The function of dry-type transformer

Dry type transformers play a crucial role in various fields such as high-voltage transmission, distribution, and industrial electricity. Its operating principle is based on electromagnetic induction, through which dry-type transformers can achieve voltage rise and fall, meeting various power needs. In addition, there are multiple classification methods for dry-type transformers. According to the number of phases, there are single-phase and three-phase transformers, which are suitable for different loads and systems. According to the cooling method, it includes dry-type and oil immersed type. The former is cooled naturally or forcibly by air convection or fan, and is commonly used for small capacity transformers; The latter relies on oil as a cooling medium, such as self cooling, air cooling, water cooling, or forced oil circulation. In addition, according to their usage, dry-type transformers also include power, instrument, testing, and special transformers.

2、 Definition of dry-type power transformer
1. Dry type transformer, in short, is a power transformer in which the iron core and coil are not immersed in insulating liquid (such as insulating oil).

2. Its core components include an iron core made of silicon steel sheets and coils cast with epoxy resin. In order to enhance electrical insulation, insulation cylinders will be placed between high and low voltage coils, and supported and constrained by pads to ensure the stable operation of the coils.
Epoxy cast dry-type transformers play a crucial role in power distribution systems. Thanks to the application of epoxy resin, a flame-retardant and self extinguishing solid insulation material, this type of transformer is not only safe and reliable, but also clean and environmentally friendly. Therefore, dry-type transformers cast with epoxy resin have been widely used in the field of power due to their oil-free, flame-retardant, low operating losses, and excellent disaster prevention capabilities. Compared with traditional oil transformers, dry-type transformers do not need to worry about issues such as fire, explosion, or pollution, and their losses and noise have been reduced to a new level. In addition, this type of transformer also provides the possibility of placing the transformer and low-voltage panel in the same distribution room.

1、 Structure
(1) Iron core
The iron core, as the magnetic circuit core of the transformer, plays a crucial role. Usually made of thick silicon steel sheets (0.35~0.5mm) to reduce iron loss. Power transformers often adopt a heart-shaped structure, which facilitates the continuity of magnetic circuits and the arrangement of windings.

(2) Winding
The winding is the circuit part of a transformer, carefully wound with copper or aluminum wires wrapped in insulating paper. The primary and secondary windings are concentric around the iron core column, forming magnetic coupling without electrical connection. To ensure good insulation performance, the low-voltage winding is usually located on the inner side, while the high-voltage winding is located on the outer side. However, in transformers with large capacity, low voltage, and high current, in order to solve the problem of lead out wire technology, the low voltage winding is sometimes placed outside the high voltage winding.

2、 Principle
The basic principle of a transformer lies in its iron core and two windings fitted onto the iron core. There is only magnetic coupling and no electrical connection between these two windings. When an alternating voltage is applied to a winding, alternating magnetic flux is generated between the primary and secondary windings, inducing electromotive forces e1 and e2 in the two windings respectively. The magnitude of the induced electromotive force follows Faraday's law of electromagnetic induction.
Electromagnetic induction phenomenon is the phenomenon of induced electromotive force caused by changes in magnetic flux. This phenomenon requires two conditions to be met: first, the magnetic flux must undergo a change; Secondly, the number of turns in the primary and secondary windings must not be equal in order to achieve voltage conversion. The nameplate of dry-type transformers usually specifies this information in detail.

Interpretation of nameplate
On the nameplate of dry-type transformers, detailed information about electromagnetic induction phenomena is usually indicated. These information include changes in magnetic flux, differences in the number of turns between primary and secondary windings, and the resulting induced electromotive force and voltage transformation. Through the data on the nameplate, we can clearly understand the working status and performance characteristics of the equipment.

Interpretation of Key Parameters of Transformers
In addition to the relevant information on electromagnetic induction phenomena, there are also some key parameters worth paying attention to on the nameplate of dry-type transformers. Among them, the insulation level of the transformer is a core indicator. It reflects the heat resistance of the insulation material used in the winding of the motor (or transformer). The insulation level is usually divided into several levels: A, E, B, F, and H, each corresponding to a specific maximum allowable temperature and winding temperature rise limit. In addition, the insulation level of transformers, also known as insulation strength, is an important indicator for measuring the equipment's ability to withstand voltage. It cooperates with other protection levels and insulation parts to ensure the safe operation of the equipment.

In addition, temperature rise and cooling method are also important contents on the nameplate. Temperature rise refers to the difference between the temperature of the measuring part and the temperature of the cooling medium, which directly affects the heat dissipation performance of the transformer. The cooling method is determined by the type and circulation of the cooling medium, and common types include dry self cooling, air cooling, oil immersed self cooling, oil immersed air cooling, etc. Accurate understanding of these parameters is crucial for evaluating the performance of transformers and ensuring their safe operation.

At the same time, the nameplate will also indicate data such as no-load current and no-load loss. The no-load current refers to the current of a transformer when the secondary winding is open and the rated voltage is applied to the primary winding, while the no-load loss is caused by the active component in the no-load current. These data help us understand the operating characteristics of transformers under no-load conditions, providing reference for their performance optimization in practical use.

5. Impedance voltage and load loss
Impedance voltage refers to the voltage value applied in a double winding transformer when the secondary winding is short circuited and the primary winding flows the rated current. Load loss refers to the active power obtained when the rated current flows through the primary winding and the secondary winding is short circuited. These parameters are crucial for evaluating the performance and efficiency of transformers.

The key to ensuring the normal operation of transformers lies in regular inspections
During the inspection process, close attention should be paid to the following two points:

Firstly, it is necessary to monitor the temperature of the transformer. The normal operating temperature range of transformers is usually set between 50 ℃ and 100 ℃. For dry-type transformers, the operating temperature within 140 ℃ is safe because the F-class insulation system used can withstand a maximum temperature of 155 ℃. Once the temperature exceeds the normal range or experiences abnormal fluctuations, it is necessary to analyze and identify the cause in a timely manner.

Secondly, pay attention to the sound changes of the transformer. Under normal operating conditions, the transformer will emit a uniform current sound. If the sound increases abnormally or there is a sound of partial discharge, it may be a sign of transformer failure, and immediate measures need to be taken to identify the cause and solve it.

In addition, regular power outage maintenance is also an important part of ensuring the continuous and stable operation of transformers. Through power outage maintenance, potential hazards can be identified and addressed in a timely manner, ensuring the safety and efficiency of transformers.
(1) Before starting maintenance, it is necessary to disconnect the low-voltage side circuit breaker of the transformer to be maintained, pull down the isolation switch, and hang appropriate signs on the handle as a warning.
(2) Next, disconnect the load switch on the high-voltage side of the transformer, confirm that it is in the disconnected state, close the grounding knife, and complete the operation of the switch's safety and hanging relevant signs.
(3) After entering the oil transformer room, the high-voltage tester should be used first to confirm that the transformer is indeed in a power outage state. Then, pull open the high-voltage isolation knife and carefully inspect the shell, porcelain bottle, and leads for any deformation or damage. If there is any damage, it should be replaced in a timely manner. At the same time, it is also necessary to pay attention to whether the oil level is normal. If oil leakage is found, the gasket should be replaced and the silicone should be checked for effectiveness. If there is discoloration or serious failure, it should be replaced immediately.
(4) After completing the above inspection, it is necessary to further verify the list of tools and materials before and after entering the transformer to confirm that there are no remaining tools. Finally, remove the suspended grounding wire and corresponding protective signs to ensure the safety and integrity of maintenance work.