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Working principle of OSG auto-transformer With primary and secondary windings directly connected in series, the transformer which couples automatically is called auto-transformer.


1. Brief Description

Working principle of OSG auto-transformer 

With primary and secondary windings directly connected in series, the transformer which couples automatically is called auto-transformer.  

1.The auto-transformer is a special transformer with the output and input sharing one group of coil. The voltage boosting and reduction is realized through different taps. The voltage will be reduced if the tap is less than the shared coils, and the voltage will be boosted if the tap is more than the shared coils. 

2. For the auto-transformer, its primary coil is also its secondary coil; for the ordinary transformer, one primary coil makes the secondary coil on the other side to generate voltage through electromagnetic induction. 
3.The auto-transformer is the transformer just with one winding. When it is used as step-down transformer, some wire turns will be withdrawn from the winding as secondary winding; when the transformer is used as step-up transformer, the external voltage is only applied on some wire turns of winding. Usually, the winding which belongs to both primary and secondary winding is called common winding, and others are called series winding. Compared with the ordinary transformer of same capacity, the auto-transformer is of small size and high efficiency and the bigger the transformer capacity is, the higher the voltage is, the more significant the advantage is. Therefore, along with the development of electric power system, the improvement of voltage class and the increase of transmission capacity, the auto-transformer is widely applied thanks to its large capacity, small loss and low cost. It can be learnt from the principle of electromagnetic induction that, it’s unnecessary for the transformer to have both primary and secondary winding, and the transformer with one coil may also achieve the purpose of converting the voltage. 


1. The dimensions may be determined according to user requirements, and those listed are for reference; the product dimension may change accordingly if the input and output are different. 

2. The rated input and output voltage listed in the table may be combined at will. 

3. The voltage and dimension listed in the table may be determined through consultation according to user requirements. 


Technical Indexes

Working frequency: 50Hz-60Hz
Efficiency: ≥95%
Waveform distortion: <0.1%
Stable performance, with the noise less than 40db
Insulation class: F
Temperature rise: Below 75℃
High-voltage test: 3000V, without breakdown within 1min.
Insulation resistance: Insulation resistance of winding to earth: ≥5MΩ; primary-to-secondary insulation resistance: ≥5MΩ
Service Conditions 
Applicable height above sea level: ≤1000m
Ambient temperature: -15℃~+45℃
Relative humidity: ≤90%
    The installation place should be free from the gas, steam, chemical sedimentation, scale, conducting dust and other explosive, inflammable and corrosive substances which may severely affect the insulating strength of the transformer.