To build a power project, we should not only build but also repair it. The most important thing is to know how to maintain it. Today, Guizhou Road Electric Power Construction Group will share with you a technical article on transformer maintenance and fault maintenance, hoping to help the power transmission envoys. At the same time, we also appeal to everyone to understand and enrich their knowledge of electricity to reduce the hidden trouble.
Brief Introduction of Transformer
Transformer is a device that uses the principle of electromagnetic induction to change AC voltage. Its main components are primary coil, secondary coil and core. The main functions are: voltage conversion, current conversion, impedance conversion, isolation, voltage stabilization (magnetic saturation transformer) and so on. It can be divided into power transformer and special transformer (electric furnace transformer, rectifier transformer, power frequency test transformer, voltage regulator, mine transformer, audio transformer, medium frequency transformer, high frequency transformer, impact transformer, instrument transformer, electronic transformer, reactor, transformer, etc.).
Maintenance of transformer is the daily work that electrician operators and electrician operators and repairmen must do in order to maintain the normal technical state of transformer and prolong its service life. Transformer maintenance is an important part of electrical equipment management. If the maintenance work is in place, it can not only reduce the failure rate of equipment, save maintenance costs and reduce costs, but also bring good economic benefits to the company and employees. So what should we pay attention to in transformer maintenance and maintenance?
In normal operation, the transformer should bear about 75-90% of the rated capacity of the transformer.
The thermometer installed on the transformer should be recorded at the same time when inspecting the transformer. The unattended transformer shall record the voltage, current and oil temperature of the transformer at each periodic inspection. In addition, for distribution transformers, the load of a three-phase should be measured during the maximum load period. If the distribution is unbalanced, it should be redistributed. The time limit for measurement shall be stipulated in the field regulations.
III. Insulation Monitoring
Before the transformer is put into operation after installation or maintenance (usually after drying) and after long-term shutdown, the insulation resistance of the coil should be measured, and the measured value and oil temperature should be recorded in the transformer's resume card.
The insulation resistance of the coil should be measured by a megohmmeter of 1000-2500 volts. The allowable value of coil insulation resistance is not specified.
The ratio of the insulation resistance measured during the operation of transformer to that measured before the transformer is put into operation after installation or overhaul and drying is the main basis for judging the insulation state of transformer in operation. Insulation resistance should be measured at the same temperature as possible, using the same megohm meter with the same voltage.
IV. Current Range
The maximum unbalanced current at low voltage of transformer shall not exceed 25% of the rated value, and the range of voltage variation of transformer power supply shall be 5% positive or negative of the rated voltage. If exceeding this range, tap-changer should be used to adjust the voltage to reach the specified range.
Usually the tap position of primary winding is changed to realize voltage regulation. The device for connecting and switching tap position is called tap changer, which adjusts the ratio by changing the turns of high voltage winding of transformer.
Low voltage has no effect on transformer itself, only reduces some output, but has an impact on electrical equipment; higher voltage, increased flux, core saturation, increased core loss, transformer temperature rise.
Under special circumstances, the transformer can operate under overload in a short time, but it should not exceed 30% of the rated load in winter and 15% of the rated load in summer. In addition, the transformer's overload capacity should be determined according to the temperature rise of the transformer and the requirements of the manufacturer.
Overload can be divided into normal overload and accident overload. Normal overload is caused by the increase of users'power consumption under normal power supply conditions. It will increase the temperature of transformer, lead to accelerated aging of transformer insulation and reduce its service life, so overload operation is not allowed in general.
There are many kinds of transformer faults, but the common fault phenomena are short circuit, circuit breaking and leakage. The causes of these faults can be summarized in three aspects: first, the design is wrong; second, the production quality is poor; third, the use conditions exceed the design requirements.
Maintenance methods of transformers:
The first step is to remove the core. Transformers are often filled with asphalt, wax and other materials. Before disassembly, the transformer should be heated to dissolve and disengage from the transformer. In addition, the transformer lead should be welded off the terminal, the fixed splint should be removed, the first silicon steel sheet should be prized with screw screwdriver, and then the silicon steel sheet should be pulled out one by one with pliers. When removing the silicon steel sheet, care must be taken not to damage the coil lead, while avoiding the breakage and bending of the silicon steel sheet. Then, the silicon steel sheets are collected together and wrapped in paper to avoid loss and damage of insulation.
The second step is to remove the coil. After removing the core, the appearance of the coil is checked first to see that the appearance is not damaged, and then the insulation resistance meter is used to check which coil the fault occurs in order to disassemble purposefully. When disassembling, attention should be paid to note down the interlayer insulation, wire diameter, number of circles and layers of each layer, so as to provide reference for rewinding. At the same time, attention should be paid to protecting the surface of insulating paint for wire for reuse, and special attention should be paid to finding out and discovering the causes of short circuit and circuit break of coil. When the faulty part is found and treated, the original winding method can be used to rewind the machine, and after winding and repairing, the machine can enter the machine.