Selection and testing methods of special transformers

1. Check the appearance of the transformer to see if there are any obvious abnormalities. The core of the transformer is composed of silicon steel sheets. In order to reduce the heating loss in the core, the core is made of silicon steel sheets with a thickness of 0.23-0.5mm. The silicon content of the silicon steel sheet is relatively high. The two sides of the silicon steel sheet are coated with insulating paint, so that the stacked silicon steel sheets can be insulated from each other, and the thickness of the insulating paint is only a few microns. The amorphous magnetic ring is Magnetic components processed with amorphous materials. Amorphous magnetic rings can be divided into iron-based amorphous, cobalt-based amorphous, etc. according to the material of the amorphous strip used. High-voltage DC power supply is also called DC high-voltage power supply. It is composed of AC mains or 3-phase power input, power supply with DC voltage output of thousands of volts or more than tens of thousands of volts, the output power of hundreds of watts to several kilowatts, generally can be regulated or stabilized. For example, whether the coil is broken, desoldered, insulated Whether the material is scorched, whether the iron core fastening screws are loose, whether the silicon steel is corroded, whether there are exposed winding coils, etc.

2. Insulation test. Use a multimeter R10k block to measure the resistance value between the iron core and the primary, the primary and the secondary, the core and the secondary, the electrostatic shielding and the secondary winding, and the multimeter pointer should be fixed at infinity. Otherwise, the transformer insulation performance is poor.

3. Detection of on-off of the coil. Put the multimeter in the R1 block and test the geotextile. If the resistance value of a working winding is infinite, it means that the winding has an open circuit fault.

4. Distinguish the primary coil and the secondary coil.

5. Detection of no-load current.

a, direct measurement method. Open all the secondary windings, and put the multimeter on the AC current to stop (500mA, string into the main winding). When the main winding plug is inserted into the 220V AC current, the meter indicates the value of the empty current. This value is not It should be greater than 10% to 20% of the full load current of the transformer. Generally, the normal air current of the power transformer of ordinary electronic equipment should be about 100mA. If it exceeds the standard too much, the transformer has a short circuit fault.

Indirect measurement. A 10 is connected in series on the main winding of the transformer? 5w resistor, the 2nd stage is still empty. Set the multimeter on the AC voltage block. After charging, the voltage drop u at the end of the resistor r2 is measured 2 meters, then by Ohm's law Calculate the no-load current i space, that is, if? No-load voltage detection. The no-load voltage value (u21, u22, u23, u24) of the winding of the primary power transformer connected to the 220v city power supply measured by the AC voltage connection method of the multimeter should meet the requirements The allowable error range is generally: the high-voltage winding is less than or equal to ±10 percent, the low-voltage winding is less than or equal to ±5 percent, and the voltage difference between the two center-tapped symmetrical windings is less than ±2 percent.

6. The allowable temperature rise of low-power power transformers is generally 40 degrees Celsius and 50 degrees Celsius. If the insulating material used is of good quality, the allowable temperature rise can be increased.

7. Detect and identify the same-named ends of each winding. When using a power transformer, sometimes companies can connect 2 or more secondary windings in series in order to obtain the secondary voltage required for development. Use in series. When the system power transformer is used, the same-named ends of the windings in the series must be connected in the correct way, and no mistakes can be made. Otherwise, the transformer cannot meet the normal management work.

8. Comprehensive detection and identification of short-circuit faults of power transformers. The main symptoms after short-circuit faults of power transformers are severe heating and abnormal output voltage of secondary windings. Generally, the more short-circuit points between turns in the coil, the greater the short-circuit current and the more serious the transformer heats. .