By hvhipot 
Transformers are almost used in all electronic products, and their principle is simple. However, the winding process of transformers may have different requirements according to different usage scenarios (different purposes). The main functions of transformers are: voltage conversion; Impedance transformation; Isolation; Voltage stabilization (magnetic saturation transformer), etc. The commonly used iron core shapes for transformers are E-type and C-type iron cores.
1、 Basic principles of transformers
When a sine AC voltage U1 is applied to both ends of the primary coil, there is an alternating current I1 in the wire and an alternating magnetic flux ф 1 is generated, which passes through the primary and secondary coils along the iron core to form a closed magnetic circuit. In the secondary coil, a mutual inductance potential U2 is induced, and at the same time, ф 1 also induces a self inductance potential E1 on the primary coil. The direction of E1 is opposite to the direction of the applied voltage U1 but with a similar amplitude, thereby limiting the magnitude of I1. In order to maintain the existence of magnetic flux ф 1, a certain amount of electrical energy consumption is required, and the transformer itself also has certain losses. Although the secondary is not connected to the load at this time, there is still a certain current in the primary coil, which we call “no-load current”.
If the secondary coil is connected to the load, a current I2 is generated in the secondary coil, and a magnetic flux ф 2 is generated as a result. The direction of ф 2 is opposite to ф 1, which cancels each other out and reduces the total magnetic flux in the iron core, thereby reducing the primary self inductance voltage E1. As a result, I1 increases, indicating a close relationship between the primary current and the secondary load. When the secondary load current increases, I1 increases and ф 1 also increases, and the increase in ф 1 precisely supplements the magnetic flux offset by ф 2 to maintain the total magnetic flux in the iron core unchanged. If the losses of the transformer are not considered, it can be assumed that the power consumed by the secondary load of an ideal transformer is the electrical power obtained by the primary from the power series resonance. Transformers can change the secondary voltage by changing the number of turns of the secondary coil as needed, but cannot change the power consumption allowed by the load.
2、 Transformer losses
When the primary winding of a transformer is energized, the magnetic flux generated by the coil flows through the iron core. As the iron core itself is also a conductor, an electric potential is induced in a plane perpendicular to the magnetic field lines. This electric potential forms a closed loop on the cross-section of the iron core and generates current, resembling a vortex, hence it is called “eddy current”. This’ eddy current ‘increases the losses of the transformer and causes the iron core of the transformer to heat up, resulting in an increase in the temperature rise of the transformer. The loss caused by “eddy currents” is called “iron loss”. In addition, winding transformers requires a large amount of copper wire, which has resistance. When current flows through this resistance, it consumes a certain amount of power, and this loss often becomes heat and is consumed. We call this loss “copper loss”. So the temperature rise of transformers is mainly caused by iron loss and copper loss.
Due to the presence of iron and copper losses in transformers, their output power is always less than their input power. Therefore, we introduce an efficiency parameter to describe this, where η=output power/input power.
The transformer products produced by HV Hipot Electric Co., Ltd. power include: YDJ series oil immersed test transformers, GTB series dry-type test transformers, YDQ series inflatable test transformers, HTRL-V transformer capacity tester, HTBS-V transformer no-load load load characteristic tester, etc.