What Is Distribution Transformer
Distribution Transformer Definition
Distribution transformer refers to a static electrical appliance used in the distribution system to transform AC voltage and current according to the law of electromagnetic induction and transmit AC energy. Chinese transformer products can generally be divided into ultra-high voltage (750KV and above), ultra-high voltage (500KV) transformers, 220-110KV transformers, and 35KV and below transformers based on voltage levels. Distribution transformers usually refer to power transformers operating in the distribution network with a voltage level of 10-35KV and a capacity of 6300KVA or below that directly supply power to end users.
Types Of Distribution Transformer
The classification of commonly used distribution transformers can be summarized as follows:
(1) According to the number of phases:
1) Single-phase distribution transformers: used for single-phase loads and three-phase distribution transformer groups.
2) Three-phase distribution transformer: used for raising and lowering voltage in three-phase systems.
(2) According to cooling methods:
1) Dry type distribution transformers: They rely on air convection for cooling and are generally used for small capacity distribution transformers such as local lighting and electronic circuits. 2) Oil immersed distribution transformers: rely on oil as the cooling medium, such as oil immersed self cooling, oil immersed air cooling, oil immersed water cooling, forced oil circulation, etc.
(3) Classified by purpose:
1) Power distribution transformer: used for voltage rise and drop in transmission and distribution systems.
2) Instrument distribution transformer: such as Voltage transformer, current transformer, measuring instrument and relay protection device.sp;
3) Test distribution transformer: capable of generating high voltage and conducting high voltage tests on electrical equipment.
4) Special distribution transformers: such as furnace distribution transformers, rectifier distribution transformers, adjustment distribution transformers, etc.
(4) Divided by winding form:
1) Double winding distribution transformer: used to connect two voltage levels in the power system.
2) Three winding distribution transformer: generally used in power system regional substations, connecting three voltage levels.
3) Autotransformer: used to connect power systems with different voltages. It can also be used as a regular step-up or step-down distribution transformer.
(5) According to the form of iron core:
1) Core type distribution transformer: used for high-voltage power distribution transformers. 2) Shell type distribution transformer: used for special distribution transformers with high current, such as furnace distribution transformers and welding distribution transformers; Or power distribution transformers for electronic instruments, televisions, radios, etc.
Parts Of Distribution Transformer
Oil immersed distribution transformers can be divided into main body, oil storage cabinet, insulation sleeve, tap changer, protection device, etc. according to their structure.
1. Body
The body includes three parts: the iron core, winding, and insulation oil. The winding is the circuit of the transformer, and the iron core is the magnetic circuit of the transformer. The two constitute the core of the transformer, which is the electromagnetic part.
1. 1 Iron 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.
1. 2 Windings
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.
1.3 Insulation oil
The composition of transformer oil is very complex, which is mainly composed of Cycloalkane, alkanes and Aromatic hydrocarbon. In distribution transformers, transformer oil plays two roles: one is insulation between transformer windings, windings and 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.
1.2 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. During Thermal expansion of transformer oil, the air on the upper part of the oil conservator can enter and exit through the breathing hole, and the oil level can rise or fall to prevent the oil tank from deformation or even damage.
1.3 Insulating 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.
1.4 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.
1.5 Protective devices
1.5.1 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;
1.5.2 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.
Distribution Transformer Application
1.Transmission and distribution applications
Transformers are widely used in various transmission and distribution applications. Power transmission can be defined as the movement of high-voltage electrical energy from a power plant to a substation, while distribution corresponds to converting high-amplitude voltage signals into significantly lower value voltage signals. In addition, the lower level voltage signals allocated by the distribution system can be used for different household and commercial applications. Energy can be circulated from the power station to the destination through wires and cables. In such applications, transformers can be used to maintain the frequency and amplitude levels of signals at constant values.
