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Why is DC resistance not equal to AC resistance

time:2021/1/31   source:华天电力  reading:242 time

1. From a microscopic point of view, many physical properties of media, including conductivity, permittivity, and permeability, are actually linked to the frequency of the electromagnetic field.

2. The distribution of electromagnetic fields and moving charges in conductors is actually related to frequency. For example, the skin effect at high frequencies.

3. The routing of conductors in the circuit, under the alternating electromagnetic field, will also induce additional effects, such as parasitic capacitance and inductance.

Impedance is divided into three parts, resistance, inductive reactance, and capacitive reactance. The latter two parts can be regarded as an imaginary resistance, and the size of the latter two parts is related to the current frequency, so the impedance of alternating currents of different frequencies is different.

Transformer DC Winding Resistance Tester.png

One end of the diode is P, which is a hole-type semiconductor, in which there are insufficient electrons, and there are many "pits" formed by lack of electrons. After the electric field is applied, these pits will move (in fact, the electrons next to them come to fill the pits, and the electrons form new ones. Of the pit). At the other end is N, which is an electronic semiconductor, in which electrons are slightly too much, forming some electrons that can move freely.

After P and N are in contact, the electrons in N at the contact site will fill the pits in P, forming a layer with no holes and no electrons, called a depletion layer. After applying the forward voltage, the electric field drives the electrons from the direction of P to N, so that the electrons of N filled with the pits in P will be driven back, the depletion layer disappears, and the current can be normally energized.

After the reverse voltage is applied, the electric field drives the electrons from the direction of N to P, so that more pits will be filled by the electrons of N, and the depletion layer is thickened, resulting in a thick layer of non-conductive areas that cannot be energized. 

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