A、To check whether the
transformer is normal by observing its appearance, such as whether the down-lead of the coil is rupture, sealingoff, whether the insulation materail has sorched mark, whether the core tighten crew is loosen, whether the sillion sheet has corroded, and whether the winding coil is bare.
B、Insulation test.To measure the resistance value between core and primary winding, the resistance value between primary and other seconary windings, the resistance value between core and othe secondary value, the resistance value between static and shielding layer, the resistance value among the secondary windings by the multimeter R X 10K block, the clock hand should point at the infinite place, or otherwise, the
transformer insulation lelve is not so good.
. C、Detection of the coil. put the multimeter in R x 1 block, and if there is a certain winding's resistance value is infinite then the winding exists the turnoff fault.
D、distinguish of the primary and secondary windings.The primary pin and the secondary pin of the power
transformer are all lead out from the two sides, and the primary windings are marked with 220V, and the secondary winding marked with the rated voltage value, such as 15V, 24V,35V and so on. And it distinguish the windings by these marks.
E、No-load current testing.(a)Direct measurement.All the secondary windings are incomplete circuit, and the multimeter was in the AC current gear (500ma, connecting in series with primary winding. When the plug was inserted into the AC 220V commercial power, what the hand of the multimeter poins at is the no-load current value. The value should no more than the 10%-20% of the value of full-load current. The general normal no-load current of the electronic equipmen-power
transformer is 100ma. If the value exceed too much that means there is short-circuit fault.(b)Indirect measurement.The primary winding connect in series with a 10/5W resistance, and the secondary winding is still the no-load. Put the multimeter in the AC current gear, and use the instrument pen to measure the voltage drop (u) of the two ends of the resistance after electrify, and then calculate the no-load current I by the Ohm's law, that is I=U/R.
F、No-load voltage detection.Conect the primary of the power
transformer with the 220V commercial power, and measure the no-load current value (U21, U22, U23, U24) of each winding by the multimeter AC vlotage connection and all the value should comply with the standard value, and the error range is : HV winding ≤±10％, LV winding ≤±5％, the voltage difference of the symmetrical winding with centretap ≤±2％.
G、The allowance of temperature rise of samll power supply
transformer is 40℃～50℃, and the allownace of temperature rise is more higher than that if the inualtion material is of good quality.
H、Detection and determine the homonymic end of each winding. In order to get the needed secondary voltage when use the power tansformer, two or more windings can be series work together. It should ensure the correct connection of the homonymic end of each winding. Otherwise, the
transformer can not work properly.
I、The comprehensive test and distinguish of the power
transformer short-circuit fault. The main symptom of the short circuit fault is severe heating and abnormal power transmission of secondary winding. The more of the coil turns, the greater of the short-circuit current. The simple way to detect whether the power
transformer has short-circuit fault is to measure the no-load current value. The no-load current value is much greater than 10% of the full-load current value if there is short-circuit fault. And the
transformer will be quick heated in a few dozen seconds when the short-circuit fault is severe and you will get a feeling of hot to touch the core. And under such a condition, there is no need to measure the no-load current to know that there is short-ciracuit point.
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