Distribution Power Transformer Basic Knowledge

In the process of power transmission, transformation and distribution in the power system, the distribution power transformer is an important electrical equipment. Whether it is an industrial enterprise, a shopping mall, an office building, or a residential area, transformers can be seen everywhere.

1. The principle of distribution power transformer

Transformer is a device that uses the principle of electromagnetic induction to change AC voltage and current. The main components are primary coil, secondary coil and iron core (magnetic core).

2. The role of the distribution power transformer

Variable voltage: increase or decrease the voltage, and convert the electricity generated by the generator into a voltage level for residential or industrial use through the process of boosting, transporting, and stepping down.

Variable current: change the magnitude of the current while changing the voltage

Isolation: Isolate the user system and the power supply system to reduce the scope of the accident.

3. What are the types of distribution power transformer?

According to the cooling method:

A. Oil immersed distribution transformer: a transformer that uses transformer oil as the insulating medium and cooling medium, and the iron core and coil are all immersed in the insulating oil.

B. Dry type distribution transformer: The iron core and coil are cast with epoxy resin material to play an insulating role.

According to the number of power phases, it can be mainly divided into single-phase transformers and three-phase transformers.

A. Functional characteristics of single phase distribution transformers

A single-phase transformer is a transformer whose primary winding is a single-phase winding. As shown in the figure, both the primary winding and the secondary winding of the single-phase transformer are wound on the iron core, the primary winding is the AC voltage input terminal, and the secondary winding is the AC voltage output terminal. The output voltage of the secondary winding is proportional to the number of turns of the coil.

Single phase distribution transformers can change high-voltage power supply into single-phase low-voltage for use in various equipment. For example, AC 6600V high-voltage can be converted into AC 220V low-voltage through single phase distribution transformer to supply power for lights or other equipment. Single-phase transformers have the advantages of simple structure, small size, and low loss, and are suitable for use in low-voltage distribution lines (below 60Hz) with small loads.

Single-phase transformers are mostly used in rural power transmission and distribution systems, as well as in the power supply of some lighting or small motors, and their application examples are shown in the figure. In addition, it can also be used as a power transformer in many electronic and electrical equipment.

B. Functional characteristics of three phase transformers

Three phase transformer is a kind of transformer that is widely used in power equipment. The three phase transformer is actually a combination of three single-phase transformers of the same capacity, the primary winding (high-voltage coil) is three-phase, and the secondary winding (low-voltage coil) is also three-phase

Three-phase transformers are mainly used for step-up or step-down in a three-phase power supply system. It is more commonly used to convert a high voltage of several thousand volts into a low voltage of 380V to provide power for electrical equipment.

Three phase transformers have a wide range of applications, such as substations, industrial and mining enterprises, construction sites, drainage and irrigation equipment, post and telecommunications, textiles, railways, schools, hospitals, national defense, elevators, etc., and are also suitable for some low-voltage power supply voltages with low and large fluctuations. in the distribution line.

7. What parts are the components of the transformer composed of?

A. Main body: including iron core, winding, insulation support

B. Voltage regulating device: tap changer, (on-load voltage regulating device and non-excitation voltage regulating device)

C. Fuel tank and sheet radiator (wings), bushing

D. Safety devices: moisture absorber, gas relay, oil filter unit and temperature measuring instrument, etc.

8. What is the use of transformer oil

(1) Insulation function: Transformer oil has very strong insulation performance, which will generate sufficient insulation strength between the winding and the shell. Common types are DB25 and DB45.

(2) Heat dissipation effect: Transformer oil naturally circulates between the body and the sheet radiator according to the principle of heating up, and dissipates heat through the radiator to keep the temperature of the coil from being too high.

(3) Arc suppression function: When the on-load voltage regulating device is operated, an arc light will be generated when the tap changer is opened, and the transformer oil can extinguish the arc light to play a protective role.

9. The role of the oil conservator (oil conservator)

The oil conservator (oil conservator) is installed obliquely above the oil tank, and there is an oil pipe communicating with the oil tank. When the volume of transformer oil expands and shrinks with the change of oil temperature, the oil conservator plays the role of oil storage and oil replenishment. Prevent oil and air from being oxidized and damp. There is an oil level tube on the oil pillow, and some are also equipped with a liquid level indicator to observe the change of the oil level.

10. What is on-load voltage regulation?

On-load voltage regulation is a voltage regulation method in which the transformer can change the voltage by changing the tap position when it is running with load.

11. What are the losses of the transformer during operation

Transformer losses include: no-load loss (iron loss): the loss caused by the eddy current of the iron core,

Load loss (copper loss): The loss caused by the resistance heating of the winding.

12. What is the function of the moisture absorber (respirator)?

A. Since the temperature of the transformer will change at any time during operation, the oil level inside the transformer will rise or fall, and the gas must be discharged, otherwise the pressure will rise; it can be understood as the process of breathing, which prevents oil and Effect of direct air contact deterioration.

B. Install a silica gel tank on the oil exhalation channel, the transformer breathes through the silica gel, and the discharged water is absorbed. When the water reaches a certain level, the color of the silica gel will change from blue to red. At this time, the silica gel needs to be replaced.

13. What is a gas relay? What is the role?

Gas relay (also known as gas relay) is a protective device used in transformers. It is installed between the oil conservator of the transformer and the pipeline between the oil tank. When the internal fault of the transformer is used to decompose the oil to generate gas or cause oil flow , to make the contact of the gas relay act, and send a "heavy gas" trip signal and a "light gas" alarm signal to the duty personnel through the internal electrical normal contact to remind the transformer that it is abnormal or faulty.