I believe everyone has seen transformers, big, small, square, round, and all kinds of transformers are everywhere around us. They range from small parts in household appliances to large transformers in power plants. As the saying goes, although a sparrow is small, it has all five internal organs. The principle of a transformer is the same regardless of its size. It uses the principle of electromagnetic induction to change the current. It consists of three parts: primary coil, secondary coil and iron core. It is often used to increase and decrease voltage, safety isolation and other fields. But we will find a question, why should the transformer core be grounded? Let me explain to you the relevant knowledge of transformer core grounding!
Introduction to transformer core
Transformer core (transformer core) is mainly responsible for the magnetic circuit part of the circuit. Most of the transformer cores on the market today are made of silicon wafers, but a small number are also made of magnetic sheets (chips made of magnetic sheets are gradually being eliminated).
The role of the transformer core
The role of the transformer core is mainly in two aspects: hysteresis loss and eddy current loss.
1. Hysteresis loss, which refers to the iron loss caused by hysteresis when the transformer is working in an AC state. The use of the transformer core can change this to a certain extent. Phenomenon. And it can also alleviate the rise of the transformer surface during operation.
2. Eddy current loss refers to the alternating current generated by the transformer when it is working. It will change with the induced current generated by the magnetic flux in the iron core. We call this change for the vortex. When eddy currents are lost, the temperature of the iron core surface will rise. However, because of the material of the iron core (silicon), our resistivity will increase during this process, which can reduce the effect of eddy currents.
Transformer core classification
It can generally be divided into the following four categories: shell type and core type core, single-phase and three-phase iron core, three-dimensional and planar type and Stacked iron core and rolled iron core.
Transformer core composition
It is mainly composed of three parts, namely the body, fasteners and insulating parts.
Calculation of transformer core cross-section
The power calculation of the transformer is based on the cross-sectional area of ??the core center column, the size of the core window, as well as the input voltage and output voltage. First, calculate the number of turns based on the cross-sectional area of ??the core and the input voltage. Then calculate the wire gauge (the wire diameter of the enameled wire) based on the window size and the number of turns, and then calculate how much current can pass based on the wire diameter. to calculate his power. According to the formula:
Turn left | Turn right N=4.4fbs/10 4 In the formula, N=number of turns, f is frequency, B is the magnetic flux density of silicon steel sheet, generally 10000 Gauss shall prevail. , s is the voltage. Calculate the number of turns step by step.
Transformer core power calculation
P(W)=S(mm)2=19*19=361w. A single-phase 220V transformer with a capacity of 300VA can be made. It is known that the cross-section of the money core is 19 square millimeters. The money core uses a silicon steel sheet with a silicon content of 9000 Gauss to select Anzabi. 45/19=2.37 takes 3 turns per volt. The primary winding is 3*220=660 turns of the secondary. Winding 3*12=36 turns. The cross-sectional area of ??the primary wire is selected, the current is 300VA/220=1.36A, and the safe passing current per square millimeter is 5A = 1.36/5=0.28 square millimeters. Optional enameled wire with a wire diameter of 0.6 mm. The cross-sectional area of ??the secondary wire is selected, 300/12=25A 25/5=5 square millimeters, and enameled wire with a wire diameter of 2.6 mm is optional. If there is room in the iron core mouth, the diameter of the primary and secondary wires can be larger.
Grounding the transformer core
During the use of the transformer, the iron core and the parts and components around the iron core are in a strong electromagnetic field, so they are affected by the electric field. The iron core itself will have a high potential to the ground. If there is no wire connecting the iron core to the ground, a potential difference will occur between the iron core and the ground, resulting in intermittent discharge.
And there will be a strong electromagnetic field near the winding. As a result, the core and components are in an unequal magnetic field, and there is a potential difference between them. Maybe the potential difference is not very big, but it is enough. If a small insulation gap is broken down, a continuous discharge will occur. This is absolutely not allowed in terms of power management, and it is difficult to check to prevent this phenomenon, because some small insulation gaps are invisible to our naked eyes. Therefore, we must connect the iron core to the ground with wires.
How to connect the grounding of the transformer iron core
The iron core is usually grounded at one point. The steel sheets in the iron core are not energized to each other, so for safety reasons, we Never ground all steel pieces. When the iron core is grounded, we only need to connect one of the steel sheets to the ground, not all of them, because although there is no electricity between the steel sheets, if all the steel sheets are connected to the ground, then The ground will become a conductor, allowing electricity to be conducted between the steel sheets, thereby disrupting the eddy currents. Therefore, one-point grounding can flow current to the earth without disturbing the eddy current, which serves the purpose of grounding the iron core.
Transformer core manufacturer
Guangdong Haihong Transformer Co., Ltd. specializes in the production of three-dimensional wound core transformer cores and is currently the largest three-dimensional wound core manufacturer in China. The single-phase wound core distribution transformers produced by our company are single-phase three-wire products and have passed all type tests and other tests. The low-voltage voltage combination of this transformer is 2×0.23kV, and its principle and use are different from ordinary single-phase two-wire transformers. The low-voltage current of this kind of transformer is only half of the rated current of an ordinary single-phase transformer (the voltage of a1-a2 is 2 times 230V, so the current is only half). The biggest benefit brought by this is that when used, the line loss of the former is only 1/4 of the total, which is the main reason why most foreign countries use this type of single-phase transformer. This product complies with the national standards GB1094 "Power Transformer" and GB/T6451 "Technical Parameters and Requirements for Three-Phase Oil-immersed Power Transformer" and JB/10317-02 "Technical Parameters and Requirements for Single-phase Oil-immersed Distribution Transformer".
Shandong Liaocheng Transformer Co., Ltd. is quite good. It is a manufacturer of power transmission and distribution equipment and complete sets of high and low voltage power equipment, mainly producing power transformers, dry-type transformers, American box transformers, European box transformers, etc. , the company is located in Liaocheng City, Shandong Province, a famous historical and cultural city in China, a water city in the north of the Yangtze River, and the location of Liaocheng University. It is 90 kilometers away from the provincial capital city Jinan and is connected by highways and railways. The Beijing-Kowloon Railway and the Ji-Han Railway intersect here, and the traffic is very convenient.
Editor’s summary: It is one of the indispensable machines in industrialization, and after our above introduction, everyone should know that the most important thing in a transformer is the quality of the iron core. Therefore, when purchasing, you must pay attention to check whether the iron core in the transformer is qualified.