid the need for troubleshooting emergency mode technical inspections and a set of capital measures to restore the elements of the system are periodically carried out.

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12. REPAIR OF TRANSFORMER

12.1.Maintenance

12.1.1. To carry out current repairs, the transformer is taken out of service. The current repair of the transformer and the on-load tap-changer is carried out once a year. At the same time, the overhaul period of transformers installed in a place of increased pollution can be reduced. Extraordinary current repair of the switching device is carried out for transformers with on-load tap-changers after a certain number of switching operations in accordance with the instructions of the factory instructions or according to test results (oil condition in the contactor, etc.)
12.1.2. During the current repair of the transformer, it is necessary to perform the following work:
- clean the transformer, components and accessories from dirt and oil; check the absence of air by briefly opening the air bleed plugs;
- examine the components of the transformer, access to which is difficult when the transformer is operating (gas and protective relays, oil tightness of air bleed plugs, built-in current transformers, tank covers of contactors of on-load tap-changers, oil indicators, external current-carrying contact connections and etc.).;
- Eliminate faults identified during the inspection and operation;
- check the operation of pointer oil indicators and other devices and devices installed on the transformer, guided by the requirements of the operating instructions for these devices and devices;
- perform routine maintenance provided for during the current repair, if the period of their implementation coincides with the period of the current repair (see Appendix No. 2 of this instruction);
- check the condition of the equipment installed in the blast cabinet and the on-load tap-changer drive, as well as the operation of the control circuit of the cooling system and the on-load tap-changer;
- check and, if necessary, adjust the oil level in the transformer and oil-filled components;
- update damaged paint coatings external surfaces; paint and varnish coatings must be combined with previously applied, light gray or dark gray;
- take oil samples from the transformer tank and contactor tank for testing and analysis;
- test the transformer, components and components in accordance with the standard GKD 34.20.302-2002;
- check the condition of the upper seals of high-voltage bushings, taking into account the tension of the busbar;
12.1.3. Drain the oil from the gas relay and replace the relay only with the valves on both sides of the gas relay closed and the air bleed valve open.
Fill the gas relay with oil from the expander by gradually opening the valve on the side of the expander until oil leaks through the open valve of the gas relay. After that, it is necessary to close the valve and fully open the valves on both sides of the gas relay.
12.1.4. Drain the oil from the on-load tap-changer and replace it as follows:
- open the cock for draining oil from the contactor tank and, after the start of draining the oil, close the cock between the body of the protective relay and the expander of the on-load tap-changer;
- open the plug to release air from the contactor tank;
- after draining the oil from the contactor tank below the installation level of the protective relay (the volume of oil that is drained must be preliminarily determined by calculation), close the valve;
It is necessary to fill the protective relay with oil from the expander by slowly opening the tap on the side of the expander until oil leaks through the open plug to release air from the contactor tank. Then close the plug and open the tap completely.
If necessary, add oil to the expander of the on-load tap-changer according to the diagram of the expander installation drawing and the operating instructions for the on-load tap-changer.
It is necessary to replace the contacts of the contactor and the oil in the tank of the contactor of the on-load tap-changer in accordance with the requirements of the instruction manual for this device.