2.Steel manufacturing
Steel manufacturing plants are a typical example of commercial applications where the use of transformers can be easily observed. The steel manufacturing process mainly involves the melting, welding, forming and cooling of raw materials. In order to melt and weld components, a very high current is required; However, in order to cool the components, a relatively low current value is required. In order to achieve frequent regulation of this current throughout the entire manufacturing process, high-voltage transformers are usually used. In the steel manufacturing industry, transformers tend to increase or decrease the voltage values at different points in the circuit and help users obtain the required current.
3.Coolant
When a transformer is used in an air dried form, it can be used to produce a cooling effect. The cooling effect of transformers can be easily used in refrigerators to keep food refrigerated and fresh. In addition to cooling, transformers used in refrigerators and other related applications also provide necessary voltage regulation to avoid surge currents and voltage imbalances, thereby ensuring the safety of the equipment. In addition, even after a sudden termination of power supply, transformers can help maintain the cooling of the refrigerator for a period of time.
4.air-conditioning
Air conditioning is another example of daily life applications, which uses a transformer for general operation to the user's desired optimal value, allowing the air conditioning and fan to work simultaneously, and controlling the power flow through the circuit according to current needs. Heating, ventilation, and air conditioning devices also use transformers in a similar way to simplify their operation, enhance their operation, and optimize power consumption.
5.Industrial use
Transformers are used in various industrial equipment, such as welding machines, electric furnaces, electroplating machines, electric motors, etc., to provide power for them.
1) Electric furnace: Electric furnace is a common heating equipment in industrial production, which requires high voltage and current to generate high temperature. For this reason, transformers are often used in industry to convert low voltage and high current power sources into high voltage and low current power sources to provide the high energy input required for electric furnaces.
2) Electric welding machine: Electric welding machines require the production of high temperature and high energy through short-term arcs to process welded components. In some high-power welding machines, transformers are used to change voltage and current to ensure power stability and overload protection.
3) Electroplating machine: The electroplating process requires a large amount of electrical energy, and it is necessary to ensure the stability of the power supply to ensure the quality of the coating. Therefore, transformers are often used in industry to convert low current and high voltage power sources into high current and low voltage power sources.
4) Industrial power generation: In the industrial field, some types of industrial generators need to transform their output voltage to adapt to different equipment and applications. Transformer is one of the basic components for achieving output voltage transformation.
5) Frequency converters: Frequency converters have been widely used in industrial equipment.
Distribution Transformer Connections
(1) Yyn0, where Y represents that the high-voltage winding is star connected, y represents that the low-voltage winding is star connected, n represents that the neutral wire is led out from the midpoint of the secondary winding, and 0 represents that the line voltage phases of the high-voltage and low-voltage are the same. It can be used as a power output for three-phase four wire or three-phase five wire systems, and is used for distribution transformers with small capacity to supply power and lighting loads.
(2) Dyn11: where D represents that the high-voltage winding is delta connected, y represents that the low-voltage winding is star connected, n represents that the neutral point of the secondary winding is directly grounded and has a neutral wire drawn out, and 11 represents a phase difference of 30 ° between the high-voltage and low-voltage line voltages. It is commonly used in TN or TT system grounding low-voltage power grid in China.
(3) Yd11: The primary winding is connected in a star shape, and the secondary winding is connected in a triangle shape. It is generally used as a power supply transformer for 10kV or 35kV power grids and as a station transformer for power plants. The secondary winding is connected in a triangle to eliminate the third harmonic voltage.
(4) YNd11: The primary winding is connected in a star shape, and the neutral wire is directly grounded from the neutral point, while the secondary winding is connected in a triangle shape. The high-voltage winding connected in a star shape bears a voltage of √ 3 times lower than that connected in a triangle shape, which can bring good economic benefits. It is generally used in power systems where the neutral point is directly grounded at 110kV and above.
Distribution Transformer Rating
50kVA，63kVA，80kVA，100kVA，125kVA，160kVA，200kVA，250kVA，315kVA，400kVA，500kVA，630kVA，800 kVA，1000kVA，1250kVA，1600kVA，2000kVA，2500kVA，3150kVA，4000kVA，5000kVA，6300kVA，8000kVA，10000 kVA
