Transformer parameters

Technical parameter of LF transformer

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 power transformer include: rated power, rated voltage and voltage ratio, rated frequency, working temperature grade, temperature rise, voltage regulation rate, insulation performance and moisture-proof performance. For general low-frequency transformers, the main technical parameters are: transformation ratio, frequency characteristics, nonlinear distortion, magnetic shielding and electrostatic shielding, efficiency, etc. Voltage ratio:

The number of coils of the two groups of transformer is N1 and N2 respectively, N1 is the primary and N2 is the secondary. When an AC voltage is applied to the primary coil, the induced electromotive force will be generated at both ends of the secondary coil. When N2 > N1, the induced electromotive force is higher than the voltage applied by the primary. This kind of transformer is called step-up transformer; When N2 < N1, the induced electromotive force is lower than the voltage applied by the primary. This kind of transformer is called step-down transformer.

n=N1/N2

Where n is called voltage ratio (turns ratio). When n > 1, N1 > N2, U1 > U2, and the transformer is a step-down transformer. Otherwise, it is the step-up transformer.

Efficiency of transformer

At rated power, the ratio of the output power and input power of the transformer is called the efficiency of the transformer, i.e

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 is improved η Equal to 100%, the transformer will not produce any loss. But in fact, there is no such transformer. Transformer always produces loss when transmitting electric energy, which mainly includes copper loss and iron loss. Copper loss refers to the loss caused by transformer coil resistance. When the current is heated through the coil resistance, part of the electric energy is converted into heat energy and lost. Because the coil is generally wound by insulated copper wire, it is called copper loss.

The iron loss of transformer includes two aspects. One is the hysteresis loss. When the AC current passes through the transformer, the direction and size of the magnetic line of force of the silicon steel sheet passing through the transformer will change accordingly, so that the molecules inside the silicon steel sheet rub against each other and release heat energy, thus losing part of the electric energy. This is the hysteresis loss. The other is eddy current loss, when the transformer is working. There is a magnetic line of force passing through the iron core, and the induced current will be generated on the plane perpendicular to the magnetic line of force. Because this current forms a closed loop, forms a circulating current and forms a vortex, it is called eddy current. The existence of eddy current makes the iron core heat and consumes 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 greater the power, the smaller the loss to output power ratio and the higher the efficiency. Conversely, the smaller the power, the lower the efficiency.

Characteristic parameter of LF transformer

Frequency response

It refers to the characteristic that the secondary output voltage of transformer changes with the working frequency.

Passband if the output voltage of the transformer at the intermediate frequency is U0, the frequency range when the output voltage (input voltage remains unchanged) drops to 0.707u0 is called passband B of satons transformer.

Primary and secondary impedance ratio

The primary and secondary impedance of the transformer are connected with appropriate impedance RI and RO to match the primary and secondary impedance of the transformer, then the ratio of RI and RO is called the primary and secondary impedance ratio. Under the condition of impedance matching, the transformer works in the best state and the transmission efficiency is the highest.