1. Check the appearance of the transformer to see if it has obvious abnormalities. If the coil lead is broken or stripped, whether the insulating material has burnt marks, whether the iron core fastening screw is loose, whether the silicon steel sheet is rusted, whether the winding coil is exposed or the like.
2. Insulation test. Use a multimeter R Ã— 10k block to measure the resistance between the core and the primary, primary and secondary, core and secondary, electrostatic shield and secondary and secondary windings. The pointer of the multimeter should mean that it does not move at the infinity position. Otherwise, the insulation performance of the transformer is poor.
3. Detection of coil on and off. Place the multimeter in the RÃ—1 gear. During the test, if the resistance value of a winding is infinite, the winding has a faulty fault.
4. Discriminate between the primary and secondary coils. The primary and secondary pins of the power transformer are generally led out from both sides, and the primary winding is marked with 220V, and the secondary winding is labeled with rated voltage, such as 15V, 24V, 35V, etc. The tag is identified.
5. Detection of no-load current.
Direct measurement method. Open all the secondary windings, place the multimeter in the AC current block 500mA, and string it into the primary winding. When the plug of the primary winding is plugged into 220V AC mains, the multimeter indicates the no-load current value. This value should not be greater than 10%-20% of the transformer's full load current. The normal no-load current of a typical common electronic equipment power transformer should be around 100 mA. If it exceeds too much, the transformer is shorted.
Indirect measurement method. A 10/5W resistor is placed in series in the primary winding of the transformer, and the secondary is still completely empty. Turn the multimeter to the AC voltage block. After power-on, the voltage drop U across the resistor R is measured with two test leads, and then the no-load current I is calculated by Ohm's law, ie, I null = U/RF.
6, temperature rise detection. Generally, the low-power power transformer allows the temperature rise to be 400C~500C. If the quality of the insulating material used is good, the temperature rise can be increased.
7. Detect and identify the same name end of each winding. When using a power transformer, sometimes two or more secondary windings can be used in series in order to obtain the required secondary voltage. When the power transformer is used in series, the same name of each winding participating in the series must be correctly connected, and no error can be made. Otherwise, the transformer cannot work normally.
8. Comprehensive detection and identification of short-circuit faults of power transformers. The main symptoms of a short circuit in the power transformer are severe heat generation and abnormal secondary winding output voltage. Generally, the more short-circuit points between turns in the coil, the larger the short-circuit current, and the more severe the transformer heat. A simple way to detect if a power transformer is shorted is to measure the no-load current. A transformer with a short-circuit fault will have a no-load current value that is much greater than 10% of the full-load current. When the short circuit is severe, the transformer will heat up quickly within a few tens of seconds after the no-load power is applied. Touching the iron core by hand will have a hot feeling. At this time, it is not necessary to measure the no-load current to conclude that the transformer has a short-circuit point.
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