Detection methods and experience of thermal power

Detection methods and experience of inductors and transformers

1. Detection of color coded inductors

place the multimeter in R × In gear 1, the red and black probes are connected to any leading out end of the color code inductor, and the pointer should swing to the right at this time. According to the measured resistance value, it can be identified in the following three cases:

a ﹐ the resistance value of the measured color code inductor is zero, and there is a short-circuit fault inside. B. the DC resistance value of the measured color code inductor is directly related to the diameter of the enameled wire used to wind the inductor coil and the number of windings. As long as the resistance value can be measured, the measured color code inductor can be considered normal

2 ﹐ detection of mid cycle transformer

a ﹐ set the multimeter to R × In gear 1, check the on-off condition of each winding one by one according to the pin arrangement law of each winding of the mid cycle transformer, and then judge whether it is normal. B ・ detection leads to the evolution of the insulation material on the wall into a brick with little insulation function

place the multimeter in R × 10K gear, do the following state tests:

(1) resistance value between primary winding and secondary winding

(2) resistance value between primary winding and housing

(3) resistance value between secondary winding and housing

the above test results can be divided into three situations:

(1) the resistance value is infinite: normal

(2) resistance value is zero: there is a short-circuit fault

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

3 ﹐ detection of power transformer

a ﹐ check whether there are obvious abnormalities by observing the appearance of the transformer. For example, whether the coil lead is broken, desoldered, whether the insulating material has scorched traces, whether the iron core fastening screw is loose, whether the silicon steel sheet is rusted, whether the winding coil is exposed, etc

B insulation test. Use multimeter R × 10K gear is used to measure the resistance between the iron core and primary, primary and secondary, iron core and secondary, electrostatic shielding layer and vent secondary, and secondary windings respectively. The multimeter pointer should point to the infinite position. Otherwise, the insulation performance of the transformer is poor

c ﹐ detection of coil on-off. Place the multimeter in R × 1 this kind of fault often produces gear. In the test, if the resistance value of a winding is infinite, it indicates that this winding has open circuit fault

d ﹐ distinguish 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 usually marked with the word 220V, while the secondary winding is marked with the rated voltage value, such as 15V, 24V, 35V, etc. Then identify according to these marks

e ﹐ detection of no-load current

(a) · direct measurement method. Open all secondary windings, Put the multimeter in the AC current gear (500mA) and connect it in series with the primary winding. When the plug of the primary winding is plugged into 220V AC mains power, the multimeter indicates the no-load current value. This value should not be greater than 10% - 20% of the full load current of the transformer. Generally, the normal no-load current of the power transformer of common electronic equipment should be about 100mA. If it exceeds too much, it indicates that the transformer has short-circuit fault.

(b) · indirect measurement method. A resistance of 10 ∨/5w is connected in series in the primary winding of the transformer, and the secondary winding is still empty. Turn the multimeter to AC voltage. After power on, use two probes to measure the voltage drop u at both ends of resistance R, and then use Ohm's law to calculate the no-load current I empty, that is, I empty =u/r

f ﹐ detection of no-load voltage. Connect the primary of the power transformer to 220V mains power, and measure the no-load voltage value (U21, u22, U23, u24) of each winding in turn with the AC voltage of the multimeter. The allowable error range is generally: high voltage winding ≤± 10%, low voltage winding ≤± 5%, and the voltage difference between the symmetrical windings of the two groups with central tap in order to promote the green development of the automotive industry should be ≤± 2%

g ﹐ generally, the allowable temperature rise of small power transformer is 40 ℃ ~ 50 ℃. If the insulation material used is of good quality, the allowable temperature rise can be increased

h ﹐ detect and identify the same name end of each winding. When using a power transformer, sometimes two or more secondary windings can be connected in series to obtain the required secondary voltage. When using the power transformer in series, the same name ends of all windings in series must be connected correctly and cannot be mistaken. Otherwise, the transformer cannot work normally

i. comprehensive detection and discrimination of short-circuit fault of power transformer. The main symptoms of power transformer after short-circuit fault are serious fever and abnormal output voltage of secondary winding. Generally, the more inter turn short-circuit points in the coil, the greater the short-circuit current, and the more serious the heating of the transformer. The simple method to detect and judge whether the power transformer has short-circuit fault is to measure the no-load current (the test method has been introduced earlier). The no-load current value of transformer with short-circuit fault will be much greater than 10% of full load current. When the short circuit is serious, the transformer will quickly heat up within dozens of seconds after no-load power on. Touching the iron core with your hand will feel hot. At this time, it can be concluded that there is a short-circuit point in the transformer without measuring the no-load current