Transformer testing method and experience

1,colorcodeinductordetectionPutthemultimeterinR×1block,redandblackpeneachreceivecolorcodeinductoratanyoftheleadingend,thepointershouldswingtotheright.Accordingtothemeasuredresistancevalue,itcanbeiden...

　　1, color code inductor detection

　　Put the multimeter in R×1 block, red and black pen each receive color code inductor at any of the leading end, the pointer should swing to the right. According to the measured resistance value, it can be identified under the following three conditions:

　　A. the resistance value of the measured color code inductor is zero, and there is A short-circuit fault inside.

　　B. There is a direct relationship between the dc resistance value of the measured color code inductor and the enameled wire diameter and winding number of coils used for winding the inductor coil. As long as the measured resistance value can be measured, the measured color code inductor is considered normal.

　　2. Detection of mid-cycle transformer

　　A. Dial the multimeter to R×1 gear, check the on and off of each winding one by one according to the rule of pin arrangement of each winding of the mid-cycle transformer, and then judge whether it is normal or not.

　　B. Test the insulation performance. Put the multimeter in the R×10k block and test the following conditions:

　　(1) the resistance value between the primary winding and the secondary winding;

　　(2) the resistance value between the primary winding and the shell;

　　(3) the resistance between the secondary winding and the housing.

　　The above test results show three situations:

　　(1) the resistance value is infinite: normal;

　　(2) zero resistance: short circuit fault;

　　(3) resistance value less than infinity, but greater than zero: leakage fault.

　　3. Power transformer detection

　　A. Check whether there is any obvious abnormal phenomenon by observing the appearance of the transformer. For example, whether the coil lead is broken, unsoldering, whether the insulation material is burnt, whether the core fastening screw is loose, whether the silicon steel sheet is corroded, whether the winding coil is exposed, etc.

　　B. insulation test. The resistance values between core and primary, primary and secondary, core and secondary, electrostatic shield and vent secondary, and secondary windings are respectively measured with a multimeter R×10k stop. The pointer of the multimeter should be fixed at an infinite position. Otherwise, the transformer insulation performance is poor.

　　C. detection of coil on and off. Put the multimeter in R×1 gear. In the test, if the resistance value of a winding is infinite, it indicates that the winding has a circuit breaking fault.

　　D. Distinguish primary and secondary coils. Power transformer primary pin and secondary pin are generally drawn from both sides, and the primary winding is marked with 220V, secondary winding is marked with rated voltage value, such as 15V, 24V, 35V and so on. According to these marks to identify.

　　E. detection of no-load current. (a) direct measurement method. Open all the secondary windings, place the multimeter in an ac current block (500mA) and string into the primary windings. When the plug of the primary winding is inserted into 220V ac mains power, the multimeter indicates the no-load current value. This value shall not exceed 10% ~ 20% of the full load current of the transformer. The normal no-load current of power transformer for common electronic equipment should be about 100mA. If the excess is too much, the transformer has a short-circuit fault. (b) indirect measurement method. A 10/5w resistor is connected in series in the primary winding of the transformer, and the secondary is still completely empty. Set the multimeter to ac voltage block. After the power is added, the voltage drop U at both ends of the resistance R is measured with two meter pens, and then ohm's law is used to calculate the no-load current I null, that is, I null =U/R.

　　F. Detection of no-load voltage. The primary power transformer shall be connected to 220V mains power, and the no-load voltage value (U21, U22, U23 and U24) of each winding shall be measured successively with the ac voltage of the multimeter. The allowable error range is generally as follows: high voltage winding ≤±10%, low voltage winding ≤±5%, and voltage difference between two groups of symmetric windings with center tap ≤±2%.

　　G. The general low-power power supply transformer allows the temperature rise to 40℃ ~ 50℃. If the insulation material used is of good quality, the allowable temperature rise can be improved.

　　H. Detect and distinguish the homonymic end of each winding. When using a power transformer, two or more secondary windings may sometimes be used in series in order to obtain the desired secondary voltage. When the power transformer is used in series, the homonymic end of the windings participating in series must be connected correctly without any mistake. Otherwise, the transformer cannot work normally.

　　I. comprehensive detection and discrimination of short-circuit fault of power transformer. The main symptoms of short circuit fault of power transformer are serious heating and abnormal output voltage of secondary winding. Generally, the more short-circuit points between turns in the coil, the greater the short-circuit current, and the more serious the transformer heating. A simple test to determine whether a power transformer has a short-circuit fault is to measure no-load current (the test method has been described above). The no-load current value of transformers with short-circuit fault will be much higher than 10% of the full-load current. When the short circuit is serious, the transformer in the no-load power within a few seconds will be quickly hot, touch the core will have a hot feeling. At this time, it is not necessary to measure the no-load current to determine that the transformer has a short-circuit point.