Sophisticated equipment, such as power transformers, periodically needs maintenance, minor and major repairs. This ensures the long life of each such device. The schedule of work with a particular transformer is clearly prescribed, and deviations from it are possible only in case of unexpected breakdowns, accidents or any other unforeseen circumstances. Over time, an electrical installation will certainly lose its original properties. For this reason, even a well-made device needs major repairs. Transformers are checked according to the plan drawn up by the technical manager.
The main types of repair work
Power equipment can be repaired in many ways. The scope of work depends on the current situation and the availability of planned need. Some high-power dimensional devices such as 1600, 2500 or 6300 kVA models require the presence of highly qualified repair personnel.
The main types of work include the following:
- Maintenance. It is carried out strictly according to the schedule developed by the leadership. All procedures are carried out without shutting down the device itself, which continues to operate at full capacity.
- Maintenance repair of the power transformer. In this case, the equipment is temporarily turned off. The sequence of such procedures is purely preventive in nature.
- Overhaul of transformers. Employees carry out the elimination of breakdowns that occurred during the operation of the device. In addition, this type of work is carried out in case of obsolescence or deterioration of the systems. The reconstruction of such transformers takes place after about 10-15 years of their continuous operation.
Additional repairs
At times, employees have to perform some intermediate service options. As an example, overhaul and after-repair tests of transformers can be given. Units with a capacity of 110 kV undergo the first overhaul 12 years after they were launched. Other transformers are repaired as necessary depending on their condition. During operation, additional repairs are allowed.
Oil models are much more often served. For example, the frequency of repair of transformers with a TSZN or TSZM cooling system is once a year, provided that their structures contain on-load tap-changer elements. If such details are not contained, then this period is extended to two years. All other installations are serviced, as a rule, once every four years. Overhaul testing should follow the recommendations of the project work. Special conditions can be assumed only for devices located in special places with high pollution.
The design and purpose of units
Transformers are used to convert an alternating electric current of a certain frequency and voltage into an electric current with the same frequency but a different voltage. Each apparatus is based on the phenomenon of electromagnetic induction discovered by Faraday. If we talk about the purpose and structure of the transformer, then it is used in almost all power supply circuits for electrical appliances, and also transfers energy over long distances. The equipment is capable of creating a voltage of 220, 380 or 660 V, which is universally used both at the domestic and industrial level.
The device, as a whole, may vary depending on the specific type of unit: pulse, current or power. The latter are most common and most often found in various places. The simplest option for the purpose and design of the transformer involves the presence of a single phase. As part of such an apparatus, one can detect a metal core and a pair of windings, each of which is an independent insulated wire. The transformer is connected to an AC source. The connection is made using the primary winding, and the other - the secondary - is used to power the consumer.
Key Specifications
The operating parameters of the unit will be considered using the TMG transformer model as an example. The abbreviation is spelling out three-phase, with oil and air cooling and tight execution. The technical characteristics of the transformer in this case are expressed in the following parameters:
- value of nominal HV;
- power indicator;
- value of nominal LV;
- climatic modification in accordance with GOST standards;
- type of winding connection of the device.
Among other parameters of the device, losses in kW for idling and short circuit, voltage at short circuit and idling current in percent can be distinguished. These parameters are determined only after acceptance tests, which are mandatory before starting the device for permanent operation. In addition, of the technical characteristics of transformers, it is also worth mentioning the overall weight. Indicators can vary greatly depending on the power output by the unit.
What are the windings on the transformer
As the main options, it is customary to call screw, continuous-coil and cylindrical. The latter are made of rectangular or round wire. All of the listed types of transformer windings are also subdivided according to secondary characteristics such as the number of moves or layers, the presence of transpositions and parallel branches.
The simplest and cheapest option for today is a cylindrical winding. The cross section of the coil should be at least 5 square millimeters. The lower limit of the winding current in the copper wire at the lowest density will be from 15 to 18 A. Manufacturers in the manufacture of transformers are guided by the following criteria when choosing the suitable option:
- load current on one rod and the power of the windings on it;
- rated voltage;
- the cross section of a winding coil;
- short circuit loss.
The principle of operation of the device
Carrying out any technical work may also depend on a certain type of units. The simpler the design, the less maintenance is required, and the process itself is somewhat facilitated. Possible types of work depend on a number of technical parameters of the transformer: the number of windings and the number of phases.
Converted current flows continuously through the connected device. The magnetic flux penetrates all the windings and induces EMF in them. There is an idle mode of operation. In this case, the secondary winding is devoid of any load. This example generally illustrates the operation of a simple single-phase transformer.
Maintenance Procedures
Regulatory documents describe the following actions performed by employees:
- cleaning tanks and insulators;
- external inspection of the device for any malfunctions and damage to the case;
- test with the measurement of key indicators in action;
- cleaning dirt deposits in expanders;
- inspection of thermosiphon type filters and replacing the sorbent in them if necessary;
- sampling of internal fluid in oil-cooled transformers;
- assessment of the condition of circulation pipes, welds, seals and fuses;
- Topping up if necessary additional oil.
In addition, maintenance of transformers may include some other procedures, if ordered by the head of the management department.
Dry Cooling Maintenance
In this case, the presence of a cast insulation system is assumed. Maintenance is carried out in accordance with the regulations, however, the number of items may vary depending on the operating conditions or the place of work of the transformer. Typically, the list includes the following procedures:
- Checking the cooling system once every six months. The functionality of the temperature controller is checked, as well as the quality of the fans spinning on an ongoing basis.
- Dirt is being cleaned. Must be repeated every six months or quarter. It is done more often if the environment has it.
- Checking the housing for cracks and damage. Elimination of those if necessary.
- Checking the integrity of the insulation and protective systems. Replacement in case of malfunctions. Held annually.
- Inspection of the quality of the winding fixation. A similar check is also carried out during the inspection. In the absence of proper quality, the transformers are completely rewound.
Oil Cooled Maintenance
Complexity generally depends on the design features and operational conditions. Among the general procedures during the ongoing repair of power transformers of this type, the following should be noted:
- Inspection of the housing for external defects.
- Cleaning the device from contamination.
- Measurement of the resistance level on the insulation of the windings.
- Elimination of minor malfunctions of the cooling system, fittings and attachments.
- Tightening fasteners if they have been loosened.
- Topping up oil and eliminating leaks.
The whole process is carried out only at the installation site of the transformer without its transportation.
Overhaul
This type of work performed includes all of the above. Also, during the overhaul of transformers, any malfunctions with windings, switches and core are checked and eliminated. Particular attention is paid to the output and contact points of the wires with the voltage switch. In addition, the current quality of the oil tank, expanders and pipelines is established.
In Russian companies, it is customary at times to carry out the so-called deep overhaul. It differs from that described, including in that it involves opening an oil tank. It is worth noting that this procedure is quite difficult and is entrusted only to highly qualified and trained employees.
Deep overhaul
The equipment is previously disconnected from the network. The list of sequential actions for the overhaul of transformers includes:
- opening the device housing;
- slight elevation of the active part;
- disconnecting the windings from the magnetic drive;
- rewinding reels according to the instructions;
- restoration or replacement of main insulation;
- tuning the operation of the magnetic system.
In addition, all oil pumps, shutoff valves, inlets and outlets, coolers, switches and fans are replaced or repaired during work.