Complex equipment, like power transformers, periodically needs maintenance, minor and major repairs. Thus, a long service life of each such device is ensured. The work schedule for a specific transformer is clearly defined, and deviations from it are possible only in the event of unexpected breakdowns, accidents or any other unforeseen circumstances. An electrical installation will certainly lose its original properties over time. For this reason, even a well-made device needs a major overhaul. Transformers are checked according to the plan drawn up by the technical manager.
Main repairs
Power equipment can be repaired in many ways. The scope of work depends on the current situation and the availability of planned needs. Some large high power devicessuch as 1600, 2500 or 6300 kVA models require highly trained maintenance personnel.
Main activities include the following:
- Maintenance. It is carried out strictly according to the schedule developed by the management. All procedures are carried out without turning off the device itself, which continues to operate at full capacity.
- Maintenance of power transformer. In this case, the equipment is temporarily disabled. The sequence of such procedures is purely preventive.
- Overhaul of transformers. Employees carry out the elimination of the breakdowns that occurred during the operation of the device. In addition, this type of work is carried out when systems become obsolete or worn out. Reconstruction of such transformers is carried out after about 10-15 years of their continuous operation.
Additional repairs
Sometimes employees have to perform some intermediate service options. An example is the overhaul and post-repair testing of transformers. Units with a capacity of 110 kW or more undergo the first major maintenance 12 years after they were launched. Other transformers are repaired as needed depending on their condition. During operation, additional repairs are allowed.
Oil models are much more frequently serviced. For example, the frequency of repair of transformers with a cooling system TSZNor TSZM is once a year, provided that their structures include adjusting elements of the tap changer. 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. Interrepair tests should follow the recommendations of the project for the production of works. Special conditions can be assumed only for devices located in special places with increased pollution.
Design and purpose of units
Transformers are used to convert alternating electric current of a certain frequency and voltage into electric current with the same frequency, but a different voltage. At the heart of each apparatus lies the phenomenon of electromagnetic induction discovered by Faraday. If we talk about the purpose and design of the transformer, then it is used in almost all power supply circuits for electrical appliances, and also transmits energy over long distances. The equipment is capable of creating a voltage of 220, 380 or 660 V, which is widely used both at the domestic and industrial levels.
The device, in general, may vary depending on the specific type of unit: pulse, current or power. The latter are the most common and most often found in various places. The simplest version of the appointment and design of the transformer assumes the presence of one phase. As part of such an apparatus, one can find a metal core and a pair of windings, each of which is an independent insulated wire. The transformer is connected to an alternating current source. The connection is made using the primary winding, and the other - the secondary - is used to power the consumer.
Main Specifications
The operating parameters of the unit will be considered using the example of the TMG transformer model. The abbreviation literally stands for three-phase, oil- and air-cooled and hermetically sealed. The technical characteristics of the transformer in this case are expressed in the following parameters:
- nominal HV value;
- power indicator;
- nominal LV value;
- climatic modification in accordance with GOST standards;
- type of connection of the windings of the device.
Among other parameters of the device, one can single out losses in kW for idling and short circuit, short circuit voltage and no-load current in percent. These parameters are determined only after carrying out acceptance tests, which are mandatory before starting the device for permanent operation. In addition, from the technical characteristics of transformers, it is also worth mentioning the overall weight. The performance can vary greatly depending on the power output of 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 listed types of windingstransformers are also subdivided according to secondary features such as the number of moves or layers, the presence of transpositions and parallel branches.
The easiest and cheapest option for today is a cylindrical winding. The cross section of the coil must be at least 5 square millimeters. The lower limit of the winding current in 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 appropriate option:
- load current per rod and winding power on it;
- rated voltage;
- cross section of winding turn;
- short-circuit losses.
How the device works
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.
A converted current flows continuously through the connected device. At the same time, the magnetic flux permeates all the windings and induces an EMF in them. There is also an idle mode. 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 to be takenemployees:
- 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 thermosyphon type filters and replacement of sorbent in them if necessary;
- sampling internal fluid in oil-cooled transformers;
- assessment of the condition of circulation pipes, welds, seals and fuses;
- topping up with additional oil if needed.
In addition, the maintenance of transformers may include some other procedures, if so ordered by the head of the management department.
Maintenance with dry cooling
In this case, a cast insulation system is assumed. Current repairs are carried out in accordance with the regulations, however, the number of points may vary depending on the operating conditions or the location of the transformer. The list usually includes the following procedures:
- Check the cooling system once every six months. The functionality of the temperature controller is checked, as well as the quality of the constantly spinning fans.
- Cleaning from dirt. It is necessary to repeat every six months or a quarter. Done more often if the environment allows it.
- Checking the hull for cracks and damage. Eliminate them if necessary.
- Checking the integrity of the insulation and protective systems. Replacement in case of malfunction. Held annually.
- Inspection of the quality of fixation of the winding. Also, a similar check is carried out during technical inspection. In the absence of proper quality, a complete rewinding of transformers is done.
Oil-cooled maintenance
Complexity generally depends on design features and operating conditions. Among the general procedures for the current repair of power transformers of this type, the following should be noted:
- Checking the hull for external defects.
- Cleaning the device from dirt.
- Measuring the resistance level on the winding insulation.
- Troubleshooting of cooling system, fittings and attachments.
- Tightening fasteners if they have been loosened.
- Adding oil and fixing leaks.
The whole process is carried out only at the place of installation of the transformer without its transportation.
Major overhaul
This type of ongoing work includes all of the above. Also, during the overhaul of transformers, any faults with windings, switches and core are checked and eliminated. Particular attention is paid to the points of output and contact of the wires with the voltage switch. Among other things, the current quality of the oil tank, expanders and pipelines is set.
In Russian companies, it is customary from time to time to carry out the so-calleddeep overhaul. It differs from the one described, among other things, in that it involves opening the oil tank. It is worth noting that this procedure is quite difficult and is entrusted only to highly qualified and trained employees.
Deep overhaul
Equipment is previously disconnected from the network. The list of sequential actions for the overhaul of transformers includes:
- opening the case of the device;
- slight raising of the active part;
- disconnecting the windings from the magnetic drive;
- rewinding coils according to the instructions;
- restoration or replacement of main insulation;
- setting up the operation of the magnetic system.
In addition, all oil pumps, shut-off valves, inlets and outlets, coolers, switches and fans are replaced or restored during the work.
