Distribution Transformer Components
DEFINE DISTRIBUTION TRANSFORMER
Distribution transformer, abbreviated as "distribution transformer". A static electrical appliance in the distribution system that transfers AC electrical energy by converting AC voltage and current according to the law of electromagnetic induction. Distribution transformers usually refer to power transformers operating in the distribution network with a voltage level of 10-35kV (mostly 10kV and below) and a capacity of 6300KVA and below that directly supply power to end users. The place and location where "distribution transformers" are installed is not only a substation. Distribution transformers should be installed on columns or on the ground in the open air.
THE MAIN COMPONENTS OF DISTRIBUTION TRANSFORMER
1. Distribution Transformer Core
The iron core is the main magnetic circuit part in a transformer. Usually composed of hot-rolled or cold-rolled silicon steel sheets with high silicon content, thickness of 0.35 or 0.5mm, and surface coated with insulation paint, the iron core is divided into two parts: an iron core column and an iron yoke. The iron core column is covered with a winding, and the iron yoke is used to close the magnetic circuit. There are two basic forms of iron core structure: core type and shell type.
2. Winding
The winding is the circuit part of a transformer, usually made by winding insulated flat copper wire or round copper wire on a winding mold. The winding is installed on the transformer core column, the low-voltage winding is installed on the inner layer, the high-voltage winding is installed on the outer layer of the low-voltage winding, and the sleeves made of insulation materials are used between the low-voltage winding and the iron core, as well as between the high-voltage winding and the low-voltage winding, to facilitate insulation.
3. Insulation oil
The composition of transformer oil is very complex, mainly composed of cycloalkanes, alkanes, and aromatic hydrocarbons. In distribution transformers, transformer oil plays two roles: one is insulation between transformer windings, windings, iron cores, and oil tanks. The second is that the transformer oil generates convection after being heated, which plays a heat dissipation role on the transformer core and winding. The commonly used transformer oil has three specifications: No. 10, No. 25, and No. 45. Its label represents the temperature at which the oil begins to solidify below zero. For example, "No. 25" oil indicates that this oil begins to solidify at -25 ℃. The oil specifications should be selected based on local climatic conditions.
4. Oil storage tank
The oil conservator is installed on the top cover of the oil tank. The volume of the oil storage tank is about 10% of the volume of the oil tank. There are pipes connected between the oil storage tank and the oil tank. When the volume of the transformer expands or contracts with the temperature change of the oil, the oil storage tank plays a role in storing and replenishing oil, ensuring that the iron core and winding are immersed in the oil; At the same time, due to the installation of an oil storage tank, the contact surface between oil and air is reduced, reducing the rate of oil degradation.
There is an oil pointer on the side of the oil conservator, and there are oil level standard lines next to the glass tube for oil temperatures of -30 ℃,+20 ℃, and+40 ℃, indicating the oil level that transformers that have not been put into operation should reach; The standard line mainly reflects whether the oil level of the transformer is sufficient when operating at different temperatures.
Breathing holes are installed on the oil storage tank to connect the upper space of the tank with the atmosphere. When the transformer oil expands and contracts during heating, the air in the upper part of the oil storage tank can enter and exit through the breathing hole, and the oil level can rise or fall to prevent the oil tank from being damaged
5. Distribution Transformer Bushing
It is the main insulation device outside the transformer box, and most of the transformer insulation sleeves use porcelain insulation sleeves. The transformer uses high and low voltage insulation sleeves to guide the leads of the high and low voltage windings of the transformer from inside the oil tank to outside the oil tank, making the transformer winding insulated from the ground (shell and core), and is also the main component connecting the fixed leads to the external circuit. The high-voltage porcelain bushing is relatively tall, while the low-voltage porcelain bushing is relatively short.
6. Distribution Transformer Tap Changer
The device for changing the tap of the high-voltage winding of a transformer and adjusting the tap position can increase or decrease the number of turns in the primary winding to change the voltage ratio and adjust the output voltage. The method of manually changing the position of the tap changer after the transformer is removed from operation and disconnected from the power grid, and adjusting the output voltage is called no-load voltage regulation.
7. Gas relay
The gas relay is installed in the middle of the connecting pipe between the transformer oil tank and the oil storage tank, and is connected to the control circuit to form a gas protection device. The upper contact of the gas relay forms a separate circuit with the light gas signal, while the lower contact of the gas relay is connected to the external circuit to form a heavy gas protection. The heavy gas action trips the high-voltage circuit breaker and sends a heavy gas action signal;
8. Explosion-Proof Tube
The explosion-proof tube is a safety protection device for transformers, installed on the large cover of the transformer. The explosion-proof tube is connected to the atmosphere, and in case of a fault, the heat will cause the transformer oil to vaporize, triggering the gas relay to send an alarm signal or cutting off the power supply to prevent the oil tank from exploding