12.2. Overhaul of transformers

12.2.1. The first overhaul of transformers (for the main transformers at the facility) must be carried out no later than 12 years after they are put into operation, taking into account the results of preventive tests; for other transformers, and in the future for the main ones - if necessary, depending on the results of electrical tests and measurements and the condition of the transformer.
12.2.2. During the overhaul, it is necessary to be guided by the requirements of the operating instructions for components and components.
material requirements, constituent parts and components that are used in the overhaul of the transformer are indicated in the general specifications for overhaul of transformers.
12.2.3. During the overhaul, it is necessary to carry out work aimed at updating performance characteristics transformer and its components.
In preparation for the repair and in the process of its implementation, it is necessary:
- measure insulation characteristics, losses and no-load current, winding resistance direct current, short-circuit resistance, check the transformation ratio, analyze the transformer oil from the transformer tank and from the tank of the contactor of the on-load tap-changer, inputs in accordance with established standards;
- make a thorough external examination and draw up a list of external defects (defective act) that must be eliminated during the repair;
- drain the oil from the tank, checking the performance of the oil indicator, dismantle the inputs, expander, cooling devices, etc.;
- take off upper part tank (if necessary);
- make a thorough inspection of the active part and check the winding crimping forces;
- check the insulation of the yoke elements;
- inspect the on-load tap-changers and taps;
- check the grounding of the nodes of the active part with a megaohmmeter;
- repair the yoke, windings, taps, on-load tap-changer;
- repair and paint the tank, expander, gas pipelines;
- check the safety control signaling devices;
- check, test, repair high-voltage bushings in accordance with the instructions for their operation;
- check and repair blower equipment;
- check and repair the on-load tap-changer in accordance with its operating instructions;
- check and repair the drive of the on-load tap-changer;
- check the control and alarm circuits of the cooling system;
- clean or change oil;
- dry the insulation;
- make the necessary tests and measurements.
12.2.4. Prepressing (pressing) of windings must be performed in accordance with RDN 34-38-058-91.
The installation locations of hydraulic jacks and winding pressing forces are indicated on the drawings of the active part, which are included in the set of operational documentation.
12.2.5. Remove, if necessary, the upper part of the tank in the following way:
- drain the oil from the transformer tank;
- dismantle the cooling system, inlets, expander, ladder, gas outlet pipes, on-load tap-changer drive (fix its position), etc.;
- supporting the tap-changer with a crane, remove the bolts of its fastening to the tank, lower the tap-changer to technological bracket, fixed on the active part;
- unscrew the upper spacer bolts through the corresponding hatches on the tank cover;
- remove the tank connector bolts and lift its upper part with a crane according to the scheme on the outline drawing.
12.2.6. In connectors that have been disassembled, check the condition of the rubber seals and, if necessary, replace them. At the same time, on the surfaces of rubber parts there should not be:
- radial stripes and transverse folds;
- cuts along the perimeters, corners of the bolt holes;
- underpressing and air bubbles, porosity at the ends;
- delaminations at the ends, divergences of the joint and thickening of the joints more than the allowance for the thickness of the part.
Gaskets must be aligned with the seat, do not stretch between the holes, do not form waves at the installation site.
During installation rubber gaskets necessary:
- when installing gaskets on a slope or vertical surface (without holes for bolts), fix them in several places using 88-N adhesive or similar;
- install the gasket along the average diameter of the surface to be sealed;
- during assembly, clamp the gasket to a value of 0.7 of its thickness, while tightening the fasteners should be gradually diagonally in a circle until the gasket is completely clamped;
- during clamping, control the compression of the gasket using feelers, gauges, limiters and measuring tools: ruler, caliper;
- make sure that after assembly the gasket does not go beyond the outer diameter of the flange.

12.3. Unscheduled maintenance of 110kV transformers

12.3.1. Oil should be added to the transformer through the expander, according to the diagram of the expander installation drawing.
12.3.2. Oil should be added to the tank of the contactor of the on-load tap-changer through its expander according to the scheme of the installation drawing of the transformer expander and the operating instructions for the on-load tap-changer.
12.3.3. If necessary, oil should be added to sealed bushings with degassed oil in accordance with the instructions for their operation.

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12. REPAIR OF TRANSFORMER

12.1.Maintenance

12.1.1. To carry out current repairs, the transformer is taken out of service. The current repair of the transformer and the on-load tap-changer is carried out once a year. At the same time, the overhaul period of transformers installed in a place of increased pollution can be reduced. Extraordinary current repair of the switching device is carried out for transformers with on-load tap-changers after a certain number of switching operations in accordance with the instructions of the factory instructions or according to test results (oil condition in the contactor, etc.)
12.1.2. During the current repair of the transformer, it is necessary to perform the following work:
- clean the transformer, components and accessories from dirt and oil; check the absence of air by briefly opening the air bleed plugs;
- inspect the components of the transformer, access to which is difficult when the transformer is operating (gas and protective relays, oil tightness of air bleed plugs, built-in current transformers, tank covers of contactors of on-load tap-changers, oil indicators, external current-carrying contact connections, etc.);
- Eliminate faults identified during the inspection and operation;
- check the operation of pointer oil indicators and other devices and devices installed on the transformer, guided by the requirements of the operating instructions for these devices and devices;
- perform routine maintenance provided for during the current repair, if the period of their implementation coincides with the period of the current repair (see Appendix No. 2 of this instruction);
- check the condition of the equipment installed in the blast cabinet and the on-load tap-changer drive, as well as the operation of the control circuit of the cooling system and the on-load tap-changer;
- check and, if necessary, adjust the oil level in the transformer and oil-filled components;
- renew damaged paint coatings of external surfaces; paint and varnish coatings must be combined with previously applied, light gray or dark gray;
- take oil samples from the transformer tank and contactor tank for testing and analysis;
- test the transformer, components and components in accordance with the standard GKD 34.20.302-2002;
- check the condition of the upper seals of high-voltage bushings, taking into account the tension of the busbar;
12.1.3. Drain the oil from the gas relay and replace the relay only with the valves on both sides of the gas relay closed and the air bleed valve open.
Fill the gas relay with oil from the expander by gradually opening the valve on the side of the expander until oil leaks through the open valve of the gas relay. After that, it is necessary to close the valve and fully open the valves on both sides of the gas relay.
12.1.4. Drain the oil from the on-load tap-changer and replace it as follows:
- open the cock for draining oil from the contactor tank and, after the start of draining the oil, close the cock between the body of the protective relay and the expander of the on-load tap-changer;
- open the plug to release air from the contactor tank;
- after draining the oil from the contactor tank below the installation level of the protective relay (the volume of oil that is drained must be preliminarily determined by calculation), close the valve;
It is necessary to fill the protective relay with oil from the expander by slowly opening the tap on the side of the expander until oil leaks through the open plug to release air from the contactor tank. Then close the plug and open the tap completely.
If necessary, add oil to the expander of the on-load tap-changer according to the diagram of the expander installation drawing and the operating instructions for the on-load tap-changer.
It is necessary to replace the contacts of the contactor and the oil in the tank of the contactor of the on-load tap-changer in accordance with the requirements of the instruction manual for this device.

