The technical parameters of the transformer are an important indicator for understanding the transformer. To use the transformer, you must know its parameters so that it can be used without accidents. Therefore, it is very important for the novices engaged in transformers to understand the parameters of the transformer. The following are some of my understanding of the transformer parameters.
There are corresponding technical requirements for different types of transformers, which can be expressed by corresponding technical parameters. For example, the main technical parameters of the power transformer are: rated power, rated voltage and voltage ratio, rated frequency, operating temperature level, temperature rise, Voltage regulation, insulation performance and moisture resistance, the main technical parameters for general low frequency transformers are: transformation ratio, frequency characteristics, nonlinear distortion, magnetic shielding and electrostatic shielding, efficiency, etc.
A. Voltage ratio:
The number of turns of the two sets of transformers is N1 and N2, N1 is the primary and N2 is the secondary. Adding an alternating voltage to the primary coil produces an induced electromotive force at both ends of the secondary coil. When N2>N1, the induction The electromotive force is higher than the voltage applied to the primary. This transformer is called a step-up transformer: when N2
In the formula, n is called voltage ratio (turn ratio). When n<1, then N1>N2, V1>V2, the transformer is a step-down transformer. Otherwise, it is a step-up transformer.
B. Efficiency of the transformer:
At rated power, the ratio of the output power of the transformer to the input power is called the efficiency of the transformer, ie
η= x100%
Where η is the efficiency of the transformer; P1 is the input power and P2 is the output power.
When the output power P2 of the transformer is equal to the input power P1, the efficiency η is equal to 100%, and the transformer will not produce any loss. However, the transformer is actually not available. The transformer always generates losses when transmitting power. The loss mainly includes copper. Damage and iron loss.
Copper loss refers to the loss caused by the resistance of the transformer coil. When the current is heated by the coil resistance, part of the electrical energy is converted into heat energy and lost. Since the coil is generally wound by insulated copper wire, it is called copper loss.
The iron loss of the transformer includes two aspects. One is the hysteresis loss. When the alternating current passes through the transformer, the direction and magnitude of the magnetic field lines passing through the silicon steel sheet of the transformer change, so that the internal molecules of the silicon steel sheet rub against each other, releasing heat energy, thereby losing. A part of the electric energy, this is the hysteresis loss. The other is the eddy current loss. When the transformer is working, the magnetic flux passes through the iron core, and an induced current is generated on the plane perpendicular to the magnetic field line, because the current is formed by the closed loop. Circulating, and spiraling, it is called eddy current. The existence of eddy current causes the iron core to heat up and consume energy. This loss is called eddy current loss.
The efficiency of the transformer is closely related to the power level of the transformer. Generally, the higher the power, the smaller the loss and output power, and the higher the efficiency. Conversely, the smaller the power, the lower the efficiency.
How to determine the power transformer parameters
The marking of the power transformer's nominal power, voltage, current and other parameters will fall off or disappear. Some commercially available transformers do not label any parameters at all. This brings great inconvenience to the use. The following describes the method for judging the parameters of the unmarked power transformer. This method also has reference value for the optional power transformer.
First, identify the power transformer
1. Identify the core of a common power transformer from the shape of E-shaped and C-shaped. The E-shaped iron core transformer has a shell structure (core wrapped coil), and uses D41 and D42 high-quality silicon steel sheets as iron cores, which are widely used. The C-shaped iron core transformer uses a cold-rolled silicon steel strip as the iron core, and has a small magnetic leakage and a small volume, and has a core structure (coil wrapped iron core).
2. Identifying the number of terminals from the windings. The power transformer usually has two windings, a primary and a secondary winding, so there are four terminals. In order to prevent hum and other interference, some power transformers often add a shielding layer between the primary and secondary windings, and the shielding layer is the grounding terminal. Therefore, the power transformer terminals are at least four.
3. From the lamination of the silicon steel sheet, the silicon steel sheet of the E-shaped power transformer is crossed and inserted, and no air gap is left between the E sheet and the I sheet, and the entire core is tightly stitched. There is a certain air gap between the E and I of the audio input and output transformers, which is the most intuitive way to distinguish between power and audio transformers. As for the C-shaped transformer, it is generally a power transformer.
Second, the power estimate
The amount of power transmitted by the power transformer depends on the material and cross-sectional area of ​​the core. The cross-sectional area, whether it is an E-shell structure or an E-core structure (including a C-shaped structure), refers to the cross-sectional (rectangular) area of ​​the segment of the core wrapped by the winding. After measuring the cross-sectional area S of the core, the power P of the transformer can be estimated by P=S2/1.5. The unit of S in the formula is cm2.
For example, the core cross-sectional area of ​​a power transformer is measured as S=7cm2, and the power is estimated. P=S2/1.5=72/1.5=33W, except for various errors, the actual nominal power is 30W.
Third, the measurement of each winding voltage
To make use of an unmarked power transformer, finding the primary winding and distinguishing the output voltage of the secondary winding is the most basic task. An example is given to illustrate the method of judgment.
Example: A power transformer is known with a total of 10 terminals. Try to judge the voltage of each winding.
The first step: distinguish the number of winding groups, draw a circuit diagram.
Use the multimeter R × 1 block measurement, where the connected terminal is a winding. It is measured that there are 3 groups in which two or two are connected, one in which three are connected, and one terminal is not connected to any other terminal. According to the above measurement results, draw a circuit diagram and number it.
It can be seen from the measurement that the transformer has four windings, wherein the numbers 5, 6, and 7 are a tapped winding, and the No. 10 terminal is not in communication with any of the windings, and is a shield lead-out terminal.
Step 2: Determine the primary winding.
For a buck-type power transformer, the primary winding has a thinner wire diameter and more turns than the secondary winding. Therefore, for a step-down transformer like Figure 4, the primary resistance is the largest.
Step 3: Determine the voltage of all secondary windings.
Connect the AC to the primary winding through a voltage regulator and slowly boost up to 220V. The no-load voltage of each winding is measured in turn and marked at each output. If the transformer does not heat up for a long time under no-load conditions, the performance of the transformer is basically intact, and it is further verified that the determined primary winding is correct.
Fourth, the determination of the maximum current of each secondary winding
The secondary winding output current of the transformer is dependent on the diameter D of the winding enameled wire. The diameter of the enameled wire can be measured directly from the lead terminals. After the diameter is measured, the maximum output current of the winding can be found according to the formula I=2D2. The unit of D in the formula is mm.
According to the classification of the shape, Telephone Cable have round telephone cable and Flat Telephone Cable.
The common specification of round telephone cable has two core and four core, the wire diameter has 0.4 and 0.5 respectively, some areas have 0.8 and 1.0.In addition to the two and four cores, there are four, six, eight, and ten cores.
If the general family is the local telephone use mode, 2 chip is enough to use.If the telephone is used by a company or part of a group, it is recommended to use a 4-cell line in consideration of the need for telephone broadband, and a 6-cell line is recommended if a digital telephone is used.
Round Telephone Cable,Communication Cable,Telephone Line,Power Wire
Shenzhen Kingwire Electronics Co., Ltd. , https://www.kingwires.com