The detection methods of transformers and power transformers mainly include:
1. Insulation test: Use the multimeter R×10k block to measure the resistance between the core and the primary, the primary and each secondary, the core and the secondary and secondary windings. The pointer of the multimeter should mean that it does not move at infinity. Otherwise, the transformer insulation performance is poor.
2. Observe the obvious abnormality by observing the appearance of the transformer: if the coil lead is broken, desoldering, 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 There are exposed and so on.
3. Detection of coil on/off: Place the multimeter in R×1 gear. During the test, if the resistance value of a certain winding is infinite, it indicates that the winding has a faulty fault.
4. Discriminate between the primary and secondary coils: the primary and secondary pins of the power transformer are respectively led out from both sides, and the primary winding is marked with 220V, and the secondary winding is labeled with the rated voltage, such as 15V. 24V, 35V, etc. Then identify them based on these markers.
5. Detection of no-load current:
(a) Direct measurement method: Open the secondary winding and place the multimeter in the AC current block (500 mA, stringed into the primary winding. When the primary winding plug 220V AC mains, the multimeter indicates the no-load current value. This value should not be greater than 10% to 20% of the transformer's full load current. The normal no-load current of the power supply transformer of the electronic equipment should be around 100mA. If it exceeds too much, the transformer has a short-circuit fault.
(b) Indirect measurement: A 10 /5W resistor is placed in series in the primary winding of the transformer, and the secondary is still idling. Turn the multimeter to the AC voltage block. After power-on, the voltage drop U across the resistor R is measured with two meter pens, and the no-load current I is calculated by Ohm's law, that is, I null = U/R.
6. Detection of no-load voltage: connect the primary of the power transformer to 220V mains, and use the multimeter AC voltage to measure the no-load voltage value (U21, U22, U23, U24) of each winding in sequence. The allowable error range is : High voltage winding ≤±10%, low voltage winding ≤±5%, voltage difference between two sets of symmetrical windings with center tap should be ≤±2%.
7, the low-power power transformer allows the temperature rise to 40 ° C ~ 50 ° C, the quality of the insulating material used, allowing the temperature rise can also be improved.
8. Comprehensive detection and identification of short-circuit fault of power transformer: The main symptoms after short-circuit fault of power transformer are severe heat generation and abnormal output voltage of secondary winding. Generally, the more short-circuit points between the turns inside the coil, the greater the short-circuit current, and the more severe the transformer heats up. A simple way to detect if a power transformer has a short-circuit fault is to measure the no-load current (tested earlier in the test method). 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. It is not necessary to measure the no-load current to conclude that the transformer has a short-circuit point.
9. Detect and identify the same name end of each winding: When using the power transformer, sometimes the required secondary voltage is obtained, and two or more secondary windings can be used in series. When the power transformer is used in series, the same name of each winding participating in the series is correctly connected, and no mistake can be made. Otherwise, the transformer will not work properly.