12.2. Overhaul of transformers

12.2.1. The first overhaul of transformers (for the main transformers at the facility) must be carried out no later than 12 years after they are put into operation, taking into account the results of preventive tests; for other transformers, and in the future for the main ones - if necessary, depending on the results of electrical tests and measurements and the condition of the transformer.
12.2.2. During the overhaul, it is necessary to be guided by the requirements of the operating instructions for components and components.
The requirements for materials, components and components that are used during the overhaul of the transformer are specified in the general technical conditions for the overhaul of transformers.
12.2.3. During the overhaul, it is necessary to carry out work aimed at updating the operational characteristics of the transformer and its components.
In preparation for the repair and in the process of its implementation, it is necessary:
- measure insulation characteristics, losses and no-load current, DC winding resistance, short circuit resistance, check the transformation ratio, analyze transformer oil from the transformer tank and from the tap changer contactor tank, bushings in accordance with established standards;
- make a thorough external examination and draw up a list of external defects (defective act) that must be eliminated during the repair;
- drain the oil from the tank, checking the performance of the oil indicator, dismantle the inputs, expander, cooling devices, etc.;
- remove the upper part of the tank (if necessary);
- make a thorough inspection of the active part and check the winding crimping forces;
- check the insulation of the yoke elements;
- inspect the on-load tap-changers and taps;
- check the grounding of the nodes of the active part with a megaohmmeter;
- repair the yoke, windings, taps, on-load tap-changer;
- repair and paint the tank, expander, gas pipelines;
- check the safety control signaling devices;
- check, test, repair high-voltage bushings in accordance with the instructions for their operation;
- check and repair blower equipment;
- check and repair the on-load tap-changer in accordance with its operating instructions;
- check and repair the drive of the on-load tap-changer;
- check the control and alarm circuits of the cooling system;
- clean or change oil;
- dry the insulation;
- make the necessary tests and measurements.
12.2.4. Prepressing (pressing) of windings must be performed in accordance with RDN 34-38-058-91.
The installation locations of hydraulic jacks and winding pressing forces are indicated on the drawings of the active part, which are included in the set of operational documentation.
12.2.5. Remove, if necessary, the upper part of the tank in the following way:
- drain the oil from the transformer tank;
- dismantle the cooling system, inlets, expander, ladder, gas outlet pipes, on-load tap-changer drive (fix its position), etc.;
- while supporting the on-load tap-changer with a crane, remove the bolts of its fastening to the tank, lower the tap-changer onto the technological bracket fixed on the active part;
- unscrew the upper spacer bolts through the corresponding hatches on the tank cover;
- remove the tank connector bolts and lift its upper part with a crane according to the scheme on the outline drawing.
12.2.6. In connectors that have been disassembled, check the condition of the rubber seals and, if necessary, replace them. At the same time, on the surfaces of rubber parts there should not be:
- radial stripes and transverse folds;
- cuts along the perimeters, corners of the bolt holes;
- underpressing and air bubbles, porosity at the ends;
- delaminations at the ends, divergences of the joint and thickening of the joints more than the allowance for the thickness of the part.
Gaskets must be aligned with the seat, do not stretch between the holes, do not form waves at the installation site.
During the installation of rubber gaskets, it is necessary:
- when installing gaskets on a slope or vertical surface (without holes for bolts), fix them in several places using 88-N adhesive or similar;
- install the gasket along the average diameter of the surface to be sealed;
- during assembly, clamp the gasket to a value of 0.7 of its thickness, while tightening the fasteners should be gradually diagonally in a circle until the gasket is completely clamped;
- during clamping, control the compression of the gasket, using probes, gauges, limiters and measuring tools: a ruler, caliper;
- make sure that after assembly the gasket does not go beyond the outer diameter of the flange.

12.3. Unscheduled maintenance of 110kV transformers

12.3.1. Oil should be added to the transformer through the expander, according to the diagram of the expander installation drawing.
12.3.2. Oil should be added to the tank of the contactor of the on-load tap-changer through its expander according to the scheme of the installation drawing of the transformer expander and the operating instructions for the on-load tap-changer.
12.3.3. If necessary, oil should be added to sealed bushings with degassed oil in accordance with the instructions for their operation.

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