Method for testing transformers (3 ways). Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Measuring technology
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1 method
Frequency range "sweep":
LF power transformers: 40-60 Hz.
Power transformers of the switching power supply: 8-40 kHz.
Isolating transformers, TDKS: 13-17 kHz.
Isolating transformers, TDKS monitors (for PC):
CGA: 13-17 kHz.
EGA: 13-25 kHz.
VGA: 25-50 kHz.
If you take a pulse power transformer, for example, a line-scan isolating transformer, connect it according to fig. 1, apply a sinusoid to the I winding U \u5d 10 - 10V F \u100d 0.1 - 1.0 kHz through C \uXNUMXd XNUMX - XNUMX μF, then on the II winding using an oscilloscope we observe the shape of the output voltage.
Rice. 1. Connection diagram for method 1
Having “driven” the AF generator at frequencies from 10 kHz to 100 kHz, you need to get a pure sinusoid in some area (Fig. 2 on the left) without emissions and “humps” (Fig. 2 in the center). The presence of diagrams in the entire range (Fig. 2. on the right) indicates interturn short circuits in the windings, etc. etc.
This technique, with a certain degree of probability, allows you to reject power transformers, various isolation transformers, partially line transformers. It is only important to choose the frequency range.
Rice. 2. Shapes of the observed signals.
2 method
Necessary equipment: Bass generator, Oscilloscope.
Principle of operation:
The principle of operation is based on the phenomenon of resonance. An increase (from 2 times and more) in the oscillation amplitude from the LF generator indicates that the frequency of the external generator corresponds to the frequency of the internal oscillations of the LC circuit.
To check, short-circuit the winding II of the transformer. The oscillations in the LC circuit will disappear. It follows from this that short-circuited turns disrupt the resonant phenomena in the LC circuit, which is what we wanted.
The presence of short-circuited turns in the coil will also make it impossible to observe resonant phenomena in the LC circuit.
Rice. 3. Connection diagram for method 2
We add that to check the pulse transformers of the power supplies, the capacitor C had a rating of 0,01 μF-1 μF. The generation frequency is selected empirically.
3 method
Necessary equipment: Bass generator, Oscilloscope.
Principle of operation:
The principle of operation is the same as in the second case, only a variant of a series oscillatory circuit is used.
Rice. 4. Connection diagram for method 3
The absence (breakdown) of oscillations (rather sharp) when the frequency of the LF generator changes indicates the resonance of the LC circuit. Everything else, as in the second method, does not lead to a sharp breakdown of oscillations on the control device (oscilloscope, AC millivoltmeter).
Publication: electroworld.narod.ru
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